Perceptual and Motor Skills, 1979,49,447-450.
@ Perceptual and Motor Skills 1979
"IT'S TIME, YOU MUST WAKE UP NOWm1 P. LAVIE, A.
OKSENBERG, AND J. ZOMER
Technion-Israel Institure of Technology, Haifa, Israel Summary.-Seven subjects who claimed to be able to awake accurately from sleep at a predetermined time were required to awake in the sleep laboratory at 03:30 and 05:30 on two separate nights. Eight of the 12 spontaneous awakenings were within 2 2 0 min. from the targer time, and 8 awakenings were from REM sleep. The two best performing subjects were tested for additional 7 nights in the laboratory but accuracy deteriorated considerably with only 2 awakenings within k 2 0 min. from target time. Approximately 50% of all awakenings, however, were from REM sleep. It is concluded that some individuals are able to awake at predetermined times and that this ability might be dependent on motivational level and the sleep stage.
The ability to wake up from sleep at predetermined time without the aid of environmental stimuli was investigated before the era of sleep laboratory. The reported results were somewhat conflicting but generally agreed that some individuals have this ability (Boring & Boring, 1917; Elder, 1941; Frobenius, 1927; Omwark & Loranz, 1933; Brush, 1930). Particularly interesting was the report by Frobenius (1927) who tested 5 subjects for 250 nights. On most occasions his subjects were 5 min. ahead of time; they awakened suddenly and some reported that in the midst of a dream they felt as though they were interrupted by the words: "it's time, you must wake up now." In a more recent study, Zung and Wilson (1971), utilizing the sleeplaboratory recording techniques, reported that randomly selected adults motivated by monetary reward were able to wake up from sleep at preselected times. They reported that this ability was not sleep-stage dependent and that the experimental task did not alter the normal sleep-stage distribution. The purpose of the present study was to find our, using recordings in the sleep laboratory, whether individuals who claim to be able to wake up at predetermined times can actually do it, to determine if the accuracy of performance is sleep-stage dependent, and to determine if the demand to wake up at preselected times has an effect on the infrastructure of sleep.
METHOD Seven subjects, 6 males and one female, 21 to 30 yr. old, were recruited by advertisement in the local campuses. All responders were carefully interviewed and those finally selected were certain about their ability to wake up from sleep at predetermined time. The experiment had two parts. First, each 'This study was conducted while Dr. Lavie was supported by a grant from the Israel Center for Psychobiology and the USA Army Grant No. DA-ERO-77-G-057. Request reprints from Peretz Lavie, Ph.D., Sleep Laboratory, Behavioral Biology Unit, Technion Faculty of Medicine, Gutwirth Bldg., Technion City, Haifa 32000, Israel.
448
P. LAVIE, ET AL.
subject slept in the laboratory for four nights (00:OO-06:OO) which included an adaptation night without recordings, a baseline night, and two experimental nights. On each experimental nighr, 20 min. before lights were turned off, subjects received a written note with the target time for that night. Target times were 03:30 and 05:30,in a balanced crossover order. Subjects were paid according to their accuracy, which was divided into four categories: k 10, f20, f30 and k 4 0 mia. from target time. T o signal awakening, subjects had to call the experimenter via the intercom system. Watches or other timing devices were removed at bedtime. In the second part of the experiment, based on the results of the first study, rhe two best performing subjects slept for seven additional nights in the laboratory. On these nights target times were randomly determined between 01:OO and 06:00,and subjects were rewarded only if they were within 2 2 0 min. from target time. In baseline and experimental nights conventional EEG, EOG, and EMG were recorded on a Beckrnan R411 polygraph. Sleep stages were scored according to Rechtschaffen and Kales (1968). RESULTS Part I
In the 14 experimental nights there were 12 spontaneous midsleep awakenings, all sudden, with accuracies as follows: 5 within f10 min. from target time (36%), 3 within f20 min. (21%), 1 within +30 min. (7%), and 5 were 40 min. or more from target time (36%). The average absolute accuracy was 28.5 min. ( S D = 36.2 min.). In two cases subjects were awakened by the experimenter since they slept more than 120 min. from rarget time. Eight of the 12 awakenings were from REM sleep ( 6 7 % ) , 3 from Stage 2 ( 2 5 % ) , and 1 from Stage 4 (8%). N o differences were observed between early and late target times. Since 67% of the spontaneous awakenings were from REM sleep, the probability that this was a chance event was calculated. Assuming that the probability of a single awakening from REM sleep was equal to the average percentages of REM sleep in the last hour of sleep (34% ) as empirically determined during the experimencal nigh:s in the laboratory, the probabilicy was less than 0.02. Sleep latency in the experimental nights was longer than during baseline nights ( M = 25.4,SD z 18.5;M = 13.6,SD = 7.8)but this difference was short of statistical significance. N o other differences in sleep parameters were found between baseline and experimencal nights. Part 2
In the second part of the experiment, borh subjects awoke spontaneously on all 14 experimental nights. Accuracy, however, deteriorated considerably.
