Midterm 2 Flashcards
What is adaptation?
looking at a pattern of stripes for a certain time will ‘tire’ the neurons and shift the balance in the opposite direction when another orientation is shown
What is a hypercolumn?
A 1-mn block of striate cortex containing all the machinery necessary to look after everything the visual cortex is responsible for
- Each hypercolumn contains cells responding to every possible orientation (0-180 degrees), with one set preferring input from the left eye and one set preferring input from the right eye
- Allows you to perceive lines of different orientations
What is the extrastriate cortex?
- Area beyond V1
- brain regions bordering primary visual cortex that contains other areas involved in visual processing
What do neurons in V4 respond to?
concave, convex, or straight edges
What is the “Where” pathway is concerned with?
the locations and shapes of objects but not their names or functions
What is the “What” pathway concerned with?
the names and functions of objects regardless of location
What is a visual agnosia?
failure to recognize objects in spite of the ability to see them
What is apperceptive agnosia?
Failure of PERCEPTION despite normal vision
- The basic elements of the object are seen but cannot be integrated into a stable percept
- Lesion closer to V1
- Cannot copy
What is associative agnosia?
There is a perceptual representation of the object, but the patient doesn’t know what the object is
- Lesion further away from V1
- Can copy, but cannot identify
- Can recognize object if presented in another modality
What is prosopagnosia?
an inability to recognize the identity of faces
What. are grandmother cells?
cells that are very specific to one type of object, like the face of your grandmother
What are receptive fields of IT neurons?
- Very large – some cover half the visual field
- Don’t respond well to spots or lines
- Do respond well to stimuli such as hands, faces, or objects
What is figure-ground assignment?
the process of determining that some regions of an image belong to a foreground object (figure) and other regions are part of the background (ground)
What is the face inversion effect?
We are better at recognizing faces that are upright
What is the global superiority effect?
the properties of the whole object take precedence over the properties of parts of the object
What is the naïve template theory?
the proposal that the visual system recognizes objects by matching the neural representation of the image with a stored representation of the same “shape” in the brain
What is the inferotemporal (IT) cortex?
Part of the cerebral cortex in the lower portion of the temporal lobe, important for object recognition
What is a feed-forward process?
a process that carries out a computation (object recognition) one neural step after another, without the need for feedback from a later stage to an earlier stage
What is population coding?
distributed activity across hundreds and thousands of neurons
What is a qualia?
entirely subjective property of an object (ex: the redness of red)
What is color-anomalous?
a term for what is usually called “color blindness” – most color-blind individuals can still make discriminations based on wavelength
What is trichromacy?
the theory that the color of any light is defined in our visual system by the relationships of 3 numbers, the outputs of 3 receptor types now known to be the 3 cones
What are metameters?
Different mixtures of wavelengths that look identical; more generally, any pair of stimuli that are perceived as identical in spite of physical differences
- Generally, we don’t see “pure” wavelengths, but rather mixtures of wavelengths
What is additive colour mixing?
a mixture of lights (center of diagram is white)
What is subtractive colour mixing?
a mixture of pigments (center of diagram is black)
What are non-spectral hues?
hues that can arise only from mixtures of wavelengths (ex: there is no purple in the spectrum), it has to come from a particular combination of activity across S, M and L cones
What is opponent colour theory?
the theory that perception of color depends on the output of 3 mechanisms, each of them based on an opponency between two colors: red-green, blue-yellow, and black-white
What is a unique hue?
any of four colors that can be described with only a single-color term: red, yellow, green, blue
What is an afterimage?
A visual image seen after a stimulus has been removed
- Caused by habituation (chromatic adaptation) of activated cones
What is a negative afterimage?
an afterimage whose polarity is the opposite of the original stimulus
What is colour constancy?
The tendency of a surface to appear the same color under a fairly wide range of illuminants
What is the principle of univariance?
An infinite set of different wavelength combinations can elicit exactly the same response from a single type of photoreceptor
What is habituation (chromatic adaptation)?
the cones activated by the illuminant spectrum get tired
What is Euclidian geometry?
The 3 dimensional world
• Images projected onto the retina are non-Euclidean
What is the difference between metrical and non-metrical cues?
Metrical: cue that provides information about distance
Non-metrical: cue that provides information about the depth order (relative depth) but not depth magnitude
What is the difference between relative and familiar size?
Relative: a comparison of size between items without knowing the absolute size of either on
Familiar: a comparison of size between items when knowing the absolute size of one of the items
What is texture gradient?
a depth cue based on the geometric fact that items of the same size form smaller, closer spaced images the farther away they get
What is motion parallax?
images closer to the observer move faster across the visual field than images farther away
What is convergence?
the ability of the two eyes to turn inward, often used to focus on near objects
What is divergence?
the ability of the two eyes to turn outward, often used to focus on farther objects
What is binocular summation?
the combination (or summation) of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone
What is binocular disparity?
The differences between the two retinal images of the same scene
- basis for stereopsis
What is stereopsis?
a vivid perception of the 3-dimensionality of the world that is not available with monocular vision
What is corresponding retinal points?
a geometric concept stating that points on the retina of each eye where the monocular retinal images of a single object are formed are at the same distance from the fovea in each eye
What is the Vieth-Müller circle (horopter)?
