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Demos: The number of attentional foci and their precision are dissociated in the posterior parietal cortex

 

The following demos are examples of several tracking conditions used in Shim, Alvarez, Vickery, & Jiang's study on "The number of attentional foci and their precision are dissociated in the posterior parietal cortex", published by Cerebral Cortex (2009 Sep 25 Epub ahead of print).

Task: Participants were asked to track the spoke(s) indicated by the green cues. They ignored pinwheels cued by the red cues. They were instructed to fixate at the center. Fixation was ensured by (1) training the participants outside of the scanner to maintain fixation, (2) the use of a concurrent central fixation task, where participants monitor the occasional dimming of the fixation point, and (3) eye monitoring in a subset of the participants. At the end of the pinwheel's rotation, participants reported (1) whether the probed spoke was the same or different from one of the tracked spoke(s), and (2) whether the fixation had dimmed during the trial.

The actual displays in the experiment are larger than the demo (pinwheel's radius = 3.12d, centered 6.1d away from fixation). The motion speed shown in the movies is an approximation, not exact value, to the speed used in the experiment.

Two factors were manipulated: the number of pinwheels to track (track-1, track-2-bilateral, or track-2-unilateral) and the speed of motion (slow, medium, fast, and very fast).

Condition 1: Track-1-slow. Only 1 pinwheel was cued for tracking and it rotated at a slow speed (in this demo: 50d/s). Click here to view track-1-slow.mov(File size: about 1.2MB)

Condition 2: Track-1-fast. Only 1 pinwheel was cued for tracking and it rotated at a fast speed (in this demo: 250d/s). Two other conditions with medium speed and very fast speed are not shown. Click here to view Track-1-fast.mov(File size: about 2.5MB)

Condition 3: Track-2-bilateral-slow. Two pinwheels, arrayed bilaterally, were cued for tracking. They rotated at a slow speed (in this demo: 50d/s). Click here to view track-2-bilateral-slow.mov(File size: about 1.2MB)

Condition 4: Track-2-bilateral-fast. Two pinwheels, arrayed bilaterally, were cued for tracking. They rotated at a fast speed (in this demo: 250d/s). Click here to view track-2-bilateral-fast.mov

Condition 5: Track-2-unilateral-slow. Two pinwheels, arrayed unilaterally, were cued for tracking. They rotated at a slow speed (in this demo: 50d/s). Click here to view track-2-unilateral-slow.mov(File size: about 1.2MB)

Condition 6: Track-2-unilateral-fast. Two pinwheels, arrayed bilaterally, were cued for tracking. They rotated at a fast speed(in this demo: 250d/s). Click here to view Track-2-unilateral-fast.mov

Note:The actual Experiment 1 involved 12 conditions (3 target number x 4 target speed). In Experiment 2 participants passively viewed the displays without tracking (4 target speed). In localizer scans, we obtained (1) retinotopic mapping, (2) visual retinotopic locations corresponding to the locations of the pinwheels, and (3) tracking localizer. The fMRI experiment used a slow event-related design (each trial of 12sec is followed by a 14-s fixation period). Data from three posterior parietal regions (superior parietal lobule, anterior IPS, and transverse occipital gyrus), one frontal region (frontal eye fields), MT, and retinotopic areas (V1, V2, and V3) were reported in the paper. The parietal ROIs showed greater activity when target number increased but was unaffected by target speed. FEF showed greater activity both when the target number increased and when the target speed increased. Behavioral accuracy showed a dramatic decline when target number increased and when target speed increased. A copy of the paper can be found here.

For more information, contact Won Mok Shim at wshim@MIT.EDU or Yuhong Jiang at jiang166@umn.edu.