ACCURATE AWAKENING
449
Only one awakening was within +-lo min. from target time ( 7 % ) , 1 within 2 2 0 min. ( 7 % ) , 3 within f 30 min. ( 2 1 % ) , 1 within +40 min. (7951, and 8 were 40 min. or more from target time ( 5 8 % ) . The average absolute accuracy dropped to 78 6 min. (SD = 67.9 rnin.). Seven awakenings were from REM sleep (50% ), 5 from Stage 2 ( 36% ) , and 2 from Stage 4 ( 1 4 % ) . The probability thac 50% of the spontaneous awakenings would be from REM sleep, by chance alone, was less than 0.001 for this part of the study. The average percentage of REM sleep in the last hour of sleep was 18%. In most nights, sleep latency was longer than during the baseline nights of these two subjects ( M = 17.1 min., SD = 9.1 rnin.; M = 5.5 min., SD = 3.5 rnin.). Combining the results of the two parts, 10 out of the 26 spontaneous awakenings were within 2 2 0 min. from target times and 15 were from REM sleep, of these 8 were within k 2 0 min. of target time.
DISCUSSION The present results generally support the common belief that some individuals are able to wake up from sleep at predetermined time with significant accuracy. The accuracy of judging the passage of time while asleep is comparable to the accuracy of estimating similar time intervals by waking subjects. Webb and Ross (1972) reported that awake subjects who estimated the passage of 3 and 4 hr. had 11 accurate estimations out of 28 estimations after 3 hr. (39.3%) and 10 accurate estimations out of 28 (35.7%) after 4 hr., both with accuracy criteria of f20 min. Subjects in the present study, who on the average slept 192 rnin., were within f20 min. from target time in I 0 of the 28 spontaneous awakenings ( 35% ) . The differences in accuracy between the first and second parts of the experiment suggest that motivation plays an important role in the awakening response. The two subjects in the second part of the experiment were clearly less motivated to be successful in waking up accurately than in the first part and complained of lack of challenge and accumulated fatigue. This conclusion agrees with the common anecdotal and personal experiences of spontaneous accurate awakenings at predetermined times before important trips or before other exciting events. Two additional findings are worth noting, the increase in sleep latency in the experimental period and the significant tendency to awake from REM sleep. The increased sleep latency might be explained by subjects' preoccupation with the experimental task. Some of them reported using various techniques to assure the accurate awakening, such as subvocal repetition of the target time before falling asleep. W e have no immediate explanation for the finding that our subjects awakened significantly more often from REM sleep. A possible explanation might be thac during REM sleep subjects are attentive to internal stimuli and can
450
P. LAVIE, ET AL.
retrieve information from long-term memory. The preponderance of awakenings from REM sleep observed in the two parts of this study might suggest that subjects did not measure more accurately che passage of time in REM sleep but, knowing that they had to wake up at preselected time, found it easier to terminate sleep in REM period. In this sense, REM periods may be seen as "gating periods" when sleep can be easily terminated, and the accuracy of performance is dependent on the termination of sleep at the appropriate REM period. It is possible, then, rhac the relative accuracy in performance observed in the first part of the study resulted from the temporal proximity of the target rimes to the expected times of the second and fourth REM periods. REFERENCES
BORING, E. G.,
BORING, L. D. Temporal judgment after sleep. In L. D. Boring & E. G. Boring (Eds.), Strrdies in psychology: Titchener commemorative uolume. &
Worchester, Mass.: Private publication, 1917. Pp. 255-279. BRUSH,E. N. Observations o n the temporal judgment during sleep. Amer. I . , Psychol., 1930,. 42,. 408-411. ELDER,J. H. Influence of assigned hour for waking o n sleep motility. Psychol. Bidl.. 1941. 38, 557-558. FROBENIUS,K. Ueber die zeitliche Orientierung irn Schlaf and einige Aufwachphaenomene. Z . Psycho!., 1927, 103, 100-110. OMWARK, K. T., & LORANZ. M. Study of ability to wake at a specified time. J. appl. Psychol., 1933. 17. 468-474. RECHTSCHAFPEN, A,, & KALES,A. (Eds.) A manrral of standardized terminology, techniqres a ~ scoring d system for sleep stages of human subjects. Washingcon, D. C.: Public Health Service, U.S. Government Printing Office, 1968. WEBB,W. B., & ROSS, W. Estimation of the passing of four consecutive hours. Percept. mot. Skills, 1972, 35, 768-770. ZUNG,W. K., & WILSON,W. D. Time estimation during sleep. Biol. Prychiat., 1971, 3, 159-164. Accepted At~gurt20, 1979.
