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Directional and nondirectional coding of a spatio-temporal modulated stimulus

Contrast thresholds for apparent flicker and direction of movement were measured separately by using a subthreshold summation technique; 4 20-40 yr old persons were Ss. The test stimulus consisted of a drifting grating superimposed on an identical grating moving in the opposite direction and set at different subthreshold contrasts. It was found that with increasing contrast of the subliminar grating (a) movement thresholds increased, (b) apparent flicker thresholds were slightly decreased, and (c) percentage of apparent flicker reports increased from 0 to 100. The distinction between flicker and movement thresholds was shown to be justified by 2 subsidiary experiments that showed that flicker is not to movement what movement is to flicker. A moving subliminar grating facilitated the detection of an objectively flickering grating whereas the reciprocal was not true. This might indicate separate detection of drifting and flickering gratings. (19 ref) (PsycINFO Database Record (c) 2005 APA, all rights reserved)



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