Intelligence and the effects of perceptual processing demands, task difficulty and processing speed on P300, reaction time and movement time

Event-related potentials (ERPs) were recorded to the memory set and probe stimuli in a Sternberg memory-scanning task and compared to intelligence scores on the Multidimensional Aptitude Battery (MAB). The memory set was changed on each trial and all items in the memory set were presented simultaneously. Only the probe stimulus required a decision and response. P300 amplitude to the memory set increased as the memory set size increased; this is thought to be a result of the effects of demands for processing resources. A pattern of weak negative correlations were observed between P300 amplitude to the memory set and MAB scores. In contrast, P300 amplitude to the probe stimulus decreased with increases in memory set load and there was a pattern of weak positive correlations with MAB scores. It is suggested that P300 amplitude to the memory set is affected by task difficulty. The latency of the P300 component of the ERP was used as an indicator of the relative speed of information processing. This allows the assessment of processing speed without requiring a physical response. Higher-ability participants displayed longer P300 latency to the memory set stimulus than lower-ability participants while there was no discernable effect on P300 latency to the probe stimulus. This contradicts a pure speed of processing explanation of the relation between P300 latency and intelligence. The longer P300 latency to the memory set suggests that higher-ability participants devoted more time to stimulus analysis and planning than-lower ability participants.