Vision-Readings

Transduction

transformation of sensory information into neural signals

Sensation

process of obtaining information about the environment and transmitting it to the brain for processing

Perception

process of interpretating sensory signals sent to the brain

Attention

a narrow focus of consciousness

Bottom up processing

the combining of simpler meanings to construct more complex meanings

Top down process

use of knowledge and expectation to interpret meanings

Electromagnetic radiation

radiation in the form of energy waves

Wavelength

distance between successive peaks of a wave; determines color in visible light

Amplitude

height of wave; in vision, the source of subjective experience of brightness

Photons

individual, indivisible, very small particles that form waves of electromagnetic energy

Nanometers

a unit of measurement equaling 10^(negative) 9m used to measure light wave frequency

Absorption

ability to retain something rather than reflect or transmit to another location

Reflection

bending back of light toward its source

Refract

deflection or changing of direction, of light at a boundary such as that between air and water

Orbit

bony opening in the skull that houses the eyeball

Blink

rapid closing of the eyelids

Sclera

white outer covering of the eye

Cornea

transparent outer layer of the eye

Anterior chamber

area of the eye located directly behind the cornea, containing aqueous humor

Aqueous humor

fluid located in the anterior chamber that nourishes the cornea and lens

Pupil

opening in the front of the eye controlled by iris

Iris

circular muscle in the front of the eye that controls the opening of the pupil

Lens

clear structure behind the pupil and iris that focuses light on the retina

Accommodation

ability of the lens to change shape to adjust to the distance of the visual stimulus

Vitreous chamber

large inner cavity of the eyeball

Vitreous humor

jellylike substance in the vitreous chamber

Retina

the elaborate network of photoreceptors and interneurons at the back of the eye that is responsible for sensing light

Photoreceptor

specialized sensory cell in the retina that responds to light

Optic disk

area in the retina where blood vessels and the optic nerve exit the eye

Macula

a 6mm round area in the retina that is not covered by blood vessels that is specialized for detailed vision

Central vision

the ability to perceive visual stimuli focused on the macula of the retina

Peripheral vision

the ability to perceive visual stimuli that are off to the side while looking straight ahead

Fovea

a small pit in the macula specialized for detailed vision

Epithelium

pigmented layer of cells supporting the photoreceptors of the retina

Ganglion cell layer

the layer of retinal interneurons farthest from the photoreceptors, which contains ganglion cells and gives rise to optic nerve

Ganglion cell

retinal cell in the ganglion cell layer whose axon leaves the eye as part of the optic nerve

Inner plexiform layer

location in the retina containing axons and dendrites that connect the ganglion, bipolar, and amacrine cells

Amacrine cell

retinal interneuron in inner nuclear layer that integrates signals across adjacent segments of the retina

Bipolar cell

a cell in inner nuclear layer of the retina that forms of the straight pathway between the photoreceptors and ganglion cells

Inner nuclear layer

layer of retinal interneurons containing amacrine, bipolar, horizontal cells

Outer plexiform layer

the retinal layer containing axons and dendrites forming connections between bipolar cells, horizontal cells, and photoreceptors

Horizontal cell

retinal interneuron located in the inner nuclear layer that integrates signals from the across surface of retina

Outer nuclear area

location in the retina containing the cell bodies of the photoreceptors

Rod

photoreceptor that responds to low levels of light but not to color

Cone

a photoreceptor that operates in bright conditions and responds differentially to color

Outer segment

portion of photoreceptor containing photopigments

Photopigment

pigment contained in the photoreceptors of the eye that absorbs light

Rhodopsin

that photopigment found in rods

Scotopic vision

the ability to perceive visual stimuli in near darkness due to the activity of rods

Photopic vision

the ability to perceive visual stimuli under bright light conditions due to the activity of cones

Opsin

protein found in photopigments

Retinal

a chemical contained in rhodopsin that interacts with absorbed light

11 cis

the form taken by retinal while it is bound to opsin in the absence of light

All trans

form taken by retinal after light is absorbed by rod outer segment

Dark current

steady depolarization maintained by photoreceptors when no light is present

Cyclic guanosine monophosphate (cGMP)

2nd messenger within photoreceptors that is responsible for maintaining the dark current by opening sodium channels

