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Jude F. Mitchell, Kristy A. Sundberg, John H. Reynolds; Attentive tracking of multiple objects by humans and monkeys. Journal of Vision 2005;5(8):30. doi: 10.1167/5.8.30.
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© ARVO (1962-2015); The Authors (2016-present)
Human observers can attentively track 3–5 stimuli as they move along independent random trajectories among distracter stimuli (Pylyshyn and Storm, 1988; Sears and Pylyshyn, 2000). We developed a multi-object tracking task suitable for monkeys, and measured task performance in two monkeys as we varied the number of tracked and distracter stimuli. Each trial began with fixation of a central point, after which 4–8 identical stimuli appeared at equally eccentric peripheral positions. A subset of these briefly flashed, identifying them as targets. All stimuli then moved along random independent trajectories for 2–3 seconds while the monkey maintained fixation. All stimuli terminated motion at equally eccentric positions that were unpredictable from their initial positions. The monkey indicated the identities of the targets by making a saccade to each. Reward was only delivered if the monkey made saccades to all targets and no distracters. After extensive training both monkeys showed reliable tracking for two items. Humans were able to track 3–4 items when tested with the same stimuli. Initial recordings in Area V4 made with one tracked target and three distracters found that V4 responses evoked by the tracked object were on average ∼20% stronger than responses evoked by the same stimulus when it was not being tracked.
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