MCAT Behavioral Science - Chapter 2: Sensation and Perception

hello everybody my name is Iman welcome back to my YouTube channel today we&#39;re covering chapter 2 for our MCAT Behavioral Science playlist and this chapter is titled sensation and perception now what we&#39;re going to cover in this chapter are the following objectives first and foremost we&#39;re going to talk about sensation versus perception here in this objective we&#39;ll touch on sensory receptors we&#39;re going to touch on thresholds signal uh detection Theory as well as adaptations then we&#39;ll move into the second objective titled Vision here we&#39;ll cover the structure and function of the eye visual Pathways and processing in the third objective we&#39;re going to do the same thing but for the ear we&#39;re going to cover structure and function of the ear auditory Pathways and we&#39;ll touch basis with hair cells as well the fourth objective will focus on some of the other senses we&#39;ll talk about smell taste somata sensation and Kines atic sense before moving into our last and final objective which is about object recognition here we&#39;re going to cover gal&#39;s principles with that being said let&#39;s go ahead and start this chapter with our first objective titled sensation versus perception now in common day-to-day use people often use sensation and perception interchangeably as synonyms however in the field of psychology these two terms have very specific definitions and they&#39;re commonly contrasted so sensation more appropriately aligns with transduction this is the conversion of physical electromagnetic auditory and other information from our internal and external environment to electrical signals in the nervous system sensation is performed by receptors in the peripheral nervous system which forward the stimuli to the central nervous system in the form of action potentials and neurotransmitters sensation can therefore be thought of as a raw signal it&#39;s unfiltered and unprocessed until it enters the central nervous system perception on the other hand it refers to the processing of this information to make sense of its significance these complex manipulations are going to include both both external sensory experience and the internal activities of the brain and spinal cords so in short perception helps us make sense of the world now with the definition of sensation versus perception being covered we want to move into a discussion about sensory receptors sensory receptors are neurons that respond on to stimuli and then they trigger electrical signals sensory receptors can encode multiple aspects of a stimulus so for example photo receptors are going to respond to light and they can encode not only the brightness of the light but also the color and the shape and so this relationship between the physical nature of the stimuli and the sensations and perceptions they evoke is something that we want to talk about in this chapter and studied in the field of psychophysics now in order to inform the central nervous system the signals from these stimuli they must pass through a very specific sensory pathway and in each case different types of receptors generally nerve endings or specific sensory cells they&#39;re going to receive the stimulus and then they&#39;re going to transmit the data to the central nervous system through sensory ganglia gangli are collections of neuron cell bodies that are found outside the central nervous system once this transduction occurs the electrochemical energy is going to be sent along neural Pathways to various projection areas in the brain and there they&#39;re going to be further analyzed the sensory input will be further analyzed now sensory receptors differ from one sense to another and there&#39;s actually over a dozen of recognized sensory receptors but for the MCAT we&#39;re only going to concern ourselves with a couple and we&#39;re going to go over those now first and foremost you want to be familiar with photo receptors these respond to electromagnetic waves in the visible spectrum then we have hair cells they respond to movement of fluid in the inner ear structures nooter they respond to painful or noxious stimuli thermal receptors are going to respond to changes in temperature osmo receptors these respond to osmol uh osmolarity and of the of the blood specifically and then Al Factory receptors these are going to respond to volatile compounds and then last but not least we have taste receptors these respond to dissolved compounds now that is sensory receptors for ourselves and what this helps us transition into is a discussion about our next topic which is thresholds perception like sensation is closely tied to the biology and physiology of interpreting the world around us however unlike sensation perception is linked to experience and both internal and external biases Sensations are relate to the brain which perceive the significance of the stimulus for example determining whether something is hot or cold that same sensation though it can produce radically different Perceptions in different people and because these variations have to be explained by central nervous system activity perception is considered part of psychology now a good example of the psychological element of perception is threshold threshold is the minimum amount of stimulus that renders a difference in perception so for example the temperature it may noticeably change from warm to cool when the sun sets but subtle fluctuations in temperature throughout the day are generally unnoticeable because they are below the difference threshold that is true unless you live in Texas where the temperature changes by the minute now there are three main types of thresholds that we want to cover and be familiar with for the MCAT this is going to be absolute threshold threshold of conscious perception and difference threshold let&#39;s go ahead and start with this first absolute threshold this is the minimum of stimulus energy that&#39;s going to be needed to activate a sensory system it is therefore a threshold in sensation not in perception the second one is threshold of conscious perception so it&#39;s possible for sensory systems to send signals to the central nervous system without a person perceiving them this may be because the stimulus is either too subtle to like demand our attention or it may last for too brief of a duration for the brain to actually fully process the information now subliminal perception often refers to the the perception of a stimulus below a given threshold and this term refers to the threshold of conscious perception now here&#39;s a good point for us to note the difference between the absolute threshold and the threshold for conscious perception a stimulus below the absolute threshold is not going to be transduced and so that means it never reaches the central nervous system but a stimulus below the threshold of conscious perception arrives at the central nervous system but it just doesn&#39;t reach the higher order brain regions that control attention and Consciousness then last but not least we want to talk about difference threshold the difference threshold or just noticeable difference this refers to the minimum difference in magnet magnitude between two stimuli before one can perceive this difference so for example most individuals without formal ear training find it pretty impossible to discriminate between sound waves at 440 H Hertz and 441 Hertz while they are two different frequencies the perception of the tones is that they&#39;re the same in this range of sound frequencies the just noticeable difference is about 3 Hertz so most individuals just begin to hear a difference between sound waves at 440 Herz and 443 Hertz now while the just noticeable difference given for sound frequencies is 3 Herz and above it&#39;s far more important actually to focus on the ratio between the change in stimulus and its original value and so that is more important it&#39;s more easy to interpret the information than just actual differences between the frequencies and so the just noticeable difference for sound frequency is more accurately Quantified as 0.68% how did we get that we got that by taking three Hertz and dividing it by 440 Herz so the just noticeable difference over the sound frequency of Interest this relationship has actually been formalized in Weber&#39;s law which states that there is a constant ratio between the change in stimulus magnitude needed to produce a just noticeable difference and between the magnitude of the original stimulus with that we&#39;ve discussed the three main types of thresholds the absolute threshold threshold of conscious perception and difference threshold now we want to move on to talking about signal detection Theory perception of stimuli it can also be affected by non-sensory factors such as experience memory motives expectations and this concept is termed signal detection Theory and it focuses on the changes in our perception of the same stimuli depending on both internal and external context so a good example to start off with to motivate this idea is how loud would someone need to yell your name in a crowd to get your attention and part of that answer comes from psychology if you heard something that sounds vaguely like your name would you likely acknowledge it or not and the answer is not just as simple yes or no but it would depend on a couple of factors what&#39;s the size of the crowd what are your expectations of being called what are the social factors at Play all right and what&#39;s your personality so all of these factors come into play when trying to answer the question if you heard something that sounds vaguely like your name would you likely acknowledge it or not now signal detection Theory also allows us to explore something called response bias and this refers to the tendency of subjects to systematically respond to a stimulus in a particular way due to non-sensory factors so a BAS basic signal detection experiment is going to consist of many trials and during each trial