Vision and attention - Matthew Rushworth Psychobiology module notes PDF

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Matthew Rushworth Psychobiology module notes...

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Vision Essay questions 1. What evidence is there for different processing streams and functional specialization in the visual system? 2. How are colour and motion processed in the visual system? 3. What does functional specialization mean? What evidence is that exists? Write short notes on: 1 Double dissociation 2 V4: area in the extrastriate cortex; is part of the ventral stream and its neurons are responsible for processing of colour/form 3 achromatopsia 4 functional magnetic resonance imaging (fMRI) 5 v5: area in extrastriate cortex; is part of the dorsal stream and its neurons are responsible for direction, motion perception and eye movements 6 akinetopsia 7 retinotopic maps

Notes from Carlson ch6: Vision Structure of the eye 

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Transduction of stimuli o Photopigments in photoreceptors are responsible for transduction of light energy to changes in membrane potential o Photoreceptors release neurotransmitters (depolarization = increase in release and hyperpolarization = decrease) Optic nerves o Axons of ganglion cells bundle together forming optic nerves, which convey info from retina to LGN o Join together at the base of the brain at the X shaped optic chiasm, where decussation occurs Visual pathway o Neurons in LGN send info to the primary visual cortex (V1, striate cortex) in the occipital lobe via optic radiations  Connected to visual association cortex (V2, extrastriate cortex) (which then convey to other cortical areas) LGN layers (6 layers) o First two = magnocellular layer with larger neurons (and receptive fields)

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o Other four = parvocellular layer with smaller neurons o Below each of the 6 layers are koniocellular sublayers Striate cortex (V1) o Function = processing/combining of info from LGN o The retinotopic map is distorted, large portion devoted to analysis of info from the fovea (centre of visual field with the most acuity) o CO blobs: groups of cells, sorted as thin, pale and thick stripes – neurons located in CO blobs are sensitive to colour Extrastriate cortex (V2-V5) o Each region has specialized function for different visual aspects o 2 pathways of visual processing  Ventral stream: thin/pale stripes in V2 to area V4, then to inferior temporal cortex  Function: recognize what an object is/colour  Dorsal stream: thick stripes in V2 to posterior cortex, or sometimes from V1 directly to V5  Function: recognize where an object is/movement  Two systems need to adequately communicate for us to be able to handle objects (know its identity and size) on a daily basis  Only parvocellular/koniocellular system receive info about colour, which feeds to ventral system o Area V4 contains cells responsible for analysis of colour (Scheine and Desimone, 1990 experiment on monkeys extrastriate cortex)  Damage to area v4 disrupts colour constancy (Walsh et al, 1993)  Damage to a region just anterior to V4, called TEO, impairs colour discrimination (Heywood et al 1995)  Conway et al. 2007 observed neurons in colour “hot spots” (found using fMRI) which either respond to colour or shape but not both; colour neurons spread across a wide range of visual association cortex so usually only damage to large regions cause severe disruptions in colour perception  Example in humans: achromatopsia caused by damage to these colour regions o Category-selective regions in the temporal lobe (for form perception)  Different parts of temporal lobe reactive to faces, body parts, objects and scenes of places  Evidence aside from fMRI scans: some people suffering from prosopagnosia = cannot recognize faces, but everything else ok; others might suffer from visual agnosia for objects, but can recognize faces  Distruption to activity of extrastriate body area (EBA) impairs ability to recognize body parts  Sometimes fusiform face area is flexible as in experts of birds/cars, it is activated when they view birds/cars  Suggests FFA is an expertise area (since we are experts in faces) rather than an exclusive face area o Perception of spatial location

