ATTENTION, CONSCIOUSNESS, SLEEP AND WAKEFULNESS 1 579 



between deeper sleep and near-waking states through- 

 out the night. In some of the lighter periods (Stage B) 

 when alpha rhythms return and eye movements per- 

 sist for 10 to 30 min. according to Dement & Wolpert 

 (58) there would be considerable opportunity for 

 drowsy, semiconscious or waking learning to occur. 

 Unless the entire period of presumed sleep were moni- 

 tored by EEG and perhaps eye movement recording 

 as well, there would be no way of knowing whether 

 any accretion of learning which occurred as a result 

 of the night's stimulation was due to learning during 

 periods of actual sleep or of relative wakefulness. 



The experiments of Simon & Emmons, though well 

 controlled with respect to sleep and wakefulness by 

 continuous EEG recording, are subject to the criticism 

 that they involved only one night of sleep-learning 

 trials for each subject. It might be argued that a 

 longer period of exposure would be required; however, 

 the nature of their material was such that it might 

 easily have been learned in one night. In one of the 

 experiments 96 items of information pretested before 

 the night of sleep and read with answers at 5-min. 

 intervals during the EEG monitored sleep, were 

 posttested the next morning for recall and recognition. 

 There was no learning of material which had been 

 presented during the B to E stages as shown by the 

 EEG, performance of the experimental group so 

 exposed being no better than that of a control group 

 given no training. The amount of correct recall 

 increased markedly for those information items 

 presented during periods when alpha waves were 

 present. Since alpha waves when present correlate 

 highly with wakefulness and consciousness, learninu 

 during their presence might well be expected. Since 

 they selected their subjects on the basis of their domi- 

 nant alpha rhythms, the absence of alpha waves for 

 prolonged periods undoubtedly meant deep drowsi- 

 ness and loss of awareness or light sleep, and as a 

 consequence no significant learning. 



What if any are the reasons one might have to 

 expect that learning would be possible during sleep? 

 Let us examine first the implications and conditions 

 of learning during normal wakefulness, then the 

 conditions which exist during sleep which might be 

 presumed to make learning possible or impossible. In 

 normal waking learning the association of two events 

 simultaneously, or successively in reasonable conti- 

 guity, one or more times under the proper conditions 

 of psychological set or attention and with the proper 

 motivation, generally results in the development of a 

 bond of relationship between the events which upon 

 the appearance of one tends to recall the other. Rep- 



etition strengthens this relationship. In a conditioned 

 reflex situation, a conditioned stimulus is paired with 

 an unconditioned stimulus until through repetition 

 it gains the potential it did not have originally of 

 releasing the response of the unconditioned stimulus. 

 In both of these instances of learning there is implied 

 perceptual discrimination of the stimuli, which re- 

 quires selective attention, a certain degree of general 

 alertness, and some degree of motivation. Although 

 these and other conditions may be necessary for 

 optimal learning in the waking state, there is no 

 certainty that they would have to obtain during 

 sleep if learning and conditioning were to occur then, 

 since electrical recordings show the cortex, reticular 

 formation, thalamus and hippocampus to be exhibit- 

 ing very different patterns of activity during sleep 

 than during waking. Since specific sensory pathways 

 remain open during sleep, impulses giving rise to 

 evoked responses still reach specific receiving zones 

 of the cortex, and also reach and affect the thalamus 

 and hippocampus. The reticular formation on the 

 other hand is less responsive and the entire unspecific 

 sensory system including the brain stem, thalamus 

 and cortex has a higher threshold of excitability and 

 exhibits a different pattern of electrical activity. 



Sensory messages reaching the cortex do not 

 result in perceptual discrimination in the absence of 

 unspecific influences. The reason for this is not 

 known, nor is it known precisely where perceptual 

 discrimination occurs. As Galambos & Morgan 

 point out in Chapter LXI of this Handbook it is not 

 known how or where learning takes place in the 

 brain, although it appears from recent studies that 

 the reticular and limbic systems may have as much to 

 do with this as the cortex. Therefore, on the basis 

 of present neurophysiological knowledge about 

 learning, one cannot prejudge nor preclude the 

 possibility of learning during sleep. However, the 

 burden of proof would seem to reside with those who 

 maintain that it can. 



With respect to the lack of consciousness during 

 sleep, and therefore the lack of awareness of and 

 memory for events which occur during sleep, one 

 might wonder how learning could be expected to 

 occur. Lacey et al. (150, 151), as well as others have 

 been able to produce what might be called 'uncon- 

 scious' conditioning. In studying autonomic responses 

 in two groups of college students, they presented a 

 list of words to which association responses were to 

 be given. A shock accompanied 1 of 40 words each 

 time it was presented. For one group that word was 

 one with a rural connotation; for the other, an urban 



