Chapter 4: Sensation and Perception

perception

the process of organizing and interpreting sensory information

sensation

the process of detecting raw sensory information from the environment, through our sense organs

distal stimulus

the physical object in the world

proximal stimulus

the optical image on the retina

difference threshold

the smallest physical difference between two stimuli that can still be recognized as a difference

Ernst Weber

Weber’s law: the just noticeable difference between stimuli is a constant fraction of the intensity of the standard stimulus

transduction

the conversion of one form of physical energy to another form; such as light into neural impulses

sensory receptors

they convert the physical form of the sensory signal into cellular signals that can be processed by the nervous system

cornea

a transparent bulge on the front of the eye

anterior chamber

the space just behind the cornea

aqueous humor

the clear liquid in the anterior chamber

pupil

behind the anterior chamber; it is an opening in the iris; the muscular disk of the iris changes the size of this structure

lens

it is behind the pupil; it is a bean-shaped clear structure that changes its shape, thinning to focus in distant objects and thickening to focus on near ones

vitreous humour

it is behind the lens

retina

a thin sheet that lines the back of the eyeball; it is where the process of converting information about the world from light waves into neural signals happens

accomodation

the process of the ciliary muscles changing the thickness of the lens

photoreceptors

receptor cells in the retina that are sensitive to light

rods

they operate best in the dark; there are approximately 120 million of these

cones

they operate best in bright and colorful situations; there are approximately 7 million of these

dark adaptation

the gradual improvement of the eyes’ sensitivity after a shift from light to darkness; your rods become more sensitive and are able to respond to less light

fovea

near the center of the retina; it contains nothin but densely packed cones (no rods); this is the area of your sharpest vision with respect to color and spatial detail

bipolar cells

nerve cells that combine impulses from many receptors and transmit the results to ganglion cells

ganglion cells

cells that integrate impulses from many bipolar cells in a single firing rate

horizontal cells

cells that integrate information across the retina; instead of sending signals toward the brain, these cells connect receptors to each other

amacrine cells

cells that integrate information across the retina; instead of sending signals toward the brain, these cells link bipolar cells to other bipolar cells and ganglion cells to other ganglion cells

optic nerve

the million axons of the ganglion cells form these in each eye

How are the axons of the optic nerves arranged?

Half of the fibers from each optic nerve stay on their respective side of the body and the half of the fibers from the inner half of each eye cross over each other; the bundles of fibers combined from each eye are known as the optic tracts

Who pioneered work on how your visual system places together information from the world?

David Hubel and Torsten Wiesel

receptive field

the area in the visual field that from which it receives stimulation

How are wavelengths measured?

in nanometers; humans see light from 400 to about 700 nanometers

trichromatic theory

a theory that there are three types of color receptors that produce the primary color sensations of red, green, and blue

Who created the trichromatic theory?

Sir Thomas Young and Hermann von Helmholtz (Young-Helmholtz theory)

opponent-process theory

all color experiences arise from three underlying systems: red vs. green, blue vs. yellow, or black vs. white

Who created the opponent-process theory?

Ewald Hering

frequency

it is the number of cycles the sine wave completes in a given amount of time; measured in hertz (Hz)

amplitude

it measures the physical property of strength of the sound wave (it its peak-to-valley height)

timbre

it reflects the complexity of a sound wave; it explains why a piano sounds different than a flute

place theory

theory that suggests perception of pitch depends on the specific location on the basilar membrane at which the greatest stimulation occurs

Who created place theory?

Hermann von Helmholtz and Georg von Békésy

frequency theory

this theory predicts that a sound wave with a frequency of 100 Hz will set the basilar membrane vibrating 100 times per second

umami

the flavor of MSG that is often added to Asian foods and is naturally occurring in foods rich in protein such as meat and aged cheese

the four primary taste qualities

sweet, sour, bitter, and saline (salty)

cutaneous senses

skin senses

vestibular sense

the sense that tells how one’s own body is oriented in the world with respect to gravity

gate-control theory

this theory suggest that cells in the spinal cord act as neurological gates, interrupting and blocking some pain signals and letting others get through to the brain

phi phenomenon

an optical illusion in which objects seem to be moving in a picture

retinal disparity

the difference in distance that you see things with each eye

convergence

the degree to which the eyes turn inward to fixate on an object

relative motion parallax

provides information about depth; as you move, the relative distance of objects in the world determine the amount and direction of their relative motion in your retinal image of the scene; closer objects look like they are moving quickly, while farther objects look like they are moving slowly

linear perspective

when creating an illusion of depth on a flat surface (like creating train tracks, angling them to give it depth)

texture gradient

when objects close to you seem to have more distinct texture details and objects farther away seem to have finer, less defined texture (a visual cue for depth perception)

bottom-up processing

interpreting information based on sensory information first and then building up the whole picture

top-down processing

interpreting information based on prior knowledge and then filling in the details with sensory information