Visual perception and memory: Occipital and temporal lobe Flashcards
Once the primary visual cortex has determined the simple features of a visual scene (i.e. light intensity, wavelength and 2D position in visual field), a process of combination and elaboration creates…?
Complex visual representations for perception and memory, including:
- Integrated information concerning form, surface, spatial relationships and movement.
- Multimodal representations - sensory modality integration.
What do neurons in the extrastriate cortex do?
Signal global rather than component properties of visual scenes and objects.
What does perceived colour of an object depend on?
The wavelength reflected by both the object and its surroundings (colour constancy).
Some neurons in V4 are ‘colour’ sensitive. What does this mean and how does it compare to primary visual pathway and V2 neurons?
They respond to wavelengths in the centre of their receptive field, depending on the wavelengths reflected from the background. They can distinguish between two colours, whereas V2 and PVP neurons are only wavelength sensitive.
From what point is visual information processing mediated by two streams and how are they differentiated?
Following V1 (perhaps earlier), and they’re anatomically and functionally differentiated.
What are the two visual information processing streams?
Dorsal and ventral.
What information does the dorsal stream process?
Visuo-spatial (where) and visuo-motor (how).
What information does the ventral stream process?
Object analysis (what).
What do inferior temporal lobe lesions (ventral stream) impair in macaques according to Mishkin et al. (1982)?
Object discrimination and recognition (what), but not object location (where).
What do posterior parietal lesions (dorsal stream) impair in macaques according to Mishkin et al. (1982)?
Object location (where) but not discrimination (what).
What did Milner and Goodale (1998) propose?
That the ventral stream processes object discrimination (what) info and the dorsal stream processes info for visuo-spatially guided action (how).
What evidence did Milner and Goodale (1998) use to support their proposition?
- Patients with occipital-temporal brain damage (e.g. DF) show severe forms of visual agnosia but intact visually guided actions, whereas patients with posterior-parietal lobe lesions show optic ataxia but are otherwise fine.
Where does the inferior temporal cortex receive input from?
The extrastriate cortex.
What part of visual processing is done in the inferior temporal cortex?
The final stage in the ventral stream.
Inferior temporal cortex neurons respond very selectively to specific shapes and objects, which can show:
- Invariance to changes in size, orientation and other properties (recognises objects regardless of viewpoint)
- Sustained activity in the absence of a visual object, reflecting short-term object memory.
What are face cells?
Neurons in the inferior temporal lobe which show highly selective responses to individual faces.
What do face cells’ highly selective properties suggest?
That they may act as gnostic units (or ‘grandmother neurons’) - neurons at the end of a processing hierarchy that ‘recognise’ individual entities.
What did Kanwischer and Yovel (2006) do?
Identified areas (e.g. the Fusiform Face Area) in the inferior temporal lobe showing selective responses to faces using functional imaging.
Where is the Medial Temporal Lobe (MTL) in terms of the visual-processing hierarchy?
At the end.
What does the MTL do?
Further processing (elaboration) of visual information and multimodal integration - it combines inputs from the ventral and dorsal streams and from other sensory modalities.
Give some examples of complex representations mediated by the MTL.
- Complex spatial representations requiring the encoding of relations between many visual stimuli.
- Multimodal representations of experiences (episodic memory) and facts (semantic memory) (together referred to as declarative memory).
What happened to HM?
Had his hippocampus and parts of surrounding cortices removed to prevent epileptic seizures, after which he lost the ability to form new memories, although other cognitive functions including procedural learning were largely intact.
