occipital and temporal lobe Flashcards
processing of visual information by the brain is…
hierarchal, with the complexity of the visual representation increasing from retina to visual association cortices and beyond
what is there at the different stages of information processing
- functional differentiation with different neuron types or different brain regions processing different properties of visual stimuli
what are simple features
- light intensity and wavelength
- 2D position in visual field
how does visual information processing go from simple to complex features
combination and elaboration via parallel channels
what are complex visual representations for perception and memory
- integrated information concerning form, surface, spatial relationships and movement
- integration with other sensory modalities
what are the components of the occipital lobe
VI
V2
V3
V3A
V4
V5/MT
what do neurons in the extrastriate cortex signal
- global properties of visual scenes and objects, rather than component properties
- V3 and V5
- neurons are differentiatley sensitive
what does perceived colour of an object depend on
- wavelength reflected by object and wavelength reflected by surroundings
what are neurons in V4 sensitive to
- colour sensitive - respond to wavelengths in the centre of their receptive field, depending on the wavelengths reflected from the background
what are neurons in the primary visual pathway and V2 sensitive to
wavelength
what happens in area V5
all information is put together for perception of pattern motion - global and holistic
- true overall direction
what 2 streams are the visual information processing mediated by
- dorsal stream
- ventral stream
what is the dorsal stream
- responsible for visuospatial and visuomotor processing
- allows movement
- directional info
where is the dorsal stream
the posterior parietal cortex
what is the ventral stream
- recognise objects and entities
where is the ventral stream
- inferior temporal lobe
what do inferior temporal lobe lesions impair
- object discrimination/recognition but not object location
what do posterior parietal lesions impair
object location but not discrimination
what did Milner and Goodale propose about the ventral and dorsal streams
- processes visual info for object perception whereas the dorsal stream processes visual info for visuospatially guided action
how do patients with occipito-temporal brain damage support ventral streams
- they show severe forms of visual agnosia - deficits in visual perception
how do patients with posterior parietal lobe lesions support dorsal streams
show optic ataxia - deficits in visually guided reaching with otherwise intact visual function
what does the inferior temporal cortex receive and form
- receives inputs from extrastriate cortex and forms the final stage in the visual processing hierarchy of the ventral stream
how do neurons in the inferior temporal cortex respond
very selectively to specific shapes and objects
what do responses from neurons in the inferior temporal lobe show
- invariance to changes in size, orientation, and other properties - e.g. recognises object regardless of viewpoint
- sustained activity in absence of visual object, reflecting short term object memory
what do some neurons in the inferior temporal lobe show highly selective responses to
individual faces
- inferior temporal lobe keeps firing for the same face despite orientation changing, doesn’t fire for different person’s face
what is at the end of the visual processing hierarchy
the medial temporal lobe
what does the MTL do
- combines inputs from ventral and dorsal stream and receives additional inputs from other sensory modalities
what is the MTL in position to do
- elaborate visual representations further and to generate multi-modal representations
