Evoked coherences of EEG in mental load: An investigation in chess players

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.