Simple features of neuron firing;
Light intensity and wavelength
2D position in visual field
With combination and elaboration from simple features;
Complex visual representations for perception and memory
Integrated information concerning form, surface, colour and texture, spatial relationships and movement
Integration with other sensory modalities
Main regions involved in visual information processing past V1;
Extrastriate cortex - V2-V5
Inferior temporal cortex - posterior parietal cortex, STS, posterior inferior temporal lobe and anterior inferior temporal
In the extrastriate cortex neurons…
Signal global properties of visual scenes and objects rather than component properties
Global colour vs component wavelength …
Perceived colour depends on wavelength reflected by the object but also wavelength reflected by the surroundings (colour constancy)
Some neurons in V4 are colour sensitive. v2 neurons are only wavelength sensitive
The hierarchy of visual information processing is…
Heirarchal with the complexity of the visual representations increasing from retina to association cortices
Global pattern motion vs component motion …
V1 = component for moving square. Register the component movements in different directions V5 = interpret the movement
Parietal cortex contains the…
Dorsal stream.
Visuo spatial and visuo motor processing - where and how
The temporal cortex contains the…
Ventral stream
Object analysis
Visual streams for what and where
The ventral stream lesions impair object discrimination or recognition but not object location
Dorsal stream lesions impair object location but not recognition
Visual streams for what and how
Milner and Goodale
The ventral stream processes visual information for object perception whereas the dorsal stream processes visual information for visuo-spatially guided actions
Evidence - occipito-temporal brain damage have visual agnosia
Posterior parietal lobe lesions show optic ataxia
Visual perception and memory in the inferior temporal cortex
The cortex receives input from extrastriate cortex and forms the final stage in the visual processing hierarchy in the ventral stream
Neurons in the inferior temporal cortex …
Can respond very selectively to specific shapes and objects
Show invariance to change in size, orientation or other properties, the neurons can recognise an object regardless of the viewpoint.
Sustained activity in the absence of a visual object which reflect short term object memory
Faces cells in the inferior temporal lobe
They show highly selective responses to individual faces.
Grandmother neurons - neurons that recognise individual entities
Kanwischer and Yovel (2006)’functional imaging support this
The medial temporal lobe (MTL)
Is at the end of the visuo processing hierarchy and combines inputs from the ventral and dorsal stream. It can also receive additional inputs from other sensory modalities
Examples of what the medial temporal lobe can generate…
Multi modal representations such as complex spatial representations and multi modal representations of experiences and facts
Morris (1982) hippocampal lesions in rats showed..
Selective place learning deficits. They took longer to navigate
Ekstrom (2003)
Place responsive hippocampal neuron during virtual navigation in humans
