Abstract
Background. Extensive research has focused on the control of saccades during reading. However, very little is known in this context about microsaccades (saccades< 0.5 deg), i.e., whether they occur and how they shift the gaze. Using new methods for precisely localizing the line of sight, we recently showed that in high acuity tasks microsaccades precisely position the preferred retinal locus, the tiny region of maximum acuity within the foveola (Ko et al, 2010; Poletti et al, 2013). These findings raise the possibility that microsaccades may also play a role in reading. Methods: Observers (N=10) were instructed to read 10th grade passages of text and answer questions regarding their content. Eye movements were recorded by means of a high resolution DPI eyetracker. Gaze-contingent calibrations were used to accurately localize the preferred retinal locus. Results: Microsaccades occur during reading: the average rate across all subjects was 18 microsaccades per minute. Interestingly, their characteristics differed from those measured when fixating on a marker. During fixation, microsaccades had approximately equal probability to shift the gaze to the left or to the right, and a considerable number (~32%) possessed vertical components. In contrast, during reading, most microsaccades (61%) directed the gaze leftwards and only 16% vertically. Therefore, microsaccades primarily relocated the gaze backward on the text, most of them just 2-3 letters back from the end of long words. Further analyses showed that this pattern of microsaccades differed significantly from what would be obtained by chance. Conclusion: Our results show that microsaccades occur and are controlled during reading. It is well known that the perceptual span normally extends asymmetrically toward the reading direction. Microsaccade backward shifts could compensate for this asymmetry.
Meeting abstract presented at VSS 2016