Lucid Dreaming: A Diary Study

Abstract

Most studies looking into the relationship between lucid dream frequency and personality were based on questionnaire measures of lucid dream frequency. Thus, the aim was to investigate the effect of keeping a dream diary on lucid dream frequency and the correlates of the frequency of lucid dreams in the diary with the Big Five personality factors. The study included 1,612 dreams reported by 425 persons. The present findings showed that lucid dreams are quite rare (1.36%) in an unselected student sample. The frequency of lucid dream in the 2-week diary period was lower than the retrospectively estimated lucid dream frequency. Whereas the negative association between lucid dream frequency and agreeableness was reported previously, the negative correlation between lucid dream frequency and neuroticism is a new finding. Furthermore, the exploratory analysis showed that a considerable number of lucid dreams did not include some form of dream control. Furthermore, it would be very interesting to study the relationship between personality, especially neuroticism and agreeableness, and lucid dreaming in a more detailed way.

Keywords

lucid dreaming dream diary personality neuroticism agreeableness

Introduction

A lucid dream is defined as a dream in which the dreamer while sleeping is aware of the fact that he or she is dreaming (LaBerge & Rheingold, 1990). In lucid dreams, it is possible to recall events from waking life to influence the dream action and to carry out tasks planned in waking (Stumbrys, Erlacher, Johnson, & Schredl, 2014).Although LaBerge (1990) showed that lucid dreaming mostly occurs during rapid eye movement (REM) sleep, a few lucid dreams were also observed during non-REM sleep (Stumbrys & Erlacher, 2012). A representative survey (Schredl & Erlacher, 2011) indicated that more than half of the general population have had at least one lucid dream in their lifetime and about 20% are frequent lucid dreamers defined as having at least one lucid dream per month (Snyder & Gackenbach, 1988). This survey used a retrospective measure for lucid dream frequency with a high retest reliability (r = .89; Stumbrys, Erlacher, & Schredl, 2013a). Analyzing dream diaries, Barrett (1991) found that that 0.7% of the reported 1,910 dreams were lucid. In that study, an additional 27 dreams (1.41%) were so-called prelucid; prelucid dreams are defined as “the subjects adopt a critical attitude towards what he is experiencing, even to the point of asking himself ‘Am I dreaming?’ but without realizing that he is fact doing so” (Green, 1968, p. 23). In another diary study, Zadra, Donderi, and Pihl (1992) reported 0.33% lucid dreams and 1.00% prelucid dreams in group of nonexperienced persons reporting 599 dreams over the 6-week dream diary period.

Comparing diary measures with questionnaire measures, Aspy (2016) found a significantly higher frequency in the 1-week diary compared with the retrospectively elicited lucid dream frequency (2.99 ± 7.50 vs. 1.45 ± 3.88 lucid dreams per month). Although this can be interpreted as a general effect of increasing dream recall frequency caused by keeping a dream diary (Schredl, 2007), the findings of Aspy (2016) have to be viewed with caution as this 1-week dream log was the baseline measure of a lucid dream induction study, that is, persons interested in increasing their lucid dream frequency were recruited. In an unselected student sample participating in a retest study regarding sleep and dream variables (Zunker et al., 2015), there was no significant increase in lucid dream frequency (0.68 ± 1.20 vs. 0.55 ± 1.00 lucid dreams per 2 weeks). The correlation between the two measures was small and only marginally significant: r = .156 (t = 1.3, p = .0926).

Previous studies (Hess, Schredl, & Goritz, 2016; Schredl, Henley-Einion, & Blagrove, 2016; Watson, 2001) showed small but significant correlations between lucid dream frequency and personality factors; openness to experience correlated positively and agreeableness negatively with lucid dream frequency. Neuroticism was also related positively to lucid dream frequency but this association was explained by nightmare frequency (Hess et al., 2016). The aforementioned studies used questionnaire scales for measuring lucid dream frequency and studies correlating lucid dream frequency elicited by diary measures and personality dimensions have not yet been carried out.

