Visuoconstructive Functioning Flashcards
Visual Agnosia
Inability to recognize familiar objects not related to loss of visual acuity – familiar objects can be seen but not recognized
Prosopagnosia
special case of agnosia in which recognition deficits specific to faces
Object Vision Pathway
VENTRAL; primary visual cortex; secondary visual cortex; inferior longitudinal fasciculus; posterior inferotemporal cortex
Spatial Vision Pathway
DORSAL; superior longitudinal fasciculus;; posterior parietal lobe
Temporal route
important for recognizing objects
Parietal route
important for spatial location of objects
Monkey Double Dissociation
temporal lobe- impaired time in object discrimination but could do the spatial task
parietal lobe- could not do spatial task as quickly but could do object recognition
Methods of Monkey Double Dissociation?
Monkeys had to either learn to choose an unfamiliar object or choose object nearest a “landmark”–> removed parts of brain in either temporal or parietal lobe–> dictated the difficulties in performance
Parietal lobe neurons
60% of neurons are responsive to peripheral (non-foveal) parts of visual field–> spatial location
Temporal lobe neurons
receptive field always includes fovea; differential sensitivity to various objects; 41% excited by various stimuli, 59% demonstrated selectivity
How are objects defined?
object constancy; color & texture; variability in sensory information
object constancy
recognize objects in infinite orientations
color & texture
even when inappropriate, still able to recognize things
variability in sensory information
viewing position; distance from retina (size constancy even though they appear different sizes bc of distance); rarely seen in isolation
Viewer centered recognition
perception depends on recognizing objects from a variety of perspectives: stored representations for each perspective, match templates in memory to stimulus
Problems with viewer centered recognition
need template for each object, need multiple templates for each object, driven by a single cell (grandmother cells &; gnostic units), loss of cell, novel objects
grandmother cells
coined to convey the notion that recognition arises from the activation of neurons that are finely tuned to specific stimuli
gnostic unit
type of neuron that can recognize a complex object (Greek “of knowledge”), cell (or cells) signal the presence of a known stimulus
object-centered recognition
sensory input gives basic properties: objects defined on relationship among basic properties; major/minor axis
object-centered recognition occurs by parts
basic building blocks analyzed; ensemble hypothesis says recognition results from specific combination of core features; explains confusion of visually similar objects; allows for recognition of novel objects
geons
attempts to try and define building blocks
apperceptive visual agnosia
failure in object recognition with basic visual functions (acuity, color, motion) preserved; difficulty with copying; deficits in object constancy;
how to test for apperceptive visual agnosia?
unusual views test; incomplete figures test—> difficulty with perceptual categorization, thus cannot recognize from usual views based on constancy
associative agnosia
not attributed to perceptual difficulties; can copy & perform subtle shape discriminations; can perform unusual views test; still can’t name it
Warrington Model
left hemisphere systems: semantic categorization & visual analysis; right hemisphere systems: perceptual categorization & visual analysis
lesion in left-hemisphere causes?
associative agnosia
lesion in right-hemisphere causes?
apperceptive agnosia
problem with warrington model
fails to capture difficulty with integration
integrative agnosia
to recognize objects, individuals examine each piece in isolation and put together; appears to be a core deficit underlying many agnosias
Behrmann et al 2006
These results
suggest that encoding the spatial arrangements of parts of an object requires a mechanism that is different
from that required for encoding the shape of individual parts, with the former selectively compromised in integrative agnosia
prosopagnosia
isolated deficits in facial recognition
damage causing prosopagnosia
most frequent following bilateral lesions; possible following right lesions; rare following left lesions; tend to be focused in occipital temporal regions