a stimulus or signal may or may not be presented trials in which the signal is presented are called catch trials and trials where that signal is not presented is called a noise signal now trials after each trial the subject is asked to indicate whether or not a signal was given and so there are actually Four possible outcomes for each trial you have hits this is where the subject correctly perceives the signal you have misses in which the subject fails to perceive a given signal false alarm this is what when the subject seems to perceive a signal but none was given and correct negatives in which the subject correctly identifies that no signal was given now something that&#39;s also important in this discussion to talk about is adaptation and this refers to the fact that our detection of a stimulus can change over time through adaptation so adaptations can have both a physiological component and a PS psychological component so in other words a sensory component and a perceptual component a good example is think about how your eyes adjust to Darkness right the pupils of the eyes are going to dilate in the dark and they&#39;re going to constrict in the light to make our vision more similar in different environments as part of physiological adaptation with that being said we&#39;ve completed everything that we wanted to talk about in our first objective and what we&#39;re going to do next is transition into our second objective which is all about Vision now vision is a highly adapted sense in human beings with the ability to sense brightness color shape and movement and then integrate this information to create a cohesive three-dimensional model of the world the visual pathways are extremely important to Everyday Life in fact vision is the only sense to which an entire lobe of the brain is devoted to and that&#39;s the oipal lobe with that being said what we first want to do in this objective is really cover the structure and the function of the eye before we move into visual Pathways and processing let&#39;s go ahead and get started by looking at this figure right here the ey is a specialized organ to detect light that&#39;s used to detect light in the form of photons most of the exposed portion of the eye is covered by a thick structural layer known as the skilla I&#39;m going to circle where that is in blue right now and this is the white of the eye the skilla though it does not cover the frontmost portion of the eye the cornea which is located right here now the eye is supplied with nutrients by two sets of blood vessels the corial vessels and the retinal vessels the innermost layer of the eye is the retina it&#39;s located right here and it contains the actual photo receptors that transduce light into electrical information that the brain can process now when entering the eye the light passes first through the cornea which is like a clear Dome likee window in the front of the eye and it essentially gathers and focuses the incoming light now the front of the eye is divided into two Chambers the anterior chamber and the posterior chamber the anterior chamber lies in front of the iris and the posterior chamber is between the iris and the lens now now the iris located over here this is the colored part of the eye it&#39;s composed of two muscles the dialator and the constrictor pupil ey the dilator opens the pupil under sympathetic stimulation and the constrictor constricts the pupil under parasympathetic stimulation now the iris is continuous with the choid as is the ciliary body which produces the aquous humor haha that bathes the front part of the eye before it drains into the canal of schlim now the lens they lie right behind the iris and it helps control the refraction of the incoming light contraction of the ciliary muscle which is a component of the ciliary body is under parasympathetic control and so as the muscle contracts it pulls on the suspensory ligaments and it changes the shape of the lens this is a phenomena that&#39;s known as accommodation then behind the lens lies the vitus this is a transparent gel that supports the retina now the retina is a really interesting part of the eye that we want to discuss further and specifically we want to talk about duplexity or duplicity theory of vision as well what I do want to show you though is that we have just verbally talked about the different parts of the eye but the notes for the functions of each of these structures that we&#39;ve talked about are written right here so what the cornea the iris the lens do ciliary body uh the vitus so on and so forth again what we want to elaborate on here now is the retina this is in the back of an the eye and it&#39;s like a screen consisting of neural elements and blood vessels and its function is to convert incoming photons of light to electrical signals it is actually considered part of the central nervous system and it develops as an outgrowth of brain tissue now the duplexity or duplicity theory of vision states that the retina contains two kinds of photo receptors those specialized for light and dark detection and those that are specialized for color detection all right so the retina is made up of approximately six million cones and 120 million rods cones are used for color vision and to sense fine details they&#39;re the most effective in bright light and they come in three forms they&#39;re come in three forms short medium and long also referred to as blue green and red respectively now in reduced elimination though rods are more functional and they only allow sensation of light and dark because they contain a signal pigment called rupin rods have low sensitivity to details they&#39;re not involved in color vision but they are involved in night vision and while there are many more rods than cones in the human eye the central section of the retina has a high concentration of cones now the connection the connection between the rods and cones and the optic nerve is not direct all right there are several layers of neurons in between and we can kind of see that looking at this figure right here we&#39;re going to talk about the different aspects there are several layers of neurons in between we have bipolar cells we have gangan cells horizontal cells and amacrine cells now rods and cones they connect with bipolar cells which highlight gradients between adjacent Rock or um cones so here you can see bipolar cells um bipolar cells also synapse with gangan cells you see gangan cells are are kind of demonstrated in this image here this is kind of what they look like in a cartoon version um and these gangan cells they group together to form the optic nerve because there are many many many more receptors than ganglion cells each gangan cell has to represent the the com combined activity of many rods and cones this results in a loss of detail as information from the photo receptors is combined now as the number of receptors that converge through bipolar neurons onto one gingan cell increases all right the resolution is going to decrease on average the number of cones converging onto a individual gangan cell is smaller than it is for rods therefore color vision has a greater sensitivity to fine detail than black and white Vision tests now we can&#39;t forget to talk about um amacrine cells and horizontal cells these receive input from multiple retinal cells in the same area before the information is passed on to gangan cells and so they can thereby uh accentuate slight differences between the visual information in each bipolar cells and these cells are very important for Edge detection because they increase our perception of contrasts with that being said we can now finally move into discussing the visual Pathways the visual Pathways refer to both the physical and atomical connections between the eyes and the Brain as well as the flow of visual information among these connections so something that&#39;s going to help us visualize this discussion is this figure right here so we&#39;re going to look at this and we&#39;re going to try to talk about it all right each ey&#39;s right visual field projects onto the left half of each um uh the left half of the visual field so let me reiterate that each ey&#39;s right visual field projects onto the left half of each ey&#39;s retina and each ey&#39;s left visual field projects onto the right half of each eyes retina and as the signal travels through the optic nerves towards the the brain the first significant events occurs at the optic kism here the fibers from the nasal half of each retina are going to cross paths and these fibers they carry the temporal visual field from each eye now because the temporal fibers do not cross in the uh in the kism this reorganization means that all fibers corresponding to the left visual field from both eyes projects onto the right side of the brain and all fibers corresponding to the right visual field from both eyes projects onto the left side of the brain so you see this kind of like opposite orientation here and these reorganized pathways are called optic tracts once they leave the optic um kism or kaym however you pronounce that word now from the optic kism the information then goes to several different places in the brain all right it goes to the lateral uh the lateral gen culate nucleus of the thalamus uh through radiations in the temporal and parietal loes to the visual cortex in the oipal lobe there&#39;re also inputs into the superior calculus which controls some responses actually to visual stimulus and reflexive eye movements all right so with that being said it&#39;s also important now that we kind of understand a little bit about the visual Pathways that we equally understand some of the processing that happens so while being able to sense all light information around us is use is useful in its own right we have to be able to make sense of visual stimuli to be able to interact with the environment one process that helps create a cohesive image of the world around us is parallel processing this is the ability to simultaneously analyze and combine information