The location of objects whose images lie on the corresponding points – the surface of zero disparity
- Objects on the horopter are seen as single images when viewed with both eyes
- Objects significantly closer to or farther away from the horopter fall on non-corresponding points in the two eyes and are seen as two images
What is diplopia?
double vision – if visible in both eyes, stimuli falling outside of Panum’s fusional area will appear diplopic
What. is Panum’s fusional area?
the region of space, in front of and behind the horopter, within which binocular single vision is possible
What is crossed disparity?
the sign of disparity created by objects in front of the plane of the horopter
What is uncrossed disparity?
the sign of disparity created by objects behind the plane of the horopter
What is a stereoscope?
a device for presenting one image to one eye and another image to the other eye
What is the correspondence problem?
in binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye
What is the random dot stereogram (RDS)?
A stereogram made of a large number of randomly placed dots
- RDSs contain no monocular cues to depth
What is cyclopean?
referring to stimuli that are defined by binocular disparity alone
What is binocular rivalry?
the competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes
What is apparent motion?
the illusory impression of smooth motion resulting from the rapid alternation of objects that appear in different locations in rapid succession
What is akinetopsia?
A rare neuropsychological disorder in which the affected individual has no perception of motion
- Can be caused by lesion of areas MT/MST
- Can just see a succession of still images
What is the aperture problem?
the fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of an object may be ambiguous
What is aftereffect (MAE)?
The illusion of motion of a stationary object that occurs after prolonged exposure to a moving object
- Existence of MAE implies an opponent process system, like that of color vision
What is vergence?
a type of eye movement, both voluntary and involuntary, in which the two eyes move in opposite directions
- ex: convergent and divergent
What are reflexive eye movements?
Automatic and involuntary movements
- Ex: when the eyes move to compensate for head and body movement while maintaining fixation on a particular target
What is a microsaccade?
An involuntary small jerk-like movement
- improves visibility of sharp details
What is the superior colliculus?
a structure in the midbrain that is important in initiating and guiding eye movements
What is the frontal eye field?
A structure in the frontal lobe that is important in initiating and guiding eye movements
- Different neurons in the FEF will move the eye to different spots in space
What is saccadic supression?
The reduction of visual sensitivity that occurs when we make saccadic eye movements
- Eliminates the smear from retinal image motion during an eye movement
- Ex: move your eye voluntarily vs by pushing it with your finger (close the other eye)
What is the comparator?
An area of the visual system that receives one copy of the order issued by the motor system when the eyes move (the other copy goes to the eye muscles)
- The comparator can compensate for the image changes caused by the eye movement
What is inattentional blindness?
a failure to notice – or at least report – a stimulus that would easily be reportable if it were attended to
What is change blindness?
the failure to notice a change between two scenes
What is overt?
directing a sense organ toward a stimulus, like turning your eyes or your head
What is covert?
Attending without giving an outward sign you are doing so
- Paying attention without directly looking at it
What is feature integration theory?
Treisman’s theory of visual attention, which holds that a limited set of basic features can be processed in parallel preattentively, but that other properties, including the correct binding of features to objects, require attention
What is a cue?
A stimulus that might indicate where (or what) a subsequent stimulus will be
- Cues can be valid (correct info), invalid (incorrect), or neutral (uninformative)
What is stimulus onset asynchrony (SOA)?
the time difference between the onset of one stimulus and the onset of another
What is Rapid serial visual presentation (RSVP)?
an experimental procedure in which stimuli appear in a stream at one location (typically the point of fixation) at a rapid rate (typically about 8 per second)
What is attentional blink?
the difficulty in perceiving and responding to the second of two target stimuli amid a RSVP stream of distracting stimuli
What is a feature search?
search for a target defined by a single attribute, such as salient color or orientation
What is a conjunction search?
Search for a target defined by the presence of two or more attributes
- The efficiency of visual search is the average increase in RT for each item added to the display
What is serial self-terminating search?
A search from item to item, ending when a target is found
What is a guided search?
attention is restricted to a subset of possible items based on information about the item’s basic features (ex: color or shape)
What is scene-based guidance?
information in our understanding of scenes that helps us find specific objects in scenes
What is the non-selective pathway?
Contributes information about the distribution of features across a scene as well as information about the ‘gist’ of the scene
- This pathway does not pass through the bottleneck of attention
What is the selective pathway?
Permits the recognition of one or very few objects at a time
- This pathway passes through the bottleneck of selective attention
What is a visual-field deficit?
a portion of the visual field with no vision or with abnormal vision, typically resulting from damage to the visual nervous system (occipital lobe)
What is neglect?
damage to the parietal lobe can cause a visual field defect such that one side of the world is not attended to
What is extinction?
in visual attention, the inability to perceive a stimulus to one side of the point of fixation (ex: to the right) in the presence of another stimulus, typically in a comparable position in the other visual field (ex: on the left side)
What is the preattentive stage?
the processing of a stimulus that occurs before selective attention is deployed to that stimulus