Typically, becoming lucid is associated with positive emotions (Green, 1968; LaBerge, 1985) and subjective ratings of positive dream emotions were indeed higher in lucid dreams compared with nonlucid dreams (Gackenbach, 1988; Gackenbach & Schillig, 1983). However, it was also found that lucid dreams were rated more negatively (Gackenbach & Schillig, 1983) and dream content analytic studies (Bulkeley, 2014; Gackenbach, 1988) eliciting explicitly mentioned emotions did not find differences between lucid and nonlucid dreams. Systematic studies, however, comparing lucid versus nonlucid dreams in a strict within-subject diary design have not yet been carried out.

Regarding lucid dream content, most common activities were those that are impossible in waking life (e.g., flying, magic, going through walls, or breathing underwater) followed by pursuing pleasant activities (e.g., sex); improving skills (sport, being assertive, academic learning, professional tasks); communication with dream characters; and spiritual experiences (Schädlich & Erlacher, 2012; Stumbrys et al., 2014). These surveys, however, recruited experienced lucid dreamers or persons with a strong interest in lucid dreaming. Content studies in samples not self-selected for interest in lucid dreaming are scarce.

The present study had three aims. First, we compared lucid dream frequency measured by questionnaire and measured by dream diary. Second, the correlation between the occurrence of lucid dreams in the diary reports and personality correlations were investigated. We expected a similar pattern as has been reported for questionnaire studies (Hess et al., 2016), that is, a positive association with openness to experience and a negative association with agreeableness. Finally, the content of lucid dreams in a sample not selected for interest in lucid dreams was studied.

Methods

Participants

Overall, 1,612 dreams of 425 participants (361 women and 64 men) were examined. The mean age of the sample was 23.40 ± 5.41 years (range: 16–61 years; two missing values). Mean word length of the dreams was 153.3 ± 130.1 words. The participants reported 3.79 ± 1.36 dreams with a range from 1 to 10 dreams.

Dream Questionnaire

Dream recall frequency was measured by a 7-point scale (0 = never, 1 = less than once a month, 2 = about once a month, 3 = about two to three times a month, 4 = about once a week, 5 = several times a week, and 6 = almost every morning) with a high retest reliability of r = .85 (Schredl, 2004). An 8-point rating scale was presented to measure lucid dream frequency (“How often do you experience so-called lucid dreams (see definition)?” 0 = never, 1 = less than once a year, 2 = about once a year, 3 = about two to four times a year, 4 = about once a month, 5 = two to three times a month, 6 = about once a week, and 7 = several times a week). The following definition was provided: In a lucid dream, one is aware that one is dreaming during the dream. Thus, it is possible to wake up deliberately, or to influence the action of the dream actively, or to observe the course of the dream passively. The retest reliability was also high: r = .89 (4 weeks retest interval; Stumbrys et al., 2013a). A similar 8-point scale was used to measure nightmare frequency (“How often do you experience nightmares?”) with a retest reliability of r = .74 (Stumbrys et al., 2013a).

To obtain units in frequency per month, the scores were recoded (see Stumbrys et al., 2013a). For example, if a participant selected the answer once a month, the recoded variable was 1 (lucid dream per month). If participants answered less than once a year, the new variable’s value was recoded as 0.042.

Personality Questionnaire

The Big Five personality factors (neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness) were measured with the German version of the Neuroticism-Extraversion-Openness Personality Inventory-Revised (Ostendorf & Angleitner, 2004) which contains 240 5-point items (coded: 0–4). The internal consistencies of the scales were high (r = 0.89–.92) and confirmatory Multitrait-Multimethod analyses replicated the findings of the English version (Ostendorf & Angleitner, 1994).

Dream Diary

The participants kept a dream diary for 14 consecutive days and were asked to record their dream(s) as completely as possible. After recording the dreams, they had to estimate the intensity of positive and negative dream emotions on two 4-point scales (0 = none, 1 = mild, 2 = moderate, and 3 = strong).