regarding color shape and motion and then these features can be compared to our memories to determine what is actually being viewed so for most for as an example most people can recognize a moving car very easily from a distance because are familiar with the usual emotions and shapes of cars now parallel processing is not only a psychological model but it also has a correlate in Neuroscience called feature detection so our visual Pathways they contain cells that are specialized in detection of things like color shape or motion that helps feed into this feature detection now we&#39;ve talked about color we said that cones are responsible for color vision but we haven&#39;t really elaborated on shape or motion shape refers not only to the three-dimensional geometry of an object but also our ability to discriminate an object of interest from The Background by detecting its boundaries shape is also detected by parvocellular cells which have a very high color spatial resolution that is they permit us to see very fine detail when we&#39;re examining an object here here&#39;s something though parvos cellular cells can only really work well with stationary or slow moving objects because they have very low temporal resolution now motion motion is detected by magnos cellular cells these have very high temporal resolution what&#39;s the trade-off though they have very low spatial resolution so much of the rich detail of an object can no longer be seen once it&#39;s in Motion in addition magnos cellular cells provide more of a blurry but moving image of an object with that we&#39;ve covered all our main objectives for vision and now we can move into our third objective which is all about hearing the ear is a complex organ that&#39;s not only responsible for our sense of hearing but also for both rotational and linear acceleration this is what&#39;s called the vular sense these senses are critical and important to our ability to get around the world and their Associated structures are encased in some of the densest bone of the body to really protect them from damage so again here first and foremost we&#39;ll talk about the structure and the function of the ear before we move into discussing the auditory Pathways here you see a little bit of the structure and anatomy of the ear the ear is divided into three parts it&#39;s divided into the outer ear the middle ear and the inner ear now a sound wave first reaches the outside part of the ear called the PA or or Oracle And the main function of the p is to channel sound waves into the external auditory canal this is going to direct the sound waves to the tanic membrane also known as the eard drum the membrane vibrates in Phase with the incoming sound waves and the frequency of the sound wave determines the rate at which the tanic membrane vibrates it moves back and forth at high rates for high frequency sounds and more slowly obviously for low frequency sounds in addition louder sounds are going to have greater intensity and that&#39;s going to correspond to an increased amplitude of this vibration now the tanic membrane it divides the outer ear from the middle ear all right so this is kind of the division between the outer outer ear and the middle ear is here this tanic membrane the middle ear the middle ear it houses the three smallest bones in the body called oses the oses they help transmit and amplify the vibrations from the tanic membrane to the inner ear the malice is a fixed to the tanic membrane it acts on the incus all right and that acts on the stapes right here the base plate of the stapes it rests in the oval window of the ccka which is the entrance to we&#39;ve made it into the inner ear now the middle ear is connected to the Nal nasal cavity via the ustan tube which really helps equalize pressure between the middle ear and the environment the inner ear sits within a bony Labyrinth which contains the ccka the Vistal and the semicircular canals I&#39;m going to briefly talk about this but we&#39;re going to hyperfocus on each of these structures in more detail here in a second so the inner ear sits within the Bony labin bony Labyrinth and it contains the ccka the Vestal and the semicircular canals these structures are continuous with each other and they&#39;re mostly filled by the membranous Labyrinth this is bed with a potassium rich fluid called the endolymph now the membranous Labyrinth it&#39;s suspended within the Bony Labyrinth by a thin layer of another fluid called perilymph Peril lymph simultaneously transmits vibrations from the outside world and then it cushions the inner the inner ear structure so with that brief overview of the outer middle and inner ear we&#39;re going to really FOC focus on the inner ear all right the inner ear is going to be something that we&#39;re going to talk about in Greater detail but just as a final review the outer ear contain uh consists of the Pina the external auditory canals and the tanic membrane and the tanic membrane really divides between the outer ear and the middle ear the middle ear consists of ticles we have malice incus and stapes and the foot plate of the stapes it rests on the oval window of the ccka um and then the middle ear is connected to the nasal cavity by the ustan tube then we have the inner ear and it has these three important structures that we&#39;re going to talk about here that&#39;s the CIA the fuul and the semicircular canals and something else that&#39;s really important is the inner ear contains the Bony Labyrinth it&#39;s filled with Peril lymph and we have the membranous uh Labyrinth it&#39;s filled with endolymph so with that statement let&#39;s start to hyperfocus on the workings of the inner ear starting first and foremost with a discussion on the ccka the ccka is a spiral shaped you can see that kind of here looks like the the shell of a snail right kind of spiral-shaped organ and it&#39;s divided into three parts called Scalia all three Scalia they run the entire length of the ccka and the middle Scalia it&#39;s going to house the actual hearing apparatus that&#39;s called the organ of cordi so I&#39;m going to kind of transition to this part where we have some of the writing so we can discuss it this organ of cordi it rests on a thin flexible membrane called the basil membrane and the organ of cordi it&#39;s composed of thousands of hair cells all bathed in endolymph on top of the organ of cordi is a relatively immobile membrane that&#39;s called the tectorial membrane the other two Scalia filled with pair lymph surround the hearing apparatus and they are also continuous with the oval and round windows of the ccka and so sound entering the ccka through the oval window is going to cause vibrations in the paril lymph which are transmitted to the to the basilar membrane now because fluids are essentially incompressible the round window which is a membrane covered hole in the ccka it permits the Peril lymph to actually move move within the ccka and like the rods and cones of the eye the hair cells in the organ of cordi they convert this physical stimulus into an electrical signal which is carried to the central nervous system by the auditory nerve all right so again the the ccka is a spiral-shaped organ it&#39;s divided into three parts the middle part contains the actual hearing apparatus that&#39;s called the organ of cordi and it rests on this basilar membrane it&#39;s composed of thousands of hair cells that are bathed in endolymph on top of the organ of cordi is a relatively immobile membrane that&#39;s called the tectorial membrane and then the other piece of information is that the other two parts of the ccka is filled with paril lymph and it surrounds the hearing apparatus it&#39;s continuous with the oval and round windows of the ccka now we can move on to the second part of the inner ear that want to talk about and that&#39;s the Vistal the Vistal refers to the PO portion of the Bon the Bony Labyrinth I&#39;m sorry that contains the utricle and the sacle these structures are really sensitive to linear acceleration so they&#39;re used as part of the balancing apparatus and they&#39;re used to determine one&#39;s orientation in threedimensional Space the utricle and the SECU they contain modified hair cells covered with autoliths and as the body accelerates these autoliths are going to resist that motion and so this bends and stimulates those underlying hair cells and it sends a signal to the brain then we have the semicircular canals while the utricle and saule are sensitive to linear acceleration the three semicircular canals are going to be sensitive to rotational acceleration the semicircular canals are arranged perpendic IC to each other and each end in the swelling is called an ampula this is where the hair cells are located so when your head rotates actually endolymph in the semicircular Canal is going to resist this motion and it&#39;s going to do so by bending the underlying hair cells which is going to send a signal to the brain with that we&#39;ve covered the structure and function of the ear we talked about the outer middle and inner ear we really focus focused on the three parts of the inner ear the ccka the Vestal and the semicircular canals now we can have a discussion on the auditory Pathways in the brain um the auditory Pathways in the brain are a bit more complex than the visual Pathways and so we&#39;re really just going to cover this at a very surface level and this kind of what you just need to know for the MCAT no not too many details here most sound information actually passes through the Vestal clear nerve and it passes through that to the um brain stem where it ascends to the medial Jula nucleus of the thalamus from there it projects to the auditory cortex in the temporal lobe for some Sound Processing some information is also sent to the superior Olive where um local where it localizes the sound and also to the inferior calculus which is involved in that startle reflex and it helps the eyes it helps keeps the eyes fixed on a point when the head is turned so that is the auditory pathway