To estimate the minimal time required to process visual information (ie "effective acquisition time") during a visual search task, we used a gaze-contingent visual masking method. In the experiment, an opaque mask that restricted the central vision was presented at a current gaze position. We manipulated a temporal delay from a gaze shift to mask movement. Participants were asked to search for a target letter (T) among distractor letters (L)s as quickly as possible under various delays. The results showed that the reaction times and search rate decreased when the delay was increased. When the delay was longer than 50 ms, the reaction times and search rate reached a plateau. These results indicate that the effective acquisition time during the visual search task used in the study is equal to or less than 50 ms. The present study indicates that the gaze-contingent visual masking method used is useful for revealing the effective acquisition time.
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