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Perception block 11 > Visual Cortex > Flashcards

Visual Cortex Flashcards

1
Q

Cerebral cortex lobes

A

Frontal, parietal, temporal, and occipital

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2
Q

Gray matter of cerebral cortex

A

Cell bodies
4mm thick
2200cm2

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3
Q

White matter

A

Underlying

2000 miles of axonal connections

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4
Q

Where is the striate cortex located

A

Occipital lobe

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5
Q

Name of straite cortex derived from

A

Gennari

-distinctive band formed by myelinated geniculate axons that synapse in layer 4B

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6
Q

Other names for the striate cortex

A
  • primary visual cortex
  • visual are 1
  • V1
  • Brodmaan area 17
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7
Q

Layers of striate cortex

A

Comprised of 6 layers

  • layer 1 is the most superficial
  • layer 6 the deepest
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8
Q

Striate cortex contains a representation of the

A

Entire visual field

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9
Q

Striate cortex is dominated by

A

The fovea input

  • fovea comprises only 0.01% of the retinal area; yet is represented in at least 8% of striate cortex
  • this cortical magnification of fovea vision may be due primarily to the increased area of cortex devoted to individual fovea ganglion cells, rather than solely to the high density of fovea ganglion cells
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10
Q

What is the cortical magnification of the fovea vision in the straite cortex due to

A

Increased are aof cortex developed to individual ganglion cells, rather than solely to the high density of fovea ganglion cells

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11
Q

Striate cortex projects to

A

Extra striate cortex

-region of visual cortex not distinguished by the line of gennari

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12
Q

Areas of extra striate cortex to study

A
  • visual area 2 (V2)
  • visual area 4 (V4)
  • inferotermporal cortex (IT)
  • middle temporal cortex (MT) or visual area 5 (V5)
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13
Q

How many areas are predominantly for processing visual info?

A

20 differnt areas

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14
Q

What are the two streams of cortical processing for visual information

A

Ventral processing stream

Dorsal processing stream

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15
Q

Ventral processing stream

A
  • temporal pathway
  • “what” system
  • though to receive its predominant input from the parvo RGN pathway
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16
Q

Dorsal processing stream

A
  • parietal pathway
  • “where” system
  • thought to receive its predominant input from the magno pathway
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17
Q

Are the two different visual systems pathways independent or do they communicate

A

There is significant communication between the two cortical processing streams

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18
Q

Other than the extra striate cortex, where does the striate cortex project

A

Major reciprocal projection to the LGN, as well as a projection to the pulvinar
-pulvinar-thalamic nucleus thought to be associated with visual attention, motion processing, and visually guided movement

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19
Q

Pulvinar-thalami nucleus

A

Thought to be associated with visual attention, motion processing, and visually guided movement

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20
Q

Projections to lower visual centers (LGM and pulvinar) from the straite cortex are from what layers

A 
Deeper layers (layer 6) 
-those to extra striate cortex are from more superficial layers (2 or 3)
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21
Q

Information flow in striate

A

Flows back toward striate cortex from extrastriate cortex via reciprocal pathways

  • analogous to the retinal centrifugal pathway and the reciprocal projection from striate cortex to the LGN
  • feedback to the receptorve field properties of V1 cells
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22
Q

Center-surround of retinal ganglion cell receptive fields

A

Science is initially looked for similar cells in straite cortex, however, experiments did not reveal such cells

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23
Q

Hubel and Wiesel

A
  • unexpectedly found neurons in cat striate cortex that were sensitive to elongated stimuli, such as bars and edges
  • divided these cells into two general categories (simple and complex cells)
  • later found comparable cells in monkey cortex
  • Nobel prize
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24
Q

Most sensitive to an edge or bar of a specific orientation

A

Simple cells

  • mus be specific width
  • bar or edge must be properly positioned within the cells receptive field
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25
Q

Mapping of simple cells

A

Simple cells receptive fields can be mapped out with small spots of light, doing so reveals receptive fields that are divided into antagonistic excitatoy and inhibitory regions

26
Q

May results from input of LGN neurons whose receptive fields lie along a straight line

A

Simple cell

27
Q

The formation of increasingly complicated receptive field arrangements from less complicated arrangements is referred to as

A

Serial, or hierarchical, processing

28
Q

Serial or hierarchical processing in retina

A

Also occurs in the retina where the comparatively simple receptive fields of distal retinal elements give rise to the spatially antagonistic receptive fields of bipolar cells

29
Q

Respond best to an elongated stimulus of a specific orientation, but stimulus position is not critical

A

Complex cells

30
Q

These are characterized by direction selectivity-for the cell to be stimulated, the stimulus must move in a specific direction. A stimulus moving in the opposite direction, even if of the proper orientation, does not elicit a response

A

Many complex cells

31
Q

Excitatory and inhibitory regions of complex cells

A

Unlike simple cells, the receptive fields of complex cells cannot be divided into separate excitatory and inhibitory regions