Regions in the intraparietal sulcus (IPS) contain neurons that are responsible for perceiving movement  Dorsal stream also guides movements (not just perceive spatial locations), damage to this stream impairs ability to interact with objects Perception of movement  Neurons in area V5 respond to movement, damage impairs ability to perceive moving stimuli  A region adjacent to V5, MST, appears to analyse optic flow  Damage to V5 area results in akinetopsia: instead of smooth movement, perceive still images that appear to refresh periodically  Further evidence: Walsh et al (1998) used TMS to temporarily deactivate V5, result was inability to detect movement 

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Vision 

Evidence for specialization o

Dorsal stream vs ventral stream 

Achromatopsia = impaired v4

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Akinetopsia = impaired v5

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Further – damage to dorsal stream = difficulty picking objects up, but damage to ventral stream (visual agnosia) can pick objects up but not describe them 

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Attention Essay questions

Double dissociation = evidence for specialization of function

Category-specific processing 

Different parts of temporal lobe reactive to faces, body parts, objects and scenes of places

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Evidence aside from fMRI scans, double dissociation: some people suffering from prosopagnosia = cannot recognize faces, but everything else ok (Bauxaum et al, 1999); others might suffer from visual agnosia for objects, but can recognize faces (Moscovitch et al. 1997)

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PPA responsible for recognizing scenes (Steeves et al. 2004: patient could not recognize objects bc of visual agnosia, but could recognize scenes)

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More recent works shows often in pairs – FFA and OFA, PPA and OPA, FBA/EBA (Zhang et al. 2018)

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VWFA for words, and recent study also discovered adjacent word processing area (OWA) (specifically for chinese characters, vs a scrambled version) in occipital cortex that works together with VWFA (Zhang et al. 2018)

1. Is the parietal cortex important for attention? 2. What do we understand about the neural basis of attention? 3. Can our understanding of the neural mechanisms of attention help us explain what happens in neglect? Write short notes on: 1 Transcranial magnetic stimulation (TMS) 2 Event related potentials (ERPs) 3 Attentional enhancement 4 Distribution of function: function is distributed across a network of areas in the brain, and not just one specific area. 5 Extinction 6 Posner task

Notes from Gazzaniga ch7: attention 

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Neglect: ignores aspects of the contralesional visual field (key: not a result of partial bias) o Neurophysiological tests: line cancellation test (cross out lines on a sheet of paper, patients with neglect miss lines on one side), replication of objects or scenes o Bisiach and Luzzati (1978) - neglect also affects memory/imagination of visual scenes  Patients asked to imagine standing in a church square facing the cathedral, reported the buildings on ipsilesional side only. Then asked to imagine standing facing other direction, this time reported buildings on ipsilesional side again (or the side they missed the first time...) o Extinction (milder form of neglect?): ignores aspects of contralesional field when a competing stimulus is presented on ipsilesional side Models of attention o Voluntary attention: a goal driven process/intentionally attend to something o Reflexive attention: stimulus driven/bottom-up process o Covert (as opposed to overt) attentional orienting – looking at A, but paying attention to B in the background o Cocktail party effect (auditory): selective attention to auditory info When does attention selection occur? Early in receiving sensory info or later on in further processing? o Early selection: stimulus can be selected for further processing, or it can be “tossed out” as irrelevant before perceptual analysis of the stimulus is complete o Late selection: all inputs are processed equally by the perceptual system, but selection determines what will be represented in awareness

