Patterns of change in ocular motor development.

This study examined development of pro- and anti-saccadic eye movements in a cross-sequential research design. A hundred and seventeen subjects aged 6-18 years at initial testing were retested 18.9 ± 1.2 months later. Pro- and anti-saccades were elicited under the gap and overlap conditions. We found strong longitudinal developmental effects on all parameters analysed, in particular those derived from the anti-saccade task. These longitudinal changes structurally resembled the cross-sectional age effects observed for the same data. However, the principal component analyses of longitudinal "true" and raw difference scores revealed a stable three-factor solution that was robust to age effects and included (a) an express saccade factor, (b) a variability factor and (c) a factor consisting of direction errors with regular latencies and pro-saccadic RT. Cross-sectional factor analysis, by contrast, merged these two last-mentioned factors. We thus conclude that longitudinal data can provide unique information regarding individual differences in the patterns of developmental change.