Dream Content Analysis

Lucidity was measured by a self-developed scale. Lucid dreams were coded if the dreamer is explicitly stating that she or he knows that she or he is dreaming. Prelucid dreams were coded if the dreamer is thinking about that this might be a dream but did not become fully lucid.

Procedure

The dream reports stemmed from a study on factors of home dream recall (Schredl, Wittmann, Ciric, & Götz, 2003). The dreams were typewritten, and all remarks not related to the dream experience itself were removed. Then reports were randomized regarding their order and coded for lucidity. A second rater coded 288 dreams independently resulting in an interrater reliability of K = .92 (Cohen’s kappa). The SAS 9.4 software package for Windows was used for statistical evaluation. For analyzing the effect of different predictors (the Big Five personality dimensions) on lucid dream recall frequency controlled for age, sex, dream recall frequency, and nightmare frequency, an ordinal regression was computed. Furthermore, the general tone in the lucid dreams was compared with that of the normal dreams of the same person by selecting a nonlucid dream which was roughly comparable regarding length with the lucid dream. The statistical comparison was carried out using t-tests for dependent samples (dream length) or sign rank tests for the two emotion scales (ordinal). In an exploratory way, one rater classified the themes in the lucid dreams and the prelucid dreams.

Results

Of all the 1,612 dreams, 22 dreams were lucid (1.36%) and 9 dreams prelucid (0.56%). Overall, 25 participants reported one prelucid or lucid dreams and three participants reported two prelucid or lucid dreams. One lucid dream was reported by 18 participants and two lucid dreams by 2 participants. The correlation between lucid dream frequency (questionnaire measure) and number of prelucid and lucid dreams in the diary was r = .152 (p = .0018). If only lucid diary dreams were considered, the correlation coefficient was r = .166 (p = .0006). As it can be seen in Table 1, participants reported a higher lucid dream frequency in the questionnaire compared with both diary measures; these differences are statistically significant: questionnaire measure versus number of prelucid and lucid dreams (sign rank test: S = 26,848.5, p < .0001) and questionnaire measure versus number of lucid dreams (sign rank test: S = 28,036, p < .0001).

Table 1.

Frequency of lucid dreams (Questionnare measure and dream diary).

	N	Mean ± SD
Lucid dreams per month (retrospectively measured)	421	1.23 ± 2.76
Prelucid and lucid dreams per month (diary)	425	0.16 ± 0.61
Lucid dreams per month (diary)	425	0.11 ± 0.52

In Table 2, the ordinal regression including the Big Five personality factors, gender, age, dream recall frequency, and nightmare frequency as predictors for the number of lucid dreams in the diary is depicted. Low neuroticism and low agreeableness were related to a higher number of lucid dreams, whereas the other personality factors were not related to the frequency of lucid dreams. Age was positively related to the number of lucid dreams reported in the diary, whereas gender was not. Dream recall frequency and nightmare frequency showed positive but nonsignificant associations with the number of lucid diary dreams. Overall, the explained variance of all factors was R²= .1348. A second analysis regarding the number of prelucid and lucid dreams was carried out; the results were comparable although the standardized estimates of the regression analysis were slightly smaller (R²= .0934).

Table 2.

Ordinal Regression Analysis for the Lucid Dream Frequency (Diary).

		Lucid dream frequency (diary)
	Mean ± SD	SE	χ²	p
Age		.2402	4.7	.0295
Gender (1 = female and 2 = male)		.0679	0.2	.6251
Dream recall frequency (questionnaire)	4.49 ± 1.15	.1512	0.9	.3462
Nightmare frequency (questionnaire)	3.59 ± 1.67	.2359	2.1	.1429
Neuroticism	100.12 ± 23.33	−.4255	5.3	.0216
Extraversion	112.32 ± 19.90	.0624	0.1	.7081
Openness to experience	129.80 ± 15.59	−.1064	0.5	.4662
Agreeableness	113.63 ± 15.78	−.2877	4.2	.0411
Conscientiousness	108.53 ± 18.95	−.1431	1.1	.2904

SE = standardized estimates.

