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Visual Attention (16 Theoretical and Behavioral Aspects of Selective…
Visual Attention
16
Theoretical and Behavioral Aspects of Selective Attention
Taxonomy
Posner (1984)
Alerting
sustain sensitivity to the incoming stimuli
Orienting
select a subset of the currently available sensory stimuli
Executive function
monitor the ongoing flow of thoughts, reactions, and responses
Chun, Golomb, Turk-Browne (2011)
External attention
attention to the outside world
Internal attention
attention to the internal states
Neisser (1967)
Pre-attentive
before the selective attention involves in
Attentive
challenge
every stage except retina involves attention
attention processes involve feedback and feedforward
Attention
Selectivity
in time
Attentional blink (AB)
much harder to report T2 after the report of T1 on the order of 200-500 msec
in space
Feature guidance
bottom-up salience
salience decreases when target and distractors become similar
feature homogeneity (heterogeneity) is related to psychophysical responses, but not physical measurement
the relative value of the attribute is important
salient items among homogeneous distractors "pop-out"
top-down user-driven factors
suggest that feature attention is separable from attention to locations
seems to apply at the same time to all locations having the attended feature
feature-based attention
Attentional cues
Endogenous cues
symbolic and typically placed at fixation
Exogenous cues
typically peripheral and placed at the intended destination of attention
object-based attention
Semantic guidance
directs attention to locations based on meaning
incorporate scene-based rules
inhibitory processes
inhibition of return (IOR)
incline a search to move forward, not to perseverate
harder to redirect attention to the location or item that has attended before
inhibition surrounding the locus of attention
attention might have a Mexican hat profile
harder to perform a task near to a recent deployment of attention
Binding
attention permits the binding of features into coherent objects
connection of thoughts or association of feelings and memory might also take use of attentional binding
others
Individuation
attention helps to individuate items
Scrutiny
allows finer perceptual decisions
Awareness
sometimes a failure to attend an item causes a failure of awareness of the existence of the item
18
Electrophysiology of Visual Attention
Steady-state visual evoked potential (SSVEP)
SSVEPs are the continuously oscillatory neural responses elicited in the visual cortex at the same fundamental freq. as the flickering stimulus.
Frequency tagging
several stimuli presented simultaneously but flickering at different freq can be separated by extracting oscillations at specific freq. of the stimulation.
advantages
reveal selection mechanisms
study the selective processing of spatially intermingled stimuli
provide a continuous measure and can reveal the speed where the selection is implemented
Attentional control
Implementation of selection
Spatial attention
ERP studies showed that attended stimuli elicit larger
N1
and
P1
but
not C1
, suggesting spatial attention modulate info. through intermediate levels of visual cortex.
SSVEPs to stimuli within attended window show enhanced amplitude than to stimuli outside the window
Feature-based attention
P1
and
N1
are not larger for stimuli containing the attended feature than for stimuli lacking of the feature, suggesting that selection based on nonspatial feature occurs at a later stage.
some studies using color stimuli showed that
P1
and
N1
are larger in attended colored stimuli than non-attended ones.
The attended color dots elicit an enhanced SSVEP in early visual cortex, the process in thought to be independent of spatial attention.
SSVEP was enhanced maximally to dots having the attended color and location, these feature and spatial selective effects were additive.
Feature-similarity gain model
paying attention to to a feature at one location results in a global facilitation of the processing of that feature throughout the entire visual field.
N2pc
a negative ERP component elicited by the contralateral
target
at posterior electrodes
reflect the focusing of attention onto a given item
Pd
a positive component elicited by the contralateral
distractor
reflect a suppression of processing of the distractor rather than attentional enhancement
Time course
N2pc onset latency provides a means of tracking the time course of attentional contral
N2pc onset latency varies with the salience of the target and is earlier for targets that are associated with large rewards.
N2pc onset latency can be used to study individual or group differences in the speed of attentional control.
Bottom-up and Top-down
Signal suppression hypothesis
attention involves both bottom-up and top-down process:
feature singletons always elicit an attention priority signal
the signal can be suppressed by top-down control processes before attention is actually allocated to the source of the priority signal
Terminating shifts of attention
shift of attention to a target leads to an N2pc that is immediately followed by a Pd
suggest Pd also plays a role in terminate a shift of attention after target processing is complete
17
Attention Priority
Attentional priority maps
attention modulates the topographical landscape of spatial maps such that the location of the most important object is associated with the highest activation level
Spatial attention
topographic maps have been identified in parietal cortex (
IPS
,
SPL
) and frontal cortex (
PCC
)
they represent the attentional priority of competing objects and provide top-down biasing signals to modulate activity in early visual cortex
controlled via an opponent processor control system in which both hemispheres direct attention to the contralateral visual fields and balanced through reciprocal inhibition
some evidences suggest a graded representation of locations in descending order of importance
Feature-based attention
modulates the gain of neurons based on their feature-tuning profile
enhances gain of neurons tuned to behaviorally relevant feature and suppresses those are not
increases the activation level of all locations in attentional priority maps that contain a potentially relevant target feature
Object-category based attention
In object-selective VTC, only task-relevant info was processed to the categorical level, even info. was not spatially attended
object-category biasing signals were also found following an abstract letter cue that indicated the target category in the absense of real visual stimulus
20
Attentional modulation
of RF profiles
Multiple stimuli inside RF
Neural responses increase when the attended stimuli consistent with the preferred tuning of the neurons
Neural responses decrease when the attended stimulus is not preferred by the neurons
RF shifts its center to the attended stimuli's location
expansion of RF
Mechanisms for changes in RF
attention might change the strength of input signals into extrasriate visual neurons
RF expands to the attended stimuli that pass through the boundary of the RF