Neuronal Attention Mechanisms Flashcards
1
Q
ATTENTION
A
- info in world competes for out attention
- can be defined as system that resolves competition between sensory inputs for access to awareness/response
2
Q
ATTENTIONAL COMPETITION IN TEMPORAL CORTEX: NEURONAL EVIDENCE
A
- monkey neurophysiology provided some og evidence for how issue = resolved at neuronal lvl
- individual neurons in monkey temporal cortex show “preferences” for particular stimuli aka. respond selectively to particular stimuli types
- ie. some neurons prefer triangles; others squares
3
Q
CHELAZZI ET AL. (1993): PROCEDURE
A
- trained monkeys to make eye movement towards target; cued which stimulus to respond to
- ie. if they saw rectangle cue -> had to make eye movement towards rectangle & ignore triangle
4
Q
CHELAZZI ET AL. (1993): RESULTS
A
- individual neuron’s response initially responded = strongly regardless of if preferred/nonpreferred stimulus = target
- BUT 180ms post onset of choice array (to which monkey responded) if preferred stimulus = target -> neurons firing remains high
- BUT if nonpreferred stimulus = target -> neuron response is suppressed
- shows that neuronal responses in inferior temporal cortex = competitive
- neuron responses diverge before eye movement; again demonstrates that visual attention operates independently of eyes & pre response
- suggests that attentional template is formed by modulation of brain regions that process relevant object (ie. enhanced neuronal firing in shape-selective cortex)
5
Q
CHELAZZI ET AL. (1993): ATTENTION IMPLICATIONS
A
- attentional competition occurs at lvl of individual neurons
- such competition involved both excitation (^ firing rate of neurons that “prefer” stimulus) & inhibition (suppression of firing rate of neurons that don’t show a “pref”)
- modulation of neuronal responses by attention occurs well before response occurs
- competition occurs NOT in separate attentional brain region but in brain regions that process visual features of relevant/irrelevant objects
- same neurons that process visual features of object (shape/colour/orientation etc.) are co-opted by attention system to resolve competition selection
6
Q
GONZALEZ ET AL. (1994): PROCEDURE
A
- neuroimaging evidence for neuronal correlates of attentional processing
- earliest studies used EEG (ERPs); suitable method due to its high temporal resolution (you can see events both early/late in trial)
- several studies using this methodology confirmed that attention can operate at earliest lvls
7
Q
GONZALEZ ET AL. (1994): RESULTS
A
- ERPs showed that when target = validly cued -> greater response in early visual areas > individually cued targets
- very early response (P1 < 100ms; N1 > 100ms) before subjects make response; supports idea that this is an attentional effect > motor response effect
- effects occurred over posterior visual cortical areas; BUT using ERPs (good temporal resolution VS poor spatial resolution) = never sure of signal
- results suggest that when target appears, if cue = previously presented pointing to that location -> brain activation in early visual cortical areas = ^ than when cue pointed to other location
- almost like if early visual areas processing info in specific locations = primed by cue so when target occurs, activation = ^ if cue/target location = congruent
8
Q
ATTENTIONAL SIGNAL ORIGINS
A
- source localisation suggests P1 = generated in extrastriate cortex (outside primary visual cortex)
- BUT conclusions about spatial EEG source signals = limited due to poor spatial resolution
- can fMRI reveal ^ accurate spatial info about precise site of attentional modulation of neural signals?
9
Q
BREFCZYNSKI & DEYOE (1999): PROCEDURE
A
- fMRI evidence for attention affects on primary visual cortex (V1) activation
- dif regions of circular area cued; pps had to make judgements on stimuli that subsequently appeared in said regions
- cues = auditory; learned numbers corresponding to each segment; cue involved hearing particular segment number over headphones
- retinotopic mapping used to map dif primary visual cortex regions w/v high precision according to which space regions they’re sensitive to
10
Q
BREFCZYNSKI & DEYOE (1999): RESULTS
A
- there was an analogue map in V1 corresponding to attentional effects in circular processing field
- aka. when left side of circle = cued -> V1 area sensitive to items appearing in said location showed enhanced activation
- when opposite side = cued -> another V1 location showed enhanced activation
- cues = auditory aka. nothing visual actually appeared in spatial locations that could have caused V1 effects
11
Q
KASTNER ET AL. (1998): RESULTS
A
- tested biased competition in humans using fMRI
- tested if stimuli compete for attention
RESULTS - when items = presented sequentially -> responses in visual cortex = ^ > when they were presented simultaneously
- BUT when they instructed subjects to attend to 1 of the objects -> effect disappeared
- response to attended object (in presence of others) was equally high as when presented alone
12
Q
KATSNER ET AL. (1998): IMPLICATIONS
A
- again demonstrates that attention modulates competitive interactions at neuronal lvl in visual cortex
- these data = interpreted as showing that competitive interactions in visual/temporal cortex play role in attentional selection
13
Q
SCHARTZ ET AL. (2005): PROCEDURE
A
