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Toni Saarela, Michael Herzog; Temporal characteristics and surround modulation of contrast masking. Journal of Vision 2007;7(9):258. doi: https://doi.org/10.1167/7.9.258.
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© ARVO (1962-2015); The Authors (2016-present)
The spatial characteristics of contextual modulation in visual processing have been widely studied, but much less is known about its temporal properties. We measured contrast detection thresholds for a brief, 40 ms Gabor target, masked with a 100 ms grating of 40% contrast. The mask was either a circular center mask spatially overlapping the target (diameter 4 cycles), an annular mask surrounding the target (inner and outer diameters 4 and 32 cycles, respectively), or a combination of the two. Masks were either iso-oriented with the target or orthogonal to it. Stimulus onset asynchrony between the target and the mask was varied, ranging from backward masking to forward masking. With the orthogonal center mask, masking was strongest (i.e., thresholds were highest) when the target onset coincided with either the mask onset or offset. With the iso-oriented center mask, however, unexpectedly strong masking occurred when the target offset coincided with the mask onset or vice versa. That is, masking was strongest when the mask immediately preceded (forward masking) or immediately followed (backward masking) the target. Further, adding a surround to the iso-oriented center mask had no effect on forward masking, but it greatly reduced the backward masking effect. Backward masking is often considered counterintuitive as a subsequently presented mask can suppress the target. The present results indicate that spatial interactions in the processing of the mask can also take place before backward masking occurs.
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