it starts from the ccka and it travels through the Vestal cckar nerve to the medial genul nucleus of the thalamus and it does that to get to the auditory cortex in the temporal lobe so that&#39;s the auditory pathway in short with that we have completed objective three and now we can finally move into objective four here we&#39;re going to talk about the other senses here we&#39;ll start off with a discussion on smell smell is considered one of the chemical senses which means that it responds to incoming chemicals from the outside world so it specifically responds to say something like a volatile compound now olfactory chemo receptors they&#39;re located in the AL Factory epithelium in the upper part of the nasal cavity chemical stimuli has to bind to their respective chemo receptors to be able to cause a signal there are a tremendous number of specific chemo receptors which allow us to recognize subtle differences in similar scents like lavender versus Jasmine for example now smell can also carry interpersonal information through the medium of pheromones pheromones have a detectable effect on humans but they also play an enormous role in animals and specifically in animals social foraging and sexual behavior fer bones are secreted by one person or animal and once bonded with chemo receptors they compel or urge another one to behave in a specific way now as true with all senses there is a defined olfactory Pathway to to the brain we&#39;re going to cover it in simple terms that we need to know for the MCAT odor molecules are going to be inhaled into the na nasal passage and then contact the olfactory nerves in thefactory epithelium these receptor cells are going to be activated then sending signals to the AL Factory bulb and then these signals are then relay via the AL Factory tract to higher regions of the brain including the lyic system so that&#39;s smell next up is taste as a sense taste is often more simple than we imagine there are five basic tastes we have Umami sour Sweet Bitter and salty Umami is also known as Savory now flavor is not synonymous with taste uh but rather it refers actually to the complex interplay between smell and taste which can be affected by non-chemical stimuli like texture or one&#39;s mood when they&#39;re eating tastes are also detected by cumo receptors however unlike Al Factory chemo receptors taste receptors are really sensitive to dissolved compounds saltiness for example is a reaction to alkaline metals it&#39;s generally triggered by the sodium that&#39;s found in table salt sourness on the other hand is a reaction to acid such as in lemons or vinegar um Sweet Bitter and flavors are also triggered by specific molecules binding to receptors The receptors for taste are groups of cells called taste buds which are found in little bumps on the tongue called um papaly these are important and taste information will actually travel from the taste buds to the brain stem and then Ascend to the T Center in the thalmus before traveling to higher order brain regions so we&#39;ve covered smell and now we&#39;ve covered taste it&#39;s time for us to move into discuss discussing somata sensation this is often reduced to touch when listed as a sense but it&#39;s actually quite complex and it can be described as having four modules pressure vibration pain and temperature all right and to this there are actually five different types of receptors that receive tactile information we&#39;re going to cover these as we need to know them for the mcap the first we&#39;re going to cover is the pacinian corpuscle this responds to deep pressure and vibration then we have the masner corpuscle this responds to light touch Merkel cells respond to deep pressure and texture ruini endings they respond to stretch and free nerve endings respond to pain and temperature now transduction occurs in the receptors and it&#39;s it&#39;s going to send the signal to the central nervous system where it eventually travels to the somata sensory cortex in the parial lob there are three additional Concepts that are related to couch perception that are going to be really important to know they are the two-point threshold physiological zero and the gate theory of pain let&#39;s go ahead and start with this first one a two-point threshold refers to the minimum dist necessary between two points of stimulation on the skin such that the points will be felt as two distinct stimuli the size of the two-point threshold really depends on the density of nerves in the particular area of the skin that&#39;s being tested now as for physiological zero well temperature is judged relative to physiological zero or the normal temperature of the skin which is anywhere between 86 86 and 97° fah so an object is going to feel cold because it&#39;s under physiological zero and an object is going to feel warm because it&#39;s above physiological zero now pain reception is part of the somata sensory system and it can result from signals sent from a variety of sensory receptors most commonly referred to as no acceptors pain also relies on thresholds and those as we talked earlier about vary greatly from person to person for example the idea of what temperature of water is so hot it hurts is going to vary by several degrees between individuals and this leads us to talk about this third Point gate theory of pain the gate theory of pain it proposes that there is a special quote unquote gating mechanism that can turn pain signals on or off and that affects whether or not we perceive receive pain in this Theory the spinal cord is able to preferentially forward the signals from other touch uh modules to the pr to the brain and that reduces the sensation of pain now this has been superseded by other theories but it still is a useful model of understanding touch processing at the spinal cord level with that we can move into our last sense that we want to talk about and that&#39;s kinesthetic sense this is also called Pro uh proprioception it refers to the ability to tell where one&#39;s body is in space so for example even with your eyes closed you can still describe the location and the position of your hand The receptors for proprioception they&#39;re found mostly in muscle and joints and they play very critical roles in hand eye coordination uh very critical roles in balance and also Mobility with that we move into our last and final objective called object recognition modern theories of object recognition assume at least two major types of psychological processing we have bottom up processing also referred to as data driven processing and then we have top- down processing also known as conceptually driven processing bottom up processing refers to object recognition by parallel processing and feature uh detection like we described earlier essentially the brain takes the individual sensory stimuli it combines them together to create a cohesive image before determining what that object is top down is driven by memories and expectations that allow the brain to recognize the whole object and then recognize the components based on these expectations in other words top- down processing allows us to quickly recognize objects without needing to analyze their specific Parts neither system though is sufficient by itself if we only performed bottom up processing we would be extremely inefficient at recognizing objects every time we looked at an object it would be like it was it would be like we were looking at it for the first time and so that&#39;s not very efficient on the other hand if we only performed top- down processing we would have difficulty discriminating slight differences between similar objects now this leads us to talk about something called perceptual organization this refers to the ability to use the two processes in tandem with all of the other sensory clues about an object to create a complete picture of an idea a now most of the images we see in everyday life are incomplete often we may only be able to see a part of an object and then we have to infer what the rest of the object look likes Now by using what information is available in terms of of depth form motion Etc we often fill in the gaps using gals principles and that actually leads us to talking about what gals principles are these generally follow the same basic idea there are ways for the brain to infer missing parts of the picture when the picture is incomplete there are dozens of gals principles but we&#39;re only going to refer to a couple of the ones that we need to know for the mcap we start off with the law of proximity which says that elements close to one another tend to be perceived as a unit then we have the law of similarity it says that objects that are similar appear to be grouped together together the law of good continuation says that elements that appear to follow the same pathway tend to be grouped together this leads us to talking about subjective Contours this has to do with perceiving Contours and therefore shapes that are not actually present in the stimulus then we also have law of closure law of closure says when a space is enclosed by a group of lines it is perceived as a complete or closed line and all these laws they operate to create the most stable consistent and simplest figures possible within a given visual field and so taken alog together the gal&#39;s principles are governed by the law of pragnant which says that perceptual organization will always be as regular as simple and as symmetric as possible and with that we have completed the second chapter titled s ation and perception I really hope that this was helpful if you have any questions comments concerns leave them down below other than that good luck happy studying and have a beautiful beautiful day future doctors

