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Christina Howard, Alex O. Holcombe; Progressively poorer perceptual precision and progressively greater perceptual lag: Tracking the changing features of one, two and four objects. Journal of Vision 2006;6(6):785. doi: 10.1167/6.6.785.
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© ARVO (1962-2015); The Authors (2016-present)
Approximate measures indicate a four-object capacity limit for tracking the changing positions of objects. More precise measures suggest a gradual decline in perceptual precision with number of objects tracked. Indeed, performance can decline substantially as load is increased from one to two (e.g. Tripathy and Barrett, 2004, Journal of Vision, 4, 1020 – 1043). Performance in continuous tracking of features other than position remains underexplored. Here we investigate the effect of attentional load on tracking smoothly changing orientations and spatial frequencies. Method: Five Gabor patches constantly changed orientation or spatial frequency in a smooth and random manner. To vary attentional load, one, two or four of these were indicated as the targets for tracking. After a random interval all Gabors disappeared and one target was indicated. To report the final state of this probed Gabor, observers adjusted the orientation or spatial frequency of a sample. Results: Tracking two Gabors yielded substantially greater error magnitudes than tracking one. Indeed, the distribution of orientation errors was not much better than that of a worst-case model wherein only one orientation is tracked at any time. Capacity thus appears very limited. A different analysis revealed that responses were more similar to previous states of the probed Gabor than to its final state. This lag increased with attentional load. The increase may represent either attention visiting each item less often with the increase in number attended, or a load-induced increase in consolidation time for visual short-term memory.
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