The role of interval underestimation in hyperactive children's failure to suppress responses over time.
The relationship between response inhibition and time estimation abilities was investigated in a group of hyperactive and non-hyperactive children. Children performed a discrete trials intertemporal response task under two conditions. Under both conditions children had to respond within a 2 s window, which was delayed for a set period (either 5 or 15 s). In condition one (signalled condition), these response requirements were signalled by changes in the expression of a face drawn on a computer screen. In condition two (unsignalled condition), always presented on the trial following the signalled condition, these changes in expression were obscured by a hand drawn over the mouth of the face so that effective performance depended on the childs ability to estimate the point at which the facial expression changed on the preceding trial. Both groups of children had little difficulty inhibiting responses when the response requirements were signalled. All children made far more errors under the unsignalled condition. Hyperactive children displayed a systematic tendency to respond before the response window occurred. Taken together, these data give no support to the idea that hyperactivity is essentially a problem of disinhibition and raise interesting questions about the role of time mis-estimation in the disorder.