The effects of event rate and signal probability on children's vigilance

Using the study of vigilance in adults as their model, the researchers examined task parameters and their interactions in a study of sustained attention in children from a non-clinical population. Two levels of event rate (low and high) were combined with two levels of signal probability (low and high) in 14-minute vigilance tasks in which children viewed small and large squares presented successively on a computer screen. Seven- and eight-year-old children were instructed to press a button whenever a small square appeared. Signal detection analyses were employed, as well as the traditional measures identifying hits, false alarms, and reaction time. The results support the traditional findings in adult tasks: participants performed most accurately and quickly in the high event rate and high probability condition; low probability elicited a more conservative decision-making criterion, a standard characterized by less willingness to risk false alarms; such conservatism increased over the periods of watch; and the vigilance decrement emerged over time. However, the finding that the high event rate condition improved perceptual sensitivity reversed the event rate effect consistently reported in the adult literature. The above findings are discussed in light of both research and clinical implications.