Lecture 7- Occipital and Temporal lobe Flashcards
In what way is the processing of visual info done in the brain?
Hierarchal processing
What is hierarchal processing of visual info within the brain?
The complexity of the visual representation increasing from retina to visual association cortices and beyond.
What is Functional differentaition?
Different neuron types or different brain regions processing different properties of visual stimuli
What are the 2 types of complex visual representations for perception and memory?
-Integrated info concerning form, surface, spatial relationships, movement
-Integration w/ other sensory modalities eg multi modal representations
How does visual processing in the extrastriate cortex occur?
When neurons in the cortex signal ‘global’ properties of visual scenes and objects, rather than ‘component’ properties.
What does perceived colour of an object depend on?
The wavelength reflected by object, but also on wavelength reflected by the surroundings (colour constancy, e.g., perceived colour of object does not change when viewed during sunset).
What are colour sensitive neurons in V4?
They respond to wavelengths in the centre of their receptive field, depending on the wavelengths reflected from the background
How do neurons in V4 differ to those in primary visual pathways and V2?
V4= colour sensitive
V2 and primary= Only wavelength sensitive
What are the 2 visual info processing streams?
Dorsal stream= Visuospatial/ visuomotor processing Ventral stream= Object analysis
How is visual info processed following V1?
Following V1, visual info processing is mediated by two streams that are anatomically + functionally differentiated.
What are the Inferior lobe lesions?
(Ventral stream)
In macaques impair object-discrimination/recognition (‘what’), but not object location (‘where’).
What are the Posterior parietal lesions?
(Dorsal stream)
Impair object location (‘where’), but not discrimination (‘what’).
What did Milner and Goodale (1998) propose about Ventral stream processes?
They proposed that the ventral stream processes visual information for object perception (‘what’), whereas the dorsal stream processes visual information for visuo-spatially guided action (‘how’).
What evidence supports the Milner and Goodale proposal about the ventral stream process?
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
Whereas patients with posterior-parietal lobe lesions show optic ataxia (deficits in visually guided reaching) with otherwise relatively intact visual function
What is an example of the Milner and Goodale proposal?
Patient DF with extensive bilateral ventral-stream lesions has profound visual agnosia, but shows intact visually guided reaching as they can act on visual stimulus but is unable to make perceptual judgements
What happens regarding visual perception in the Inferior temporal cortex?
-The inferior temporal cortex receives inputs from extrastriate cortex and forms the final stage in the visual processing hierarchy of the ventral stream.
-Neurons in the inferior temporal cortex can respond very selectively to specific shapes and objects.
What do the responses in the Inferior temporal cortex show?
-Invariance to changes in size, orientation, and other properties – i.e., the neuron ‘recognizes’ object regardless of the viewpoint.
-Sustained activity in absence of visual object, reflecting short-term object memory.
What are Face Cells?
-Some neurons in the inferior temporal lobe show highly selective responses to individual faces.
-The highly selective properties have been compared to those of ‘gnostic units’ or ‘grandmother neurons’
What are ‘gnostic units’ or ‘grandmother neurons’ ?
Hypothetical neurons at the end of a processing hierarchy that ‘recognize’ individual entities
What is the Medial Temporal Lobe (MTL)?
MTL is at end of visual-processing hierarchy, combining inputs from ventral and dorsal stream, and receives additional inputs from other sensory modalities. -It is thus in position to elaborate visual representations further and to generate multi-modal representations.
What does the case study of HM show?
After surgery, HM showed severe and pervasive deficit in remembering new and recent experiences, facts, and places, whereas other cognitive functions, including procedural learning, were largely intact.
