CORTICAL DC POTENTIAL SHIFTS ACCOMPANYING THE CENTRAL PROCESSING OF VISUALLY PRESENTED ANALOG AND DIGITAL TIME DISPLAYS

According to studies in brain-lesioned patients, the cortical substrat e subserving the reading of digitally presented time displays seems to differ from that of reading analogue displays. While the right hemisp here has been assumed to be important for reading analogue displays, r eading digital displays is attributed to the left hemisphere. This stu dy attempts to localize the cortical substrate of reading analogue ver sus digital time displays in the intact human brain using scalp-record ed event-related slow negative DC potential shifts. In the arithmetic tasks, subjects had to judge whether or not the time conveyed by the l ast out of three tachistoscopically presented (analogue or digital) sl ides was the exact difference between the time conveyed by the first a nd the second slide. In the control condition, subjects only had to at tend to (analogue or digital) time displays. With analogue slides, fro ntolateral recording sites revealed a right hemispheric preponderance of DC shifts measured in the interval between the second and third sli de. Anterior temporal recording sites revealed a right hemispheric pre ponderance only when calculations were performed. By contrast, there w as no hemispheric lateralization with digital slides. The arithmetic v ersus control manipulation modulated waveforms, but did not influence hemispheric laterality. (C) 1997 Elsevier Science Ltd.