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112 Cards in this Set
- Front
- Back
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Which parts of the visual pathway include center-surround signals?
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Both the ganglion cell inputs to the LGN and the outputs of the cells in LGN are sensitive to spots of light (ON) or decrements of light (OFF) of particular size.
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Mapping within each layer of the LGN is...
Mapping in the striate cortex is... |
Mapping within each layer is retinotopic, i.e. if we record perpendicular to the surface of the LGN we’ll find that neighboring locations across each layer correspond to neighboring locations on the retina (and therefore the visual field).
SAME for v1 |
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Describe how the layers of the LGN are organized
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The ipsilateral eye (or the eye on the same side) projects to layers 2,3, and 5. The contralateral eye projects to layers 1,4, and 6.
In addition to being organized by eye, the layers are also differentiated by the cells that they contain that are sensitive to different types of stimuli. Layers 1 and 2 contain M-cells or magnocelluar cells. These cells have medium to large cell bodies that are sensitive to low spatial frequency information, and that are sensitive to flickering or moving stimuli. Layers 3 through 6 contain P-cells or parvocellular cells which have smaller cell bodies, and are sensitive to sustained stimuli, high spatial frequency information. |
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What does the parvocelluar pathway detect? Magnocellular?
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Parvo: color, pattern, fine texture
Magno:movement, flicker |
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Describe complex cells
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Most common cell type in V1 (75% of cells in V1). Larger RFs than simple cells.
Also stimulated by bars of particular orientations, but less sensitive to location within the RF (bar can be anywhere in RF to elicit response). In addition, many are sensitive to particular directions of motion of the bar, frequently in a direction perpendicular to the orientation of the bar. |
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Describe hypercomplex cells
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- prefer bars or edges at a particular orientation, moving in a particular direction, but the bar/edge must be of a particular length. If it is smaller or larger than the optimal size of the receptive field, the cell will fire less.
- made up of multiple complex cell RFs (excitatory and inhibitory) |
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Describe simple cells
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Simple cells like bars oriented at particular orientations.
RFs can be mapped out by individual spots of light. |
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Describe cortical cells
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Cortical cells are also organized in terms of the orientations they prefer and the eye from which they project, so if we record perpendicular to the cortical surface, we’ll find cells that like a particular orientation, or that project from one eye or the other.
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How are all these columns of specific cell types organized in cortex?
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cells are organized in hypercolumns: 1 mm square of cortex, devoted to processing information at one location in the visual field, containing an ocular dominance column for each eye, where each ocular dominance column is divided into a number of orientation columns.
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What is distortion of the cortical area favoring the fovea called
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cortical magnification
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Describe migraine fortification illusions
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Starts as small disturbance w/serrated arcs normally close to fovea, radiates outward, gets faster, and arcs get bigger.
Hallucinations caused by constriction of blood vessels traveling across cortex (affect on vision similar to electrical stimulation). Subsequent pain caused by re-dilation of vessels following the same path. |
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When cortical areas are connected with forward connections..
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When areas are connected with forward connections they are almost always also connected with backward connections. This forms feedback loops.
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Describe the ventral pathway
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"what"; temporal lobe.
originates small and medium ganglion cells-> in P cells; synapse in the parvocellular layers of LGN |
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describe the dorsal pathway
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Dorsal pathway begins in large ganglion cells
"where"; parietal lobe Called M-cells Axons synapse in layers 1 & 2 of LGN Called magnocellular layers |
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Describe the flow in the ventral pathway
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P ganglion cell- parvo pathway- v1-v2-v4- IT
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Describe the flow in the dorsal pathway
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M ganglion cell - magno pathway- v1-v2-v3-MT- parietal
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Which pathway is also called the action pathway
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Where
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Describe left hemisphere processing
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more piecemeal, analytic, special emphasis on temporal relationships
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Describe right hemisphere processing
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more global, holistic, special emphasis on spatial relationships
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The spotlight of attention can be specific to...
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a depth plane or an object
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Attentional effects are created in the genticulostriate pathway by ...
