Rhythms in human performance: 1 1/2-hour oscillations in cognitive style.

Performance on verbal and spatial matching tasks was assessed every 15 minutes for 8 hours. Significant 60- to 100-minute oscillations were observed for each task. These oscillations were 180 degrees out of phase, supporting the hypothesis that in humans the basic rest activity cycle involves alternating activation of processing systems residing in the two cerebral hemispheres.