32
Q

Theory of complex cells

A
  • initially thought that complex cell receptive fields are result of hierarchical processing. Complex cells do not manifest separate excitatory and inhibitory areas, so this doesn’t work
  • spatially nonlinear LGN calls play a larger role in the formation of complex cell receptive fields than for simple cells
33
Q

Complex cells: neurons that are sensitive to the stimulus length

A
  • these send stopped neurons were originally classified as hyper complex cells
  • subsequent examination of visual cortex revealed this feature to be common to many cortical cells
  • therefore, hypercomplex cells are generally not considered to be a separate category of cortical neurons
34
Q

Hierarchical processing model holds that receptive fields of higher neurons are

A

Constructed from those of preceding neurons
-explains why stimulus parameters required to activate neurons become more specific at progressively higher levels of the visual system

35
Q

Hierarchical processing of the cells

A

PR respond to diffuse light
Ganglion cells respond to light of certain diameter
Simple cells to a bar of light of a specific orientation
-complex cells to this same bar of light moving in the proper direction

36
Q

The higher I up in the visual system, the more

A

Stringent are the requirements to drive a visual neuron

37
Q

The concepts of parallel proecssing and hierarchical processing

A

Are compatible

38
Q

Hierarchical processing occurs along each of the

A

Parallel pathways

39
Q

Cortical neurons respond well to ____ and are selective for a particular

A

Sine0wave gratings

Spatial frequency

40
Q

Most critical neurons are ____, meaning they receive input from both eyes

A

Binocular

-demonstrated by recording from a binocular cortical cell while stimulating one eye

41
Q

Horopter

A

Line or surface containing all those points in space whose images fall on corresponding points of each eyes retina

42
Q

What may mediate stereo-sis

A

Binocular cortical cells

43
Q

Binocular cortical cells and stereo-sis

A

The cortical receptive fields do overlap at a critical distance form the eyes

  • because the inputs from the two eyes are summed, a stimulus located at this critical distance maximally activates the cortical neuron
  • the stimulus distance can thereby encode, presumably contributing to the physiological basis for stereo-sis
44
Q

The majority of striate cortical neurons are binocular, however

A

Mose are dominated by one eye

Stimulation of a neuron through the dominant eye causes a stronger response than stimulation though the fellow eye

45
Q

Ocular dominance

A

Laid out in a regular pattern of alternating right nad left ocular dominance bands, sometimes called ocular dominance slabs or columns

  • the bands run though the substance of the cortex, perpendicular to its surface
  • an electrode that penetrates the cortex perpendicular to its surface tends to encounter neurons dominated by the same eye
46
Q

How is the striate cortex organized

A

According to its orientation as well as ocular dominance

47
Q

A complete set of ocular dominance columns (both eyes) and orientation columns (all orientations)

A

Hypercolumn

-each hypercolumn has dimensions of approximately 1x 1mm

48
Q

Orientation sensitivity is seen to be arranged in a ______ where each sector extending from the center of this represents a different orientation, when looking upon the surface of the cortex

A

Pinwheel
-with such an arrangement, an electrode penetrating the cortex parallel to its surface may encounter a systematic change n orientation as originally described by hubel and Wiesel

49
Q

Development of standard cortical architecture and normal visual input early in life

A

Cortical architecture may be altered by environmental deprivation early in life
May occur in certain forms of anisometropia and strabismus

50
Q

The parallel processing found in the RGN pathway continues

A

Continues into the striatecortex and beyond
-stringing striate reveals irregular pattern of blobs within its superficial layers, regular pattern of stripes in adjoining visual area 2

51
Q

____ are rush with concentrially organized double color-opponent neurons that result from parvo input

A

Straite blobs

-optimally repsosnive to stimuli that manifest color contrast

52
Q

Interblob region

A

Superficial region of striate cortex between blob

Also appears to receive substantial parvo input

53
Q

Striate cortex architecture: magno and blobs

A

The magno pathway apparently bypasses blobs and the interblob regions, the parvo and magno pathways provide input to the ventral and the dorsal processing stream, respectively. Neither of the RNG pathways, however, feeds exclusively into one of the cortical processing streams

54
Q

Lesion that destroys the striate cortex

A

A patient with blindsight has no conscious visions

55
Q

Double opponent receptive field in the striate cortex

A

Red center and a green annulus is most responsive stimuli

56
Q

Single opponent striate cortex

A

Most responsive to a red center and a dark annulus, not a green annulus

57
Q

Magno and blob

A

Bypasses blood and interblob

58
Q

Secondary to a lesion that has destroyed all of striate cortex, a patient with ______ has no conscious vision

A

Blindsight

59
Q

Lesion to striate cortex and blindsight: under certain circumstances

A

The patient will respond to a visual stimulus while claiming that no stimulus is seen
-force choice methodology

60
Q

Results of forced choice in blind with lesion at striate cortex

A

Performance as locating the stimulus is above chance

  • visual information is presumably processed along pathways that bypass striate cortex, but may activate extrastriate cortex
  • superior colliculus and pulvinar
  • this may result in nonconscious vision-blindsight

Perception block 11 (8 decks)

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