Effectiveness of motor practice in lucid dreams: a comparison with physical and mental practice

Abstract

Motor practice in lucid dreams is a form of mental rehearsal where the dreamer can consciously rehearse motor skills in the dream state while being physically asleep. A previous pilot study showed that practice in lucid dreams can improve subsequent performance. This study aimed to replicate those findings with a different task (finger-tapping) and compare the effectiveness of lucid dream practice (LDP) not only to physical but also to mental practice (MP) in wakefulness. An online experiment was completed by 68 participants within four groups: LDP group, MP group, physical practice (PP) group and control (no practice) group. Pre-test was accomplished in the evening, post-test in the next morning, while the practice was done during the night. All three practice groups significantly improved their performance from pre-test to post-test, but no significant improvements were observed for the control group. Subjective sleep quality was not affected by night practice. This study thus corroborates the previous findings that practice in lucid dreams is effective in improving performance. Its effects seem to be similar to actual PP and MP in wakefulness. Future studies should establish reliable techniques for lucid dream induction and verify the effects of LDP in sleep laboratory conditions.

Full text

Effectiveness of motor practice in lucid dreams: a comparison with
physical and mental practice
TADAS STUMBRYS
1
, DANIEL ERLACHER
2
& MICHAEL SCHREDL
3
1
Institute of Sports and Sports Sciences, Heidelberg University, Heidelberg, Germany,
2
Institute of Sport Science, University
of Bern, Bern, Switzerland and
3
Central Institute of Mental Health, Medical Faculty Mannheim/Heidelberg University,
Mannheim, Germany
(Accepted 13 March 2015)
Abstract
Motor practice in lucid dreams is a form of mental rehearsal where the dreamer can consciously rehearse motor skills in the
dream state while being physically asleep. A previous pilot study showed that practice in lucid dreams can improve
subsequent performance. This study aimed to replicate those findings with a different task (finger-tapping) and compare
the effectiveness of lucid dream practice (LDP) not only to physical but also to mental practice (MP) in wakefulness. An
online experiment was completed by 68 participants within four groups: LDP group, MP group, physical practice (PP)
group and control (no practice) group. Pre-test was accomplished in the evening, post-test in the next morning, while the
practice was done during the night. All three practice groups significantly improved their performance from pre-test to post-
test, but no significant improvements were observed for the control group. Subjective sleep quality was not affected by night
practice. This study thus corroborates the previous findings that practice in lucid dreams is effective in improving
performance. Its effects seem to be similar to actual PP and MP in wakefulness. Future studies should establish reliable
techniques for lucid dream induction and verify the effects of LDP in sleep laboratory conditions.
Keywords: lucid dreams, motor learning, lucid dream practice, mental practice, finger-tapping
Introduction
Mental practice (MP) is the cognitive rehearsal of a
physical activity in the absence of overt physical
movements (Richardson, 1967). It is a well-estab-
lished technique in sports (Morris, Spittle, & Watt,
2005). Several meta-analyses demonstrated that MP
significantly improves performance, albeit to a smal-
ler extent than actual physical practice (PP)
(Driskell, Copper, & Moran, 1994; Feltz &
Landers, 1983). A novel and relatively unknown
type of mental rehearsal is motor practice in lucid
dreams (Erlacher, 2007).
Lucid dreams are dreams in which the dreamer is
asleep but aware that he or she is dreaming and often
can influence the dream plot (LaBerge, 1985). This
ability to be aware in the dream state and deliber-
ately perform actions while physically asleep opens
up opportunities to use lucid dreams for sports prac-
tice, for example, to consciously rehearse specific
motor tasks without waking up (Tholey, 1990).
Practice in lucid dreams is similar to MP in wakeful-
ness: movements are rehearsed with a representation
of the body on a cognitive level without overt physi-
cal movements (cf. Erlacher, 2007).