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Posner tasks/cuing tasks: valid tasks where cues correspond to where target will appear, or invalid tasks where cues misleads where target will appear. Participants asked to keep eyes on a fixation spot (so viewing cue covertly) until target appears. o Measure: reaction time for participant to redirect attention to target Visuospatial attention effect on V4 neuron firing rate in monkeys (Moran and Desimone, 1985) o Certain neurons respond better to red stimuli than to green stimuli o When monkey attended to red stimuli (ignored green), neuron had stronger response than when monkey attended to green stimuli and avoided the red one o Further research shows that this effect extends to other visual areas in ventral pathway Attention effect on V1 neurons (earlier processing) (McAdams and Reid, 2005) o Spatial attention enhanced the responses of the simple cells but did not affect the spatial or temporal organization of their receptive fi elds Event related potentials and fMRIs revealed that selective attention activated multiple parts of visual cortex Desimone and Duncan biased competition model for selective attention o Multiple stimuli in one receptive field area compete for the firing of that neuron; attention is responsible for resolving this competition. Explains:  Why is the effect of attention larger when there are multiple stimuli?  How does attention operate a different levels of the visual hierarchy?  As sizes of receptive fields increase as you go up the visual hierarchy, more attention is needed to resolve increasing competition o Kastner et al. (1998) used fMRI to investigate this  Attention focused on one stimulus (in a simultaneous presentation of multiple stimuli) reduces the competition from other stimuli o Studies on LGN neurons in monkeys (McAlonan, Cavanaugh, and Wurtz (2008)) showed that, based on attention, surrounding TRN neurons that inhibit LGN to cortex pathway can either be excited or suppressed (respectively inhibiting or increasing LGN to cortex transmission).  Support for early selection models TBC... ????

How is attention controlled?

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Dorsal attention system (spatial attention) o Hopfinger et al (2000) used fMRI and spatial cuing paradigm to test goal-directed attentional control network o Dorsal frontoparietal network showed activity, which reflects the sources of attention signals in goal-directed attention  When participants viewed cues passively, no activity o FEFs: coordinate eye movement and gaze shifts, which are important for orienting and attention Ventral attention system (non-spatial aspects of attention)

Attention 

Distribution of function in a network of areas in brain, together responsible for attention o

Circuit PPC-FEF-SC for visual attention

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Top down (goal driven) attentional control in the dorsal network 

Frontal cortex: FEF contributes to control over attention (Moore and Fallah, 2001); stimulated FEF neurons w/ low currents in monkeys = enhanced attention 

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Further studies show FEF signals, in the form of impulses that code info about an attentional task that needs to be performed, modulate neural activity in the visual cortex

Parietal cortex: IPS correlated with attentional shifts; whenever attention is directed to a stimulus, the firing rates of primate parietal neurons increase for both overt (saccade) and covert (reaching task) attention (Wurtz et al. 1982) 

In particular neurons in the LIP are recorded (Bisley and Goldberg), activity in LIP appears to provide a salience map

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Bottom up (stimulus driven) control in the ventral network 

temporoparietal junction (TPJ) in the PPC acts as an alert system when there is unexpected stimuli, breaking the circuit in the dorsal network

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PPC is damaged in patients with neglect/extinction. The dorsal and ventral network work together to engage attention (dorsal) and disengage or reorient attention (ventral)

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SC superior colliculus responsible for directing eye movements/shifts by sending outputs to thalamus and motor system

Limited processing capacity and specialization in the extrastriate cortex

Essay plan Abstract – define functional localization and functional specialization Par 1 – intro -

Brief overview of visual pathway

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Explain dorsal / ventral stream and how it is related to v4 and v5

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Zeki et al. Experiment discovered specialization in these two areas

Par 2– specialization in extrastriate areas: v4 and v5 -

Role of area v4 o

“Colour region” evidence from achromatopsia, colour after effect illusions

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Subsequent studies suggest also responsible for a diverse range of functions including surface properties (color, brightness, texture), shape (orientation, curvature), motion and motion contrast, and depth (Roe et al. 2012)

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In metanalysis, they conclude that V4 is responsible for figure-ground separation.

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How V4 is specialized: Colour “hotspots” in V4 and TEO (Conway et al. 2007), however outside these spots discovered neurons that are responsive for shape

Processing of motion, evidence from akinetopsia, enigma illusions 

Further evidence: Walsh et al (1998) used TMS to temporarily deactivate V5, result was inability to detect movement

Par 3 – attentional enhancement in the extrastriate cortex (v4?) -

Limited processing capacity and Kastner et al. Experiment

Par 4 – attentional control -

Distribution of function over network of areas...