1.6/2.1: Sensation and Perception

Sensation

Detecting physical energy from the environment.

Sensory receptors

Cells that convert stimuli into neural signals.

Perception

Organizing and interpreting sensory input.

Bottom-up processing

Start with sensory info → brain builds meaning.

Top-down processing

Use experience and expectations to interpret input

Transduction

Converting stimulus energy into neural impulses.

Psychophysics

Study of physical stimuli and mental experience. 

Gustav Fechner

Founder of psychophysics.

Absolute threshold

Minimum stimulation detected 50% of the time.

Signal detection theory

Detecting stimuli depends on strength + mindset

Subliminal

Below conscious awareness threshold.

Priming

Unconscious activation influencing response or perception.

Difference threshold (JND)

Smallest detectable difference between stimuli.

Ernst Weber

Found that JND depends on proportion. 

Weber’s Law

Stimuli differ by a constant percentage to be noticed.

Weber’s Law

Stimuli differ by constant percentage to be noticed

Sensory adaptation

Reduced sensitivity after constant stimulation

Wavelength

Determines color (short = blue, long = red)

Hue

The color we see.

Intensity

Brightness, based on wave amplitude. 

Cornea

Clear outer layer; bends light.

Pupil

Opening that lets light in.

Iris

Colored muscle controlling pupil size.

Lens

Focuses light on retina; changes shape.

Retina

Light-sensitive inner surface; contains receptors.

Accomodation

Lens adjust focus for distance.

Rods

See dim light; black and white. 

Cones

See color and detail

Optic nerve

Sends visual signals to brain.

Blind spot

No receptors; optic nerve exits.

Fovea

Central focus area; sharpest vision

Young—Helmholtz trichromatic theory

Three color receptors—red, green, blue

Opponent-process theory

Colors in opposing pairs (red-green, blue-yellow)

David Hubel & Torsten Wiesal

Discovered visual feature detectors.

Feature detectors

Neurons responding to shapes, edges, motion.

Parallel processing

Brain handles color, motion, depth, and form together. 

Audition

Sense of hearing

Frequency

Number of sound waves per second

Pitch

Highness or lowness of sound.

Middle ear

Three bones transmitting vibrations.

Cochlea

Fluid-filled snail shape; where transduction happens.

Inner ear

Contains cochlea and balance organs.

Sensorineural hearing loss

Problem conducting sound to cochlea.

Cochlear implant

Converts sound to electrical signals.

Place theory

Pitch + location of vibration on cochlea

Frequency theory

Pitch = rate of neural firing

Gate-control theory

Spinal cord “gate” opens/closes for pain signals.

Gustation 

Sense of taste.

Olfaction

Sense of smell.

Kinesthesis

Awareness of body position/movement

Vestibular sense

Balance and spatial orientation (inner ear)

Sensory interaction

Senses influence each other (smell + taste)

Embodied cognition

Body states affect thoughts and emotions.

Selective attention

Focusing on one stimulus while ignoring other (e.g., cocktail party effect)

Inattentional Blindness

Failing to notice something visible when attention is elsewhere.

Change blindness

Failing to notice changes in the environment (e.g., someone switches shirts).

Perceptual set

A mental predisposition to perceive things a certain way based on expectations, experience, or context.

Gestalt psychology

We perceive objects as organized wholes rather than separate parts.

Gestalt

Means “whole” — our brain tends to integrate pieces into meaningful wholes

Figure-ground

We separate main objects (figure) from background (ground).

Grouping

We organize stimuli into meaningful units based on proximity, similarity, continuity, closure, and connectedness.

Proximity

nearby objects go together

Similarity

similar-looking items grouped together.

Continuity

we see smooth, continuous patterns.

Closure

we fill gaps to create a whole image.

Connectedness

elements that move or look linked are seen as a unit.

Depth perception

The ability to see objects in 3D, even though our eyes see 2D images.

Visual cliff

Experiment showing infants can perceive depth (won’t crawl off “cliff”).

Binocular cues (two eyes)

Cues that require both eyes to judge distance.

Retinal disparity

Each eye sees a slightly different image; brain compares them to perceive depth.

Convergence

Eyes turn inward for close objects; brain uses muscle strain to judge distance.

Monocular cues (one eye)

Cues that perceive depth using just one eye:

Relative Size:

Smaller = farther away

Interposition

Closer objects block farther ones.

Relative height

Higher in visual field = farther

Linear perspective

Parallel lines converge with distance.

Relative motion

Objects closer move faster across field of view

Light and shadow

Shadows give depth cues

Stroboscopic movement

Brain perceives continuous motion from rapid series of slightly different images (basis of animation).

Phi Phenomenon

Two or more adjacent lights blink → perceived as moving.

Autokinetic effect

A stationary point of light in darkness appears to move because of tiny eye movements.

Perceptual Constance

Perceiving objects as stable (same shape, size, color).

Color constance

Recognizing color as constant despite lighting changes.

Shape constancy

Knowing shape stays the same despite viewing angle

Size constancy

Knowing an object’s size doesn’t change with distance.

Perceptual adaptation

The ability to adjust to changed sensory input — like when new glasses feel “weird” at first, but your brain adjusts over time.