Receptive field

a location on the retina at which light affects the activity of a particular visual interneuron

Antagonistic center surround organization

a characteristic of visual interneuron receptive fields, in which light illuminating the center has the opposite effect on the cell’s activity as light in the surround

Lateral inhibition

ability of an active neuron to inhibit the activity of adjacent neurons

P cell

small ganglion cell that responds to high contrast and color

M cell

large ganglion cell that responds to all wavelengths regardless of color, subtle differences in contrast and stimuli that come and go rapidly

K cell

a ganglion cell that doesn’t fit the criteria for P or M cells exactly and responds to blue and yellow light

Optic chiasm

the area at the base of the brain where the optic nerves cross to form the optic tracts, the location of a partial decussation of the optic nerves in humans

Optic tracts

the fiber pathways between the optic chiasm and destinations in the forebrain and brainstem

Superior colliculus

a structure in the tectum of the midbrain that guides movements of the eyes and head toward newly detected objects in the visual field

Lateral geniculate nucleus (LGN)

nucleus within the thalamus that receives input from the optic tracts

Magnocellular layers

the 2 ventral layers of the LGN that receive input from M cells in the ganglion layer of the retina

Parvocellular layers

the 4 dorsal layers of LGN that receive input from P cells in the ganglion layer of retina

Koniocellular layers

layers of very small neurons between the larger 6 layers of the lateral geniculate nucleus that receive input from K cells in the ganglion layers of the retina

Primary visual cortex or striate

location of the occipital lobe for the initial cortical analysis of visual input. Aka V1 (visual area 1)

Simple cortical cell

a cortical interneuron that responds stimuli in the shape of a bar or edge with a particular slant or orientation in a particular location on the retina

Complex cortical cell

a cortical interneuron that shows a preferred stimulus size and orientation, and in some cases direction of movement, but not location within the receptive field

End stopped cells

cortical interneuron that responds most vigorously to a stimulus that doesn’t extend beyond the boundaries of its receptive field

Ocular dominance column

a column of cortex perpendicular to the cortical surface that responds to input from either the right or left eye, but not to both

Orientation columns

a column of primary visual cortex that responds to lines of single angle

Hypercolumn

a complete set of orientation columns that span 180 degrees

Cytochrome oxidase blobs

an area of primary visual cortex rich in the enzyme cytochrome oxidase that responds to color

Cortical module

a unit of primary visual cortex containing 2 sets of ocular dominance columns, 16 blobs and 2 hypercolumns

Dorsal stream

pathway leading from primary visual cortex in a dorsal direction thought to participate in the perception of movement

Ventral stream

pathway of information from primary visual cortex to the inferior temporal lobe that is believed to process object recognition

Area MT

an area in medial temporal lobe believed to participate in motion analysis

Area MST

an area in medial temporal lobe believed to participate in large scale motion analysis

Area IT

an area in inferior temporal lobe believed to participate in object recognition

Fusiform face area (FFA)

an area in inferior temporal lobe believed to participate in the recognition of familiar faces, especially in the right hemisphere

Grating

a striped stimulus used to study responses to spatial frequency

Spatial frequency analysis

a way of describing visual processing as a basic mathematical analysis of visual field

Contrast sensitivity function (CSF)

the mapping of an individual’s thresholds for contrast over a range of frequencies

Retinal disparity

slightly different views of the visual field provided by the 2 eyes

Binocular cell

a cell in the cerebral cortex that responds to input from both eyes

Disparity selective cell

binocular cortical cell that responds when its preferred features are seen by different parts of the 2 eyes

Trichromatic theory

the theory that suggests human color vision is based on our possessing 3 different color photopigments

Opponent process theory

a theory of human color vision based on 3 antagonistic color channels= red green, blue yellow, black white

Dichromacy

having eyes that contain 2 different cone photopigments

Monochromacy

the ability to see in black and white only

Anomalous trichromacy

a condition characterized by having 3 cone photopigments that respond to slightly different wavelengths than normal

Color contrast

fact that colors can look different depending on the surrounding colors

Color constancy

the concept that an object’s color looks the same regardless of type of light falling on the object

Presbyopia

the reduced rate and extent of accommodation by the lens that results from aging

Amblyopia

condition also known as lazy eye, in which one does not track visual stimuli