The ABCs of Sensation

3.1 Transduction

• Sensation: the process that occurs when special receptors in the sense organs are activated, allowing various forms of outside stimuli to become neural signals in the brain.

• Transduction: the process of converting outside stimuli, such as light, into neural activity.

• Synesthesia: disorder in which the signals from the various sensory organs are processed in the wrong cortical areas, resulting in the sense information being interpreted as more than one sensation.

3.2

• Just Noticeable Difference (jnd or Difference threshold): the smallest difference between 2 stimuli that is detectable by 50% of the time

• Absolute Threshold: the lowest level of stimulation that a person can consciously detect 50% of the time the stimulation is present

• Signal Detection Theory:  provides a method for assessing the accuracy of judgments or decisions under uncertain conditions; used in perception research and other areas. An individual’s correct “hits” and rejections are compared against their “misses” and “false alarms”

3.3

• Habituation: the tendency of the brain to stop attending to constant, unchanging info

• Sensory Adaptation: the tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging

The Science of Seeing

3.4 Light and the Eye

• Visual Accommodation: the change in the thickness of the lens as the eye focuses on objects that are far away close

• Rods: visual sensory receptors found at the back of the retina, responsible for noncolor sensitivity to low levels of light.

• Cones: visual sensory receptors found at the back of the retina, responsible for color vision and sharpness of vision.

3.5 The Visual Pathway

• Blind Spot: area in the retina where the axons of the three layers of retinal cells exit the eye to form the optic nerve; insensitive to light

• Dark Adaptation: the recovery of the eye’s sensitivity to visual stimuli in darkness after exposure to bright lights

• Light Adaptation: the recovery of the eye’s sensitivity to visual stimuli in light after exposure to darkness

3.6 Perception of Color

• Trichromatic Theory: theory of color vision that proposes three types of cones: red, blue, and green; “three colors” theory

• Opponent-process theory: theory of color vision that proposes visual neurons (or groups of neurons) are stimulated by light of one color and inhibited by light of another color.

• Afterimage: images that occur when a visual sensation persists for a brief time even after the original stimulus is removed.

• Color Blindness: monochrome(full grayscale)  & dichromatic(one cone doesn’t work, ex. Red-green color-blindness)

The Hearing Sense

3.7 Sound Waves and The Ear

• Hertz (Hz): cycles or waves per second, a measurement of frequency

• Pinna: the visible part of the ear

• Auditory canal: a short tunnel that runs from the pinna to the eardrum

• Cochlea: snail-shaped structure of the inner ear that is filled with fluid.

3.8

• Auditory nerve: bundle of axons from the hair cells in the inner ear

• Pitch: psychological experience of sound that corresponds to the frequency of the sound waves; higher frequencies are perceived as higher pitches

• Place Theory: theory of pitch that states that different pitches are experienced by the stimulation of hair cells in different locations on the organ of Corti

• Frequency Theory: theory of pitch that states that pitch is related to the speed of vibrations in the basilar membrane

• Volley Principle: theory of pitch that states that frequencies from about 400 Hz to 4000 Hz cause the hair cells (auditory neurons) to fire in a volley pattern, or take turns in firing

3.9 Types of Hearing Impairments

• Conduction Hearing impairment: aka conductive hearing loss, refers to problems with the mechanics of the outer or middle ear and means that sound vibrations can’t be passed from the eardrum to the cochlea

• Nerve Hearing Impairment: aka sensorineural hearing loss, the problem lies either in the inner ear or in the auditory pathways and cortical areas of the brain

Chemical Senses: It Tastes Good and Smells Even Better

3.10 Gustation: How we Taste the World

• Gustation: the sensation of taste

3.11 The Sense of Scents: Olfaction

• Olfaction (olfactory sense): the sensation of smell

• Olfactory Bulb: two bulb-like projections of the brain located just above the sinus cavity and just below the frontal lobes that receive information from the olfactory receptor cells

The Other Sense: What the Body Knows

3.12 Somesthetic Senses

• Somesthetic Senses: the body sense consisting of the skin senses, the kinesthetic and proprioceptive senses, and the vestibular sense

3.13 Body Movement and Position

• Kinesthesia: the awareness of body movement

• Vestibular Sense: the awareness of the balance, position, and movement of the head and body through space in relation to gravity’s pull

• Proprioception: awareness of where the body and body parts are located in relation to each other in space

• Sensory Conflict Theory: an explanation of motion sickness in which the information from the eyes conflicts with the info from the vestibular, resulting in dizziness, nausea, and other physical discomforts

The ABC’s of Perception

3.14 How We Organize Our Perceptions

• Perception: the method by which the sensations experienced at any given moment are interpreted and organized in some meaningful fashion

• Size Constancy: the tendency to interpret an object as always being the same actual size, regardless of its distance.

• Shape Constancy: the tendency to interpret the shape of an object as being constant, even when its shape changes on the retina

• Brightness Constancy: the tendency to perceive the apparent brightness of an object as the same even when the light conditions change

• Figure-Ground: the tendency to perceive objects, or figures, as existing on a background

• Reversible Figures: visual illusions in which the figure and ground can be reversed

• Proximity: a Gestalt principle of perception, the tendency to perceive objects that are close to each other as part of the same grouping; physical or geographical nearness.

• Similarity: a Gestalt principle of perception, the tendency to perceive things that look similar to each other as being part of the same group

• Closure: a Gestalt principle of perception, the tendency to complete figures that are incomplete

• Continuity: a Gestalt principle of perception, the tendency to perceive things as simple as possible with a continuous pattern rather than with a complex, broken-up pattern

• Contiguity: a Gestalt principle of perception, the tendency to perceive two things that happen close together in time being related

3.15 Depth Perception

• Depth Perception: the ability to perceive the world in three dimensions.

• Monocular cues (pictorial depth cues): cues for perceiving depth based on one eye only.

• Binocular Cues: cues for perceiving depth based on both eyes

• Linear Perspective: monocular depth perception cue, the tendency for parallel lines to appear to converge on each other.

• Relative Size: monocular depth perception cue, perception that occurs when objects that a person expects to be of a certain size appear to be small and are, therefore, assumed to be much farther away

• Interposition: monocular depth perception cue, the assumption that an object that appears to be blocking part of another object is in front of the second object and closer to the viewer

• Aerial (atmospheric) perspective: monocular depth perception cue, the haziness that surrounds objects that are farther away from the viewer, causing the distance to be perceived as greater

• Texture Gradient: monocular depth perception cue, the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases

• Motion Parallax: monocular depth perception cue, the perception of motion of objects in which close objects appear to move more quickly than objects that are farther away

• Accommodation: as a monocular cue of depth perception, the brain’s use of information about the changing thickness of the lens of the eye in response to looking at objects that are close or far away

• Convergence: binocular depth perception cue, the rotation of the two eyes in their sockets to focus on a single object, resulting in greater convergence for closer objects and lesser convergence if objects are distant

• Binocular Disparity: binocular depth perception cue, the difference in images between the two eyes, which is greater for objects that are close and smaller for distant objects

3.16 Perception Illusions

• Müller-Lyer illusion: illusion of line length that is distorted by inward-turning or outward-turning corners on the ends of the lines, causing lines of equal length to appear to be different

• Perceptual Set (Perceptual Expectancy): the tendency to perceive things a certain way because previous experiences or expectations influence those perceptions

• Top-Down Processing: the use of preexisting knowledge to organize individual features into a unified whole

• Bottom-Up Processing: the analysis of the smaller features to build up to a complete perception