APPARENT MOTION CONFOUNDS EARLY VERNIER VISUAL-EVOKED POTENTIALS

Human scalp potentials evoked by vernier stimuli have been recorded fo r offsets less than the diameter of a foveal cone, but always for abru ptly moving stimuli. Those evoked potentials were related to the magni tude of vernier offset. Here we report results for stimuli containing no apparent motion confound, using multichannel recordings and multiva riate analysis methods which stress the concept of a sampling of the s calp field. We found evidence of cortical activity dependent on the di rection of vernier offset, at much shorter latencies (ca. 75 ms) than previously reported, but no evidence of early cortical activity relate d to the magnitude of offset. Repeating the experiments and analysis u sing a stimulus containing apparent motion, we found evidence of corti cal activity dependent on the magnitude of offset at both 75 and 200 m s, but none related to direction of offset. These findings sugggest th at previous studies which contained the apparent motion confound might not have obtained visual evoked potentials entirely due to vernier of fset.