The influences of reading direction on inhibitory control of eye movements

Since written language is linear, eye movements in reading are constrained to largely follow that direction. Difficulties in reading modify the pattern of eye behavior, typically prolonging eye fixation times, shortening forward saccades and increasing the number of regressive movements. These changes are usually attributed to direct cognitive control of eye behavior, moving the eyes to locations from which information is needed to resolve the difficulty. However, Yang & McConkie (2001, Vision Research) have argued for indirect cognitive influences, mediated by different types of inhibitory signals produced by the detection of processing difficulty and acting upon a bilateral system, probably involving the superior colliculus. The current study tested this proposal by comparing the eye movements of skilled Chinese readers as they read horizontal text and vertical text, both directions being highly familiar. As they read, during occasional saccades the text was replaced by alternate stimulus patterns with the normal text returning during the following saccade. These single-fixation stimulus patterns signaled the reader to make specific intentional saccades (forward, regressive, or stop). The effects were observed on the timing and directions of the saccades ending these critical fixations. The results indicate that 1) the oculomotor system uses automated and controlled inhibitory signals to regulate saccade generation, 2) inhibitory signals are directionally selective, only being applied to the forward direction, 3) the direction of eye movements affects saccade latencies, and 4) the direction of reading affects direction-selectivity by producing bi-directional effects on saccade generation. These results provide information about how the oculomotor system produces responses to reading difficulty and task demands during reading.