Monitoring changes in cognitive load during reading: an event-related brain potential and reaction time analysis.

Factors that contribute to cognitive load during reading were examined using a secondary task procedure. In three experiments, subjects read sets of passages twice in succession while auditory probes were presented. The N1-P2 and P300 components of the event-related brain potential and reaction time (RT) responses to secondary auditory probes were used as measures of load. N1-P2 responses indicated decreased load during the second reading, whereas P300 and RT responses indicated increased load during the second reading. The results are interpreted as reflecting changes in task demands. Lower level elements of the task, such as word recognition and local aspects of comprehension, required fewer resources during the second reading. The N1-P2 reflected this reduction in resource demands. By contrast, the amount of resources devoted to higher level processes, such as comparing the text with one's prior representation and updating memory, increased during the second reading. This resulted from task demands, which emphasized memory of the material. P300 and RT reflected this increase in higher level demands. Results are described in terms of attentional and task demands and are taken as support for a componential description of reading and task difficulty.