Ch 6 Definitions: Vision Flashcards
transduction
the transformation of sensory information into neural signals
sensation
the process of obtaining information about the environment & transmitting it to the brain for processing
perception
the process of interpreting 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 processing
the use of knowledge & expectation to interpret meanings
electromagnetic radiation
radiation emitted in the form of energy waves
wavelength
the distance between peaks of a wave; determines color in visible light
amplitude
the height of a wave; in vision, the source of the subjective experience of brightness
photons
individual, indivisible, very small particles that form waves of electromagnetic energy
nanometers
a unit of measurement equaling 10^-9m
used to measure light wave frequency
absorption
the ability to retain something rather than reflect or transmit it to another location
reflection
the bending back of light towards its source
refract
the deflection, or changing of direction, of light at a boundary such as that between air & water
orbit
the bony opening in the skull that houses the eyeball
blink
a rapid closing of the eyelids
sclera
the white outer covering of the eye
cornea
the transparent outer layer of the eye
anterior chamber
the area of the eye located directly behind the cornea, containing aqueous humor
aqueous humor
the fluid located in the anterior chamber that nourishes the cornea & lens
pupil
the opening in the front of the eye controlled by the iris
iris
the circular muscle in the front of the eye that controls the opening of the pupil
lens
the clear structure behind the pupil & iris that focuses light on the retina
accommodation
the ability of the lens to change shape to adjust to the distance of the visual stimulus
vitreous chamber
the large inner cavity of the eyeball
vitreous humor
the jellylike substance in the vitreous chamber
retina
the elaborate network of photoreceptors & 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
the area in the retina where blood vessels & the optic nerve exit the eye
macula
a 6 mm 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
the 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 & gives rise to the 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
the location in the retina containing axons & dendrites that connect the ganglion, bipolar, and amacrine cells
amacrine cell
a retinal interneuron in the inner nuclear layer that integrates signals across adjacent segments of the retina
bipolar cell
a cell in the inner nuclear layer of the retina that forms part of the straight pathway between photoreceptors & the ganglion cells
inner nuclear layer
the layer of retinal interneurons containing amacrine, bipolar, and horizontal cells
outer plexiform layer
the retinal layer containing axons & dendrites forming connections between bipolar cells, horizontal cells, and the photoreceptors
horizontal cell
a retinal interneuron located in the inner nuclear layer that integrates signals from across the surface of the retina
outer nuclear layer
the location in the retina containing the cell bodies of the photoreceptors
rod
a photoreceptor that responds to low levels of light but not to color
cone
a photoreceptor that operates in bright conditions & responds differentially to color
outer segment
the portion of a photoreceptor containing photopigments
photopigment
a pigment conaitained in the photoreceptors of the eye that absorb light
rhodopsin
the 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
a 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
the form taken by retinal after light is absorbed by the rod outer segment
dark current
the steady depolarization maintained by photoreceptors when no light is present
cyclic guanosine monophosphate (cGMP)
a second messenger within photoreceptors that is responsible for maintaining the dark current by opening Na+ 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
the ability of an active neuron to inhibit the activity of adjacent neurons
P cell
small ganglion cell that responds to high contrast & color
M cell
large ganglion cell that responds to all wavelengths regardless of color, subtle differences in contrast, and stimuli that come & go rapidly
K cell
a ganglion cell that does not fit the criteria for P or M cells exactly & responds to blue & 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 & destinations in the forebrain & brainstem
superior colliculus
a structure in the tectum of the midbrain that guides movements of the eyes & head toward newly detected objects in the visual field
lateral geniculate nucleus (LGN)
the nucleus within the thalamus that receives input from the optic tracts
magnocellular layers
the two ventral layers of the LGN that receives input from P cells in the ganglion layer of the retina
parvocellular layers
the four dorsal layers of the LGN that receive input from P cells in the ganglion layer of the retina
koniocellular layers
layers of very small neurons between the larger six layers of the lateral geniculate nucleus that receive input from K cells in the ganglion layer of the retina
primary visual cortex/striate cortex
the location in the occipital lobe for the initial cortical analysis of visual input
also known as V1 (visual area 1)
simple cortical cell
a cortical interneuron that responds to 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 & orientation, and in some cases movement, but not location within the receptive field
end-stopped cells
a cortical interneuron that responds most vigorously to a stimulus that does not 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 column
a column of primary visual cortex that responds to lines of a single angle
hypercolumn
a complete set of orientation columns that span 180 degrees
cytochrome oxidase blobs
an area of the 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
a pathway leading from the primary visual cortex in a dorsal direction thought to participate in the perception of movement
ventral stream
a pathway of information from the primary visual cortex to the inferior temporal lobe that is believed to process object recognition
Area MT
an area in the medial temporal lobe believed to participate in motion analysis
Area MST
an area in the medial superior temporal lobe believed to participate in large-scale motion analysis
Area IT
an area in the inferior temporal lobe believed to participate in object recognition
fusiform face area (FFA)
an area in the 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 the visual field
contrast sensitivity function (CSF)
the mapping of an individual’s thresholds for contrast over a range of frequencies
retinal disparity
the slightly different views of visual field provided by the two eyes
binocular cells
a cell in the cerebral cortex that responds to the input from both eyes
disparity-selective cell
a binocular cortical cell that responds when its preferred features are seen by different parts of the two eyes
dichromacy
having eyes that contain two different cone photopigments
monochromacy
the ability to see in black & white only
anomalous trichromacy
a condition characterized by having three cone photopigments that respond to slightly different wavelengths than normal
color contrast
the 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 the type of light falling on the object
presbyopia
the reduced rate & extent of accommodation by the lens that results from aging
amblyopia
a condition also known as lazy eye, in which one eye does not track visual stimuli
cataract
clouding of the lens
myopia
an acuity problem resulting from an elongated eyeball;
also known as nearsightedness
hyperopia
an acuity problem resulting from a short eyeball;
also known as farsightedness
astigmatism
a distortion of vision caused by the shape of the cornea
scotoma
an area in the visual field that can’t be seen, usually due to central damage by stroke or other brain injury
blindsight
an abnormal condition in which parts of the visual field are not consciously perceived but can be subconsciously perceived by extrastriate cortex
visual agnosia
a disorder in which a person can see a stimulus by cannot identify what is seen
prosopagnosia
the inability to recognize known faces
