Sensation and Perception

Sensation

The process by which our sensory receptors and nervous system detect physical energy from the environment.

Perception

The process of organizing and interpreting sensory information so we can recognize meaningful objects and events.

Bottom-up Processing

Processing that starts with sensory input and builds up to form a perception.

Top-down Processing

Processing guided by experience, expectations, and prior knowledge.

Selective Attention

Focusing your awareness on a specific stimulus while ignoring others.

Inattentional Blindness

Failing to see something visible because your attention is focused elsewhere.

Change Blindness

Not noticing a change in the environment when your attention is diverted

Transduction

Converting one form of energy into another (e.g., light into neural signals).

Psychophysics

The study of how physical energy relates to our psychological experience of it.

Absolute Threshold

The minimum amount of stimulation needed to detect something 50% of the time.

Signal Detection Theory

Predicts when we will detect weak signals based on experience, expectations, motivation, and alertness.

Subliminal

Stimuli below the absolute threshold (not consciously detected).

Priming

Exposure to a stimulus influences your response to a later stimulus, often unconsciously.

Difference Threshold (Just Noticeable Difference)

The minimum difference between two stimuli needed to detect a change 50% of the time.

Weber’s Law

To notice a difference, the stimuli must differ by a constant percentage, not a constant amount.

Sensory Adaptation

Reduced sensitivity to a constant, unchanging stimulus.

Perceptual Set

A mental predisposition that influences what you perceive (based on expectations, culture, etc.)

Extrasensory Perception (ESP)

The claim that people can perceive things without using normal senses (telepathy, clairvoyance, etc.).

Wavelength

Distance between light wave peaks; determines color (hue).

Hue

The color we experience (red, blue, etc.), determined by wavelength.

Intensity

The amount of energy in a light wave; determines brightness.

Pupil

The adjustable opening in the eye that lets light in.

Iris

The colored muscle around the pupil that controls pupil size.

Lens

The structure that focuses light onto the retina.

Retina

The light-sensitive inner surface of the eye containing rods and cones

Accommodation

The process by which the lens changes shape to focus near or far objects.

Rods

Retinal receptors that detect black, white, and gray; help in low light and peripheral vision.

Cones

Retinal receptors for color and detail; work best in bright light.

Optic Nerve

The nerve that carries visual information from the eye to the brain.

Blind Spot

Area on the retina where the optic nerve leaves — there are no receptors there.

Fovea

The central point of the retina with the highest concentration of cones; sharpest vision.

Feature Detectors

Neurons in the brain that respond to specific features like edges, angles, or movement.

Parallel Processing

The brain's ability to process multiple aspects of a scene at once (color, motion, form, depth).

Young–Helmholtz Trichromatic Theory

We see color because our retina has three types of cones: red, green, and blue.

Opponent-Process Theory

Color vision depends on opposing color pairs (red–green, blue–yellow, black–white)

Gestalt

A school of thought emphasizing that we perceive whole forms, not just pieces.

Figure–Ground

Organizing visual fields into objects (figures) that stand out from the surroundings (ground).

Grouping

Organizing stimuli into coherent groups using rules like proximity, similarity, continuity, closure.

Depth Perception

The ability to see objects in three dimensions.

Visual Cliff

A laboratory device used to test depth perception in infants and animals.

Binocular Cues

Depth cues that require both eyes (e.g., retinal disparity).

Retinal Disparity

Difference between images in the two eyes; the brain uses this to judge distance.

Monocular Cues

Depth cues available to one eye (relative size, linear perspective, interposition, etc.).

Phi Phenomenon

The illusion of movement when two or more adjacent lights blink on and off.

Perceptual Constancy

Perceiving objects as unchanging (color, shape, size) even when lighting or perspective changes.

Color Constancy

Recognizing consistent color even when lighting changes.

Perceptual Adaptation

Adjusting your perception after being exposed to a changed visual input (e.g., upside-down goggles).

Audition

The sense of hearing.

Frequency

The number of sound wave cycles per second; determines pitch.

Pitch

How high or low a sound is.

Middle Ear

The chamber with the eardrum and three tiny bones (hammer, anvil, stirrup) that amplify vibrations.

Cochlea

A fluid-filled, snail-shaped inner-ear structure where sound waves become neural impulses.

Inner Ear

Contains the cochlea, semicircular canals, and vestibular sacs.

Sensorineural Hearing Loss

Hearing loss caused by damage to the cochlea or auditory nerve.

Conduction Hearing Loss

Hearing loss from problems with the mechanical system that sends sound waves to the cochlea.

Cochlear Implant

A device that converts sound into electrical signals to stimulate the auditory nerve.

Place Theory

We hear different pitches because different places on the cochlea’s membrane are activated.

Frequency Theory

We hear pitch based on how fast neurons fire (how frequently).

Gate-Control Theory

The spinal cord has “gates” that block or allow pain signals; pain can be lessened by closing the gates.

Kinesthesia

The sense of body position and movement of body parts.

Vestibular Sense

Sense of balance and head movement (located in inner ear).