Sensation and Perception

Sensation

the process of detecting a physical stimulus, such as light, sound, heat, or pressure

Perception

the process of integrating, organizing, and interpreting sensations

Sensory receptors

specialized cells unique to each sense organ that respond to a particular form of sensory stimulation

Sensory threshold

the point at which a stimulus is strong enough to activate a sensory receptor cell

Absolute threshold

smallest possible strength of a stimulus that can be detected from zero half the time

Difference threshold

the smallest possible difference between two stimuli that can be detected half the time (just noticeable difference/jnd)

Weber's law

the size of a just noticeable difference is a constant proportion of the size of the initial stimulus

Transduction

the process by which physical energy is converted into a coded neural signal that can be processed by the nervous system

Sensory adaptation

the gradual decline in sensitivity to a constant stimulus

Cornea

clear membrane covering front of the eye, helps gather and direct incoming light

Pupil

opening in the middle of the iris that changes size to vary light amount

Iris

surrounds pupil; contracts or expands to control size of pupil

Lens

actively focuses/bends light as it enters the eye

Myopia

nearsightedness; light reflected off of distant objects focuses in front of the retina

Hyperopia

farsightedness; light reflect off of objects near eyes is focused behind the retina

Presbyopia

lens becomes brittle and inflexible

Visible light electromagnetic energy range

Humans can only see small portion of electromagnetic energy range (350-750nm wavelengths)

Astigmatism

Curved eyeball results in blurry vision for lines in a particular direction.

Retina

Thin, light-sensitive membrane located at the back of the eye, which contains sensory receptors for vision.

Rods

Long, thin, blunt sensory receptors that are highly sensitive to light but not to color; ~125M in each eye; adapt slowly to changes in amount of light; maximum sensitivity in ~30m.

Cones

Short, thick, pointed sensory receptors that detect color; ~7M in each eye; adapt quickly to bright light; maximum sensitivity in ~5m; require much more light to function effectively.

Fovea

Small area in the center of the retina made up of cones where visual information is most sharply focused.

Blind spot

Point at which optic nerve leaves the eye, producing a small gap in the field of vision; lacks rods and cones altogether.

Ganglion cells

Specialized neurons in the retina that do preliminary processing of visual information.

Bipolar cells

Cells that collect information from sensory receptors and funnel raw data to ganglion cells.

Optic nerve

Ganglion cell axon bundle; thick nerve exiting back of the eye and carrying visual information to visual cortex in brain.

Optic chiasm

Intersection in the brain where optic nerve fibers from each eye meet and cross over to the other side of the brain.

Primary pathway

Pathway for information about form, color, brightness, depth.

Secondary pathway

Detour to areas in midbrain; processes location of object.

Blindsight

Damage to occipital cortex causes a person to believe they cannot see; thalamus & eye sensory input is intact but perception is not possible.

Feature detectors

Specialized neurons that detect particular features or aspects of more complex visual stimuli.

Synesthesia

Condition in which one sense is perceived simultaneously alongside another sense or senses; results from atypical connections in the brain.

Color vision components

The perceptual experience of different wavelengths of light, involving hue, saturation (purity), and brightness (intensity).

Hue

Varies with wavelength of light; different wavelengths as different colors.

Saturation

Purity of wavelength; single wavelength will appear vivid while multiple wavelengths will be faded.

Brightness

Amplitude of wavelength; higher the amplitude, brighter the color.

Color perception process

Color is perceived because an object reflects only the wavelength of light that we perceive as the 'color;' absorbs all other wavelengths.

White

Reflects all wavelengths.

Black

Absorbs all wavelengths.

Trichromatic Theory

The theory that sensation of color results because cones are especially sensitive to red light (long wavelengths), green light (medium wavelengths), or blue light (short wavelengths).

Opponent-Process Theory

Theory that color vision is the product of opposing pairs of color receptors: red-green, blue-yellow, and black-white; one color is stimulated and the other is inhibited.

Bottom-up processing

Emphasizes sensory receptors in detecting the basic features of a stimulus; attention focuses on the parts of the pattern before moving to the whole.

Top-down processing

Emphasizes observer's experience in arriving at meaningful perceptions; attention moves from the whole to part of the pattern.

Collectivistic cultures

See object and background as single perceptual image & pay more attention to relationship between them—'holistic' style.

Hallucination

A false or distorted perception that seems vividly real to the person experiencing it.

Strength of Trichromatic Theory

Good explanation for red-green color blindness (blue cone fine, red/green cones only sensitive to one). Initial coding of color in cones

Strength of Opponent-Process Theory

Good explanation of aftermirages.

These elements do opponent-process theory

Ganglion cells, thalamus, visual cortex

Visual perception answers these

What is it, how far away is it, where is it going

Figure-ground relationship

Gestalt principle stating that a perception is automatically separated into the figure, which is the main element of the scene, and the ground, which is its background.

Perceptual grouping

We organize forms that seem to go together--similarity, closure, good continuation, and proximity

Depth perception

The use of visual cues to perceive the distance or the three-dimensional characteristics of an object.

Monocular cues

Distance or depth cues that can be processed by either eye alone--include relative size, overlap, aerial perspective, texture gradient, linear perspective, motion parallax

Binocular cues

Distance or depth cues that require the use of both eyes.

Convergence

The degree to which muscles rotate your eyes to focus on an object; greater convergence → perceived as closer.

Binocular disparity

Degree of similarity between two retinal images; very different → perceived as closer.

Motion perception

Compare moving object to stationary background.

Perceptual constancies

The tendency to perceive objects, especially familiar objects, as constant and unchanging despite changes in sensory input.

Size constancy

Perception that object remains the same size despite its changing image on the retina.

Shape constancy

Perception that a familiar object remains the same shape despite its changing image on the retina.

Müller-Lyer Illusion

Visual illusion involving the misperception of the identical length of two lines, one with arrows pointed inward, one with arrows pointed outward.

Moon Illusion

A visual illusion involving the misperception that the moon is larger on the horizon than when it is directly overhead.

Perceptual set

Tendency to perceive objects or situations from a particular frame of reference.