@ Perceptual and Motor Skills 1979
"IT'S TIME, YOU MUST WAKE UP NOWm1 P. LAVIE, A.
OKSENBERG, AND J. ZOMER
Technion-Israel Institure of Technology, Haifa, Israel Summary.-Seven subjects who claimed to be able to awake accurately from sleep at a predetermined time were required to awake in the sleep laboratory at 03:30 and 05:30 on two separate nights. Eight of the 12 spontaneous awakenings were within 2 2 0 min. from the targer time, and 8 awakenings were from REM sleep. The two best performing subjects were tested for additional 7 nights in the laboratory but accuracy deteriorated considerably with only 2 awakenings within k 2 0 min. from target time. Approximately 50% of all awakenings, however, were from REM sleep. It is concluded that some individuals are able to awake at predetermined times and that this ability might be dependent on motivational level and the sleep stage.
The ability to wake up from sleep at predetermined time without the aid of environmental stimuli was investigated before the era of sleep laboratory. The reported results were somewhat conflicting but generally agreed that some individuals have this ability (Boring & Boring, 1917; Elder, 1941; Frobenius, 1927; Omwark & Loranz, 1933; Brush, 1930). Particularly interesting was the report by Frobenius (1927) who tested 5 subjects for 250 nights. On most occasions his subjects were 5 min. ahead of time; they awakened suddenly and some reported that in the midst of a dream they felt as though they were interrupted by the words: "it's time, you must wake up now." In a more recent study, Zung and Wilson (1971), utilizing the sleeplaboratory recording techniques, reported that randomly selected adults motivated by monetary reward were able to wake up from sleep at preselected times. They reported that this ability was not sleep-stage dependent and that the experimental task did not alter the normal sleep-stage distribution. The purpose of the present study was to find our, using recordings in the sleep laboratory, whether individuals who claim to be able to wake up at predetermined times can actually do it, to determine if the accuracy of performance is sleep-stage dependent, and to determine if the demand to wake up at preselected times has an effect on the infrastructure of sleep.
METHOD Seven subjects, 6 males and one female, 21 to 30 yr. old, were recruited by advertisement in the local campuses. All responders were carefully interviewed and those finally selected were certain about their ability to wake up from sleep at predetermined time. The experiment had two parts. First, each 'This study was conducted while Dr. Lavie was supported by a grant from the Israel Center for Psychobiology and the USA Army Grant No. DA-ERO-77-G-057. Request reprints from Peretz Lavie, Ph.D., Sleep Laboratory, Behavioral Biology Unit, Technion Faculty of Medicine, Gutwirth Bldg., Technion City, Haifa 32000, Israel.
448
P. LAVIE, ET AL.
subject slept in the laboratory for four nights (00:OO-06:OO) which included an adaptation night without recordings, a baseline night, and two experimental nights. On each experimental nighr, 20 min. before lights were turned off, subjects received a written note with the target time for that night. Target times were 03:30 and 05:30,in a balanced crossover order. Subjects were paid according to their accuracy, which was divided into four categories: k 10, f20, f30 and k 4 0 mia. from target time. T o signal awakening, subjects had to call the experimenter via the intercom system. Watches or other timing devices were removed at bedtime. In the second part of the experiment, based on the results of the first study, rhe two best performing subjects slept for seven additional nights in the laboratory. On these nights target times were randomly determined between 01:OO and 06:00,and subjects were rewarded only if they were within 2 2 0 min. from target time. In baseline and experimental nights conventional EEG, EOG, and EMG were recorded on a Beckrnan R411 polygraph. Sleep stages were scored according to Rechtschaffen and Kales (1968). RESULTS Part I
In the 14 experimental nights there were 12 spontaneous midsleep awakenings, all sudden, with accuracies as follows: 5 within f10 min. from target time (36%), 3 within f20 min. (21%), 1 within +30 min. (7%), and 5 were 40 min. or more from target time (36%). The average absolute accuracy was 28.5 min. ( S D = 36.2 min.). In two cases subjects were awakened by the experimenter since they slept more than 120 min. from rarget time. Eight of the 12 awakenings were from REM sleep ( 6 7 % ) , 3 from Stage 2 ( 2 5 % ) , and 1 from Stage 4 (8%). N o differences were observed between early and late target times. Since 67% of the spontaneous awakenings were from REM sleep, the probability that this was a chance event was calculated. Assuming that the probability of a single awakening from REM sleep was equal to the average percentages of REM sleep in the last hour of sleep (34% ) as empirically determined during the experimencal nigh:s in the laboratory, the probabilicy was less than 0.02. Sleep latency in the experimental nights was longer than during baseline nights ( M = 25.4,SD z 18.5;M = 13.6,SD = 7.8)but this difference was short of statistical significance. N o other differences in sleep parameters were found between baseline and experimencal nights. Part 2
In the second part of the experiment, borh subjects awoke spontaneously on all 14 experimental nights. Accuracy, however, deteriorated considerably.
