Changes in evoked potentials on increases in the difficulty of visual searches in humans

Monopolar evoked potentials (EP) in the frontal, parietal, temporal, and occipital leads in 16 young healthy subjects were analyzed during visual searches of increasing difficulty. Increases in the complexity of the visual search and addition of "noise" to visual stimuli added significant difficulty to the image recognition task, which was reflected in increases in search times and errors. Correlation of changes in EP and search parameters was seen mainly in the frontal leads: there were significant positive relationships between the N2 and P4 components and the SN-SP difference wave on the one hand and search difficulty on the other; there was a negative relationship with the P3 component, probably due to an increase in the duration and amplitude of the preceding N2 component. The N2 and P4 components were most marked in the frontal leads. We suggest that these data provide evidence of increasing dominance of frontal structures in the attention control system as the visual task increases in difficulty. © 2011 Springer Science+Business Media, Inc.