Distinguishing between parallel and serial accounts of multiple object tracking

Abstract

Humans can track multiple moving objects. Is this accomplished by attending to all the objects at the same time or do we attend to each object in turn? We addressed this question using a novel application of the classic simultaneous-sequential paradigm. We considered a display in which objects moved for only part of the time. In one condition, the objects moved sequentially, whereas in the other condition they all moved and paused simultaneously. A parallel model would predict that the targets are tracked independently, so the tracking of one target should not be influenced by the movement of another target. Thus, one would expect equal performance in the two conditions. Conversely, a simple serial account of object tracking would predict that an observer's accuracy should be greater in the sequential condition because in that condition, at any one time, fewer targets are moving and thus need to be attended. In fact, in our experiments we observed performance in the simultaneous condition to be equal to or greater than the performance in the sequential condition. This occurred regardless of the number of targets or how the targets were positioned in the visual field. These results are more directly in line with a parallel account of multiple object tracking.

Resource demands of object tracking and differential allocation of the resource

“…According to a parallel account, all of the targets' positions are updated simultaneously, but devoting more resource to a target results in positions being updated more accurately. According to the serial account, target positions are updated one by one; the more targets there are, the less frequently their positions are updated (Howe et al, 2010;Oksama & Hyönä, 2008;Pylyshyn & Storm, 1988;Tripathy & Howard, 2012;Tripathy et al, 2011). At higher speeds, the targets travel farther between position updates, resulting in a greater speed limit cost for larger tracking loads (Holcombe & Chen, 2012, 2013.…”

“…According to this account, only one slot or spotlight is available to track targets, and it must be rapidly switched among targets for tracking to succeed (Holcombe & Chen, 2013;Tripathy & Howard, 2012;Tripathy, Öğmen & Narasimhan, 2011; but see Howe, Cohen, Pinto & Horowitz, 2010). When more targets are present, then, each target receives proportionally less processing time.…”

Perceiving expressions of emotion: What evidence could bear on questions about perceptual experience of mental states?

“…Pylyshyn & Storm (1988) showed that humans are able to track multiple moving objects simultaneously; and it seems they do this by means of parallel processes (Howe et al 2010). …”

Exhausting attentional tracking resources with a single fast-moving object

“…A critical remaining issue for theories of tracking is whether multiple targets are processed entirely in parallel or instead their locations must be updated one by one (Tripathy, Ogmen, & Narasimhan, 2011;Howe, Cohen, & Horowitz, 2010). In terms of the current theoretical framework, serial processing can be considered a specific implementation of resource theory where the resource is time-shared among the targets.…”

“…Therefore, serial processing accounts are particularly compatible with the present findings. Serial accounts are undermined however by other results (Howe, Cohen, & Horowitz, 2010), so perhaps a parallel resource theory should be favored. Parallel resource theory explains our results with the proposition that even a single target can exhaust the tracking resource if presented at a high enough speed.…”