Vertical eye movements during mental tasks: a re-examination and hypothesis.

Previous research has shown that both vertical and lateral eye movements occur during mental tasks, although the neuropsychological basis for such movements remains unclear. Vertical and lateral eye movements were recorded from 24 right-dominant subjects as they performed three different mental tasks: a mental arithmetic task, a visuospatial imagery task, and a proverb interpretation task. Significant upward biases in the direction of the initial eye movement were observed as subjects answered a series of arithmetic and visuospatial questions along with a nonsignificant upward bias following a series of proverbs that subjects had to interpret. By contrast, no consistent lateral eye movement biases were found during any task. The results are interpreted according to Previc's recent theory linking processing in the upper and lower visual fields to ventral versus dorsal posterior cortical activation, respectively.