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The detection of multiple global directions: Capacity limits with spatially segregated and transparent-motion signals

Greenwood, JA; Edwards, M; (2009) The detection of multiple global directions: Capacity limits with spatially segregated and transparent-motion signals. Journal of Vision , 9 (1) , Article 40. 10.1167/9.1.40. Green open access

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Abstract

An important constraint on motion processing is the maximum number of directions that can be perceived at the same time. When transparent-motion stimuli are constructed based solely on direction differences, prior studies demonstrate that no more than two directions are seen simultaneously. However, this limit has been extended to three when signal directions drive independent speed- or disparity-tuned global-motion systems. The present study sought to determine whether this three-direction capacity reflects the specific mechanisms of transparent-motion detection or a more general restriction on global-motion processing. Using both transparent and spatially segregated stimuli, observers indicated which of the two intervals contained the most directions, with simultaneous processing ensured through brief durations and n vs. n + 1 signal comparisons. When spatially segregated directions were interleaved in patches, no more than two were seen, as with direction-defined transparent motion. In contrast, separating these directions into distinct spatial regions allowed the detection of up to three. Signal-detection thresholds did not vary across these signal arrangements, suggesting that the two-direction capacity results from signal-to-noise pooling across the entire stimulus, with the higher capacity for spatially distinct directions arising from independent pooling within each region. Together, these results provide further evidence for an upper capacity of three directions within the global-motion stage.

Type: Article
Title: The detection of multiple global directions: Capacity limits with spatially segregated and transparent-motion signals
Open access status: An open access version is available from UCL Discovery
DOI: 10.1167/9.1.40
Publisher version: http://doi.org/10.1167/9.1.40
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Motion perception, transparency, global motion, capacity limit, attention
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > Div of Psychology and Lang Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > Div of Psychology and Lang Sciences > Experimental Psychology
URI: https://discovery.ucl.ac.uk/id/eprint/135752
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