occipital & temporal lobe - visual perception & memory Flashcards
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
what do some neurones in the inferior temporal lobe show?
- some show highly selective responses to individual faces
- these are called face cells
what have the highly selective properties of neurones in the inferior temporal lobe been compared to?
- gnostic units
- grandmother neurones
i.e.:
hypothetical neurones at end of processing hierarchy that recognise individual entities (such as your Grandmother)
you have individual neurones (gnostic units) that are responsible for recognising certain concepts/entities
what are face cells?
- neurones that specifically respond to faces
- not all faces, specific faces
what has been shown in human inferior temporal lobe using functional imaging?
areas showing selective responses to faces
what is at the end of the visual-processing hierarchy?
- the medial temporal lobe
what does the medial temporal lobe do?
- combines inputs from ventral and dorsal stream
- receives additional inputs from other sensory modalities
- this helps elaborate visual representations further and to generate multi-modal representations
where is the final stage of purely visual processing hierarchy?
within the inferior temporal lobe
what is also included in the medial temporal lobe?
- hippocampus
- amygdala
where is the medial temporal lobe located?
- sits close to temples
give examples of complex representations mediated by the medial temporal lobe
complex spatial representations
- that requires encoding of relations between many visual stimuli
multimodal representations
- of experiences (episodic memories)
- of facts (semantic memory)
- both of these together = declarative memory
outline the case of Patient H.M.
- following surgery, HM showed severe deficit in remembering new/recent experiences, facts, places
- despite deficit, other cognitive functions including procedural learning = largely intact
what does study looking into rats with hippocampus lesions show about spatial learning?
- rats with no lesions were able to escape using spatial cues
- rats with lesions failed to
- provided evidence for marked impairment of spatial learning following damage to hippocampus
explain what John O’Keefe and colleagues did with rats and electrodes in the hippocampus
- implanted electrodes into the hippocampus
- had rats move around in square arena chasing Cheerios
- found that specific neurones in hippocampus only fire if animal = in particular location
- because of very clear firing correlates with these neurones, they were called place cells
what are place cells?
- neurones that only fire in a particular place/location
- found in humans and animals
