NEUROPHYSIOLOGICAL DIFFERENCES BETWEEN PERCEPTION AND IMAGERY

The present study was designed to examine brain activity underlying me ntal imagery. Since mental imagery is conceptualized as behavior guide d by internal representation only, the activity of the prefrontal lobe s was assumed to be a measure of differentiation of imagery from perce ption. Twenty-one subjects were requested to observe and imagine a swi nging pendulum and to touch and imagine a coshball in separate trials. The EEG was recorded from 15 standard electrode sites and analyzed wi th (1) traditional alpha power and (2) an estimation of dimensional co mplexity (a measure derived from nonlinear dynamics). Both EEG measure s revealed expected object-related differences during perception as we ll as during imagery. The visual pendulum showed relative to the tacti le coshball increased dimensional complexity and less alpha power at p arietal and frontal sites. However, only the EEG dimension supported t he main hypothesis: Imagery resulted in increased prefrontal dimension al complexity in comparison to perception independent of the modality of the image. In contrast, for alpha power the difference between imag ery and perception was due to stimulus modality.