Learning during visual search in children with attentional and learning problems: a trial to trial evaluation of RT and ERP measures.
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Trial to trial Event Related Potentials (ERPs) were recorded from children with attentional problems (APs), learning problems (LPs), and from children without these problems (NCs). The task required the subjects to memorize two figures and to selectively respond to their occurrence in a series of stimuli. Stimuli consisted of a display of figures at eight locations in a circle, whereby the targets were presented at a random or a fixed location. Learning from knowledge of prior displays was possible only in the fixed condition. Learning during presentation of the fixed series was manifest in several components. A Slow Wave (SW) difference between series, initially not present, developed within seven trials, and thus corresponded to the rapidity with which the reaction times (RTs) decreased over trials. A larger occipital SW difference was discovered in AP children and a larger frontocentral one in LP children compared to normals. The latency of this SW and the P300 difference between series were delayed with about 200 msec in APs compared to NCs. The task difference in the earliest component, the P120, that increased after behavioral task acquisition was completed, was seen in normal children only. This probably reflected feature-specific (location) attentional demands, that decreased slowly in normal children when the task became more predictable following a number of trials. Task differences of the N200, possibly reflecting covert orienting of attention, were initially smaller in APs and LPs than those of NCs, but they increased in APs (and in LPs more slowly) over trials. Differences were found for parietal amplitudes of the P300 in LPs and NCs, but not for APs. We concluded that AP children show early deficits that could originate from a limited capacity in focussing attention, which in turn prolongs stimulus evaluation. All subsequent processes are delayed by a similar amount of time. In addition, the relatively small frontocentral ERP's of the AP group suggest diminished frontal functioning. Problems in task acquisition and a prolonged process of memory updating might be induced by the slow adaptation to task differences in LP's, and delayed parietal SWs during task acquisition together with a marked frontocentral distribution and no RT difference.