Is Multiple Object Tracking Color Blind?? ... Can color improve tracking by individuating items or ... As before, colors shifted continuously during each trial.
Is Multiple Object Tracking Color Blind??
C10
Sarah B. Klieger , Todd S. Horowitz , & Jeremy M. Wolfe 1
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Vision Sciences Society 2004
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Brigham & Women’s Hospital and Harvard Medical School
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General Methods
We often need to track several independently moving objects in our environment.
1. Does inter-item occlusion impair tracking?
Initially, we presented a static display of 10 disks; 5 were flashed to cue them as targets. Objects moved at a speed of 6°/sec for 5 seconds. When motion ceased, observers identified targets with a mouse click.
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We tested the hypothesis that inter-item occlusion would not interfere with tracking.
In the lab, observers are able to track ~ 4 to 5 independently moving targets among identical distractors (Pylyshyn & Storm, 1988), but in the real world, targets are typically heterogenous, differing on a number of features.
We used two types of displays. In one, items “bounced” off each other. In the other, items could occlude each other.
We tested the hypothesis that individuating objects by color could improve tracking.
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tracking Note: Numbers on the disks are for illustrative purposes and were not present in the actual experiment.
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We can use this impairment to test the ability of features to aid tracking.
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3. Is tracking “colorblind”? It seems surprising that vivid color had no positive effect on tracking. Can tracking use color at all? In Experiment 3, we gave the tracked set one color and the untracked set another color. As before, colors shifted continuously during each trial
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Bounce
Results
Discussion
Unique Same
Color did not improve tracking in either condition.
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Occlusion
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Color is not a feature that is used to individuate objects when tracking.
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Bounce
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Occlusion
Segregated Mixed
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Bounce
Results
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Bounce
Note: Ts designate targets. They are for illustrative purposes and were not present in the actual experiment.
The visual system can track objects behind occluders, but inter-item occlusion presents a special problem: Moving stimuli can be confused with one another. Using color to individuate objects does not help. However, this is not because the system cannot use color information. When color segregates targets from distractors, inter-item occlusion is no longer a problem. This suggests that the challenge of multiple object tracking is segregating targets from distractors rather than individuating objects.
Future Directions What other attributes can be used to form groups of targets and groups of distractors?
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Occlusion
We tested the hypothesis that tracking cannot use color information at all.
General Conclusions
Are spatiotemporal properties (such as motion type) helpful?
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Segregated
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Therefore, it has been widely assumed that allowing items to occlude one another should not impair tracking. However, Yantis’ (1992) data suggest otherwise. In Experiment 1, we directly tested this prediction.
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Bounce
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Depth cues improve tracking when items overlap (Viswanathan & Mingolla, 2002), and occluding surfaces do not impair tracking (Scholl & Pylyshyn, 1999).
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Occlusion
Average AverageCorrect Correct
Each disk had a unique color to reduce inter-item confusion. Colors shifted continuously during each trial. 5
Background: Occlusion
Occlusion
2. Can color overcome the occlusion deficit?
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In prior work, observers had difficulty reporting changes in featural properties of tracked objects (Scholl, Pylyshyn, & Franconeri, 2004). However, those features might still be used to individuate items and improve tracking.
5 Responses
Track for 5 Secs
Average Correct
On & Off for 2 Secs
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Experiments 2 and 3 investigate the effects of a color feature on tracking. Can color improve tracking by individuating items or by disinguishing a group of targets from distractors?
Inter-item occlusion significantly impairs tracking, even when depth cues, such as borders, are present.
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Mixed
Objects can usually be distinguished by various features, including, size, shape and color.
Discussion
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Today’s question: Can distinctive feature information improve tracking?
Background: Features
Results
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Average Correct
Multiple Object Tracking
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Discussion We can easily reject the hypothesis that tracking is colorblind.
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Segregating targets and distractors by color eliminates the inter-item occlusion impairment, and makes tracking easier overall.
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Occlusion
Bounce
If inter-item occlusion only occurs among objects in the same category (targets, distractors), will it still be a problem?
Is it easier or harder to track unique objects?
References • Pylyshyn, Z.W., & Storm, R.W. (1988). Tracking multiple independent targets: Evidence for a parallel tracking mechanism. Spatial Vision, 3, 179 - 197. • Scholl, B.J., Pylyshyn, Z.W., & Franconeri, S.L. (2004). The relationship between property-encoding and object-based attention: Evidence from multiple object tracking. Submitted. • Scholl, B.J., & Pylyshyn, Z.W. (1999). Tracking multiple items through occlusion: Clues to visual objecthood. Cognitive Psychology, 38, 259 - 290. • Viswanathan, L., & Mingolla, E. (2002). Dynamics of attention in depth: Evidence from multi-elment tracking. Perception, 31, 1415 - 1437. • Yantis, S. (1992). Multielement visual tracking: Attention and perceptual organization. Cognitive Psychology, 24, 295 - 340. This research was supported by NIH grant MH65576.
