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Roger W Strong, George A Alvarez; Hemifield-specific information is exchanged as targets move between the hemifields. Journal of Vision 2019;19(10):52c. doi: https://doi.org/10.1167/19.10.52c.
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Tracking moving targets with attention is more difficult when targets cross between the left and right visual hemifields (compared to when targets move within their original hemifields), providing evidence for separate control of attentional tracking in each hemifield (Strong & Alvarez, VSS 2018). There are at least two possible explanations for this between-hemifield cost. One possibility is that hemifield-specific attentional spotlights inefficiently exchange target information as targets cross between hemifields; this explanation predicts that tracking accuracy should decrease with increasing numbers of between-hemifield crosses. A second possibility is that hemi-field-specialized attentional spotlights continue to track their original targets after the targets cross between hemifields, but do so less effectively; this explanation predicts that tracking performance should decrease as the time targets spend in a new hemifield increases. To test these two possibilities, observers tracked two targets (one in each hemifield) that varied in A) the number of times they crossed between hemifields and B) the time they spent within a new hemifield (Experiment 1). Tracking accuracy decreased as the number between-hemifield crosses increased, but was not influenced by the time targets spent in a new hemifield. These results indicate that the between-hemifield tracking cost occurs because of an inefficient information exchange between hemifield-specific attentional spotlights. Experiment 2 explored whether this information exchange is aided or hindered by the vertical midline between hemifields, an area represented by both cerebral hemispheres during tracking (Drew et al., 2014). The between-hemifield cost increased when targets “teleported” through occluders (Scholl & Nevarez, 2002) at the vertical and horizontal midlines, suggesting that the exchange of target information is aided by tracking at the vertical midline. Together, these experiments show that hemifield-specific attentional spotlights exchange their representational content during between-hemifield movements, and suggest that this exchange is enabled by representational overlap at the vertical midline between hemifields.
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