occipital & temporal lobe - visual perception & memory Flashcards
(38 cards)
what is the role of the occipital lobe?
- visual processing area of the brain
what is the role of the inferior temporal lobe?
- important role in visual recognition of objects
what is the order visual processing in the brain?
visual processing in the brain = hierarchal
- visual complexity increases from retina to visual association cortices
what is there at different stages of information processing?
- functional differentiation with different neurone types
AKA:
- different brain regions processing different properties of visual stimuli
give step by step of different brain regions processing different properties of visual stimuli
- simple features
(e.g.: cones dealing with wavelength) - at different hierarchical stages, information from different neuronal types = combined via processing in parallel channels
- results in more complex visual representation for perception and memory
in later stages of occipital temporal lobe:
(e.g. integrated information for surface - colour, texture etc.)
when moved into the medial temporal lobe:
(e.g.: integration with other sensory modalities - smell, touch, sound etc.)
identify the primary visual pathway sequence
- retina
- optic nerve
- lateral geniculate nucleus (LGN) of the thalamus - - visual cortex of occipital lobe
how is visual information further processed following the primary visual cortex?
- first major stage occurs within occipital lobe
- occurs in the extrastriate/prestriate cortex
- primary visual cortex sends input to extrastriate cortex
- information from the “colour”, “shape/form”, “location” and “motion” detected in primary visual cortex (V1)
- neurones are sent to different areas of the extrastriate cortex
- neurones in extrastriate cortex signal ‘global’ properties of visual scene rather than ‘component’ properties
- global properties = features of scene environment, describes an image’s spatial layout, affordances, or surface properties
what is the general principle of visual processing in the extrastriate cortex (compared to primary visual pathway)?
- specialises in colour perception
- neurones within the region of the extrastriate cortex signal global properties of visual scene rather than component
compared to primary visual pathway:
- at photoreceptor level, neurones signal absence/presence of light of distinct wavelength
- not real colour vision
- neurones only represent contrast and boundaries
- complex cells represent movement of small parts of visual field
what is real colour vision?
- where the colour of one part of a scene is represented depending on the bits of the surrounding colour
where is colour vision mediated?
- area V4 of extrastriate cortex
- this is where you have global colour vision
what is perceived colour of an object dependent on?
- wavelength reflected by object
- wavelength reflected by surroundings of an object
what is the functional significance of being able to perceive wavelengths reflected by objects and surrounding objects?
- colour constancy
what is colour constancy?
- being able to perceive colour of objects independently of different light levels
identify a difference between the neurones in the primary visual pathway and the extrastriate cortex
- neurones in area V4 (extrastriate cortex) are colour sensitive (where global colour sensitivity comes from)
- neurones in primary visual pathway are only wavelength sensitive
how is the perception of global/pattern motion formed?
- in area V5
- combination of neurones is combined to result in perception of global/pattern motion
what are the two visual information processing streams?
- dorsal stream
- ventral stream
these are both anatomically and functionally different
describe the dorsal stream
- goes up to parietal cortex
- processes visual information for the purpose of executing movements
- main responsibility = visual processing that allows us to determine WHERE objects are
- help us with visuo-motor processing (HOW you direct your movement to something)
describe the ventral stream
- goes down to inferior temporal lobe
- processes visual information for the purpose of visual perception (“vision for perception”)
- main responsibility = visual object analysis
- helps recognise what object is
describe evidence for ventral stream
- lesions in inferior temporal lobe (ventral stream) in monkeys
- found this impaired object-discrimination/recognition
- could not identify WHAT object was
- however could still locate WHERE object was
describe evidence for dorsal stream
- posterior parietal lesions (dorsal stream) impairs ability to locate WHERE object is
- but could still determine WHAT object was
what did Milner and Goodale propose about the ventral and dorsal stream?
- suggested dorsal steam = processes visual information for visuo-spatially guided action (HOW we direct movement to object)
- suggested ventral stream = processes visual information for object perception (WHAT an object is)
outline key evidence from Milner and Goodale regarding the two visual streams
- patients with occipito-temporal brain damage show severe forms of visual agnosia
- visual agnosia = where person can see visual information but not recognise/interpret visual information
EXAMPLE:
- patient DF with extensive ventral-stream (identifying object) lesions has profound visual agnosia BUT shows visually guided reaching
- DF can act of visual stimulus
- DF unable to make perceptual judgements
what is the role of the inferior temporal cortex?
- inferior temporal cortex receives input from extrastriate cortex
- forms the final stage in visual processing hierarchy of ventral stream
- neurones in this cortex respond very selectively to specific shapes and objects
what do the responses of the neurones in the inferior temporal cortex show?
- neurones can show invariance to changes in size, orientation of object
- neurone recognises object regardless of viewpoint
- sustained activity of neurones that represent certain visual objects even when visual object = removed
- thought to reflect short-term object memory
