Some Observations on the Occipital Alpha Rhythm

Abstract

In order to test the hypothesis that the behaviour of the alpha rhythm is related to the kind of imagery used by different subjects, and in particular that the disappearance of the alpha rhythm during mental work is associated with the use of visual imagery, occipital EEG records were taken from groups of early blind, late blind, and sighted subjects during the performance of two spatial tests. Since the test scores differentiated between the groups it was argued that the performance probably involved a visual component. When the subjects were classified into the three suggested alpha-rhythm types, M, R, and P, the groups so obtained did not differ significantly from one another in terms of test scores. This was regarded as negative evidence so far as the hypothesis under investigation is concerned, especially since the alpha rhythm type supposedly associated with prevalently visual imagery was found most frequently among the blind.

It is clear that blindness is a complicating factor here as the amount and amplitude of alpha rhythm found in the blind records was less than in the case of the normal subjects. This, however, does not seem to invalidate the argument, but rather constitutes a problem for those who claim that absence of the alpha rhythm is associated with visual imagery. The hypothesis under investigation seems at present to be too simple and to need some reformulation before it will fit the facts.