A comparison of saccade evoked potentials recorded during reading and tracking tasks

The influence of visual processing demands on saccade-triggered evoked potentials was investigated at P3, P4 and Oz recording sites during reading and tracking tasks. To maximize the physical similarities between tasks, subjects tracked a series of lights that flashed in a stereotypic reading pattern behind a page of text; eye movements recorded during reading initiated the light sequence. In the first experiment, a significant decrease observed in the latency of the major positive peak recorded from Oz during tracking was attributed to the smaller amplitude of tracking, relative to reading, saccades. To confirm this interpretation, the experiment was repeated with modification to the light display. As anticipated, equating saccade amplitudes across tasks eliminated waveform differences in the second experiment. Although peak latencies and amplitudes were not influenced reliably by visual processing demands, tracking potentials exhibited a negative DC shift relative to reading waveforms that was significant at 174 msec at the Oz site. These data suggest that the saccade-triggered evoked potential components generally are insensitive to task differences within the visual modality when visual configuration and eye movement parameters are controlled.