Transcript Document

Bilateral Superiority in Detecting Gabor Targets Among Gabor Distracters
Nestor Matthews
Poster # 23.407
Abstract # 773
Department of Psychology, Denison University, Granville OH 43023 USA
Introduction
Stimulus Sequence On Each Trial
Attentional Cue
Stimuli
Noise Masks
Laterality & Distracter Conditions
Response Prompts
Bilateral:
Distracters Absent
Bilateral:
Distracters Present
Unilateral:
Distracters Absent
Unilateral:
Distracters Present
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1. Which Letter?
2. Target Present?
Yes (y)
Or
No (n)
m
Experiment 1: Two Targets versus One Target
Results
Experiment 2: Spatial Frequency Effects
Low Spatial Frequency Target
One Target
Two Targets
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Unilateral
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Absent
Bilateral
Detection (d')
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Detection (d')
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Unilateral
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Absent
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Laterality Effects: Two Targets
Distracter Absent F(1,23)=1.29, p=0.268, partial h2=0.053
Distracter Present F(1,23)=23.26, p<0.001, partial h2=0.503
Laterality Effects: One Target
Distracter Absent F(1,23)=1.73, p<0.201, partial h2=0.070
Distracter Present F(1,23)=21.80, p<0.001, partial h2=0.487
Experiment 3: Orientation Effects
Laterality Effects: High SF Target
High SF Distracter F(1,19)=8.07, p=0.010, partial h2=0.298
Low SF Distracter F(1,19)=3.21, p=0.089, partial h2=0.145
Distracter Absent F(1,19)=1.36, p=0.257, partial h2=0.067
Experiment 4: Striped versus Solid Distracters
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Across the four experiments, independent groups
showed distracter-induced BSE’s in detection. The
effect had modest spatial frequency dependence, but no
orientation dependence. Distracter-induced BSE’s in
detection may reflect neural events that occur earlier in
the visual pathway than do those that generate
distracter-induced BSE’s in motion tracking 1 and
orientation discrimination 2,3. Although the present
method did not include standard ‘litmus tests’ for visual
crowding 4,5 , the results are more consistent with
masking (specifically, surround suppression5) than with
crowding because detection was impaired 6 , and
because the distracter effects were stronger for vertical
than for horizontal configurations7. Lastly, although
there is fMRI evidence for two spotlights of attention
within and across cortical hemispheres8, the present
data are consistent with separate capacity-limited
pools of resources within each cortical hemisphere –
even for the fundamental visual task of detection.
References
Solid Distracters
Detection (d')
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Low SF
Laterality Effects: Low SF Target
Low SF Distracter F(1,19)=20.04, p<0.001, partial h2=0.513
High SF Distracter F(1,19)=7.89, p=0.011, partial h2=0.294
Distracter Absent F(1,19)=4.78, p=0.041, partial h2=0.201
Cardinal Target
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High SF
Distracters
Distracters
Distracters
Detection (d')
It has long been known that for a given point of
visual fixation, the left visual field projects to the
right cortical hemisphere while the right visual field
projects to the left cortical hemisphere. Recent
research has shown that performance on a motion
tracking task is twice as good when the stimuli are
distributed across both visual hemi-fields than when
the stimuli are restricted to just one hemi-field, i.e.,
project to just one cortical hemisphere1. (It is as if the
unilaterally presented stimuli “flood the cortex’s zone
defense”.) Even more recently, distracter-induced
bilateral superiority effects (BSE’s) have been
observed on rudimentary orientation discrimination
tasks2,3.
The present study was conducted to determine
whether distracter-induced BSE’s occur for the most
basic visual task – detection. Each trial began with
attentional cues marking the potential positions of
Gabor targets (SF=1.3 c.p.d., size=3x3 deg window,
eccentricity=14.4 deg to nearest edge, 90% contrast,
duration=183 msec), which were present with 50%
probability. Participants identified a central letter to
ensure fixation before indicating whether a target was
present or not. Across trials, bilateral and unilateral
cues were randomly interleaved, as were Gabor
distracters positioned between the target locations.
Stimulus variations were examined across four
experiments to determine which distracter-features
most reliably generate BSE’s in visual detection.
Discussion
General Method
1. Alvarez & Cavanagh (2005). Psychol Sci. PMID: 16102067
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2. Chakravarthi & Cavanagh (2006). VSS Abstracts. # 1216, p. 274
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3. Matthews & Cox (2007). VSS Abstracts. # 689, p. 180
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Absent
Orthogonal
Configuration
Parallel Configuration
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M ixed Polarity
Distracters
Laterality Effects: Oblique Target
Distracter Absent F(1,14)=1.20, p=0.291, partial h2=0.079
Random Orientation F(1,14)=8.34, p=0.012, partial h2=0.373
Target Orientation F(1,14)=5.34, p=0.037, partial h2=0.276
Laterality Effects: Cardinal Target
Distracter Absent F(1,14)=0.82, p=0.381, partial h2=0.055
Orthogonal Configuration F(1,14)=12.16, p=0.004, partial h2=0.465
Parallel Configuration F(1,14)=17.41, p=0.001, partial h2=0.554
All White
Chromatic
Distracters
Laterality Effects: Oblique Target
Distracter Absent F(1,39)=1.00, p=0.323, partial h2=0.025
Gabor F(1,39)=17.97, p<0.001, partial h2=0.315
Bulls-eye F(1,39)=18.55, p<0.001, partial h2=0.322
Laterality Effects: Solid Distracters
Mixed Polarity F(1,39)=5.60, p=0.023, partial h2=0.126
All White F(1,39)=2.50, p=0.126, partial h2=0.060
Chromatic F(1,39)=1.22, p=0.275, partial h2=0.030
4. Levi (2008). Vision Research. PMID: 18226828.
5. Petrov, Popple, & McKee (2007). Journal of Vision. PMID: 18217827
6. Pelli, Palomares, & Majaj (2004). Journal of Vision. PMID: 15669917
7. Feng, Jiang, & He (2007). Journal of Vision. PMID: 18217828
http://www.denison.edu/~matthewsn/bilateralsuperiorityvss2008.html
8. McMains & Sommers (2004). Neuron. PMID: 15157427