ATTENTION, CONSCIOUSNESS, SLEEP AND WAKE FULNESS 



158/ 



appeared while listening to rhythmic music and 

 maintaining apparent wakefulness while tapping to 

 the rhythms. Because of the special interest of the 

 subjects in the music and some tendency to concen- 

 trate upon particular instruments or passages, there 

 is possible reason to see in these results the influence 

 of selective attention, with suppression of activity in 

 some periods and not in others, and the alternation 

 or variation of these patterns of attention with sleep- 

 like suppressions of alpha rhythm. It is conceivable 

 also that different areas of the cortex may react 

 differently to selective attention, although this has 

 not been the particular subject of extensive study. 



The effect of alerting upon reaction time has been 

 studied by Lansing et al. (154)- It was found that 

 ordinary visual reaction times to the onset of a visual 

 stimulus without special alerting and when alpha 

 waves were absent or present spontaneously averaged 

 280 msec. When a brief auditory signal was introduced 

 as a forewarning up to 1 sec. before the visual stimulus, 

 the reaction time was markedly reduced to about 

 206 msec, if the auditory stimulus preceded the visual 

 stimulus by at least three tenths of a second. Reaction 

 time was reduced if the forewarning stimulus was 

 less than three tenths of a second ahead of the visual 

 stimulus, but much less, and the alpha waves had 

 not been blocked by the time the visual stimulus was 

 presented. In other words unless the interval between 

 the auditory and visual stimuli is greal enough, 

 activation or alpha blocking does not occur in time 

 to facilitate the response. Figure 15 shows the curve 

 of reduction of reaction time as a function of the 

 length of the forewarning period and also the curve 

 for the degree of alpha blocking. The two curves 

 show remarkable similarity, suggesting that alpha 

 blocking or activation is indeed related to reduction 

 in reaction time. The set to respond after an alerting 

 signal is presumed to be triggered by the auditory 

 signal acting upon the ARAS, the influence of which 

 is known to be alpha blockade or activation. This 

 process in turn facilitates the speed of processing the 

 over-all reaction. Since input and output time in a 

 visual reaction time situation are relatively constant 

 and fixed, the reduction in reaction time is probably 

 mainly a reduction in central cortical processing time. 



A similar type of influence has been demonstrated 

 by Fuster (83) in monkeys trained to make perceptual 

 discriminations between two objects exposed tachisto- 

 scopically (see fig. 16). The monkey has been trained 

 to select the correct object in order to get a food 

 reward from under it. After thorough training, he is 

 placed before the one-way screen and can only see 



i' T 1 1 111 1 1 1 1 i_ 



200 400 600 800 1000 



F0REPERI0D IN MILLISECONDS 



in. 1 -,. Reaction time and alpha blocking plotted as a 



function of the fbrepe 1 interval. Note that the reaction time 



is reduced to a minimum when the foreperiod ranges from 300 

 to iooo msec, and that the alpha-blocking curve follows a similai 

 time course. Once activation occurs there is no further reduc- 

 tion of the reaction time, Relaxed unalerted reaction time, 280 

 msec , alerted reaction time, minimum -;oii msec. From 

 Lansing et nl. 1 154).] 



the objects when the tachistoscopic flash of varying 

 durations is presented. As he makes his correct choice, 

 he reaches through a door in front of the object 

 selected which stops the cluck and provides an over-all 

 reaction time for the process The monkey has 

 electrodes implanted in the mesencephalic reticular 

 formation and can be thus stimulated. Figure 17 

 shows the curves for per cent correct response and 

 reaction time for trials without (control I and with 

 reticular stimulation. It will be noted that reticular 

 stimulation improved performance and reduced 

 reaction time. Here again is .m example of facilitation 

 through ARAS influence. Activation or alerting 

 induced in this experiment by direct stimulation of 

 the reticular formation reduced perceptual discrimi- 

 nation reaction time. In the human experiment just 

 cited indirect activation was produced by a fore- 

 warning signal and reduced over-all reaction time. 

 In both experiments there is further indication of 

 the facilitation, and thereby a reduction, of central 

 processing time. 



eeg in hypnosis. The question arises, since hypnosis 

 has some characteristics in common with sleep, such 

 as trance-like states with limited awareness, and some 

 in common with selective attention, whether the 

 EEG is one of wakefulness or sleep, and whether any 

 indications of specific arousal or alerting are evident. 



