Attentional Enhancement of Tracked Stimuli in Early Visual Cortex Has Limited Capacity

Nika Adamian*, Søren K. Andersen


Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review


Keeping track of the location of multiple moving objects is one of the well documented functions of visual attention. However, the mechanism of attentional selection that supports such continuous tracking is unclear. In particular, it has been proposed that target selection in early visual cortex occurs in parallel, with tracking errors arising because of attentional limitations at later processing stages. Here, we examine whether, instead, total attentional capacity for enhancement of early visual processing of tracked targets is shared between all attended stimuli. If the magnitude of attentional facilitation of multiple tracked targets was a key limiting factor of tracking ability, then one should expect it to drop systematically with increasing set-size of tracked targets. Human observers (male and female) were instructed to track two, four, or six moving objects among a pool of identical distractors. Steady-state visual evoked potentials (SSVEPs) recorded during the tracking period revealed that the processing of tracked targets was consistently amplified compared with the processing of the distractors. The magnitude of this amplification decreased with increasing set size, and at lateral occipital electrodes it closely followed inverse proportionality to the number of tracked items, suggesting that limited attentional resources must be shared among the tracked stimuli. Accordingly, the magnitude of attentional facilitation predicted the behavioral outcome at the end of the trial. Together, these findings demonstrate that the limitations of multiple object tracking (MOT) across set-sizes stem from the limitations of top-down selective attention already at the early stages of visual processing. SIGNIFICANCE STATEMENT The ability to selectively attend to relevant features or objects is the key to flexibility of perception and action in the continuously changing environment. This ability is demonstrated in the multiple object tracking (MOT) task where observers monitor multiple independently moving objects at different locations in the visual field. The role of early attentional enhancement in tracking was previously acknowledged in the literature, however, the limitations on tracking were thought to arise during later stages of processing. Here, we demonstrate that the strength of attentional facilitation depends on the number of tracked objects and predicts successful tracking performance. Thus, it is the limitations of attentional enhancement at the early stages of visual processing that determine behavioral performance limits.

TidsskriftJournal of Neuroscience
Udgave nummer46
Sider (fra-til)8709-8715
StatusUdgivet - 16. nov. 2022

Bibliografisk note

Funding Information:
Received Mar. 28, 2022; revised Sep. 22, 2022; accepted Sep. 26, 2022. Author contributions: N.A. and S.K.A. designed research; N.A. and S.K.A. performed research; S.K.A. contributed unpublished reagents/analytic tools; N.A. analyzed data; N.A. wrote the first draft of the paper; N.A. and S.K.A. edited the paper; N.A. and S.K.A. wrote the paper. This work was supported by the Biotechnology and Biological Sciences Research Council Grant BB/ P002404/1 (to S.K.A.) and the Leverhulme Early Career Fellowship ECF-2020-488 (to N.A.). We thank Alex O. Holcombe and Christian Merkel for their many insightful comments and suggestions. We also thank Rafael Lemarchand for his help in data collection. The authors declare no competing financial interests. Correspondence should be addressed to Nika Adamian at Copyright © 2022 the authors

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© 2022 the author.


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