Some problems of occipital alpha block in man

Abstract

(1) Experiments were carried out in 10 human subjects to try to evaluate the relative importance of visual attentiveness, a patterned visual input, oculomotor control functions and mental effort with respect to attenuation of the occipital alpha rhythm. (2) Alpha rhythm was almost completely blocked when alert subjects were involved in reading even when the near triad of accommodation had been experimentally eliminated or minimized. Thus ‘visual attentiveness’ alone is sufficient to block the alpha rhythm. (3) Visual sensory detail alone was not a sufficient stimulus to block the alpha rhythm, even though accompanied by saccadic movements. Rather it is the attentiveness to the detail which blocks the alpha rhythm. (4) Progressively more difficult mental effort, as in serial multiplication, eventually led to an attenuation of the alpha rhythm. A sustained type of mental effort such as blindfold chess led to an initial attenuation of the alpha rhythm followed by a gradual return after the first few minutes of play to resting eyes closed levels. However, during periods in which subjects claimed that they required exceptional increases in mental effort, the alpha rhythm again became attenuated. The possible significance of alpha block is discussed.