hello everybody my name is Iman welcome back to my YouTube channel today we&amp;#39;re covering chapter 2 for our MCAT Behavioral Science playlist and this chapter is titled sensation and perception now what we&amp;#39;re going to cover in this chapter are the following objectives first and foremost we&amp;#39;re going to talk about sensation versus perception here in this objective we&amp;#39;ll touch on sensory receptors we&amp;#39;re going to touch on thresholds signal uh detection Theory as well as adaptations then we&amp;#39;ll move into the second objective titled Vision here we&amp;#39;ll cover the structure and function of the eye visual Pathways and processing in the third objective we&amp;#39;re going to do the same thing but for the ear we&amp;#39;re going to cover structure and function of the ear auditory Pathways and we&amp;#39;ll touch basis with hair cells as well the fourth objective will focus on some of the other senses we&amp;#39;ll talk about smell taste somata sensation and Kines atic sense before moving into our last and final objective which is about object recognition here we&amp;#39;re going to cover gal&amp;#39;s principles with that being said let&amp;#39;s go ahead and start this chapter with our first objective titled sensation versus perception now in common day-to-day use people often use sensation and perception interchangeably as synonyms however in the field of psychology these two terms have very specific definitions and they&amp;#39;re commonly contrasted so sensation more appropriately aligns with transduction this is the conversion of physical electromagnetic auditory and other information from our internal and external environment to electrical signals in the nervous system sensation is performed by receptors in the peripheral nervous system which forward the stimuli to the central nervous system in the form of action potentials and neurotransmitters sensation can therefore be thought of as a raw signal it&amp;#39;s unfiltered and unprocessed until it enters the central nervous system perception on the other hand it refers to the processing of this information to make sense of its significance these complex manipulations are going to include both both external sensory experience and the internal activities of the brain and spinal cords so in short perception helps us make sense of the world now with the definition of sensation versus perception being covered we want to move into a discussion about sensory receptors sensory receptors are neurons that respond on to stimuli and then they trigger electrical signals sensory receptors can encode multiple aspects of a stimulus so for example photo receptors are going to respond to light and they can encode not only the brightness of the light but also the color and the shape and so this relationship between the physical nature of the stimuli and the sensations and perceptions they evoke is something that we want to talk about in this chapter and studied in the field of psychophysics now in order to inform the central nervous system the signals from these stimuli they must pass through a very specific sensory pathway and in each case different types of receptors generally nerve endings or specific sensory cells they&amp;#39;re going to receive the stimulus and then they&amp;#39;re going to transmit the data to the central nervous system through sensory ganglia gangli are collections of neuron cell bodies that are found outside the central nervous system once this transduction occurs the electrochemical energy is going to be sent along neural Pathways to various projection areas in the brain and there they&amp;#39;re going to be further analyzed the sensory input will be further analyzed now sensory receptors differ from one sense to another and there&amp;#39;s actually over a dozen of recognized sensory receptors but for the MCAT we&amp;#39;re only going to concern ourselves with a couple and we&amp;#39;re going to go over those now first and foremost you want to be familiar with photo receptors these respond to electromagnetic waves in the visible spectrum then we have hair cells they respond to movement of fluid in the inner ear structures nooter they respond to painful or noxious stimuli thermal receptors are going to respond to changes in temperature osmo receptors these respond to osmol uh osmolarity and of the of the blood specifically and then Al Factory receptors these are going to respond to volatile compounds and then last but not least we have taste receptors these respond to dissolved compounds now that is sensory receptors for ourselves and what this helps us transition into is a discussion about our next topic which is thresholds perception like sensation is closely tied to the biology and physiology of interpreting the world around us however unlike sensation perception is linked to experience and both internal and external biases Sensations are relate to the brain which perceive the significance of the stimulus for example determining whether something is hot or cold that same sensation though it can produce radically different Perceptions in different people and because these variations have to be explained by central nervous system activity perception is considered part of psychology now a good example of the psychological element of perception is threshold threshold is the minimum amount of stimulus that renders a difference in perception so for example the temperature it may noticeably change from warm to cool when the sun sets but subtle fluctuations in temperature throughout the day are generally unnoticeable because they are below the difference threshold that is true unless you live in Texas where the temperature changes by the minute now there are three main types of thresholds that we want to cover and be familiar with for the MCAT this is going to be absolute threshold threshold of conscious perception and difference threshold let&amp;#39;s go ahead and start with this first absolute threshold this is the minimum of stimulus energy that&amp;#39;s going to be needed to activate a sensory system it is therefore a threshold in sensation not in perception the second one is threshold of conscious perception so it&amp;#39;s possible for sensory systems to send signals to the central nervous system without a person perceiving them this may be because the stimulus is either too subtle to like demand our attention or it may last for too brief of a duration for the brain to actually fully process the information now subliminal perception often refers to the the perception of a stimulus below a given threshold and this term refers to the threshold of conscious perception now here&amp;#39;s a good point for us to note the difference between the absolute threshold and the threshold for conscious perception a stimulus below the absolute threshold is not going to be transduced and so that means it never reaches the central nervous system but a stimulus below the threshold of conscious perception arrives at the central nervous system but it just doesn&amp;#39;t reach the higher order brain regions that control attention and Consciousness then last but not least we want to talk about difference threshold the difference threshold or just noticeable difference this refers to the minimum difference in magnet magnitude between two stimuli before one can perceive this difference so for example most individuals without formal ear training find it pretty impossible to discriminate between sound waves at 440 H Hertz and 441 Hertz while they are two different frequencies the perception of the tones is that they&amp;#39;re the same in this range of sound frequencies the just noticeable difference is about 3 Hertz so most individuals just begin to hear a difference between sound waves at 440 Herz and 443 Hertz now while the just noticeable difference given for sound frequencies is 3 Herz and above it&amp;#39;s far more important actually to focus on the ratio between the change in stimulus and its original value and so that is more important it&amp;#39;s more easy to interpret the information than just actual differences between the frequencies and so the just noticeable difference for sound frequency is more accurately Quantified as 0.68% how did we get that we got that by taking three Hertz and dividing it by 440 Herz so the just noticeable difference over the sound frequency of Interest this relationship has actually been formalized in Weber&amp;#39;s law which states that there is a constant ratio between the change in stimulus magnitude needed to produce a just noticeable difference and between the magnitude of the original stimulus with that we&amp;#39;ve discussed the three main types of thresholds the absolute threshold threshold of conscious perception and difference threshold now we want to move on to talking about signal detection Theory perception of stimuli it can also be affected by non-sensory factors such as experience memory motives expectations and this concept is termed signal detection Theory and it focuses on the changes in our perception of the same stimuli depending on both internal and external context so a good example to start off with to motivate this idea is how loud would someone need to yell your name in a crowd to get your attention and part of that answer comes from psychology if you heard something that sounds vaguely like your name would you likely acknowledge it or not and the answer is not just as simple yes or no but it would depend on a couple of factors what&amp;#39;s the size of the crowd what are your expectations of being called what are the social factors at Play all right and what&amp;#39;s your personality so all of these factors come into play when trying to answer the question if you heard something that sounds vaguely like your name would you likely acknowledge it or not now signal detection Theory also allows us to explore something called response bias and this refers to the tendency of subjects to systematically respond to a stimulus in a particular way due to non-sensory factors so a BAS basic signal detection experiment is going to consist of many trials and during each trial a stimulus or signal may or may not be presented trials in which the signal is presented are called catch trials and trials where that signal is not presented is called a noise signal now trials after each trial the subject is asked to