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. 2009 Jun;49(13):1638-46.
doi: 10.1016/j.visres.2009.03.026. Epub 2009 Apr 10.

Bilateral field advantage in visual crowding

Ramakrishna Chakravarthi  1 , Patrick Cavanagh
Affiliations

Bilateral field advantage in visual crowding

Ramakrishna Chakravarthi et al. Vision Res. 2009 Jun.

Abstract

Thirty randomly oriented T's were presented in a circle around fixation at an eccentricity of 11 degrees such that each T was crowded by its neighbors. Two locations within the same hemifield (unilateral condition) or one location in each hemifield (bilateral condition) were precued for subsequent probing. Observers were then asked to report the orientation of a target T at one of these locations. A bilateral field advantage was found: target identification was better when the two precued targets were in different hemifields than when they were within the same hemifield. This bilateral advantage was absent when only targets were presented, without any distracters. Further controls showed that this advantage could not be attributed to differences between horizontal and vertical target alignments or to visual field anisotropies. A similar bilateral advantage has been reported for multiple object tracking (Alvarez, G. A., & Cavanagh, P. (2005). Independent resources for attentional tracking in the left and right visual fields. Psychological Science 16(8), 637-643) and other attentional tasks. Our results suggest that crowding also demonstrates separate attentional resources in the left and right hemifields. There was a cost to attending to two targets presented unilaterally over attending to a single target. However, this cost was reduced when the two crowded targets were in separate hemifields.

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Figures

Figure 1
Figure 1. The three conditions in experiment 1
Each panel represents one condition. Black placeholders were present throughout a session. T’s always appeared within these placeholders. Locations to be attended in each condition are highlighted in white. Left: Attend 1 condition: one location was precued; subjects had to attend to that location and report the orientation of the T presented there. Middle: Attend 2-Bilateral condition: two locations, one in each hemifield, were precued. Right: Attend 2-Unilateral conditions: two locations within a hemifield were precued. In the latter two conditions subjects were finally required to report the orientation of the T in one the two precued locations.
Figure 2
Figure 2. Trial sequence in experiment 1A
Placeholders were present throughout the experiment. For illustrative purposes, the number of placeholders shown here is fewer than in the actual experiment. Two locations in the Attend 2 conditions or one location in the Attend 1 condition were precued for 150ms (indicated in white here). 300ms later, target and distracter T’s in various orientations were presented briefly for 200ms. A post-cue followed this display after 300ms indicating the target T to be reported.
Figure 3
Figure 3. Experiment 1A results
The graph plots mean accuracy (n=10) in the three experimental conditions. Error bars represent one SEM.
Figure 4
Figure 4. Trial sequence in experiment 1B
Four targets were presented at 9, 3, 3 and 9 deg (left to right) respectively on the horizontal meridian. Each target was flanked by two distracters (one above and one below). The T’s at 9 deg were scaled versions of the one’s at 3 deg. Two locations in the Attend 2 conditions or one location in the Attend 1 condition were precued for 100ms (indicated in white here). 100ms later, target and distracter T’s in various orientations were presented briefly for 100ms. A post-cue followed this display after 100ms indicating the target T to be reported.
Figure 5
Figure 5. Experiment 1B results
The graph plots mean accuracy (n=5) in the three experimental conditions. Results from the experiment where the size and spacing of the stimuli were scaled are indicated in dark gray; results from the experiment where all stimuli are the same size are indicated in light gray. The light gray bars represent performance on targets at 9 deg eccentricity (the farther and harder to see targets). Error bars represent one SEM.
Figure 6
Figure 6. Trial sequence in experiment 2A
Placeholders were absent in this experiment. With that exception, the sequence was the same as in Experiment 1A. Two locations in the Attend 2 conditions or one location in the Attend 1 condition were precued for 150ms (indicated in white here). 300ms later, target and distracter T’s in various orientations were presented briefly for 200ms. A post-cue followed this display after 300ms indicating the target T to be reported.
Figure 7
Figure 7. Experiment 2 results
The graph plots mean accuracy in the three experimental conditions. Results from the experiment 2A (no distracters, no placeholders) are indicated in dark gray; results from the experiment 2B (no distracters but placeholders present) are indicated in light gray. Error bars represent one SEM.
Figure 8
Figure 8. Trial sequence in experiment 2B
The sequence and stimuli were the same as in Experiment 2A. However placeholders were present in this experiment.
See this image and copyright information in PMC

References

    1. Alvarez GA, Cavanagh P. Independent resources for attentional tracking in the left and right visual fields. Psychological Science. 2005;16(8):637–643. - PubMed
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