Reaction time changes in workers exposed to lead.

This article provides a detailed examination of lead workers' reaction times to elucidate the underlying basis for the slowing found. Seventy workers, classified as either low, medium, or high lead exposed, completed a five-choice reaction time task using response-stimulus intervals (RSIs) between 0 and 4 s. Performance was assessed by analysing the distributional properties of correct reaction times. The effect of lead on movement time was constant across the entire movement time distribution and thus simply characteristic of slowed motor reaction time. By contrast, the effect of lead on decision time became increasingly evident at higher points in the percentile distribution, particularly at the shortest RSIs. This suggests that decision slowing is due to central, not peripheral, factors and is consistent with alternative analyses showing that the incidence of decision gaps also provide a sensitive indicator of lead effects. Subsidiary analyses showed that movement and decision slowing was correlated solely with levels of blood lead, but not with zinc protoporphyrin or urinary ALA levels.