Assessing inhibitory control: a revised approach to the stop signal task.

The stop signal task (stop task) is designed to assess inhibitory control and is a frequently used research tool in clinical disorders such as ADHD and schizophrenia. Previous methods of setting stop signal delay and of assessing inhibitory control are problematic. The current study reports two modifications that improve the task as a measure of inhibitory control. The first modification was to set stop signal delays proportional to go mean reaction time (go MRT) to better account for inter-subject variability in go MRT. Twenty-eight normal children were tested, and all standard, stop task dependent measures were obtained when delays were set by this method. The second modification was to calculate a novel dependent measure called the area of inhibition (AOI) which provides a more complete measure of inhibitory control than the slope of the relative finishing time z-scores (ZRFT-slope). Implications for the assessment of inhibitory control in clinical populations are discussed.