- pps performed 2 conditions:
1) low load (detect any red shape)
2) high load (detect specific conjunctions of shape/colour ie. yellow upright T/green inverted T) - exactly same amount of visual stimulation used in 2 conditions
- perceptual load = perceptual difficulty
- main task = flanked by checkerboard stimuli producing ^ activation lvls in visual cortex
14
Q
SCHWARTZ ET AL. (2005): RESULTS
A
- visual cortex activation due to checkboard stimuli = much ^ in low load condition (neurophysiological correlate to Lavie’s research)
- high load = pps focused on main task so filter out irrelevant checkerboards BUT doesn’t operate well in low load
15
Q
SUMMARY I
A
- competitive effects of attention can be observed at lvl of individual neurons at earliest stages of visual processing (V1/V4)
- selective attention enhances baseline neuronal firing in task-relevant areas of visual cortex
16
Q
O’CRAVEN ET AL. (1999): PROCEDURE
A
- imaging studies have shown attentional modulation of neuronal signals throughout visual processing stream
- pps presented w/overlapping faces w/houses
- face/house moved; pps attended to face/house/direction of motion
17
Q
O’CRAVEN ET AL. (1999): RESULTS
A
- 2 brain regions “preferred” dif object categories
- FFA prefers faces (^ activation > faces)
- PPA prefers houses
- when pps asked to attend to moving object & preferred object (face) moves -> FFA activation elevates
- BUT asking pps to attend to moving object & non-preferred object (house) moves -> FFA activation suppresses
- similar to results from Duncan & Desimone’s monkey study; demonstrates competitive interactions within neurons that are responsible for sensory processing of objects at latest stages of visual processing
18
Q
BIASED COMPETITION MODEL OF ATTENTION
A
- many brain areas = activated by visual input; within most systems activations for dif objects compete
- we can observe attentional competition effects throughout visual processing pathways
- BUT these may be merely results of attentional signals arriving from elsewhere
19
Q
HOPFINGER ET AL. (2000): PROCEDURE
A
- fMRI study; tested possibility that attentional signal source = frontoparietal cortex
- presented subjects w/directional cue; asked to make judgement on checkerboards (ie. are there grey checks?) BUT only when they appeared in cued location
- aka. instead of looking at target locked activation they looked at cue-locked activation
20
Q
HOPFINGER ET AL. (2000): RESULTS
A
- found extensive activation across frontal/parietal cortex time locked to cue
- so these regions = activated in preparation for upcoming target stimulus
- in contrast activation to targets = more posterior regions (ie. parietal/occipital cortices)
- shows value of event-related fMRI being able to differentiate activation to dif timepoints within single trial
21
Q
TAYLOR ET AL. (2006): PROCEDURE
A
- EEG evidence for top-down bias signals originating in frontoparietal cortex; effects of TMS over frontal eye fields on activation in visual cortex
- pps performed Posner cueing task where central cue pointed left/right; target then appeared on left/right
- researchers used TMS to stimulate frontal eye fields between cue/target
22
Q
TAYLOR ET AL. (2006): RESULTS
A
- pps = faster to respond to validly cued targets > invalidly cued targets
- responses = slower during TMS of frontal eye fields
- ERP figure shows effects of stimulating control site (sensorimotor cortex) VS FEF
- normal attention-related negativity when no TMS occurs = markedly reduced in TMS condition
- demonstrates that signals over prefrontal cortex have causal effect on signals in visual cortex during attention
23
Q
SPECIFIC NEURONAL MECHANISMS TO PRIORITISE TASK-RELEVANT INFO PROCESSING
A
- neuronal frequency synchronisation (rhythmic/repetitive patterns of neuronal activity)
- neuronal signals oscillate at particular frequencies
- dif frequencies may correspond to dif functions
- frequency synchronisation between brain regions might support selective attention
24
Q
BUSCHMAN & MILLER (2007): PROCEDURE
A
- researchers got monkeys to perform visual search task involving either pop-out/easy VS conjunction/difficult search
- examined extent to which regions in parietal (LIP)/prefrontal cortex oscillated at same frequency (aka. coherence measure)
25
BUSCHMAN & MILLER (2007): RESULTS
- coherence = higher in middle frequency band during conjunction search BUT higher in upper frequency band during pop-out search
- provides mechanistic explanation for 2 dif attentional selection types:
1) top-down (voluntary attention depends on frequency synchronisation between parietal/prefrontal cortex in middle frequency band aka. beta)
2) bottom-up (reflexive attention depends on frequency synchronisation between regions in upper frequency band aka. gamma)
- aka. network lvl explanation; shows how distal remote regions of brain work together via neuronal synchronisation process
26
SUMMARY II
- competition for selection = evident at multiple neuronal lvls
- competition = resolved by top-down neural priming
- prefrontal/parietal cortex (PFC) plays key role as source of top-down modulation in form of biasing signal leading to enhancement/suppression in lower lvl sensory-specific brain regions
- coherence (frequency synchronisation) provides mechanism whereby frontoparietal cortex can communicate w/sensory regions to enable attentional selection
