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Alejandro Lleras, Michael Ambinder; How to kill a fly: on the difficulties of tracking a smooth and sometimes saccadic moving target. Journal of Vision 2007;7(9):893. doi: 10.1167/7.9.893.
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Myriad studies have investigated the ability of human observers to track smooth moving objects under both free-viewing and fixation-controlled conditions and shown that observers are generally good at this task. However, no research to our knowledge has investigated humans' ability to track smoothly moving targets that can sometimes abruptly shift direction and speed, such as flies do in a natural environment. Unlike the multiple-object tracking task where observers can typically track four smooth-moving targets, in our daily life we usually experience great difficulty in tracking the motion of a single fly. Indeed, we often experience the fly “flying out” of awareness. In the current set of experiments, we investigated observers' ability to track a simulated fly in a computer display. A single pixel moved around the display, randomly alternating between slow-and-smooth (“continuous”) and fast-and-jerky (“jump”) motions, simulating abrupt changes in speed and direction normally observed in a fly's flight. The observers' task was to detect brief luminance increments in the “fly” that occurred four times during each 20-second trial. In Experiment 1, participants observed the fly under free-viewing conditions. Detection of flashes during continuous motion was significantly greater than detection during jump motions, which might be expected due to saccadic suppression. Interestingly, this difference was substantially increased when participants were asked to maintain fixation (i.e., not move their eyes), even though one might have expected the sudden onset of the luminance increment in the jump condition to capture attention. We take this decrement during jump motions to reflect more than just a reduction in stimulus visibility; in fact, we believe it stems from the actual phenomenal disappearance of the fly during this type of motion, which would be consistent with reports from post-experimental interviews. Is this a form of saccadic camouflage? Current experiments are aimed at further testing this phenomenon.
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