U Buhss’s research while affiliated with TUD Dresden University of Technology and other places

This paper presents a pilot study on the differences in evoked EEG coherence measures (computed as zero-lagged cross-correlation, “EC”) between chess experts and novices while solving chess problems. One of our earlier investigations (Volke, 1999) had shown that both location and direction of EC changes in task processing (compared with a resting condition) depend on the degree of task performance. As a result we postulated that when solving the same tasks experts and novices would show different EC. The results of the recent study confirmed this supposition. Chess tasks of varying difficulty were presented to 25 chess players of different performance levels. The EEG was recorded from 29 positions (enhanced 10:20-system). EC were computed for post-stimulus intervals of 1.6s. A special averaging procedure (considering Fisher's Z transformation) was applied for summarizing the single EC of each type of task. These subject- and task-related EC-values (29 × 28/2 = 406 values per frequency band) were subjected to a MANOVA after a two-staged principal component analysis. Significant differences between experts and novices, compared with the resting condition, were found in the delta frequency range. The relevant cortical areas of experts, defined by a topological analysis of the differentiating principal components, were located rather posterior and more in the right hemisphere, compared with those of the novices. Furthermore, the essential EC of the experts showed higher values in the task situation (“on-coupling”), compared with the resting condition, whereas those of the novices were lower (“off-coupling”). The results are interpreted as a higher task-related functional integration of the cortical areas in experts.

The present work investigates the validity of evoked coherences of the EEG as an indicator of mental load. Previous studies have shown that coherences of EEG, generally, react sensitively to subtle changes of a subject's mental date. Instead of the usually calculated ,,steady-state" values, the present study used evoked coherences, that, like evoked potentials, reflect neural information processing in the context of discrete events. Considering the well-known difficulties with the induction of mental load in laboratory conditions, especially in connection with EEG recording, chess playing was chosen as a model of mental activity. Chess diagrams of different complexity were presented for solution to 25 active members of chess clubs. For a differentiation between cognitive and perceptive load, a number of diagrams was provided with visual noise, which hampered recognition. Evoked coherences of EEG showed highly significant differences, nor only between perceptive and cognitive load, but also between different cognitive operations. In our experiment, perceptive load was reflected in the Theta frequency range, whereas cognitive load was reflected in Beta. A two-staged factor analysis procedure, in connection with a topological analysis, allowed the definition of cortical areas participating significantly in the discrimination of different conditions. The results were confirmed in a re-test study. Evoked coherences of EEG, thus, represent a sensitive tool for the investigation of mental load.