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Haluk Ogmen, Bruno G. Breitmeyer; Dissociation between visual awareness and sensori-motor performance fails in paracontrast but not metacontrast. Journal of Vision 2002;2(7):19. doi: https://doi.org/10.1167/2.7.19.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. A metacontrast mask suppresses the visibility of, without influencing reaction time (RT), to the target. We investigated if this dissociation holds in paracontrast. Methods. The target was a 13.3 ms, .86 deg diameter disk shown 2 deg to either the left or else the right of, and 1.6 deg above, fixation. Two 13.3 ms mask rings (inner and outer diameters of .89 deg and 1.66 deg) were centered at the two possible target locations. Mask/target (M/T) contrast ratios were 1 or 3. Observers' task was to indicate, by key press, the target position. SOAs ranged from −293 ms to 224 ms. To control for “bottleneck” effects on RT when stimuli are in rapid succession, we also used “pseudo-masks” (an array of 4 .6deg x .6deg squares separated from the target contour by 1.69 deg) designed to not mask the target. Differences between the RTs in the mask and pseudo-mask conditions (D RT) defined the sensori-motor effects of the mask. In other experiments, observers used a staircase method to match the perceived brightness of the target to that of an unmasked reference. Results. For target visibility, para- and metacontrast yielded the usual U-shaped functions. Peak paracontrast occurred at SOAs of −150 to −100 ms, compared to prior reports in the −60 to −20ms range. D RTs for metacontrast fluctuated around averages of −5.5 ms and 1.7 ms for M/T ratios of 1 and 3. However, for paracontrast D RTs depend strongly on SOA, peaking at SOA = −150 ms. The peak D RT values are 28.7 ms and 51.1 ms for M/T ratios of 1 and 3. Conclusions. The dissociation between visual awareness and sensori-motor performance in masking does not result from a sensori-motor pathway immune to masking effects. The dependence of the dissociation on stimulus timing can be explained by a dual-channel model wherein fast and slow activities interact.
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