indicate whether or not a signal was given and so there are actually Four possible outcomes for each trial you have hits this is where the subject correctly perceives the signal you have misses in which the subject fails to perceive a given signal false alarm this is what when the subject seems to perceive a signal but none was given and correct negatives in which the subject correctly identifies that no signal was given now something that&amp;#39;s also important in this discussion to talk about is adaptation and this refers to the fact that our detection of a stimulus can change over time through adaptation so adaptations can have both a physiological component and a PS psychological component so in other words a sensory component and a perceptual component a good example is think about how your eyes adjust to Darkness right the pupils of the eyes are going to dilate in the dark and they&amp;#39;re going to constrict in the light to make our vision more similar in different environments as part of physiological adaptation with that being said we&amp;#39;ve completed everything that we wanted to talk about in our first objective and what we&amp;#39;re going to do next is transition into our second objective which is all about Vision now vision is a highly adapted sense in human beings with the ability to sense brightness color shape and movement and then integrate this information to create a cohesive three-dimensional model of the world the visual pathways are extremely important to Everyday Life in fact vision is the only sense to which an entire lobe of the brain is devoted to and that&amp;#39;s the oipal lobe with that being said what we first want to do in this objective is really cover the structure and the function of the eye before we move into visual Pathways and processing let&amp;#39;s go ahead and get started by looking at this figure right here the ey is a specialized organ to detect light that&amp;#39;s used to detect light in the form of photons most of the exposed portion of the eye is covered by a thick structural layer known as the skilla I&amp;#39;m going to circle where that is in blue right now and this is the white of the eye the skilla though it does not cover the frontmost portion of the eye the cornea which is located right here now the eye is supplied with nutrients by two sets of blood vessels the corial vessels and the retinal vessels the innermost layer of the eye is the retina it&amp;#39;s located right here and it contains the actual photo receptors that transduce light into electrical information that the brain can process now when entering the eye the light passes first through the cornea which is like a clear Dome likee window in the front of the eye and it essentially gathers and focuses the incoming light now the front of the eye is divided into two Chambers the anterior chamber and the posterior chamber the anterior chamber lies in front of the iris and the posterior chamber is between the iris and the lens now now the iris located over here this is the colored part of the eye it&amp;#39;s composed of two muscles the dialator and the constrictor pupil ey the dilator opens the pupil under sympathetic stimulation and the constrictor constricts the pupil under parasympathetic stimulation now the iris is continuous with the choid as is the ciliary body which produces the aquous humor haha that bathes the front part of the eye before it drains into the canal of schlim now the lens they lie right behind the iris and it helps control the refraction of the incoming light contraction of the ciliary muscle which is a component of the ciliary body is under parasympathetic control and so as the muscle contracts it pulls on the suspensory ligaments and it changes the shape of the lens this is a phenomena that&amp;#39;s known as accommodation then behind the lens lies the vitus this is a transparent gel that supports the retina now the retina is a really interesting part of the eye that we want to discuss further and specifically we want to talk about duplexity or duplicity theory of vision as well what I do want to show you though is that we have just verbally talked about the different parts of the eye but the notes for the functions of each of these structures that we&amp;#39;ve talked about are written right here so what the cornea the iris the lens do ciliary body uh the vitus so on and so forth again what we want to elaborate on here now is the retina this is in the back of an the eye and it&amp;#39;s like a screen consisting of neural elements and blood vessels and its function is to convert incoming photons of light to electrical signals it is actually considered part of the central nervous system and it develops as an outgrowth of brain tissue now the duplexity or duplicity theory of vision states that the retina contains two kinds of photo receptors those specialized for light and dark detection and those that are specialized for color detection all right so the retina is made up of approximately six million cones and 120 million rods cones are used for color vision and to sense fine details they&amp;#39;re the most effective in bright light and they come in three forms they&amp;#39;re come in three forms short medium and long also referred to as blue green and red respectively now in reduced elimination though rods are more functional and they only allow sensation of light and dark because they contain a signal pigment called rupin rods have low sensitivity to details they&amp;#39;re not involved in color vision but they are involved in night vision and while there are many more rods than cones in the human eye the central section of the retina has a high concentration of cones now the connection the connection between the rods and cones and the optic nerve is not direct all right there are several layers of neurons in between and we can kind of see that looking at this figure right here we&amp;#39;re going to talk about the different aspects there are several layers of neurons in between we have bipolar cells we have gangan cells horizontal cells and amacrine cells now rods and cones they connect with bipolar cells which highlight gradients between adjacent Rock or um cones so here you can see bipolar cells um bipolar cells also synapse with gangan cells you see gangan cells are are kind of demonstrated in this image here this is kind of what they look like in a cartoon version um and these gangan cells they group together to form the optic nerve because there are many many many more receptors than ganglion cells each gangan cell has to represent the the com combined activity of many rods and cones this results in a loss of detail as information from the photo receptors is combined now as the number of receptors that converge through bipolar neurons onto one gingan cell increases all right the resolution is going to decrease on average the number of cones converging onto a individual gangan cell is smaller than it is for rods therefore color vision has a greater sensitivity to fine detail than black and white Vision tests now we can&amp;#39;t forget to talk about um amacrine cells and horizontal cells these receive input from multiple retinal cells in the same area before the information is passed on to gangan cells and so they can thereby uh accentuate slight differences between the visual information in each bipolar cells and these cells are very important for Edge detection because they increase our perception of contrasts with that being said we can now finally move into discussing the visual Pathways the visual Pathways refer to both the physical and atomical connections between the eyes and the Brain as well as the flow of visual information among these connections so something that&amp;#39;s going to help us visualize this discussion is this figure right here so we&amp;#39;re going to look at this and we&amp;#39;re going to try to talk about it all right each ey&amp;#39;s right visual field projects onto the left half of each um uh the left half of the visual field so let me reiterate that each ey&amp;#39;s right visual field projects onto the left half of each ey&amp;#39;s retina and each ey&amp;#39;s left visual field projects onto the right half of each eyes retina and as the signal travels through the optic nerves towards the the brain the first significant events occurs at the optic kism here the fibers from the nasal half of each retina are going to cross paths and these fibers they carry the temporal visual field from each eye now because the temporal fibers do not cross in the uh in the kism this reorganization means that all fibers corresponding to the left visual field from both eyes projects onto the right side of the brain and all fibers corresponding to the right visual field from both eyes projects onto the left side of the brain so you see this kind of like opposite orientation here and these reorganized pathways are called optic tracts once they leave the optic um kism or kaym however you pronounce that word now from the optic kism the information then goes to several different places in the brain all right it goes to the lateral uh the lateral gen culate nucleus of the thalamus uh through radiations in the temporal and parietal loes to the visual cortex in the oipal lobe there&amp;#39;re also inputs into the superior calculus which controls some responses actually to visual stimulus and reflexive eye movements all right so with that being said it&amp;#39;s also important now that we kind of understand a little bit about the visual Pathways that we equally understand some of the processing that happens so while being able to sense all light information around us is use is useful in its own right we have to be able to make sense of visual stimuli to be able to interact with the environment one process that helps create a cohesive image of the world around us is parallel processing this is the ability to simultaneously analyze and combine information regarding color shape and motion and then these features can be compared to our memories to determine what is actually being viewed