The comparison between a lucid and a nonlucid dream of comparable word length did not reveal any significant differences (see Table 3), although the self-ratings of the intensity of positive emotions was higher for the lucid dream. A similar comparison for prelucid dreams also did not show any significant differences (see Table 4); emotional quality did not differ between the two types of dreams.

Table 3.

Within-Subject Comparison of Lucid and Nonlucid Dream Regarding Self-Rated Dream Emotions.

Lucid (N = 10)
	Lucid dream	Control dream	Test
	Mean ± SD	Mean ± SD		p
Number of words	175.90 ± 161.67	138.40 ± 77.31	t = 1.1	.3047
Positive tone	1.70 ± 1.16	1.20 ± 0.92	S = 4.5	.6875
Negative tone	1.60 ± 0.67	1.60 ± 1.17	S = −1.5	.8594

Table 4.

Within-Subject Comparison of Prelucid and Nonlucid Dream Regarding Self-Rated Dream Emotions.

Prelucid (N = 6)
	Prelucid dream	Control dream	Test
	Mean	Mean		p
Number of words	118.17 ± 97.53	162.50 ± 93.42	t = −1.3	.2455
Positive tone	1.67 ± 1.37	1.50 ± 1.38	S = 0.5	1.000
Negative tone	1.50 ± 1.05	1.00 ± 1.10	S = 3	.5625

Regarding the actions in lucid dreams, 24 activities associated with lucidity were identified in the 22 lucid dreams (see Table 5). In a considerable number of dreams, the dreamer was aware that she or he was dreaming but this resulted in no reaction or action—mainly the lucidity occurred at the end of the dream just before awakening. In three cases, the dreamer stated that they were able to control the dream action but did not specify what exactly they were doing. In three dreams, the dreamer was aware that the dream differed from waking life, for example, the ex-boyfriend was willing to reconcile but the dreamer also knew that this was different from his waking attitude. In two dreams the dreamer was flying and in another dream looking for or experiencing erotic activities. In two cases, nightmarish content was altered, for example, the son of the dreamer is in danger and the dreamer altered the scenario so he was safe. Similarly, there is the knowledge that one can wake up, for example, to end an intense feeling of dizziness during the dream by awakening. Two interesting dreams were characterized by the opposite wish of the dreamer, experiencing a wonderful encounter with a relative already dead or an ex-lover and knowing this will be over if she or he wakes up. Finally, one dreamer tried to materialize an object (lost camera) for a friend, but the occurrence of three tape recorders was the result.

Table 5.

Actions Associated With Lucidity (N = 21 Dreams).

Category	Frequency
Lucid but not controlling the dream	7
Controlling the dream (without specific reference)	3
Comparing dream action with waking life (aware of the differences)	3
Flying	2
Sex, love	2
Changing a nightmarish situation	2
Being able to awaken from the dream	2
Wishing not to wake up but to prolong the dream situation with a significant other	2
Materializing an object	1

Discussion

In accordance with previous studies (Barrett, 1991; Zadra et al., 1992), the present findings indicate that lucid dreams are quite rare (1.36%) in an unselected student sample. The frequency of lucid dream in the 2-week diary period was lower than the retrospectively estimated lucid dream frequency. Whereas the negative association between lucid dream frequency and agreeableness was reported previously (Hess et al., 2016; Watson, 2001), the negative correlation between lucid dream frequency (diary measure) and neuroticism is a new finding. Furthermore, the exploratory analysis showed that a considerable number of lucid dreams did not include some form of dream control.

