Abstract
Topographic EEG measures were compared in 12 adult male subjects during performance of a signal recognition task, presented at three difficulty levels. EEG data were recorded from 17 standard cortical sites, referenced to linked earlobes. Digitized mean spectral magnitude values were calculated for sequential 2 second epochs for each condition, log transformed and subjected to statistical analysis. A good and a poor performance group was established on the basis of scores registered at the highest difficulty level and confirmed statistically.
Within-group comparisons showed different EEG patterns for the two performance groups, both within and across difficulty level. The poor performance group showed a progressive pattern of disengagement (increase in 8-12 Hz activity) which diminished gradually as difficulty escalated and was replaced by a pattern of increasing engagement (decrease in 8-12 Hz activity). Good performers showed the same level of engagement independent of difficulty. Performance data alone failed to differentiate between groups under low and moderate task demands. Detailed evaluation of the underlying mechanisms revealed a tendency for all subjects to develop brief periods of disengagement after each stimulus presentation. This pattern became increasingly generalized in poor performers during the low gain task but was also present at the most difficult test level.
These findings provide some insight into the dynamics of Central Nervous Systems regulatory mechanisms which modulate sustained cognitive performance under varying demand conditions. They document a propensity for some individuals to become disengaged over time, thereby requiring greater cognitive resource mobilization as task demand increases. Assessment of this trait may be useful in the prediction of performance capability under high demand conditions.
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