Ch. 13 Flashcards
Area V1 of the visual cortex is sometimes also called the ______ cortex?
Striate cortex -> due to distinct layers
What are blob & interblob regions responsible for, respectively?
Blob (cytochrome rich areas) -> color perception; Interblob -> form & motion perception
Which two areas of the visual cortex are functionally heterogeneous?
V1 & V2
After V2, what are the three distinct parallel pathways that emerge on route to the parietal & temporal cortices?
Dorsal stream, Superior Temporal Sulcus stream (STS), Ventral stream
What is the main difference between the dorsal, STS, and ventral streams?
Dorsal -> movement perception; Ventral & STS -> object & color perception, & certain movements
What is one interesting effect that can occur from V1 damage?
Patients appear completely blind, yet some information is sent to other processing areas; ex. patient unable to see, but somewhat able to respond to visual information
What is the main role of area V1?
Form, Color, & Motion perception -> information then sent to all other higher processing areas
What is the main role of area V2?
Form, Color, & Motion perception -> information then sent to all other higher processing areas
What is the main role of area V3?
Specialized in dynamic form; shape of objects in motion; form analysis
What is the main role of area V4?
Mainly color information processing, & some form perception
What is the main role of area V5?
Motion perception specialization
What is another name for area V5?
The middle temporal area/area MT
What is “vision for action” processing and what stream is responsible for it?
Visual processing required to direct specific movements (ex. reaching for an object) -> parietal lobe in dorsal stream
What is “action for vision” processing?
Searching/scanning for some part of a target object to attend it selectively
What are the two kinds of “visual space” processing? (Hint: _____centric & _____centric)
Egocentric space -> objects have a location relative to the individual; Allocentric space -> objects have a location relative to one another
What does “visual attention” processing mean?
Neurons in cortex have many attentional mechanisms; may respond selectively to certain stimuli
What did David Milner & Melvyn Goodale propose?
They proposed that the dorsal stream is a set of systems for visual control of action
What 3 findings were Milner & Goodale’s proposal about the function of the dorsal stream based on?
1) Visual neurons in PPC are only active when the brain is acting on visual information; 2) Visual neurons in PPC act as an interface between analysis of visual world & action taken on it; 3) Most visual impairments due to lesions in PC are visuomotor/visuospatial
What are polysensory neurons and which of the three visual processing streams are they associated with?
Polysensory neurons -> respond to visual & auditory input, or visual & somatosensory input; found in the STS stream
What is the proposed function of the STS stream?
Perception of biological motion; i.e., actions of others & visuospatial relation among elements in a scene
What are the two key ways that the brain & eyes organize visual fields?
1) Left half of each retina sends projections to left side of the brain; vice versa for right halves, 2) Different parts of the visual field are topographically represented in different areas of V1
What is monocular blindness?
Complete blindness in one eye only
What is bitemporal hemianopia?
Loss of vision in both temporal fields
What is right nasal hemianopia?
Loss of vision in one nasal field
What is homonymous hemianopia?
Blindness of one entire visual field (i.e., left field of both eyes; NOT blindness of both eyes as a whole)
What is quadratanopia?
Blindness in only one quadrant of the visual field (ex. top left quadrant in both eyes)
What is macular sparing?
The central visual field is not lost despite entire temporal or nasal fields being lost
What is a scotoma?
A small blind spot in the visual field
What is perimetry?
A standardized testing measure; Patient fixates on black dot in the center of a large, white hemisphere; a small light is moved around the field, the task is to indicate when the light is visible
What is the difference of visual agnosia & visual form agnosia?
Visual agnosia -> inability to recognize objects; Visual form agnosia -> inability to recognize the form of object (ex. line drawings of objects)
What are the three identifying features of Balint syndrome?
1) Optic ataxia (deficit in visually guided hand movements); 2) Oculomotor apraxia (deficit in voluntary horizontal eye movements); 3) Simultagnosia (inability to perceive two objects presented simultaneously)
What is prosopagnosia?
Deficit in facial & handwriting recognition (including their own)
What are the two types of object agnosia?
Apperceptive agnosia (aka Visual form agnosia); Associative agnosia
What is the difference between apperceptive (visual form) & associative agnosia?
Apperceptive (ex. simultagnosia) -> any failure of object perception in which basic visual functions (acuity, color, motion) are preserved; Associative -> inability to recognize an object despite being able to perceive it
What is the difference between dorsal & ventral simultagnosia?
Dorsal simultagnosia -> cannot see more than one object at a time; Ventral simultagnosia -> can see more than one object at the same time; unable to perceive unified picture/derive meaning from it
Visual agnosias are always associated with which visual perception stream?
Ventral
What is visuospatial agnosia?
Disorder of spatial orientation; loss of one’s sense of “whereness”/deficit in understanding spatial relationships of objects
What is topographic disorientation?
The loss of ability to orient oneself around a familiar environment -> one kind of visuospatial agnosia
What is aphantasia?
The inability to generate mental images
What do the stripe differences represent in area V2?
Thin stripe -> color perception; Thick stripe -> form; Pale stripe -> motion