From a methodological viewpoint, it has to be noted that the present sample was an unselected sample, that is, the subjects participated in a study entitled “Personality, dreaming, and sleep,” and the question about lucid dream frequency at the beginning of the study was embedded in a dream questionnaire with more than 20 items. The dream content analysis was carried out long after the empirical part of the study was concluded. So, the participants were not primed in any way to the lucid dream topic which is different to other studies (Aspy, 2016; Stumbrys et al., 2014). This methodological difference is important for comparing the present findings with previous studies.

The correlation between questionnaire scale and diary measure of lucid dream frequency was relatively small (r = .166)—comparable with the figure of r = .156 reported by Zunker et al. (2015). These coefficients are considerably smaller compared with the correlation for overall dream recall frequency: r = .557 (Schredl, 2002) and r = .562 (Schredl et al., 2003). As the retest reliability indices of the questionnaires are similar for lucid dream frequency and overall dream recall frequency and are above r = .80 (Schredl, 2004; Stumbrys et al., 2013a), a factor that might have reduced the correlation is the reliability of the diary measure. Although the internal consistency of a 2-week diary and the retest reliability is also about r = .80 for dream recall frequency (Schredl & Fulda, 2005), it is very probable that for the much lower occurrence of lucid dreams (compared with general dream recall), longer diary periods are necessary to achieve sufficient reliability of the diary measure.

Another methodological issue is measuring lucidity by content analysis by external judges as they only rely on explicitly mentioned references to lucidity. There might be persons with frequent lucid dreams (e.g., Gackenbach, Cranson, & Alexander, 1986) not bothering mentioning this fact in every dream report they record. In the present sample, however, the percentage of persons with very frequent lucid dreams (several times a week) was very small (2.5%; Schredl & Erlacher, 2004), so the possible underestimation due to this factor is presumably small. For other dream characteristics like emotions and number of bizarre elements, a considerable underestimation of these characteristics by external judges compared with self-ratings of the dreamer was reported (Schredl & Doll, 1998; Schredl & Erlacher, 2003; Sikka, Valli, Virta, & Revonsuo, 2014). Using a 7-point rating scale “Where you aware of dreaming while in the dream?” ranging from 1 = not at all to 7 = very yielded a high percentage (45%) of dreams including some form of lucidity. As this figure is much higher than the percentage of “full-blown” lucid dreams, that is, the dreamer is sure that she or he is dreaming and includes this statement explicitly in the dream report (Barrett, 1991; Zadra et al., 1992), the question how lucid dreams are defined and operationalized arises (Kühle, 2015; Noreika, Windt, Lenggenhager, & Karim, 2010). It would be very interesting to use both types of measures (self-reported lucidity and judge-rated lucidity) in diary studies.

Keeping a dream diary did not promote lucid dreaming in the present study; the diary measure was even lower than the questionnaire measure. This was unexpected as most studies (Aspy, Delfabbro, & Proeve, 2015) report an increase in overall dream recall frequency by keeping a dream diary with overall dream recall frequency highly related to lucid dream frequency (Schredl & Erlacher, 2004) and the study of Aspy (2016) reported a higher lucid dream frequency in the 1-week diary period compared with the retrospective measure. On the other hand, Zunker et al. (2015) found—despite a considerable increase in overall dream recall frequency by keeping a diary—no increase in lucid frequency. As already pointed out, the major difference was that the data of Aspy (2016) were the baseline data of a lucid dream induction study, that is, the participants were aware of the topic, whereas in the present study and in the study by Zunker et al., the topic of lucid dreaming was not mentioned; that is, the finding indicates that just keeping a dream diary without any intention to promote lucid dreaming is not an effective induction technique. Whereas the present findings might be explained by a possible underestimation of lucidity by external judges relying solely on explicitly mentioned references, the study by Zunker et al. (2015) used self-estimates for the occurrence of lucid dreams in the diary.

