occipital and temporal lobe - visual perception and memory Flashcards
(28 cards)
what does it mean that processing of visual information by the brain is hierarchical?
complexity of visual representation increases from retina to visual association cortices and beyond
what is functional differentiation?
at different stages of information processing
different neuron types or brain regions processing different properties of visual stimuli
what are simple features?
start of hierarchy
light intensity and wavelength
2D position in visual field - different parts of vision activate different parts of retina
how does it go from simple features to complex features?
via combination and elaboration via parallel channels
what are the complex visual representations for perception and memory?
integrated information concerning form, surface (colour, texture), spatial relationships, movement
integration with other sensory modalities (multimodal representations)
how is visual information processed in the extrastriate cortex?
just outside striate cortex
neurons signal “global properties” of visual scenes and objects rather than “component” properties
in retina level, primary visual pathway neurons are differentially sensitive
what is the V1?
simple and complex cells that signal orientation and movement of small part of visual field
what is the V3 and V5?
holistic global signalling
what is the V4?
depends on the wavelengths of light that are reflected
which neurons are only wavelength sensitive?
neurons in primary visual pathway and V2
does the primary visual cortex have holistic representation?
no
neurons that only respond to elongated stimuli of certain orientation
signal component orientation
where is holistic representation from?
V5
what are the two visual information process streams?
following V1 (and perhaps earlier) visual information processing is mediated by two streams that are anatomically and functionally differentiated
dorsal and ventral stream
what is the dorsal stream?
ends in parietal cortex
visuo-spatial (“where”) processing
visuo-motor (“how”) processing
directional information and integration of visual and motor information
what is the ventral stream?
ends in inferior temporal lobe
object analysis (“what”)
helps us to identify objects
what are the effects of lesions in the what/where visual streams?
inferior temporal lobe lesions (ventral stream) in macaques impair object-discrimination (what) but not object location (where)
posterior parietal lesions (dorsal stream) impair object location (where) but not discrimination (what)
what was Milner and Goodale’s study into the what/how visual streams?
ventral stream processes visual information for object perception (what)
dorsal stream processes visual information for visuo-spatially guided action (how)
what does damage/lesions in the occipito-temporal brain and posterior-parietal lobe cause?
patients with occipito-temporal brain damage show severe forms of visual agnosia (deficits in aspects of visual perception without blindness) but intact visually guided actions
patients with posterior-parietal lobe lesions show optic ataxia (deficits in visually guided reaching) with otherwise relatively intact visual function
who was DF?
extensive bilateral ventral-stream lesions
profound visual agnosia
intact visually guided reaching
can act on visual stimulus (visuomotor posting) but is unable to make perceptual judgements (perceptual orientation matching)
what happens in the inferior temporal cortex?
receives inputs from extrastriate cortex and forms final stage in visual processing hierarchy of ventral stream
neurons respond very selectively to specific shapes and objects
stimulus presented and then taken away but neurons keep firing
face cells
what do responses in the inferior temporal cortex show?
invariance to changes in size, orientation and other properties
sustained activity in absence of visual object, reflecting short-term object memory
what are face cells?
some neurons in inferior temporal lobe show highly selective responses to individual faces
highly selective properties compared to those of “gnostic units” or “grandmother neurons”
face cells typically respond to several faces
areas showing selective responses to faces also identified in human inferior temporal lobe using functional imaging
what are “gnostic units” or “grandmother neurons”?
hypothetical neurons at end of processing hierarchy that recognise individual entities
what role does the medial temporal lobe (MTL) play in the processing of visual information?
at end of visual processing hierarchy
combining inputs from ventral and dorsal stream
receives additional inputs from other sensory modalities
in position to elaborate visual representations further and to generate multi-modal representations
