Chapter 6.6 Flashcards
primary visual cortex
is the area of the cortex that receives most of its input from visual relay nuclei of the thalamus (i.e. from the lateral geniculate nuclei). Located in the posterior region of the occipital lobes, much of it hidden from view in the longitudinal fissure.
secondary visual cortex
areas that receive most of their input from the primary visual cortex. Located in two general regions: in the prestriate cortex and in the inferotemporal cortex.
visual association cortex
areas that receive input from areas of secondary visual cortex as well as from the secondary areas of other sensory systems.
prestriate cortex
band of tissue in the occipital lobe that surrounds the primary visual cortex.
inferotemporal cortex
the cortex of the inferior temporal lobe.
The major flow of visual information in the cortex is
from the primary visual cortex to the various areas of the secondary visual cortex to the areas of association cortex. As one moves up, the neurons have larger receptive fields and the stimuli to which the neurons respond are more specific and more complex.
scotoma
an area of blindness; happens when an area of the primary visual cortex is damaged and is produced in the corresponding area of the contralateral visual field of both eyes.
perimetry test
given to neurological patients with suspected damage to the primary visual cortex. Put head on a chin rest and the patient then stares with one eye at a fixation point on a screen. A small dot of light is then flashed on various parts of the screen and the patient presses a button to record when the dot is seen. Result is a map of the visual field of each eye, which indicated any areas of blindness.
Many patients with extensive scotomas are
not consciously aware of their deficits, which may be caused by completion.
hemianopsic
having a scotoma covering half of the visual field. May see an entire face when the focus on a person’s nose, even when the side of the face in the scotoma has been covered by a blank card.
conscious awareness
if a person sees something, he or she will be consciously aware of seeing it.
blindsight
displayed in patients with scotomas resulting from damage to primary visual cortex; the ability to respond to visual stimuli in their scotomas even though they have no conscious awareness of the stimuli.
Perception of motion is most likely to
survive damage to primary visual cortex.
first neurological interpretation of blindsight
The striate cortex is not completely destroyed and the remaining islands of functional cells are capable of mediating some visual abilities in the absence of conscious awareness.
second neurlogical interpretation of blindsight
Visual pathways that ascend directly to the secondary visual cortex from subcortical visual structures without passing through the primary visual cortex are capable of maintaining some visual abilities in the absence of cognitive awareness.
Secondary visual cortex and the portions of association cortex are involved
in visual analysis are both composed of different areas, each specialized for a particular type of visual analysis.
Although connections between areas are
virtually always reciprocal, the major flow of signals is from more simple to more complex areas.
Most visual information enters the primary visual cortex via the
lateral geniculate nuclei and the information from these two nuclei is received in the primary visual cortex, combined, and then segregated into multiple pathways that project separately to the various functional areas of secondary, and then association, visual cortex.
dorsal stream
flows from the primary visual cortex to the dorsal prestriate cortex to the posterior parietal cortex.
ventral stream
flows from the primary visual cortex to the ventral prestriate cortex to the inferotemporal cortex.
Most visual cortex neurons in the dorsal stream respond
most robustly to spatial stimuli, such as those indicating the location of objects or their direction of movement.
Most neurons in the ventral stream respond to
the characteristics of objects, such as color and shape. Each cluster of neurons responds specifically to a particular class of objects – faces, bodies, letter, animals, tools, etc.
Ungerleider and Mishkin
proposed that the dorsal stream is involved in the perception of “where” objects are and the ventral stream is involved in perception of “what” objects are.
“where” versus “what” theory of vision
damage to some areas of cortex may abolish certain aspects of vision while leaving others unaffected.
Goodale and Milner
suggested that the primary function of the dorsal stream is to direct behavioral interactions with objects, whereas the primary function of the ventral stream is to mediate the conscious perception of objects. Been termed “control of behavior” versus “conscious perception” theory.
“control of behavior” versus “conscious perception” theory
suggests that patients with dorsal stream damage may do poorly on tests of location and movement because most tests of location and movement involve performance measures, and that patients with ventral stream damage may do poorly on tests of visual recognition because most tests of visual recognition involve verbal response, and thus conscious, awareness.
Prosopagnosia
visual agnosia for faces. Can recognize a face as a face, but have problems recognizing whose face it is. Some have a general problem of recognizing specific objects that belong to complex classes of objects. Often associated with damage to the fusiform face area because parts of it are selectively activated by human faces.
Agnosia
failure of recognition that is not attributable to a sensory deficit or to verbal or intellectual impairment.
visual agnosia
specific agnosia for visual stimuli. Can see visual stimuli, but they don’t know what they are. Often specific to a particular aspect of visual input.
specific visual agnosia
results from damage to an area of secondary visual cortex that mediate the recognition of that particular attribute.
fusiform face area
ventral surface of the brain at the boundary between the occipital and temporal lobes.
Tranel and Damasio
demonstrated that prosopagnosics can recognize faces in the absence of conscious awareness.
Akinetopsia
deficiency in the ability to see movement progress in a normal smooth fashion. Can be triggered by high doses of certain antidepressants. Often associated with damage to the MT area of the cortex.
MT area (middle temporal area)
located near the junction of the temporal, parietal, and occipital lobes. Sometimes called V5 or MT/V5. Function appears to be the perception of motion. 95% of the neurons here respond to specific directions of movement and little else.
MT neurons
each has a large binocular receptive field, allowing it to track movement over a wide range.