Interestingly, the personality correlates for the retrospectively estimated lucid dream frequency (Schredl & Erlacher, 2004) differed from the correlates of lucid dream frequency measured in the diary: Only openness to experience was slightly related to the questionnaire measure, whereas the diary measure was related to low neuroticism and low agreeableness. Based on the present data, it seems difficult to explain these differences. As mentioned earlier, future studies should include self-rating scales to measure lucidity (Kahan, 1994; Stumbrys, Erlacher, & Schredl, 2013b) in dreams elicited by dream diaries.

In this sample, neuroticism correlated negatively with the frequency of lucid dreams in the diary, a finding that differs from the studies applying questionnaire-based measures of lucid dream frequency reporting no correlation to neuroticism (Schredl & Erlacher, 2004; Watson, 2001) or a small positive correlation which was explained by the association between lucid dream frequency and nightmare frequency (Hess et al., 2016). On the other hand, positively toned dreams like flying dreams are also associated with lower neuroticism scores (Schredl, 2008), that is, as the reported lucid dreams are somewhat more positively toned, the inverse relation between lucid dream frequency (diary measure) and neuroticism would be in line with the continuity hypothesis of dreaming.

As has been reported previously (Hess et al., 2016; Watson, 2001), agreeableness was negatively related to lucid dreaming frequency. A possible explanation might be that lucid dreamers are more likely to be focused on fulfilling their own needs (Stumbrys et al., 2014) and less likely to reflect on the needs of others; they might thus be less agreeable (facets of agreeableness are straightforwardness and altruism) in waking life. To test this idea, future studies could investigate whether specific contents of lucid dreams are related to waking-life agreeableness. Unfortunately, the present sample of lucid dreams was too small to pursue this line of inquiry.

Regarding the within-subject comparisons, for only a small number of participants could the lucid dreams and prelucid dreams be matched with comparable nonlucid dreams; the differences regarding dream emotions are small, except for the (nonsignificant) higher positive emotions in lucid dreams. As retrospectively collected lucid dream reports often showed, more positive emotions (Green, 1968; LaBerge, 1985) as well as lucid dreams collected in samples of persons with high interest in lucid dreaming (Gackenbach & Schillig, 1983), it would be very interesting to carry out diary studies with larger samples of unselected students and compare lucid dreams with nonlucid dreams. Collecting and analyzing the thematic content of lucid dreams in samples not selected for lucid dreaming (Stumbrys et al., 2014) would be beneficial for shedding light on the variety and frequency of different topics—as seen in the present (small) sample of lucid dreams including quite a few dreams without any control within the dream or a dream of not wanting to wake up because the dreamer wished to spend time with a loved one.

To summarize, lucid dreams in diaries of unselected students are relatively rare and might differ regarding content from experienced lucid dreamers. Keeping a diary without any references to the lucid dream topic did not increase the frequency of lucid dreams, that is, keeping a diary is only useful in combination with other induction techniques (Stumbrys, Erlacher, Schädlich, & Schredl, 2012). The present findings indicate that studying lucid dreaming in unselected samples is very promising and complement the findings obtained from samples that include skilled lucid dreamers. Furthermore, it would be very interesting to study the relationship between personality factors, especially neuroticism and agreeableness, and lucid dreaming in a more detailed way.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by a grant (SCHR 637–2/1) from the Deutsche Forschungsgemeinschaft (DFG) given to the first author.

Author Biographies

Michael Schredl has been a dream researcher since 1990 and head of research of the sleep laboratory of the Central Institute of Mental Health, Mannheim, Germany. He teaches at the University of Mannheim and is also the editor of the online journal International Journal of Dream Research.

Alina Noveski is a bachelor student of psychology at the University of Bochum, Germany and worked as in intern of the sleep lab on the project “Lucid dreaming and personality”

References

Aspy

D. J.

(2016) Is dream recall underestimated by retrospective measures and enhanced by keeping a logbook? An empirical investigation. Consciousness and Cognition 42: 181–203. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1016/j.concog.2016.03.015.

