Overview
This lecture introduces Unit 3: Attention and Perception, covering types of attention, factors affecting it, transformation from sensation to perception, Gestalt principles, perceptual constancies, depth cues, color attributes, afterimages, and common visual illusions.
Attention
- Attention is focusing awareness on certain stimuli while ignoring others.
- Selective attention allows us to focus on important stimuli among distractions.
- Sustained attention is the ability to focus on a stimulus for long durations.
- Voluntary attention requires cognitive effort and is under conscious control.
- Involuntary attention doesn't require effort and is triggered by physical or psychological factors.
Factors Affecting Attention
Physical Factors
- Bigger size, bright colors, movement, sudden change, high intensity, and high contrast attract more attention.
Psychological Factors
- Stimuli related to needs, interests, or emotions receive more attention.
Transformation: Sensation to Perception
- Sensation: Sensory receptors detect stimuli.
- Transduction: Sensory input is converted into electrical impulses.
- Transmission: Impulses are sent via neurons to the brain through the synapse using neurotransmitters.
- Processing: The brain organizes and interprets information.
- Perception: Stimuli are selected, organized, and interpreted based on experience and knowledge.
Gestalt Principles of Perceptual Organization
Figure-Ground Principle
- We separate objects (figure) from the background (ground).
Laws of Grouping
- Law of Similarity: Similar items are grouped together.
- Law of Simplicity (Pragnance): We perceive complex images as simple figures.
- Law of Continuity: We see smooth, continuous patterns.
- Law of Closure: We fill in gaps to perceive complete figures.
- Law of Proximity: Items close together are grouped as one.
Perceptual Constancies
- Size constancy: Objects appear the same size despite changes in distance.
- Shape constancy: Objects retain shape regardless of orientation.
- Color constancy: Objects retain color under different lighting.
- Brightness constancy: Objects maintain brightness despite lighting changes.
Depth Perception
Monocular Cues (One Eye)
- Texture gradient, shadow, interposition, relative size, linear perspective, aerial perspective, height in field.
Binocular Cues (Both Eyes)
- Retinal disparity: Slight differences between eyes help judge depth.
- Convergence: Eyes turn inward when viewing close objects.
- Accommodation: Lens shape adjusts for distance.
Attributes of Color
- Hue: Defines color (red, green, blue) and depends on wavelength.
- Brightness: Amount of light emitted or reflected.
- Saturation: Vividness or purity of a color.
Afterimages
- Afterimage: Image seen after looking away from a stimulus.
- Positive afterimage: Same colors, short-lived.
- Negative afterimage: Inverted colors, longer-lasting.
Visual Illusions
- Muller-Lyer Illusion: Lines appear unequal due to arrowheads.
- Height-Width Illusion: Perpendicular line looks longer than base.
- Ponzo Illusion: Identical lines on converging lines appear different in length.
- Zollner Illusion: Parallel lines appear to converge due to diagonals.
- Pogendorf Illusion: Misperception of alignment when a line passes behind an object.
Key Terms & Definitions
- Attention — Concentration on selected stimuli.
- Selective Attention — Focusing on specific stimuli, ignoring others.
- Sensation — Detection of stimuli by sensory organs.
- Transduction — Conversion of sensory input to electrical impulses.
- Perception — Brain’s interpretation of sensory information.
- Gestalt Principles — Rules explaining how we organize perceptions.
- Constancy — Perceiving objects as unchanging despite changes in stimulus.
- Monocular/Binocular Cues — Depth cues using one or both eyes.
- Afterimage — Residual visual impression after stimulus removal.
- Illusion — Misinterpretation of real visual stimulus.
Action Items / Next Steps
- Review and draw diagrams of Gestalt laws and major illusions.
- Prepare examples for each perceptual cue and constancy.
- Practice identifying cues and principles in case studies.
- Review definitions of all key terms.