so for most for as an example most people can recognize a moving car very easily from a distance because are familiar with the usual emotions and shapes of cars now parallel processing is not only a psychological model but it also has a correlate in Neuroscience called feature detection so our visual Pathways they contain cells that are specialized in detection of things like color shape or motion that helps feed into this feature detection now we&amp;#39;ve talked about color we said that cones are responsible for color vision but we haven&amp;#39;t really elaborated on shape or motion shape refers not only to the three-dimensional geometry of an object but also our ability to discriminate an object of interest from The Background by detecting its boundaries shape is also detected by parvocellular cells which have a very high color spatial resolution that is they permit us to see very fine detail when we&amp;#39;re examining an object here here&amp;#39;s something though parvos cellular cells can only really work well with stationary or slow moving objects because they have very low temporal resolution now motion motion is detected by magnos cellular cells these have very high temporal resolution what&amp;#39;s the trade-off though they have very low spatial resolution so much of the rich detail of an object can no longer be seen once it&amp;#39;s in Motion in addition magnos cellular cells provide more of a blurry but moving image of an object with that we&amp;#39;ve covered all our main objectives for vision and now we can move into our third objective which is all about hearing the ear is a complex organ that&amp;#39;s not only responsible for our sense of hearing but also for both rotational and linear acceleration this is what&amp;#39;s called the vular sense these senses are critical and important to our ability to get around the world and their Associated structures are encased in some of the densest bone of the body to really protect them from damage so again here first and foremost we&amp;#39;ll talk about the structure and the function of the ear before we move into discussing the auditory Pathways here you see a little bit of the structure and anatomy of the ear the ear is divided into three parts it&amp;#39;s divided into the outer ear the middle ear and the inner ear now a sound wave first reaches the outside part of the ear called the PA or or Oracle And the main function of the p is to channel sound waves into the external auditory canal this is going to direct the sound waves to the tanic membrane also known as the eard drum the membrane vibrates in Phase with the incoming sound waves and the frequency of the sound wave determines the rate at which the tanic membrane vibrates it moves back and forth at high rates for high frequency sounds and more slowly obviously for low frequency sounds in addition louder sounds are going to have greater intensity and that&amp;#39;s going to correspond to an increased amplitude of this vibration now the tanic membrane it divides the outer ear from the middle ear all right so this is kind of the division between the outer outer ear and the middle ear is here this tanic membrane the middle ear the middle ear it houses the three smallest bones in the body called oses the oses they help transmit and amplify the vibrations from the tanic membrane to the inner ear the malice is a fixed to the tanic membrane it acts on the incus all right and that acts on the stapes right here the base plate of the stapes it rests in the oval window of the ccka which is the entrance to we&amp;#39;ve made it into the inner ear now the middle ear is connected to the Nal nasal cavity via the ustan tube which really helps equalize pressure between the middle ear and the environment the inner ear sits within a bony Labyrinth which contains the ccka the Vistal and the semicircular canals I&amp;#39;m going to briefly talk about this but we&amp;#39;re going to hyperfocus on each of these structures in more detail here in a second so the inner ear sits within the Bony labin bony Labyrinth and it contains the ccka the Vestal and the semicircular canals these structures are continuous with each other and they&amp;#39;re mostly filled by the membranous Labyrinth this is bed with a potassium rich fluid called the endolymph now the membranous Labyrinth it&amp;#39;s suspended within the Bony Labyrinth by a thin layer of another fluid called perilymph Peril lymph simultaneously transmits vibrations from the outside world and then it cushions the inner the inner ear structure so with that brief overview of the outer middle and inner ear we&amp;#39;re going to really FOC focus on the inner ear all right the inner ear is going to be something that we&amp;#39;re going to talk about in Greater detail but just as a final review the outer ear contain uh consists of the Pina the external auditory canals and the tanic membrane and the tanic membrane really divides between the outer ear and the middle ear the middle ear consists of ticles we have malice incus and stapes and the foot plate of the stapes it rests on the oval window of the ccka um and then the middle ear is connected to the nasal cavity by the ustan tube then we have the inner ear and it has these three important structures that we&amp;#39;re going to talk about here that&amp;#39;s the CIA the fuul and the semicircular canals and something else that&amp;#39;s really important is the inner ear contains the Bony Labyrinth it&amp;#39;s filled with Peril lymph and we have the membranous uh Labyrinth it&amp;#39;s filled with endolymph so with that statement let&amp;#39;s start to hyperfocus on the workings of the inner ear starting first and foremost with a discussion on the ccka the ccka is a spiral shaped you can see that kind of here looks like the the shell of a snail right kind of spiral-shaped organ and it&amp;#39;s divided into three parts called Scalia all three Scalia they run the entire length of the ccka and the middle Scalia it&amp;#39;s going to house the actual hearing apparatus that&amp;#39;s called the organ of cordi so I&amp;#39;m going to kind of transition to this part where we have some of the writing so we can discuss it this organ of cordi it rests on a thin flexible membrane called the basil membrane and the organ of cordi it&amp;#39;s composed of thousands of hair cells all bathed in endolymph on top of the organ of cordi is a relatively immobile membrane that&amp;#39;s called the tectorial membrane the other two Scalia filled with pair lymph surround the hearing apparatus and they are also continuous with the oval and round windows of the ccka and so sound entering the ccka through the oval window is going to cause vibrations in the paril lymph which are transmitted to the to the basilar membrane now because fluids are essentially incompressible the round window which is a membrane covered hole in the ccka it permits the Peril lymph to actually move move within the ccka and like the rods and cones of the eye the hair cells in the organ of cordi they convert this physical stimulus into an electrical signal which is carried to the central nervous system by the auditory nerve all right so again the the ccka is a spiral-shaped organ it&amp;#39;s divided into three parts the middle part contains the actual hearing apparatus that&amp;#39;s called the organ of cordi and it rests on this basilar membrane it&amp;#39;s composed of thousands of hair cells that are bathed in endolymph on top of the organ of cordi is a relatively immobile membrane that&amp;#39;s called the tectorial membrane and then the other piece of information is that the other two parts of the ccka is filled with paril lymph and it surrounds the hearing apparatus it&amp;#39;s continuous with the oval and round windows of the ccka now we can move on to the second part of the inner ear that want to talk about and that&amp;#39;s the Vistal the Vistal refers to the PO portion of the Bon the Bony Labyrinth I&amp;#39;m sorry that contains the utricle and the sacle these structures are really sensitive to linear acceleration so they&amp;#39;re used as part of the balancing apparatus and they&amp;#39;re used to determine one&amp;#39;s orientation in threedimensional Space the utricle and the SECU they contain modified hair cells covered with autoliths and as the body accelerates these autoliths are going to resist that motion and so this bends and stimulates those underlying hair cells and it sends a signal to the brain then we have the semicircular canals while the utricle and saule are sensitive to linear acceleration the three semicircular canals are going to be sensitive to rotational acceleration the semicircular canals are arranged perpendic IC to each other and each end in the swelling is called an ampula this is where the hair cells are located so when your head rotates actually endolymph in the semicircular Canal is going to resist this motion and it&amp;#39;s going to do so by bending the underlying hair cells which is going to send a signal to the brain with that we&amp;#39;ve covered the structure and function of the ear we talked about the outer middle and inner ear we really focus focused on the three parts of the inner ear the ccka the Vestal and the semicircular canals now we can have a discussion on the auditory Pathways in the brain um the auditory Pathways in the brain are a bit more complex than the visual Pathways and so we&amp;#39;re really just going to cover this at a very surface level and this kind of what you just need to know for the MCAT no not too many details here most sound information actually passes through the Vestal clear nerve and it passes through that to the um brain stem where it ascends to the medial Jula nucleus of the thalamus from there it projects to the auditory cortex in the temporal lobe for some Sound Processing some information is also sent to the superior Olive where um local where it localizes the sound and also to the inferior calculus which is involved in that startle reflex and it helps the eyes it helps keeps the eyes fixed on a point when the