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Doran, M. M., &Hoffman, J.E
(under revision). The Role of Visual Attention in Multiple Object Tracking:
Evidence from ERPs. |
We examined the role of visual attention
in MOT by measuring ERPs elicited by probes presented on targets, distractors,
or areas of the background. The objects and background were composed of random
dot textures in order to equate the physical change associated with object and
background probes. In Experiment 1, observers tracked 2 out of 4 objects while
maintaining central fixation and all probes were irrelevant to the observers
since they did not require any behavioral response. In this case we found
evidence of visual attentional selection in the N1 component. Note that the
following are demonstration versions of these displays. The displays in the
actual experiment were higher resolution, about twice as long, and the motion
was smooth.
In Experiment 2,
participants performed the same MOT task as in Experiment 1. However, the
probes were relevant since a subset of probe presentations required a
behavioral response. These “response probes” were identical to the probes that
did not require a response except that they had a small gray square in their centers.
In this case, no evidence of selection was observed in the N1 component as if
visual attention was diffusely allocated throughout the display in order to
detect the probes. This suggests that
visual attention may not be necessary for MOT –at least when tracking is fairly
easy.
In Experiment 3, we increased tracking
difficulty by adding a target and distractor to the displays. Participants
performed the same MOT and probe detection tasks as in Experiment 2 except that
they tracked 3 out of six objects. In this case, selection was once again
observed in the N1 component even though probes were still relevant. This
suggests that early visual attention may aid tracking when MOT is difficult.