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by feedback from higher areas (backward connections)
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What modulates activity in V1
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attention; Stronger with context dependent responses
Occurs with late rather than early responses |
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What is involved in shifting attentoin
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parietal lobe (area 7)
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What is unilateral neglect
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The patient is unaware of things in the contralateral field if there are competing things in the ipsilateral field
The patient has difficulty in shifting attention to contralateral field This is due to difficulty in disengaging attention from the ipsilateral field ** due to parietal lobe damage** |
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What is balint's syndrome
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Bilateral parietal/occipital damage
Almost complete inability to see anything except a single fixated visual object |
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What are the symptoms of baliants syndrome
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Ocular apraxia – inability to change fixation
Simultagnosia – only one object at a time Spatial disorientation – inability to localize Optic ataxia – inability to reach to an object |
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Where are effects of selective attention seen in the visual pathway
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V4 & IT
color & orientation tuning curves in V4 are enhanced by attention receptive fields in V4 and IT contract around the attended location, filtering out stimuli in other locations |
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what causes visual agnosia? what is it?
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Cortical temporal lobe damage
failure to visually recognize familiar objects not due to sensory, attentional, or cognitive deficits |
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What is aperceptive agnosia? what causes it?
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Recognition fails because of an impairment of higher-level visual perception
patient unable to piece together visual elements to make a whole cannot copy, match, or discriminate simple visual forms this is a failure of pattern organization |
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What is associative agnosia
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Perception adequate to allow recognition and yet recognition does not take place
can trace, copy, and match stimuli unable to make the association between the perceptual experience and its meaning |
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What is prosopagnosia
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Inability to recognize familiar faces
may perform normally on face discrimination and matching patient may not recognize his or her own face (e.g., in a photograph) associated with the “fusiform face area” (FFA) in the fusiform gyrus |
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Describe the lateralization of the agnosias
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Apperceptive agnosia: usually right hemisphere
Associative agnosia: usually bilateral Prosopagnosia: usually right hemisphere or bilateral |
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What are the laws of gestalt psychology
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1.) good continuation- smooth contour percieved as a unit
2.) proximity- items near eachother tend to be grouped 3.) common fate- motions in the same direction tend to be grouped 4.) symmetry- symmetrical forms tend to be grouped as figure 5.)similarity- similar forms or figures tend to be grouped |
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what are the evidences for parallel and serial processing
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texture segregation and visual search
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DO feature conjunctions create texture segregations?
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no
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Texture segregation is based on...
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simple features, such as color or orientation, or straight vs curved
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Describe parallel processing
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Simultaneous across visual field (parallel)
pre-attentive (“pops out”) early stages of cortical processing produces texture segregation single features, not conjunctions |
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Describe serial processing
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One-at-a-time (successive) processing
requires attention later stages of cortical processing does not produce texture segregation produces conjunctions of features |
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Whats the difference between parallel and serial search
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serial search time increases with the number of distractors
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What is automatization
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Boundary between parallel and serial can change somewhat over time
serial processes can become more parallel with practice *the STROOP TEST** measures automatization in reading |
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What is "bottom up" processing?
WHat is is influenced by? |
Bottom up: Retina -> LGN -> V1 ->
Influenced by top down- attentoin, memory... etc ** top down strongest when bottom up is weak** |
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What is perceptual flexibility
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using incomplete figures to test ability to actively search and find perceptual organization
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what do taking into account mechanisms involve?
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perception of the relevant physical variable
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What together give good distance perception in near space
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Accommodation, vergence, and binocular disparity (horizontal plus vertical); needs an extended target (not a point)
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The relation between elevation and distance is ...
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nonlinear; at further distances, elevation seems more compressed
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what is the effect of angular magnification on distance perception
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compresses distances
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how does vergence relate to size constancy
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vergence always scales size directly; vergence/size relation is always correct
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what is the disctinction between a linear and a compression gradient
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linear has CONVERGING parallel lines! compression_> lines do not converge
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describe geometric illusions
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illusions are simple line figures that produce large errors in perception
They produce illusions of extent (length), alignment, size, angle, and shape *most popular type of illusion* |
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Which are illusions of extent?