head is turned so that is the auditory pathway it starts from the ccka and it travels through the Vestal cckar nerve to the medial genul nucleus of the thalamus and it does that to get to the auditory cortex in the temporal lobe so that&amp;#39;s the auditory pathway in short with that we have completed objective three and now we can finally move into objective four here we&amp;#39;re going to talk about the other senses here we&amp;#39;ll start off with a discussion on smell smell is considered one of the chemical senses which means that it responds to incoming chemicals from the outside world so it specifically responds to say something like a volatile compound now olfactory chemo receptors they&amp;#39;re located in the AL Factory epithelium in the upper part of the nasal cavity chemical stimuli has to bind to their respective chemo receptors to be able to cause a signal there are a tremendous number of specific chemo receptors which allow us to recognize subtle differences in similar scents like lavender versus Jasmine for example now smell can also carry interpersonal information through the medium of pheromones pheromones have a detectable effect on humans but they also play an enormous role in animals and specifically in animals social foraging and sexual behavior fer bones are secreted by one person or animal and once bonded with chemo receptors they compel or urge another one to behave in a specific way now as true with all senses there is a defined olfactory Pathway to to the brain we&amp;#39;re going to cover it in simple terms that we need to know for the MCAT odor molecules are going to be inhaled into the na nasal passage and then contact the olfactory nerves in thefactory epithelium these receptor cells are going to be activated then sending signals to the AL Factory bulb and then these signals are then relay via the AL Factory tract to higher regions of the brain including the lyic system so that&amp;#39;s smell next up is taste as a sense taste is often more simple than we imagine there are five basic tastes we have Umami sour Sweet Bitter and salty Umami is also known as Savory now flavor is not synonymous with taste uh but rather it refers actually to the complex interplay between smell and taste which can be affected by non-chemical stimuli like texture or one&amp;#39;s mood when they&amp;#39;re eating tastes are also detected by cumo receptors however unlike Al Factory chemo receptors taste receptors are really sensitive to dissolved compounds saltiness for example is a reaction to alkaline metals it&amp;#39;s generally triggered by the sodium that&amp;#39;s found in table salt sourness on the other hand is a reaction to acid such as in lemons or vinegar um Sweet Bitter and flavors are also triggered by specific molecules binding to receptors The receptors for taste are groups of cells called taste buds which are found in little bumps on the tongue called um papaly these are important and taste information will actually travel from the taste buds to the brain stem and then Ascend to the T Center in the thalmus before traveling to higher order brain regions so we&amp;#39;ve covered smell and now we&amp;#39;ve covered taste it&amp;#39;s time for us to move into discuss discussing somata sensation this is often reduced to touch when listed as a sense but it&amp;#39;s actually quite complex and it can be described as having four modules pressure vibration pain and temperature all right and to this there are actually five different types of receptors that receive tactile information we&amp;#39;re going to cover these as we need to know them for the mcap the first we&amp;#39;re going to cover is the pacinian corpuscle this responds to deep pressure and vibration then we have the masner corpuscle this responds to light touch Merkel cells respond to deep pressure and texture ruini endings they respond to stretch and free nerve endings respond to pain and temperature now transduction occurs in the receptors and it&amp;#39;s it&amp;#39;s going to send the signal to the central nervous system where it eventually travels to the somata sensory cortex in the parial lob there are three additional Concepts that are related to couch perception that are going to be really important to know they are the two-point threshold physiological zero and the gate theory of pain let&amp;#39;s go ahead and start with this first one a two-point threshold refers to the minimum dist necessary between two points of stimulation on the skin such that the points will be felt as two distinct stimuli the size of the two-point threshold really depends on the density of nerves in the particular area of the skin that&amp;#39;s being tested now as for physiological zero well temperature is judged relative to physiological zero or the normal temperature of the skin which is anywhere between 86 86 and 97° fah so an object is going to feel cold because it&amp;#39;s under physiological zero and an object is going to feel warm because it&amp;#39;s above physiological zero now pain reception is part of the somata sensory system and it can result from signals sent from a variety of sensory receptors most commonly referred to as no acceptors pain also relies on thresholds and those as we talked earlier about vary greatly from person to person for example the idea of what temperature of water is so hot it hurts is going to vary by several degrees between individuals and this leads us to talk about this third Point gate theory of pain the gate theory of pain it proposes that there is a special quote unquote gating mechanism that can turn pain signals on or off and that affects whether or not we perceive receive pain in this Theory the spinal cord is able to preferentially forward the signals from other touch uh modules to the pr to the brain and that reduces the sensation of pain now this has been superseded by other theories but it still is a useful model of understanding touch processing at the spinal cord level with that we can move into our last sense that we want to talk about and that&amp;#39;s kinesthetic sense this is also called Pro uh proprioception it refers to the ability to tell where one&amp;#39;s body is in space so for example even with your eyes closed you can still describe the location and the position of your hand The receptors for proprioception they&amp;#39;re found mostly in muscle and joints and they play very critical roles in hand eye coordination uh very critical roles in balance and also Mobility with that we move into our last and final objective called object recognition modern theories of object recognition assume at least two major types of psychological processing we have bottom up processing also referred to as data driven processing and then we have top- down processing also known as conceptually driven processing bottom up processing refers to object recognition by parallel processing and feature uh detection like we described earlier essentially the brain takes the individual sensory stimuli it combines them together to create a cohesive image before determining what that object is top down is driven by memories and expectations that allow the brain to recognize the whole object and then recognize the components based on these expectations in other words top- down processing allows us to quickly recognize objects without needing to analyze their specific Parts neither system though is sufficient by itself if we only performed bottom up processing we would be extremely inefficient at recognizing objects every time we looked at an object it would be like it was it would be like we were looking at it for the first time and so that&amp;#39;s not very efficient on the other hand if we only performed top- down processing we would have difficulty discriminating slight differences between similar objects now this leads us to talk about something called perceptual organization this refers to the ability to use the two processes in tandem with all of the other sensory clues about an object to create a complete picture of an idea a now most of the images we see in everyday life are incomplete often we may only be able to see a part of an object and then we have to infer what the rest of the object look likes Now by using what information is available in terms of of depth form motion Etc we often fill in the gaps using gals principles and that actually leads us to talking about what gals principles are these generally follow the same basic idea there are ways for the brain to infer missing parts of the picture when the picture is incomplete there are dozens of gals principles but we&amp;#39;re only going to refer to a couple of the ones that we need to know for the mcap we start off with the law of proximity which says that elements close to one another tend to be perceived as a unit then we have the law of similarity it says that objects that are similar appear to be grouped together together the law of good continuation says that elements that appear to follow the same pathway tend to be grouped together this leads us to talking about subjective Contours this has to do with perceiving Contours and therefore shapes that are not actually present in the stimulus then we also have law of closure law of closure says when a space is enclosed by a group of lines it is perceived as a complete or closed line and all these laws they operate to create the most stable consistent and simplest figures possible within a given visual field and so taken alog together the gal&amp;#39;s principles are governed by the law of pragnant which says that perceptual organization will always be as regular as simple and as symmetric as possible and with that we have completed the second chapter titled s ation and perception I really hope that this was helpful if you have any questions comments concerns leave them down below other than that good luck happy studying and have a beautiful beautiful day future doctors

Transcript for:MCAT Behavioral Science - Chapter 2: Sensation and Perception

Transcript for:
MCAT Behavioral Science - Chapter 2: Sensation and Perception