Academic journal article Attention, Perception and Psychophysics

Speed Has an Effect on Multiple-Object Tracking Independently of the Number of Close Encounters between Targets and Distractors

Academic journal article Attention, Perception and Psychophysics

Speed Has an Effect on Multiple-Object Tracking Independently of the Number of Close Encounters between Targets and Distractors

Article excerpt

Abstract Multiple-object tracking (MOT) studies have shown that tracking ability declines as object speed increases. However, this might be attributed solely to the increased number of times that target and distractor objects usually pass close to each other ("close encounters") when speed is increased, resulting in more target-distractor confusions. The present study investigates whether speed itself affects MOT ability by using displays in which the number of close encounters is held constant across speeds. Observers viewed several pairs of disks, and each pair rotated about the pair's midpoint and, also, about the center of the display at varying speeds. Results showed that even with the number of close encounters held constant across speeds, increased speed impairs tracking performance, and the effect of speed is greater when the number of targets to be tracked is large. Moreover, neither the effect of number of distractors nor the effect of target-distractor distance was dependent on speed, when speed was isolated from the typical concomitant increase in close encounters. These results imply that increased speed does not impair tracking solely by increasing close encounters. Rather, they support the view that speed affects MOT capacity by requiring more attentional resources to track at higher speeds.

Keywords Attention: object-based . Attention: selective . Attention: divided attention and inattention

Published online: 13 September 2012

© Psychonomic Society, Inc. 2012

An important task of the visual system is to track objects that are moving in the world around us. Automobile drivers tracking surrounding vehicles and athletes tracking opponents on the field demonstrate this ability. This capability is typically studied using the multiple-object tracking (MOT) paradigm originated by Pylyshyn and Storm (1988), in which observers track a subset of target items moving among identical distractors. Intuition tells us that tracking the vehicles surrounding a driver, for example, will become more difficult when the speed of the vehicles increases, the number of vehicles increases, or the vehicles become more crowded together. All of these intuitions have been evidenced by MOT studies, although the mechanisms by which these factors affect tracking are still a matter of debate.

It is well established that as the number of targets that need to be tracked increases, tracking performance declines (e.g., Pylyshyn & Storm, 1988; Yantis, 1992). While most studies have suggested that a maximum of about four or five objects can be tracked with high accuracy (e.g., Cavanagh & Alvarez, 2005; Pylyshyn & Storm, 1988; Yantis, 1992), some recent studies have shown that depending on task parameters, up to eight objects can be tracked (Alvarez & Franconeri, 2007; Howe, Cohen, Pinto, & Horowitz, 2010). This finding led to the proposal of the flexible-resource model, according to which there is a limited pool of resources for tracking that can be flexibly allocated to targets depending on task demands (Alvarez & Franconeri, 2007). As the resource demands to track each target increase, the number of targets that can be tracked decreases. Conversely, as the number of targets being tracked increases, the amount of resources that can be allotted to each target must decrease, causing a decline in tracking performance.

MOT performance also declines as the number of distractors increases (Bettencourt & Somers, 2009; Feria, 2012; Sears & Pylyshyn, 2000; Tombu & Seiffert, 2011). One reason that distractors interfere with tracking the targets is that when a distractor passes near a target, the observer may confuse the distractor with the target (Alvarez & Franconeri, 2007; Bae & Flombaum, 2012; Bettencourt & Somers, 2009; Feria, 2012; Horowitz et al., 2007; Intriligator & Cavanagh, 2001; Iordanescu, Grabowecky, & Suzuki, 2009; Oksama & Hyönä, 2004; Pylyshyn, 2004; Sears & Pylyshyn, 2000). …

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