The evidence suggests that imagined and executed
actions to some extent seem to share the same neural
structures (Decety, 1996). Motor and associated cor-
tical areas involved in programming and preparations
of actual movements are also active during mental
simulation of movement (reviews: Jeannerod, 2001;
Lotze & Halsband, 2006; Munzert, Lorey, &
Zentgraf, 2009), autonomic responses of imagined
actions mimic the actual autonomic responses during
the exercise (review: Guillot & Collet, 2005a), and the
timing of imagined and actual motor actions are clo-
sely related (reviews: Guillot & Collet, 2005b;
Guillot, Hoyek, Louis, & Collet, 2012). According
to the theory of neural simulation of action by
Jeannerod (2001), in general, covert actions are actual
actions, except for the fact that they are not executed.
The theory thus predicts a neural similarity between
the state where an action is simulated (“S-state”) and
the state of execution of this action. While for some S-
states, such as action observation, the functional
Correspondence: Tadas Stumbrys, Institute of Sports and Sports Sciences, Heidelberg University, Im Neuenheimer Feld 700, 69120 Heidelberg, Germany.
E-mail: tadas.stumbrys@issw.uni-heidelberg.de
Journal of Sports Sciences, 2015
http://dx.doi.org/10.1080/02640414.2015.1030342
© 2015 Taylor & Francis
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equivalence has been called into question (Lorey
et al., 2013), the limited evidence from dream
research suggest that dreamed actions do seem to
share the same neural mechanisms with executed
actions (Erlacher & Schredl, 2008b). For example,
correspondences exist in underlying brain activity
(cf. Dresler et al., 2011), autonomic responses (cf.
Erlacher & Schredl, 2008a) and temporal dynamics
(cf. Erlacher, Schädlich, Stumbrys, & Schredl, 2014).
Empirical evidence on lucid dream practice
(LDP) is rather scarce. In a sample of 840 German
athletes from various sports, 57% stated that they
had at least one lucid dream in their life, 24%
reported frequent lucid dreams (one or more lucid
dreams per month), however only 9% of the lucid
dreamers used this dream state to practice sport
skills (Erlacher, Stumbrys, & Schredl, 2011–2012).
Yet, the majority of those who practiced had the
impression that the rehearsal within the lucid
dream improved their subsequent performance in
wakefulness. Several such anecdotal accounts on
how practice in lucid dreams improved waking per-
formance have also been reported in the literature
(e.g. Erlacher, 2007; LaBerge & Rheingold, 1990;
Tholey, 1990).
In a qualitative study, Tholey (1981) asked six
proficient lucid dreamers to perform and practice
movements and complex sport skills, such as skiing
on gymnastics, with which they were already familiar
from waking life. The participants reported no diffi-
culties while performing complex sport skills in their
lucid dreams and had an impression that their move-
ments improved following the practice.
Further, Erlacher and Schredl (2010) conducted a
pilot study (field experiment) with a pre-post design
in which the participants were asked to practice a
simple motor task –to toss 10-cent coins into a cup,
positioned at the distance of two meters, as many
times as possible out of 20 trials. Twenty participants
attempted to practice the task in a lucid dream on a
single night and seven of them succeeded. Their
performance was compared to a group which accom-
plished actual PP (n= 10) and a control group with-
out practice (n= 10). Both practice groups showed
significant increases in hitting the target from pre-
test to post-test, while no increase was found for the
participants who did not practice the task. Although
the improvements following lucid dreaming practice
were somewhat lower in comparison to PP, the dif-
ferences were not significant.
The present study aimed to replicate these find-
ings with a different motor task (a sequential finger-
tapping task; cf. Karni et al., 1998; Walker,
Brakefield, Morgan, Hobson, & Stickgold, 2002)
and compare the effectiveness of LDP not only to
awake PP but also to MP in wakefulness. It was
expected that all three types of practice will improve
subsequent performance. The gains from PP were
expected to be higher than the ones from MP (cf.
