Methods for Investigating Attentional Selection

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Methods for Investigating Attentional Selection
and Visual Search
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Attentional limitations central fact of
cognition. What is the nature of the selection
process? What gets selected, and how?
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Reaction Times Eye Movements Bayesian
Principles Classification Images Computational
models of search process
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Posner Paradigm Attentional Cueing
Central Cue - voluntary/endogenous
attention Peripheral Cue - automatic/exogenous
attention
Attentional selection can operate independently
of fixation called covert attention. Fixation
point indicates overt attention
Posner, 1980
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Reaction Time advantage for valid
trials. Peripheral cue advantage when cue
precedes stimulus by 100 msec Central cue
advantage when cue precedes stimulus by 300 msec
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Concept of an attentional spotlight spatially
based selection. Spotlight enhances
processing. Spotlight takes time to move. More
time for an endogenous cue. Note assumption
that faster better
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Visual Search Paradigm Another approach to
investigating the selection process. (Treisman,
1980s)
Task Find a target among distractors.
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Parallel/ automatic processing of simple
features. Selective attention required to bind
features into objects.
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Effect of set size reveals nature of search
Parallel search for simple features Serial search
for items requiring feature binding
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Interpretation of slopes in terms of msec/item as
speed of covert attention - eg 20 msec/item.
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Wolfe search varies in difficulty - no real
dichotomy
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Distributions of slopes are not bi-modal
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Wolfes Guided Search selection on the basis of
simple feature, followed by serial analysis
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Difficult to distinguish between serial and
parallel mechanisms
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Texture segmentation usually consistent with
reaction time data.
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Search difficulty depends on relation of target
to distractors
Similarity of target distractors
Homogeneity of distractors
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Stimulus Taxonomy
Note assumption that the stimulus is the
critical variable.
Presumably reflects the signal/noise
characteristics of selection on basis of these
properties.
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Reaction Time is a useful measure, but a single
number cant account for much of the complexity
of the brain Computations.
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Bayesian Approach
Cueing effect in Posner paradigm without
enhanced processing at attended
location. Eckstein et al, 2002.
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Greater prior liklihood of stimulus at cues
location leads to better performance
(detectability).
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Classification Image Technique Subject
detects a signal in noise Sort out the False
Alarm trials Add all the images that resulted in
false alarms Reveals the information that led to
a false alarm. Cf reverse correlation technique
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Simulation results using classification images
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Classification images from simulations using
different filters in cued and uncued locations.
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Classification images from subjects in Posner
experiment.
Supports Bayesian interpretation of performance,
not use of different filters in cued and uncued
locations.
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Attention is a hypothetical internal variable
with limited/no explanatory power.
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Eye Movements Overt Attention Is there
any advantage to covert attention in absence of
fixation? Findlay reaction time to peripheral
stimulus may be faster if subject allowed to
fixate.
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Visual Acuity degrades rapidly with eccentricity
Advantage of re-fixation much greater than covert
attention
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Similar performance for reaction time and sacadic
eye movements. Williams, Zelinsky
Reaction Time
Number of Saccades
serial
serial
parallel
parallel
Set size
Set size
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RSVP Method to measure speed of attention
RSVP Rapid Serial Visual Presentation
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Various experiments that pit saccades
against other tasks such as letter recognition
show interference. (Kowler, Deubel) Implication
is that saccadic target selection involves a
shift of attention to the target location.
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Saccadic eye movement circuitry
target selection
LIPlateral intra- parietal
saccade decision
saccade command
inhibits SC
signals to muscles
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fMRI shows similar areas involved in covert
attention and sacadic eye movements. Corbetta
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Eye Movements during Search in Naturalistic
Scenes. Zelinsky et al
Center-of-gravity fixations
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Analytical approaches to understanding search
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Image is filtered at different orientations and
spatial scales. Gives a filter template for each
location.

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Rao et al
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Correlate template with image only one location
has a high correlation
Search target
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Saliency Map for saccade target selection and
perceptual decision
Multi-scale Image representation
Compare target to fliter template
Decision process Compare peak to S and
N distributions
Oculomotor process
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Predicting saccade location rather than reaction
time
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Dual Task Paradigms
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Psychological Refractory Period - PRP
Pashler
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Attention Operating Characteristic
Measurement of extent of task interference.