THE ROLE OF INTERVAL UNDERESTIMATION IN HYPERACTIVE CHILDRENS FAILURETO SUPPRESS RESPONSES OVER TIME

The relationship between response inhibition and time estimation abili ties was investigated in a group of hyperactive and non-hyperactive ch ildren. Children performed a discrete trials intertemporal response ta sk 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 requirem ents were signalled by changes in the expression of a face drawn on a computer screen. In condition two (unsignalled condition), always pres ented on the trial following the signalled condition, these changes in expression were obscured by a hand drawn over the mouth of the face s o that effective performance depended on the childs ability to estimat e the point at which the facial expression changed on the preceding tr ial. Both groups of children had little difficulty inhibiting response s when the response requirements were signalled. All children made far more errors under the unsignalled condition. Hyperactive children dis played a systematic tendency to respond before the response window occ urred. Taken together, these data give no support to the idea that hyp eractivity is essentially a problem of disinhibition and raise interes ting questions about the role of time mis-estimation in the disorder. (C) 1998 Elsevier Science B.V. All rights reserved.