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 ment al date. Instead of the usually calculated ,,steady-state" values, the pres ent study used evoked coherences, that, like evoked potentials, reflect neu ral information processing in the context of discrete events. Considering t he 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 complexit y were presented for solution to 25 active members of chess clubs. For a di fferentiation between cognitive and perceptive load, a number of diagrams w as provided with visual noise, which hampered recognition. Evoked coherence s of EEG showed highly significant differences, nor only between perceptive and cognitive load, but also between different cognitive operations. In ou r experiment, perceptive load was reflected in the Theta frequency range, w hereas cognitive load was reflected in Beta. A two-staged factor analysis p rocedure, in connection with a topological analysis, allowed the definition of cortical areas participating significantly in the discrimination of dif ferent conditions. The results were confirmed in a re-test study. Evoked co herences of EEG, thus, represent a sensitive tool for the investigation of mental load.