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Introduction: Speed of information processing (SIP) is an important factor for cognitive development. Determining the developmental trajectory of SIP has been difficult due to a lack of continuity in the paradigms comparing adults’ and infants’ SIP nor continuity in the stimulus feature set (spatial vs content) of uncertainty. Further, for spatial uncertainty, although adults’ manual RTs have been shown to increase linearly with increasing choices, their saccadic RTs seem to not. Seven-month-old infants’ saccadic RTs, in contrast, have been shown to increase with more target choices as expected (Dougherty & Haith, 1997). What is the developmental course from infancy that enables this discrepancy in saccadic RTs that increase with uncertainty at 7 months but not in adults? Method: To address this question, the present study used the same eye movement paradigm across ages as a means to bridge the discontinuities and assess the developmental discrepancy. Adults’ and 5- and 9-month-old infants’ reactive saccades were measured across 100 trials in a comparable choice reaction time task. Participants had to make an eye movement, starting from a central fixation, to a target at one of a possible 1, 2, 4, 6, or 8 spatial locations arranged as a circular array. Results: Both 5- and 9-month-olds’ saccadic RTs increased linearly with more choice alternatives (i.e. more uncertainty), but 9-month-olds’ increased at a shallower rate, approaching adults’ saccadic RT function which did not exhibit an increase with more choices. Conclusion: Findings revealed that there exists a developmental trend in saccadic RTs for spatially-defined SIP, in that as infants age, saccadic responses become less sensitive to spatial uncertainty, and approach adult-like performance. Decreasing saccade sensitivity may be due to developmental changes in the influence of response selection or in the functioning of inhibitory mechanisms.
Acknowledgements: The Hallward Fund of the Toronto Foundation