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