Aspy

D. J.

Delfabbro

Proeve

(2015) Is dream recall underestimated by retrospective measures and enhanced by keeping a logbook? A review. Consciousness and Cognition 33: 364–374. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1016/j.concog.2015.02.005.

Barrett

(1991) Flying dreams and lucidity: An empirical study of their relationship. Dreaming 1: 129–134. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1037/h0094325.

Bulkeley

(2014) Lucid dreaming by the numbers. In: Hurd

Bulkeley

(eds) Lucid dreaming: New perspectives on consciousness in sleep – Vol. 1: Science, psychology, and education, Santa Barbara, CA: Praeger, pp. 1–22.

Gackenbach

(1988) The psychological content of lucid versus nonlucid dreams. In: Gackenbach

LaBerge

(eds) Conscious mind, sleeping brain – Perspectives on lucid dreaming, New York, NY: Plenum Press, pp. 181–220.

Gackenbach

Cranson

Alexander

(1986) Lucid dreaming, witnessing, and the transcendental meditation: A developmental relationship. Lucidity Letter 5(2): 34–41.

Gackenbach

Schillig

(1983) Lucid dreams: The content of conscious awareness of dreaming during the dream. Journal of Mental Imagery 7: 1–13.

Green

(1968) Lucid dreams, London, England: Hamish Hamilton.

Hess

Schredl

Goritz

A. S.

(2016) Lucid dreaming frequency and the big five personality factors. Imagination, Cognition and Personality 36(3): 240–253. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1177/0276236616648653.

10.

Kahan

T. L.

(1994) Measuring dream self-reflectiveness: A comparison of two approaches. Dreaming 4: 177–193. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1037/h0094411.

11.

Kühle, L. (2015). Insight: What Is It, Exactly?. In: T. K. Metzinger & J. M. Windt (Eds.), Open MIND. Frankfurt am Main: MIND Group. pp. 1–13.

12.

LaBerge

S. P.

(1985) Lucid dreaming, Los Angeles, CA: Jeremy P. Tarcher.

13.

LaBerge

S. P.

(1990) Lucid dreaming: Psychophysiological studies of consciousness during REM sleep. In: Bootzin

R. R.

Kihlstrom

J. F.

Schacter

D. L.

(eds) Sleep and cognition, Washington, DC: American Psychological Association, pp. 109–126.

14.

LaBerge

S. P.

Rheingold

(1990) Exploring the world of lucid dreaming, New York, NY: Ballentine Books.

15.

Noreika

Windt

J. M.

Lenggenhager

Karim

A. A.

(2010) New perspectives for the study of lucid dreaming: From brain stimulation to philosophical theories of self-consciousness. International Journal of Dream Research 3: 36–45.

16.

Ostendorf

Angleitner

(1994) A comparison of different instruments proposed to measure the Big Five. European Review of Applied Psychology 44: 45–53.

17.

Ostendorf, F., & Angleitner, A. (2004). NEO-PI-R - NEO Persönlichkeitsinventar nach Costa und McCrae - Revidierte Fassung (NEO–PI–R – NEO personality inventory by Costa and McCrae – revised edition) (Vol. 44). Göttingen, Germany: Hogrefe.

18.

Schredl

(2002) Questionnaire and diaries as research instruments in dream research: Methodological issues. Dreaming 12: 17–26. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1023/A:1013890421674.

19.

Schredl

(2004) Reliability and stability of a dream recall frequency scale. Perceptual and Motor Skills 98: 1422–1426. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.2466/pms.98.3c.1422–1426.

20.

Schredl

(2007) Dream recall: Models and empirical data. In: Barrett

McNamara

(eds) The new science of dreaming – Volume 2: Content, recall, and personality correlates, Westport, CT: Praeger, pp. 79–114.

21.

Schredl

(2008) Personality correlates of flying dreams. Imagination, Cognition and Personality 27: 129–137. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.2190/IC.27.2.d.

22.

