Transoccipital EEG was monitored from 12 subjects during three conditions of gaze. The subject fixated continuously on the eyes of the experimenter. The experimenter smiled at the subject, looked at the subject or averted his eyes. Each condition was repeated six times (20 sec. per trial, overall viewing time 6 min.). The EEG was integrated automatically in 5 sec. epochs, to yield abundance scores. There is a general tendency for EEG abundance to be inversely related to the arousing properties of the viewed stimulus. This effect is statistically significant for 8ṁ5–11ṁ5 Hz (alpha frequencies), and for 2ṁ0–4ṁ5 Hz.

The occipital EEG of subjects differing in reported vividness of mental imagery was monitored during a series of mental imagery tasks. (i) Vivid imagers (selected on the basis of the Betts Vividness of Imagery Scale) had a higher mean dominant alpha frequency (m.d.f.) than weak imagers (P < 0·025), but there were no individual differences for alpha abundance. The difference for m.d.f. held for only one task ‐ an eyes‐open, minimal imaging condition, (ii) Greater alpha suppression followed presentation of High Imagery (High I) words than followed presentation of Low Imagery (Low I) words (P < 0·005). (iii) High I words elicited more imagery than Low I words, for both vivid and weak imagers (P < 0·005). (iv) Reported elicited imagery was greater for the vivid imagers (P < 0·005). (v) For two voluntary imaging tasks, alpha suppression was greater in that task reported by the subjects as being harder to visualize (P < 0·01), thus reversing the findings for (ii) above, (vi) Subjects completed the Eysenck Personality Inventory. None of the above findings could be attributed to individual differences in either extraversion or neuroticism. It is concluded that the act of imaging per se does influence the EEG and that alpha suppression is not merely a by‐product of the arousing nature of imaging tasks. However, difficulty in the act of imaging also influences the EEG. The equivocal results of earlier research may therefore be accounted for in terms of the differential effects of instruction to image, upon the EEG, as demonstrated in the present study.

The EEG was monitored during an auditory vigilance task. The wanted signal consisted of three consecutive odd digits. Five other types of signal varied in their approximation to the wanted signal and were ranked on that criterion for their ‘arousal’ value. Each signal was followed by a rest period. The key results were: (i) alpha abundance (8·5–13·5 Hz) diminished as the arousal value of the signal increased (P < 0·005); (ii) theta (4·5–6·5 Hz) and beta (13·5–19·5 Hz) showed either weak or no effects; (iii) a very‐low‐frequency filter (2·0–4·5 Hz) yielded a strong effect for one class of signal only (P < 0·021); (iv) during rest periods which followed the three most arousing types of signal, alpha abundance was greater than during the preceding signal (P < 0·025): the reverse held for the least arousing signals (P < 0·025); (v) theta abundance was very much lower following response (rest period following the wanted signal) than following other signal types (P < 0·01) and theta abundance during rest was generally smaller than during signals (P < 0·021); (vi) for the three least arousing signals, activity at 2·0–4·5 Hz was lower during rest than during signals (P < 0·05); (vii) subjects rated themselves as being more ‘keyed up’ as cue or arousal value of the signals increased (P < 0·001) and (viii) similarly, reported that alertness increased during rest periods associated with signals of increasing cue value (P < 0·01). These findings demonstrate that during a task of this sort, the subject experiences variation in alertness; this variation in subjective state is reflected by systematic change in the EEG. It is concluded that these results lend support to arousal models of vigilance and to Lindsley's activation theory.

Twenty Ss each attended, on four occasions at four times of day, on a randem schedule. The times of day were 0700, 1100, 1500, and 2000 h. The resting EEG was recorded on each occasion during eyes•open and eyes-closed trials. The results were: (1) there were no general effects for the time of day nor any indication of an interaction between time of day and personality (extroversion-introversion and neuroticism); (2) the Ss maintained rank order for alpha abundance, within the group, over the four visits (p < .01); (3) extroversion was directly related to degree of variability across sessions (p < .05); and (4) alpha abundance was greater on the first visit than on the last visit (p < .05). These results demonstrate the within-S stability of the EEG and show that, for simple tasks of this nature, time of day has no effect on the EEG.

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