Further evidence for inhibition of moving nontargets in Multiple Object Tracking

 

James E. Reilly, Zenon W. Pylyshyn & Charles E. King, Rutgers Center for Cognitive Science

 

Using the Multiple Object Tracking (MOT) task, Pylyshyn & Leonard (VSS03) showed that a small brief probe dot was detected more poorly when it occurred on a nontarget than when it occurred either on a target or in the space between items, suggesting that moving nontarget items were inhibited.  Here we generalize this finding by comparing probe detection performance against a baseline condition in which no tracking was required.  We examined both a baseline condition in which objects did not move and one in which they moved exactly as in the probe detection task, but without tracking.  Detection in the nonmoving control was essentially error-free, but probe detection performance in the moving (non-tracking) control task did depend on the probe location.  Nonetheless, the findings reported earlier (worse detection on nontargets than anywhere else) remained after we took account  of the baseline performance (using several different baseline comparison methods).  Using this new baseline-control method we also showed that inhibition does not spread more than about 1.3 degrees of visual angle from the nontargets as the latter move during a tracking trial.  In the present report we also describe some preliminary studies of conditions under which enhancement of targets, as well as inhibition of nontargets, may be obtained.  Increasing the number and type of nontargets appeared to improve the detection of probes on targets, relative to baseline.  However, we failed to find evidence that potentially distracting nontarget objects were inhibited more than clearly task-irrelevant objects, as would be expected if inhibition were a top-down process applied in order to improve performance on the main tracking task.  For example, using the comparison with its matching baseline, we showed that task-irrelevant stationary items (which are never confused with targets in the tracking task) appeared to be inhibited even more than nontargets.

 

This  research was supported by NIH research grant  R01  MH60924 to ZWP.

Using multiple-object tracking  (MOT) to test whether cerebral hemispheres share visual attention resources   (1980 characters)

Jonathan Rein and Zenon W. Pylyshyn, Rutgers Center for Cognitive Science;  George Alvarez, Harvard Vision Laboratory

Alvarez & Cavanagh (VSS 2004) showed that attentive tasks presented to left and right cerebral hemispheres appear to be carried out independently, so observers can perform a pair of tasks presented to different hemispheres much better than the same pair of tasks presented to the same hemisphere.  We explore this finding by using a pair of multiple object tracking (MOT) tasks (performed in two separate quadrants of the display) and asking whether stressing one of the two tasks results in poorer performance on the stressed task and on the paired task when the two tasks are performed in the same-hemisphere compared with dual-hemisphere presentations. In addition to replicating the original A & C finding we used several baseline measures to show that there was less cross-talk in the dual-hemisphere presentations than in matched single-hemisphere presentations. One of a pair of MOT tasks (tracking 2 targets out of 4 identical objects) was made more difficult by doubling the speed of the random motion of the objects.  This increase in difficulty of one task resulted in a greater drop in accuracy for the second task in the same-hemisphere condition than in the dual hemisphere condition. Moreover, the decrement in performance on the speeded-up task itself was greater in the dual-hemisphere condition than in the same-hemisphere condition. This pattern of results would be expected if resources for the speeded-up task could be borrowed from a same-hemisphere task (reducing the decrement for the speeded-up task, but resulting in a greater decrement in the second task), but resources could not be borrowed from the second task in the dual-hemisphere condition (thus increasing the decrement for the speeded-up task, and leaving the opposite hemisphere task relatively unaffected). These findings add support to the A & C conclusion that one hemisphere is unable to draw upon attentional resources from the other hemisphere to help with increasingly difficult tasks.

This  research was supported by NIH research grant R01 MH60924 to ZWP.