Occipital and Temporal Lobe – Visual Perception and Memory, Summaries of Psychology

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Occipital and Temporal Lobe –

Visual Perception and Memory

Tobias Bast, School of Psychology, University of Nottingham 1

LIFE3082 Sensational Neuroscience

The primary visual pathway includes:

a) Retina, lateral geniculate body, primary visual cortex.

b) Retina, lateral geniculate body, primary visual cortex,

hippocampus.

c) Retina, superior colliculus, primary visual cortex.

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Hierarchy and functional differentiation in visual information processing Processing of visual information by the brain is hierarchical , with the complexity of the visual representation increasing from retina to visual association cortices and beyond. At the different stages of information processing there is functional differentiation , with different neuron types or different brain regions processing different properties of visual stimuli. Simple features:

• Light intensity and wavelength
• 2D position in visual field Complex visual representations for perception and memory:
  • Integrated information concerning form, surface (colour, texture), spatial relationships, and movement
  • Integration with other sensory modalities (multimodal representations) Combination and elaboration via parallel channels 4

eye LGN V1 V V V V3A V5/MT TEO (posterior IT) STS TE (anterior IT) Posterior Parietal ctx. Superior colliculus Visual information processing beyond V Extrastriate/prestriate ctx Inferior temporal (IT) ctx Occipital lobe 5

• Perceived colour of an object depends not only 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).
• Some neurons in V 4 are ‘colour’-sensitive (i.e., respond to wavelengths in the centre of their receptive field, depending on the wavelengths reflected from the background), whereas neurons in primary visual pathway and V 2 are only ‘wavelength’-sensitive. Global colour vs. component wavelength http://www.thenakedscientists.com/HTML/articles/article/martinwestwellcolumn9.htm/ 7

Global/pattern motion vs. component motion Taken from: Zeki S (1993) A vision of the brain. Blackwell Science Publications. 8

Visual Streams – what/where

• Inferior temporal lobe lesions (‘ventral stream’) in macaques impair

object- discrimination/recognition (‘what’), but not object location (‘where’).

• Posterior parietal lesions (‘dorsal stream’) impair object location (‘where’),

but not discrimination (‘what’).

Mishkin M, Ungerleider LG, Macko KA (1982) Object vision and spatial vision: two cortical pathways. Trends Neurosci. 6:414-417. 10

Visual Streams – what/how

• Milner and Goodale 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’).

• Key evidence: patients with occipito-temporal brain damage show severe

forms of visual agnosia (i.e., deficits in aspects of visual perception without

blindness), but intact visually guided actions, whereas patients with posterior-

parietal lobe lesions show optic ataxia (i.e., deficits in visually guided

reaching) with otherwise relatively intact visual function.

• For example, patient DF with extensive bilateral ventral-stream lesions has

profound visual agnosia, but shows intact visually guided reaching:

DF can act on visual stimulus (e.g., visuomotor posting), but is unable to make perceptual judgements (e.g., perceptual orientation matching) Milner AD, Goodale MA (1998) The visual brain in action. Psyche 4(12) http://psyche.cs.monash.edu.au/v4/psyche- 4 - 12 - milner.html 11

eye LGN V1 V V V V3A V5/MT TEO (posterior IT) STS TE (anterior IT) Posterior Parietal ctx. Superior colliculus Two visual information processing streams Dorsal stream: Visuo-spatial (‘where’)/ visuo-motor (‘how’) processing Ventral stream: Object analysis (‘what’) Extrastriate/prestriate ctx Inferior temporal (IT) ctx Occipital lobe Dorsal stream Ventral stream 13

Visual perception and memory in 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.
• These responses can 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 Neuron in TE responds to fractal shape in i regardless of size, orientation, and colour Other fractal shapes fail to trigger strong response Sustained response during retention delay on matching-to- sample task Retention delay (16 s) Miyashita Y, Chang HS (1988) Neuronal correlate of pictorial short-term memory in the primate temporal cortex. Nature 331:68-70. 14

MTL The Medial Temporal Lobe (MTL): Further processing of visual information and multimodal integration Hippocampus

• Ventral Dorsal Streams
• Other sensory information (auditory, olfactory, gustatory, somatosensory, etc.
• 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.
• Examples of complex representations mediated by MTL structures include:
• 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). 16

What does neuroanatomy indicate about the MTL:

a) MTL receives only visual information, but highly processed.

b) MTL receives visual, auditory, olfactory, and other sensory

information.

c) MTL should only respond to visual stimuli.

d) Both a) and c) are correct.

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RGM Morris et al (1982) Nature 297: Hippocampal lesion Watermaze Representative swim paths on trial 28 Hippoc. lesion Cortical lesion Control Search preference for target region during 'probe’ trials ( ) 19 Trials

Selective place learning deficits after hippocampal lesions in rats

Target region

The discussed lesion studies suggest that:

a) The hippocampus is necessary for spatial and declarative

memory.

b) The hippocampus is sufficient for such memory.

c) Both a) and b).

d) None of the above.

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