Attentional shifting and disengagement in Rett syndrome.

Objective: The purpose of the present study was to deepen our understanding of attention (a core cognitive ability) in Rett syndrome (RTT), an x-linked neurodevelopmental disorder caused by mutations in the MECP2 gene. We focused on two key aspects of visual orienting--shifting and disengaging attention--both of which are critical for exploring the visual world. We used gaze-based measures and eye-tracking technology to minimize demands on the limited verbal and motor abilities associated with RTT. Method: Shifting and disengaging attention were examined in 31 children (2-12 years) with Rett Syndrome (RTT) and 31 age-matched typically-developing (TD) controls. Using the gap-overlap paradigm, the frequency/speed of shifting attention from a central to peripheral target were compared on Baseline trials, where the central stimulus disappears as the peripheral target appears, and Overlap trials, where the central stimulus remains, thus requiring disengagement. Results: Our findings revealed that children with RTT had more ‘sticky fixations’(p<.001). That is, they had fewer saccades to the peripheral target than TD children, and this was true on both baseline (77% vs 95%), and overlap trials (63% vs 90%); the younger ones also had slower saccadic reaction times (SRTs)(p=.04). Within the RTT group, SRTs correlated with symptom severity. Surprisingly, disengagement cost (the relative difference between gap and overlap SRTs) did not differ across groups. Conclusion: Our results suggest that children with Rett have difficulty shifting attention and, to a lesser extent, disengaging attention, whereas with other disorders, problems with disengagement are paramount.