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Justin Ericson, Jeff Nyquist, Joe Lappin, Adriane E. Seiffert; Multiple object tracking in the periphery does not show hemifield independence. Journal of Vision 2007;7(9):899. doi: 10.1167/7.9.899.
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Attention can be divided amongst several spatial locations, allowing people to track several objects moving independently. Alvarez and Cavanagh (2005) have shown that participants were able to track twice as many targets when they were presented in the left and right hemifields as when they were all presented within the same hemifield. This result suggests that there is hemifield independence in attentional tracking. Our experiment was designed to test this hypothesis by examining attentional tracking in the far periphery to determine if hemifield independence holds when attentional foci are farther apart. Observers maintained fixation in the center of the screen while viewing two square display boxes (11.3° visual angle to a side) in one of two configurations. Boxes were aligned either vertically (unilaterally in either the left or right hemifield), or horizontally (bilaterally to the left and right of fixation) close to fixation with 1.25° to the nearest edge. A third condition extended the horizontal configuration into the far periphery (20.1° to the nearest edge) with larger display boxes (17.7° to a side). Each display box contained 4 dots (dot diameter: 0.64° for the close condition and 1.27° for the far condition) moving randomly at approximately 15° per second such that no two dots overlapped. Participants attentionally tracked either 2 target dots in a single box or 4 target dots (2 in each box) for 5 seconds. Replicating Alvarez and Cavanagh (2005), participants were able to track twice as many targets when presented bilaterally close to fixation than when targets were displayed unilaterally. However, participants could not track twice as many targets when displays were presented bilaterally farther in the periphery. This suggests that attentional resources used in tracking are not completely hemifield independent, and attentional tracking becomes more taxing farther in the periphery
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