Academic journal article Attention, Perception and Psychophysics

Resource Demands of Object Tracking and Differential Allocation of the Resource

Academic journal article Attention, Perception and Psychophysics

Resource Demands of Object Tracking and Differential Allocation of the Resource

Article excerpt

Abstract The attentional processes for tracking moving objects may be largely hemisphere-specific. Indeed, in our first two experiments the maximum object speed (speed limit) for tracking targets in one visual hemifield (leftor right) was not significantly affected by a requirement to track additional targets in the other hemifield. When the additional targets instead occupied the same hemifield as the original targets, the speed limit was reduced. At slow target speeds, however, adding a second target to the same hemifield had little effect. At high target speeds, the cost of adding a same-hemifield second target was approximately as large as would occur if observers could only track one of the targets. This shows that performance with a fast-moving target is very sensitive to the amount of resource allocated. In a third experiment, we investigated whether the resources for tracking can be distributed unequally between two targets. The speed limit for a given target was higher if the second target was slow rather than fast, suggesting that more resource was allocated to the faster of the two targets. This finding was statistically significant only for targets presented in the same hemifield, consistent with the theory of independent resources in the two hemifields. Some limited evidence was also found for resource sharing across hemifields, suggesting that attentional tracking resources may not be entirely hemifield-specific. Together, these experiments indicate that the largely hemisphere-specific tracking resource can be differentially allocated to faster targets.

Keywords Cognitive and attentional control. Divided attention. Object tracking

Published online: 29 January 2013

* Psychonomic Society, Inc. 2013

Playing a team sport, eluding a group of predators, or taking children to the beach benefits from maintaining attention on multiple moving objects. The multiple-object tracking (MOT) task (Pylyshyn & Storm, 1988) has been widely used to study this process (Cavanagh & Alvarez, 2005; Scholl, 2009). In this task, a number of identical objects are presented and a target subset to be tracked is cued for a few seconds. The cues then disappear, so that the targets are identical to the nontargets, and all objects move about the screen for several seconds. At the end of the trial, all of the objects stop moving, and observers must indicate which objects were the targets. With commonly used display parameters, people typically succeed at tracking up to four or five targets (Alvarez & Cavanagh, 2005; Pylyshyn & Storm, 1988; Yantis, 1992).

The number of objects that people can track varies with the circumstances, and various theories have been proposed to explain the varying limits. Franconeri and his collaborators suggested that spatial interference is the only factor that limits the number of targets that can be tracked, writing that "barring object-spacing constraints, people could reliably track an unlimited number of objects as fast as they could track a single object" (Franconeri, Jonathan & Scimeca, 2010, p. 924). Decreases in tracking performance with additional targets were proposed to be due to the cortical representations of two nearby targets interfering with each other (Franconeri, 2013). Specifically, when two targets are close to each other, a suppressive surround of one target may overlap with the spotlight of attention focused on the other target, and vice versa, inducing worse tracking performance for both targets (Franconeri, 2013; Franconeri, Lin, Pylyshyn, Fisher & Enns, 2008). Spatial interference undoubtedly can contribute to the capacity limit when traditional MOT displays are used, because in those displays objects pass very close to each other, which can cause crowding (Intriligator & Cavanagh, 2001; Pelli & Tillman, 2008).

Evidence from widely spaced target configurations has indicated a second reason for the decrease in performance with increasing target loads. …

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