Evidence for image-scanning eye movements during transitive inference

Contrary to earlier work, recent studies have demonstrated a reduction in eye movements during the solution of tasks that seem to require visual imagery, relative to verbal tasks. The present study provides evidence that the nature of the visual imagery required by a task determines whether saccades are evoked and in which spatial pattern. In two experiments, subjects solved transitive inference problems with the relational terms left/right and above/below, while the horizontal and vertical EOG were recorded. Subjects made more horizontal and fewer vertical saccades while solving problems with the left/right terms than while solving identical problems with above/below. The results of silent counting tasks showed that the rate of subvocalization can also influence saccadic rate, especially in the horizontal plane, but cannot explain the eye-movement patterns observed during transitive inference. The results are discussed in terms of a motor theory of voluntary thinking.