Wolfe chapter 3 + 4

acuity

smaller spatial detail that can be resolved

grating

organization of black and white lines

cycle

for a grating, a pair consisting of one black and one white line

visual angle

angle subtended by an object at the retina

sine wave grating

grating with a sinusoidal luminance profile

aliasing

misperception of a grating due to under sampling

spatial frequency

number of grating cycles in a given unit of space

cycles per degree

number of pairs of dark and light bars per degree of visual angle

contrast sensitivity function (CSF)

function describing how the sensitivity to contrast (reciprocal to contrast threshold) depends on spatial frequency (size) of stimulus

contrast threshold

smallest amount of contrast required to detect a pattern

phase

relative positioning of grating (in receptive field)

lateral geniculate nucleus (LGN)

structure in thalamus, part of midbrain that receives input from retinal ganglion cells and has input/output on connections to visual cortex

magnocellular layer

either of 2 lowest layers in LGN, cells are larger than other layers

parvocellular layer

any of 4 top neurons in LGN, smaller cells

konicelluar cells

cells between magno + parvocellular layers of LGN, each layer has a different function

topographical mapping

shows how world is viewed by LGN and visual cortex

striate cortex

area of cerebral cortex that receives direct input from LGN and feedback from other brain areas, is responsible for processing all visual info

cortical magnification

amount of cortical area devoted to a specific region in visual field

visual crowding

deleterious effect of clutter on peripheral object recognition

orientational tuning

tendency for neurons in striate cortex to respond optimally to certain orientations over others

filter

neurons that allow passage of some frequencies or digital elements and blocks the passage of others

ocular dominance

property of receptive fields of striate cortex neurons by which they demonstrate a preference (when info is in one eye over the other, respond more rapidly)

simple cell

cortical neuron with clearly defined excitatory and inhibitory regions (phase-sensitive)

complex cells

neuron whose receptive field characteristics can’t be easily predicted by mapping with spots of light (phase-insensitive)

end stopping

process by which a cell in the cortex first increases its firing rate as bar length increases, then decreases its firing rate as bar is lengthened further

columns

vertical arrangement of neurons, organization of neurons with similar orientation preferences

hypercolumns

1 mm block of striate cortex containing two sets of columns, each covering every possible orientation (0-180 deg.), with one set preferring input from L eye and one set preferring input from R eye

cytochrome oxidase

enzyme that reveals regular array of “CO blobs”, which are spaced ~0.5 mm apart in primary visual cortex

adaptation

a reduction in response caused by prior or continuing stimulation

tilt after-effect

perceptual illusion of tilt, produced by adaptation to a pattern of given orientation

spatial-frequency channels

pattern analyzer, implemented by an ensemble of cortical neurons, each set of neurons is tuned to a limited range of spatial frequencies

amblyopia

developmental disorder with reduced spatial vision in an otherwise healthy eye (aka “lazy eye”)

strabismus

misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye, and on the non foveal region of the other (turned) eye

anisometropia

condition in which the two eyes have different refractive errors (ex: one is farsighted and the other is not)

extra striate cortex

region of cortex bordering the primary visual cortex and controlling multiple areas involved in visual processing

agnosia

failure to recognize objects despite seeing them

inferotemporal (IT) cortex

part of cerebral cortex, in lower portion of temporal lobe, important for object recognition

feed-forward process

process that carries out computation (ex: object-recognition) one neural step after another, without need for feedback from a later stage to an earlier stage

middle (midlevel) vision

loosely defined stage of visual processing that comes after basic features have been extracted from the image and before object recognition and scene understanding

illusory contour

contour that’s perceived even though nothing changes from one side of it to the other of an image

structuralism

school of thought believing that complex object perception could be understood by analysis of components

gestalt

school of thought stressing that the perceptual whole could be greater than apparent sum of parts

gestalt grouping rules

set of rules describing which elements in an image will appear to group together

good continuation

Gestalt grouping rule stating that 2 elements will tend to group together if they seem to lie on same contour

texture segmentation

carving an image into regions of common texture properties

similarity

gestalt grouping rule, tendency of two features to group together will increase as the similarity between them increases

proximity

gestalt grouping rule that says that the tendency of two features to group together will increase as the distance between them decreases

parallelism

rule for figure-ground assignment, stating that parallel contours are more likely to belong to same figure

symmetry

rule for figure-ground assignment stating that symmetrical regions are more likely to be seen as figure

necker cube

outline of cube, brain is most likely to perceive as bistable, instead of many flat regions

accidental viewpoint

viewing position that produces some regularity in the visual image that’s not present in world

figure-ground assignment

process of determining the some regions of an image belong to a foreground object (figure) and other regions are part of the background (ground)

non accidental features

a feature of the object that is not dependent on the exact (or accidental) viewing position of observer

global superiority

finding in various experiments that properties of whole object overtake properties of parts of object