Countermanding saccades in children

The countermanding saccade task is a widely used test of reactive inhibitory oculomotor control. The test comprises "Go" trials, in which saccades are directed towards target onsets, interspersed with "Stop" trials, where a signal sometime after target onset indicates that a saccade should be withheld or "countermanded". Computational models of the task assume a race to threshold between internal go and stop processes, the outcome of which determines whether a programmed response is cancelled. In this study, 181 typically developing primary-school-aged children completed child-friendly versions of the task. Three experiments examined the effect of task instruction (either to countermand saccades or ignore stop signals), stop signal characteristics (with and without an overlapping fixation cue) and practice (one versus two blocks). Children often failed to make saccades even when they were instructed to ignore the signal and make a response to the target on every trial. Saccade reaction times were longer on Stop compared with correct Go trials and significant "dips" (reductions in expected response frequency within discrete time bins) were observed in reaction time distributions associated with the change in the colour of the fixation stimulus that served as a stop signal. It is concluded that visual stop signals exert an exogenous inhibitory effect on saccades which decreases with increasing age. As such, care should be taken in interpreting the oculomotor stop signal task as a straightforward test of developing inhibitory control or the maturation of an internal stop process. OPEN ACCESS STATEMENT: Experiment task code, raw trial-level data, and analysis files for all experiments are available via the Open Science Framework: https://doi.org/10.17605/OSF.IO/Q4PGH . The study protocol was not preregistered.