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Ponzo, Muller-Lyer
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WHich are illusions of alignment
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Morinaga, Poggendorff
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Which are illusions of size
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Jastrow, Ebbinghaus
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Which are illusions of angle
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Zollner, twisted cord
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Which are illuisions of shape
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Horizontal/vertical bisection, Shepard's
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What is the prevailing theory behind geometric illusions
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acute angle expansion (though eye movement and lateral inhibition are also thought to play roles)
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what are the 2 scene processing theories
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1- attend to 3d scene
2- attend to the information about the flat surface of the picture ** cross talk between the 2 prodces illusions!** |
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what is the primary scaling theory?
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Secondary scaling theory says the illusion is perceived as a 3-D picture in depth
then perceived size is scaled by perceived depth Primary scaling theory says perceived size is scaled directly by the contextual configuration ***It describes illusions as being produced by mid-level, rather than high-level mechanisms*** |
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What causes lightness constancy
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ratios of luminance remain constant as illuminance changes -- this provides a basis for lightness constancy
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What are the low level lightness constancy mechanisms
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“sensory”, early stages of visual processing; very local
1.)lateral inhibition 2.) simultaneous contrast |
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What are the mid level lightness constancy mechanisms
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perceptual; at a higher level of processing, operate over a wider spatial range but are still somewhat local
1.)uses ancoring- lightest seen as white 2.)uses grouping 3.)uses articulation |
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what are the two ilusions that use grouping?
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koffka's rings and white's illusion
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What causes the illusion of occlusion?
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1.) familiarity not necessary
2.) t junctions 3.) relatability - can envision a complete object underneath |
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what does transparency depend on?
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relations between regions:
-x junctions -contrast reduced by transparent surface -contrast polarity maintained by transparent surface |
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Describe the 4 kinds of edges
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1.) orientation- due to abrupt changes in surface orientation
2.)depth edges- due to gaps between surfaces at different distaces 3.) reflectance edges- due to changes in surface material 4.)illumination edges- due to shadows |
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what is subject relative motion
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motion relative to the observer (“subject”)
the observer is stationary with one spot of light moving in the dark there is only subject-relative motion |
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what is corollary discharge
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a copy of the eye movement commands that is sent to the perceptual system
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what cortical area is responsible for sensing "real movement" in monkies
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V3
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What is object relative motion
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motion of objects relative to eachother
*independent of eye movements* |
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What is induced motion
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environment moves, not object, but visual system percieves it as the object moving, not the envt
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what does the assumption of stability do to induced motion
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evt moves slow- only object seen as moving
envt moves moderately- both seen as moving envt moves too fast- illusion broken, only envt seen as moving |
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What are the 6 possible motions of a rigid object
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3 in the frontal plane (2 translations, one rotation), 3 in depth(one translation, 2 rotations)
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What is looming
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The expansion produced by an approaching object
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What are the responses to looming
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includes ducking, blinking, etc. as well as the perception of an approaching object
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where is the neuronal basis for perception of motion in depth in cats? monkeys?
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cats: V2
Monkeys: MST |
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Are static and stereo motions in depth processed the same way?
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No- different systems for processing
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What is the KDE
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kinetic depth effect; If an entire object rotates in depth, every point on it follows a circular path
we see a single coherent object rotating in depth |
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What does polar projection result in
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perception that the front of the circle is rotating faster than the back
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What does parallel projection result in
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ambiguous direction of rotation because the path is exactly halved into front and back
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What can stereo rotation in depth be used for
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discerning direction of rotation;
people who have difficulty w static rotatoin in depth may be able to see stereo rotation in depth |
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what does the rigidity assumption result in
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expansion is seen as looming
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What is structure of motion
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A rotating object gives us information about its motion and also about its 3D structure; seen in KDE.
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describe dynamic occlusion in rotating objects
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When an opaque object rotates, one part occludes (hides) another
this occlusion removes the ambiguity of parallel projection occlusion specifies only the order of depth, not the amount of depth removing the ambiguity about depth order also removes the motion ambiguity |
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The visual system is very good at using motion parallax to ...
