Inhibitory Control of Saccade Generation Mediated by Various Oculomotor Regions in Response to Reading Difficulty

Abstract

Cognitive influences on saccade patterns during reading have been well documented, indicating that difficulties often result in prolonged fixation duration, shortened forward saccade length, and increased regressive saccades.1 Nevertheless, the underlying neural mechanisms of the observed effects are not yet understood. A commonly accepted behavioral hypothesis suggests that the process of saccade generation in reading is triggered by the completion of certain psycholinguistic events, such as the completion of word identification or at least the execution of a familiarity check on the foveated words.2 Several studies conducted in our laboratory have shown that increasing the difficulty of identifying the fovated words (i.e., degrading word stimuli or replacing normal words with random letters) does not prolong the overall latency of all following saccades. Analyzing the frequency distributions of the durations of critical fixations (those on which the difficulty occurs) indicates that the cancellation or delay of saccades only begins at about 175–225 msec after the fixation onset.3,4 Thus, the oculomotor mechanism for saccade generation actually proceeds normally, unaffected by cognitive difficulty, until some later time when the detected difficulty can exert an inhibitory influence on saccade generation. In this report, we present results from two studies by Yang and McConkie,5 using gaze-continent display change during saccades. In these studies, people read continuous text from a computer display while their eye movements were recorded. The normal text was replaced with an alternative stimulus pattern during randomly selected saccades, with normal text returning during the following saccade, thus occasionally producing an inappropriate stimulus pattern for a single fixation. We then observed the effect of the abnormal stimulus patterns on the time, direction, and length of the following saccade.