Use of Eeg in Study of Imagery

An experiment was designed to test hypothesis that suppression of amplitude of alpha rhythm provides a reliable objective index of visual imagery under two conditions of problem solution, namely, solving a ‘verbal’ problem and solving a ‘visual’ problem. Sixty‐nine subjects were examined in following way: first, preliminary ‘runs’ were made with each subject for EEG recording under conditions ( a ) eyes‐shut, relaxed and ( b ) eyes‐open, relaxed, yielding base lines for comparison; secondly, EEG recordings were made under conditions ( a ) concurrently with solution of ‘verbal‐reasoning’ problem and ( b ) concurrently with solution of ‘visual‐reasoning’ problem. It was found that, although visual content of awareness during two problem‐solution periods as reported by subjects differed markedly, suppression of alpha rhythms occurred under both conditions, amplitudes in both cases falling about half‐way between two values recorded in preliminary ‘runs’. There was, however, a greater suppression effect in case of the’ visual’ problem. results, as a whole, therefore, suggest that hypothesis is not tenable, since ‘imagery’ appears to be only one of many factors that may produce suppression effects. This conclusion is supported by a breakdown of subject sample, according to reports of imagery on verbal problem, which showed that there was no difference in basic patterns as between those who visualized verbal problem and those who did not. Repeated solution in a check period, immediately following solution period, made no significant difference to suppression of alpha in verbal problem, but did so in visual problem. suggested interpretation follows Fisher (1916) in regarding this as a possible decrease in image content.