Event related potentials (ERPs) in elementary cognitive tasks reflect task difficulty and task threshold

Abstract

ERPs have been used to investigate individual differences related to intelligence and, more recently, those related to elementary task thresholds. In the visual inspection time (VIT) task, threshold-related differences have been reported in the rising phase of the P200 component of the ERP, whereas in pitch discrimination they occur slightly later, between P200 and N240. However, the ERP waveform from tasks such as inspection time (IT) or pitch threshold (PT) will vary in ways that reflect the difficulty of the discrimination presented to the participant as well as the individual's threshold. This article examines the effects on ERP waveform of (a) differences in the stimuli (and therefore in task difficulty) and (b) differences in threshold. Vertex ERPs were obtained from 35 undergraduates performing a VIT task and 30 performing a pitch discrimination task, each presented at three levels of difficulty. In both tasks, P300 amplitude was lower in difficult trials than in easy trials and P300 latency was greatest in difficult trials, as expected from the P300 literature. Individual differences in VIT or PT were reflected in the ERP waveforms. IT-related differences appeared between 100 ms and the end of the rising phase of the P200 component, and could readily be distinguished from variation in the ERP waveform related to task difficulty. Differences related to pitch threshold appeared around the peak of the P200 component, at which point they were confounded with variation reflecting task difficulty. However, across a range of levels of difficulty, differences in ERPs related to threshold and accuracy could be distinguished. In future, studies that relate ERP waveform to threshold or intelligence, and include stimuli that are presented near to threshold, must take account of effects of task difficulty on ERP waveform, either by varying difficulty systematically and analyzing its effects, or by presenting stimuli at the individual's threshold to equate difficulty across subjects.