The Effects of Event Rate and Array Size on a Cognitive Vigilance Task with Associated EEG Rhythms and a Derived Engagement Index

Abstract

This study investigated the effects of event rate and stimulus array size during a vigilance task on performance and relative EEG power bandwidths (alpha, beta, theta) and a derived EEG engagement index, EI = (beta/(alpha+ theta)). Forty participants, ages 18 to 40, engaged in a visual search task. Participants were required to distinguish a green “K” from an array of stimuli (yellow-green, green, and blue-green factorially combined with K, X, N, R). Each participant searched for the signal in arrays of 2 or 5 stimuli presented at either 12 or 24 events per minute over forty minutes. The design was a 2×2 factorial with four groups. The results indicated poorer performance, higher false alarm rates in the first 10-minute period, and longer response times associated with the larger array size. There were no performance effects for event rate. The EI decreased over periods. Relative alpha and beta power in the midline sites (PZ, CZ, and FZ) were greater for the higher event rate, but were unrelated to array size. These EEG findings are discussed in the context of earlier vigilance studies using EEG measures.