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Daryl Fougnie, René Marois; Is the capacity limit of attentional tracking and visual working memory one and the same?. Journal of Vision 2004;4(8):358. doi: 10.1167/4.8.358.
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© ARVO (1962-2015); The Authors (2016-present)
Our capacity to select visual targets out of a scene of distractors is severely limited. Likewise, our capacity to hold visual stimuli in mind once the scene is out of sight is impoverished. These reflect the capacity limits of attention and visual short-term memory (VSTM), respectively. Attentional capacity limits have been studied with the multiple object tracking (MOT) task, in which subjects track a variable number of moving objects among similarly moving objects. VSTM limits are revealed with a task that requires the retention of the identity and/or location of objects over a delay period. Both MOT and VSTM tasks show similar capacity limits of 4 +/−1 items, and attention is known to be important for the maintenance of visual information in VSTM. These findings raise the possibility that the capacity limit of attention and VSTM may be one and the same. We have begun to test this hypothesis by determining the effect of varying the load of a MOT task that was performed during the retention interval of a VSTM task. For each trial, subjects were briefly presented with a VSTM display of 3 or 4 colored circles, followed 1200 ms later by a MOT display consisting of 12 colored circles, with subjects tracking either 1 or 3 of the circles for 9 seconds. Following the MOT display, subjects made a single probe detection judgment for the VSTM task. When the VSTM task required only to encode object information, subjects' performance was not affected by the MOT task. By contrast, when the VSTM task required encoding both objects' color and location, subjects' performance was considerably affected by tracking one object in the MOT task. However, increasing the MOT load to three objects did not further affect VSTM performance, even though tracking 3 items was more difficult than tracking one. These results suggest that even though attentional tracking and VSTM tasks are mechanistically related, the processes responsible for their capacity limits may not be.
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