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percieve 3d structure
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Describe gradients of motion parallax
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If a surface is slanted, motion parallax decreases gradually with distance
this is a “gradient” of motion parallax it produces accurate perception of 3D slant the gradient of motion parallax is object relative motion and so is independent of eye movements |
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describe perceptually reversible 3d structures
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This is easier with monocular vision or at larger distances
When the observer moves, the structure appears to transform |
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What is an example of a perceptually reversible 3d structure
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the mach-eden card
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The sensing of self-motion with vision is called...
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visual kinaesthesis
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Describe the neural response to optical flow
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-Single cell recording in the primate neurons
-area MST (medial superior temporal) receives input -neurons in the dorsal portion, MSTd, have receptive fields selective for optical flow some of these neurons may also help to integrate optical flow with eye movements |
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What are the nonvisual sensors of self motion
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Joint receptors in the limbs
pressure receptors in the feet vestibular system |
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Describe the vestibular system
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- in the temporal bones
otolith organs sense linear acceleration semicircular canals sense angular acceleration major output to vestibular nuclei contributes to compensatory eye movements also sends output to cortex and cerebellum |
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Describe the visual-vestibular problem
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visual kinaesthesis is the perception of self motion, depends on assumption that the ENVT is STABLE
-vestibular system suggests env is NOT stable |
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Vection is strongest for...
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slow accelerations and constant velocities
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WHen does the vestibular system dominate perception of motion
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with rapid accelerations
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What are the visual requirements for vection
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1. will be seen down to scotopic conditions'
2.vection is maintained with BLUR 3.vection increases as visual field increases |
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Visual input dominates when...
Vestibular input dominates when... |
visual input dominates at low linear and angular accelerations
vestibular input dominates at high linear and angular accelerations |
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What are the results of unilateral vestibular defecits? bilateral?
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unilateral damage produces nausea & vertigo, head tilt, perceived scene tilt, nystagmus, and postural imbalance
bilateral damage leads to postural instability |
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Where does environmental agnosia affect? What are its causes?
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Posterior parietal cortex deficits
Damage comes from various sources, such as stroke, tumor, or head trauma Produces spatial disorientation, called environmental agnosia Can also produce difficulty with various tasks, such as getting dressed (called dressing apraxia) |
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Initial size of negative aftereffect is usually about...
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85% of the prism displacement
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Recalibration of visual direction could be produced in two ways:
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purely visual adaptation
change in felt position of the eye in the orbit |
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In reading, which is more important: number of character spaces or visual angle?
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Number of character spaces is usually a more meaningful measure in reading than visual angle
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Describe saccades while reading
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The saccades average about 20 to 35 msec
They average about 7 to 9 character spaces Reading occurs during fixations averaging 200 to 250 msec There are no smooth pursuit movements *great variation, though* |
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How many saccades are regressive? why>
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10-15 percent; due to comprehension problems or are corrective
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What is the perceptual span
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The ‘perceptual span’ is the area over which information is taken in on a fixation
It is determined both by acuity and by the reading process Acuity would allow information to be obtained from the line below the one being read Because reading is sequential this information is ignored and does not influence reading The perceptual span overlaps from one fixation to the next -in english, smaller on the left than on the right; starts 4 characters inbon the left, goes 15 out on the right |
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How can perceptual span be measured
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"moving window" technique
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Where is the window of consciousness
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typically only the word being fixated on; smaller than the perceptual span
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What determines duration of fixation
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Where to move the eyes is determined by low-level information (word boundaries)
When to move the eyes is determined by the actual processing of the word information |
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What is Hebb's rule
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“If neuron A repeatedly takes part in firing neuron B, then some growth process of metabolic change takes place in one or both cells, such that A’s efficiency, as one of the cells firing B, is increased.”
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WHere is "working memory" stored
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prefrontal areas
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What is the temporal lobes role in long term memory
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hippocampus: long-term memory formation; removal of hippocampus- retention of old memories, no EPISODIC memories made, but NEW PROCEDURAL MEMORIES POSSIBLE
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What are the characteristics of perception
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1. perception is a physiological process
2.) perception is mechanistic 3. perception is functional (ecological) 4. perception is modular 5. perception is selective 6. perception is active |
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what is Synaesthesia
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stimulating one sense modality produces an experience in another sense modality
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what is the perceptual cycle
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information-processing-perception--action-information
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