Overview
This lecture covers how sensory information is detected and processed by the nervous system, explaining sensation versus perception, major sensory systems, and key perception theories such as gestalt.
Sensation vs. Perception
- Sensation is the detection of stimuli by sensory receptors (e.g., light, sound, taste).
- Perception is the interpretation and conscious experience of those sensory inputs.
- Transduction converts sensory stimulus energy into neural activity (action potentials).
- Sensory adaptation allows us to ignore unchanging stimuli.
- Attention and motivation influence what is sensed and perceived.
Thresholds and Sensory Processing
- Absolute threshold: minimum stimulus energy detectable 50% of the time.
- Difference threshold (just noticeable difference): smallest detectable difference between two stimuli, varies by intensity (Weber’s law).
- Subliminal messages are stimuli below conscious awareness but can still affect processing.
Properties of Light and Sound
- Amplitude (height of wave) relates to brightness (light) and loudness (sound).
- Wavelength determines color (light) and pitch (sound).
- Human visible spectrum: 380–740 nm; audible sound: 20–20,000 Hz.
- Timbre is the quality or "purity" of sound, shaped by wave complexity.
The Visual System
- Major structures: cornea, pupil, lens, retina (contains rods and cones).
- Cones detect color and detail; rods are sensitive in low light.
- Optic nerve transmits visual info to the brain; the optic chiasm sorts left/right visual fields.
- "What" and "Where/How" pathways process object identity and spatial location.
Color and Depth Perception
- Trichromatic theory: three cone types sensitive to red, green, or blue.
- Opponent process theory: colors encoded in opponent pairs (e.g., red-green).
- Depth perception uses binocular (two-eye) and monocular (one-eye) cues.
- Binocular disparity and linear perspective help us perceive 3D space.
The Auditory System
- Ear anatomy: outer (pinna, canal), middle (ossicles), inner (cochlea).
- Sound waves cause hair cells in cochlea to generate neural impulses.
- Temporal and place theories explain pitch perception.
- Sound localization uses monaural (one ear) and binaural (two ear) cues.
Other Sensory Systems
- Chemical senses: taste (gustation) and smell (olfaction), both respond to molecules.
- Taste includes sweet, salty, sour, bitter, umami, and possibly fat.
- Touch receptors detect pressure, vibration, temperature (thermoception), and pain (nociception).
- Vestibular sense (inner ear) provides balance; proprioception and kinesthesia sense body position and movement.
Gestalt Principles and Perceptual Set
- Gestalt psychology: we perceive wholes, not just the sum of sensory parts.
- Figure-ground: distinguish object (figure) from background (ground).
- Principles: proximity, similarity, continuity, closure.
- Perceptual set: expectations and experiences shape perception.
- Culture, beliefs, and biases can influence perception and interpretation.
Key Terms & Definitions
- Sensation — detection of external stimuli by sensory receptors.
- Perception — organization and interpretation of sensory information.
- Transduction — conversion of stimulus energy to neural signals.
- Absolute threshold — minimum stimulus intensity detected 50% of the time.
- Difference threshold (JND) — smallest noticeable change required to detect a difference.
- Trichromatic theory — color vision based on three cone types.
- Opponent process theory — color vision through opposing color pairs.
- Depth perception — ability to perceive spatial relationships in three dimensions.
- Gestalt principles — rules describing how we organize sensory information into meaningful patterns.
Action Items / Next Steps
- Review diagrams of eye and ear anatomy.
- Study the properties of waves relating to sensory processing.
- Read further on Gestalt principles and perceptual set examples.