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Gregory Francis; The role of temporal integration in backward masking. Journal of Vision 2005;5(8):762. doi: 10.1167/5.8.762.
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Visibility of a brief target is reduced by the appearance of a mask 50 ms after target onset. At shorter or longer SOAs masking is weaker, which produces a u-shaped masking function of target percept against SOA. Many quantitative theories have explained why backward masking has this property, but as we reported last year, all of the quantitative theories predict that the shape of the masking function is related to the overall strength of masking. We reported data inconsistent with this prediction. One alternative theory that might account for the results hypothesizes that when the target and mask are presented with a short SOA they temporally integrate to form a single percept. In this percept, the target may be identified and thus lead to weak masking at short SOAs (Navon & Purcell, 1981). Here, we report a conceptual replication of a study by Reeves (1982) to explore the role of integration in a u-shaped masking function. Observers were asked to identify the location of a target (rectangle) among three distracter squares arranged on a virtual square around a fixation point. The target frame was followed by a mask frame (both 27 ms duration) of outline squares around each element in the target frame. The SOAs between target and mask frames were 0, 13, 27, 40, 53, 67, 133 or 267 ms. On each trial an observer was asked to identify the location of the target element and then to judge whether the target and mask elements were presented simultaneously or consecutively. Regardless of the temporal alignment report, a u-shaped masking function was found. This finding deviates from Reeves (1982), which found different monotonic shaped curves for reports of perceived simultaneous and consecutive target and mask frames. The new result suggests that temporal integration of the target and mask is not necessary to produce a u-shaped masking function. We discuss the differences between the present study and Reeves' and what kinds of models might account for the results.
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