Schredl

Doll

(1998) Emotions in diary dreams. Consciousness and Cognition 7: 634–646. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1006/ccog.1998.0356.

23.

Schredl

Erlacher

(2003) The problem of dream content analysis validity as shown by a bizarreness scale. Sleep and Hypnosis 5: 129–135.

24.

Schredl

Erlacher

(2004) Lucid dreaming frequency and personality. Personality and Individual Differences 37: 1463–1473. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1016/j.paid.2004.02.003.

25.

Schredl

Erlacher

(2011) Frequency of lucid dreaming in a representative German sample. Perceptual and Motor Skills 111: 60–64. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.2466/09.PMS.112.1.104-108.

26.

Schädlich

Erlacher

(2012) Applications of lucid dreams: An online study. International Journal of Dream Research 5: 134–138. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.11588/ijodr.2012.2.9505.

27.

Schredl

Fulda

(2005) Reliability and stability of dream recall frequency. Dreaming 15: 240–244. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1037/1053-0797.15.4.240.

28.

Schredl

Henley-Einion

Blagrove

(2016) Lucid dreaming and personality in children/adolescents and adults: The UK library study. International Journal of Dream Research 9: 75–78. doi: 10.11588/ijodr.2016.1.26454.

29.

Schredl

Wittmann

Ciric

Götz

(2003) Factors of home dream recall: A structural equation model. Journal of Sleep Research 12: 133–141. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1046/j.1365-2869.2003.00344.x.

30.

Sikka

Valli

Virta

Revonsuo

(2014) I know how you felt last night, or do I? Self- and external ratings of emotions in REM sleep dreams. Consciousness and Cognition: An International Journal 25: 51–66. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1016/j.concog.2014.01.011.

31.

Snyder

T. J.

Gackenbach

(1988) Individual differences associated with lucid dreaming. In: Gackenbach

LaBerge

(eds) Conscious mind, sleeping brain – Perspectives on lucid dreaming, New York, NY: Plenum Press, pp. 221–259.

32.

Stumbrys

Erlacher

(2012) Lucid dreaming during NREM sleep: Two case reports. International Journal of Dream Research 5: 151–155. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.11588/ijodr.2012.2.9483.

33.

Stumbrys

Erlacher

Johnson

Schredl

(2014) The phenomenology of lucid dreaming: An online survey. The American Journal of Psychology 127(2): 191–204. doi:10.5406/amerjpsyc.127.2.0191.

34.

Stumbrys

Erlacher

Schädlich

Schredl

(2012) Induction of lucid dreams: A systematic review of evidence. Consciousness and Cognition 21(3): 1456–1475. doi: 10.1016/j.concog.2012.07.003.

35.

Stumbrys

Erlacher

Schredl

(2013a) Reliability and stability of lucid dream and nightmare frequency scales. International Journal of Dream Research 6: 123–126. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.11588/ijodr.2013.2.11137.

36.

Stumbrys

Erlacher

Schredl

(2013b) Testing the involvement of the prefrontal cortex in lucid dreaming: A tDCS study. Consciousness and Cognition 22(4): 1214–1222. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1016/j.concog.2013.08.005.

37.

Watson

(2001) Dissociations of the night: Individual differences in sleep-related experiences and their relation to dissociation and schizotypy. Journal of Abnormal Psychology 110: 526–535. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1037/0021-843X.110.4.526.

38.

Zadra

A. L.

Donderi

D. C.

Pihl

R. O.

(1992) Efficacy of lucid dream induction for lucid and non-lucid dreamers. Dreaming 2: 85–97. Retrieved from https://dx-doi-org.web.bisu.edu.cn/10.1037/h0094350.

39.

Zunker

Althoff

H. K.

Apel

Lässig

H. S.

Schültke

Schredl

(2015) Comparing questionnaire and diary measures for eliciting nightmare frequency. International Journal of Dream Research 8: 129–134. 10.11588/ijodr.2015.2.23395.