EEG time and frequency domain measures of cerebral specialization

Electroencephalographic (EEG) studies of lateralized cognitive functions have primarily relied upon measures of averaged evoked potentials (AEP) and power spectra (PS) to demonstrate hemispheric differences. The nature of the tasks appropriate to each of these methods of signal analysis generally require different cognitive activities and suggest different assumptions about cerebral specialization. This study investigated whether the tasks associated with either method were more likely to produce EEG asymmetries. Eighteen right-handed subjects participated in a three phase experiment which varied the amount of subject involvement in task performance. Phase I entailed passive listening to speech and nonspeech sounds. Phase II required active attention to speech and nonspeech sounds. Phase III involved a verbal matching task, a spatial rotations task, and a noncognitive control task. Auditory AEPs were measured in Phases I and II, and PS were measured in Phase II and III. EEG recordings were obtained from frontal and parietal areas of both hemispheres (F3, F4, P3, P4) referred to linked ears. Power spectra were derived from the 4-8, 8-13, and 13-20 Hz frequency bands at each lead. Despite statistically significant task and/or stimuli differences found in all three phases of study, essentially no task by lead interactions were obtained. That is, interhemispheric activity did not covary with differing stimuli and tasks. The absence of such interactions calls into question uncritical acceptance of a simple direct relation between task performance, EEG activity, and hemisphere specialization.