ACCURATE AWAKENING
449
Only one awakening was within +-lo min. from target time ( 7 % ) , 1 within 2 2 0 min. ( 7 % ) , 3 within f 30 min. ( 2 1 % ) , 1 within +40 min. (7951, and 8 were 40 min. or more from target time ( 5 8 % ) . The average absolute accuracy dropped to 78 6 min. (SD = 67.9 rnin.). Seven awakenings were from REM sleep (50% ), 5 from Stage 2 ( 36% ) , and 2 from Stage 4 ( 1 4 % ) . The probability thac 50% of the spontaneous awakenings would be from REM sleep, by chance alone, was less than 0.001 for this part of the study. The average percentage of REM sleep in the last hour of sleep was 18%. In most nights, sleep latency was longer than during the baseline nights of these two subjects ( M = 17.1 min., SD = 9.1 rnin.; M = 5.5 min., SD = 3.5 rnin.). Combining the results of the two parts, 10 out of the 26 spontaneous awakenings were within 2 2 0 min. from target times and 15 were from REM sleep, of these 8 were within k 2 0 min. of target time.
DISCUSSION The present results generally support the common belief that some individuals are able to wake up from sleep at predetermined time with significant accuracy. The accuracy of judging the passage of time while asleep is comparable to the accuracy of estimating similar time intervals by waking subjects. Webb and Ross (1972) reported that awake subjects who estimated the passage of 3 and 4 hr. had 11 accurate estimations out of 28 estimations after 3 hr. (39.3%) and 10 accurate estimations out of 28 (35.7%) after 4 hr., both with accuracy criteria of f20 min. Subjects in the present study, who on the average slept 192 rnin., were within f20 min. from target time in I 0 of the 28 spontaneous awakenings ( 35% ) . The differences in accuracy between the first and second parts of the experiment suggest that motivation plays an important role in the awakening response. The two subjects in the second part of the experiment were clearly less motivated to be successful in waking up accurately than in the first part and complained of lack of challenge and accumulated fatigue. This conclusion agrees with the common anecdotal and personal experiences of spontaneous accurate awakenings at predetermined times before important trips or before other exciting events. Two additional findings are worth noting, the increase in sleep latency in the experimental period and the significant tendency to awake from REM sleep. The increased sleep latency might be explained by subjects' preoccupation with the experimental task. Some of them reported using various techniques to assure the accurate awakening, such as subvocal repetition of the target time before falling asleep. W e have no immediate explanation for the finding that our subjects awakened significantly more often from REM sleep. A possible explanation might be thac during REM sleep subjects are attentive to internal stimuli and can
450
P. LAVIE, ET AL.
retrieve information from long-term memory. The preponderance of awakenings from REM sleep observed in the two parts of this study might suggest that subjects did not measure more accurately che passage of time in REM sleep but, knowing that they had to wake up at preselected time, found it easier to terminate sleep in REM period. In this sense, REM periods may be seen as "gating periods" when sleep can be easily terminated, and the accuracy of performance is dependent on the termination of sleep at the appropriate REM period. It is possible, then, rhac the relative accuracy in performance observed in the first part of the study resulted from the temporal proximity of the target rimes to the expected times of the second and fourth REM periods. REFERENCES
BORING, E. G.,
BORING, L. D. Temporal judgment after sleep. In L. D. Boring & E. G. Boring (Eds.), Strrdies in psychology: Titchener commemorative uolume. &
Worchester, Mass.: Private publication, 1917. Pp. 255-279. BRUSH,E. N. Observations o n the temporal judgment during sleep. Amer. I . , Psychol., 1930,. 42,. 408-411. ELDER,J. H. Influence of assigned hour for waking o n sleep motility. Psychol. Bidl.. 1941. 38, 557-558. FROBENIUS,K. Ueber die zeitliche Orientierung irn Schlaf and einige Aufwachphaenomene. Z . Psycho!., 1927, 103, 100-110. OMWARK, K. T., & LORANZ. M. Study of ability to wake at a specified time. J. appl. Psychol., 1933. 17. 468-474. RECHTSCHAFPEN, A,, & KALES,A. (Eds.) A manrral of standardized terminology, techniqres a ~ scoring d system for sleep stages of human subjects. Washingcon, D. C.: Public Health Service, U.S. Government Printing Office, 1968. WEBB,W. B., & ROSS, W. Estimation of the passing of four consecutive hours. Percept. mot. Skills, 1972, 35, 768-770. ZUNG,W. K., & WILSON,W. D. Time estimation during sleep. Biol. Prychiat., 1971, 3, 159-164. Accepted At~gurt20, 1979.
