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The "Supervisor"—A Hypothetical Mental Function Impaired by Brain Damage

ABSTRACT

A simple paper-and-pencil technique is described in which normal and brain-damaged subjects write digits one by one, at random, in five timed runs. Restrictions are imposed in Runs 2, 3 and 4, where the subject is forbidden to use certain digits.

Several statistical parameters of the resulting utterances are defined, shown to have characteristic "behaviours" and interpreted in terms of information theory. The information output rate (C) increases linearly with the symbol rate () in 85 per cent. of all subjects, and the script-information output rate (C₀) can probably be deduced from this relationship. Restrictions reduce C and their withdrawal causes a "rebound" in every normal subject.

"Reversibility" is illustrated. The parameter theta () is defined and shown have a "behaviour". It is substantially reversible for most normals and some patients.

The "Supervisor" is postulated as a specific mental function—that of monitoring the output—and theta is interpreted as the reaction-time of the Supervisor. Certain implications are discussed and the rate of information feedback through the Supervisor (A) is shown to react to restrictions in qualitatively the same manner as the information output rate (C).

Comparing the two groups of subjects, brain damage reduces C, C₀ and A by 63 per cent., 65 per cent. and 70 per cent. respectively. Subject by subject, combining both groups, there is obvious correlation between each pair of these three information-handling rates, taking personal mean values of (A and C) but the ratio between any two rates may vary; the ratio C₀C varies more widely among this miscellaneous group of patients than among the normals.

Brain damage also increases , reduces the reversibility of and tends to make exceed t. It is argued that impairment of the Supervisor is reflected in a maladaptation of and t. The "hysteresis" (Y) which measures this maladaptation is shown to discriminate very sharply between normal and brain-damaged subjects.