Driskell et al., 1994), whereas the gains from LDP
were expected to fall in between, as the cognitive
simulation in the dream state is much more realistic
(cf. Tholey, 1990) and the perception in lucid
dreams appears to be much more closer to actual
perception than to waking imagination (LaBerge &
Zimbardo, 2000).
Methods
Participants
The sample included 68 individuals (32 male and 36
female) who completed an online experiment. Their
ages ranged from 19 to 54 years, with the mean age
of 31.3 ± 7.3 years. Participants were recruited via
electronic advertisements (posted on lucid dream-
ing-related discussion boards, social networking
sites and via personal contacts) and assigned to one
of four groups: (1) LDP group (if they were frequent
lucid dreamers; n= 21); (2) MP group (n=15); (3)
PP group (n= 16); (4) control (no practice) group
(n= 16). The data of four participants from the LDP
group were excluded (reducing the sample to
n= 17) as three participants reported that they prac-
ticed the task only very briefly (tapping the sequence
only 2–4 times) and one participant reported addi-
tional practice in the evening while awake. Group
characteristics are depicted in Table I. Participation
Table I. Group characteristics.
LDP (n= 17) MP (n= 15) PP (n= 16) Control (n= 16) Statistical test P
Age (y) 31.2 ± 8.1 32.1 ± 8.1 31.3 ± 6.0 30.1 ± 8.1 F
3,60
= 0.18 .909
Male/Female 11/6 6/9 7/9 6/10 χ
23
= 3.08 .379
Right-/Left-handers 13/4 15/0 15/1 15/1 χ
23
= 5.93 .115
VMIQ-2
External visual 31.4 ± 12.3 32.9 ± 10.3 33.3 ± 9.3 29.8 ± 9.6 F
3,60
= 0.36 .781
Internal visual 30.7 ± 11.4 30.1 ± 9.3 29.2 ± 11.4 27.1 ± 10.8 F
3,60
= 0.34 .800
Kinesthetic 28.8 ± 11.1 31.5 ± 9.3 24.8 ± 6.9 25.9 ± 9.3 F
3,60
= 1.63 .192
Lucid dreams/month 8.8 ± 7.0 0.5 ± 1.1 0.4 ± 0.7 0.3 ± 0.6 χ
23
= 36.1 <.001
Sleep quality 1.9 ± 0.7 1.9 ± 0.8 2.3 ± 0.8 1.8 ± 0.4 χ
23
= 3.70 .296
2T. Stumbrys et al.
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was voluntary and unpaid. The study was conducted
according to the principles of the Declaration of
Helsinki. All participants signed an electronic
informed consent form and were free to withdraw
from the experiment at any time.
Motor task
A computerised online version of the sequential fin-
ger-tapping task was used, which requires the parti-
cipant to press four keys on a computer keyboard
with a non-dominant hand producing a sequence of
five elements “as quickly and accurately as possible”
for a period of 30 s (Walker et al., 2002). Each
sequence started and finished with the little finger;
index, middle and ring fingers were used once (e.g.
“4–1–3–2–4”; cf. Karni et al., 1998). Four different
sequences were prepared for each hand, allowing
repeating the experiment up to four times. During
the initial (learning) phase, the participants were
asked to memorise the sequence shown on the
screen and tap it correctly 10 times. Each correct
key press produced a green dot on a corresponding
finger in a hand picture presented on the screen,
while an incorrect key press produced a red dot.
The assessment phase consisted of two test periods
of 30 s with a 30 s rest period in between. Each key
press produced a white dot. No other feedback was
provided. The number of correct sequences com-
pleted and the number of incorrect key presses
were recorded. The average scores of two test peri-
ods were calculated.
Procedure
The study was conducted as a field experiment, that
is, the participants accomplished the procedure by
themselves in their home setting. Participants had to
fill out an initial online questionnaire, which
included demographical data (age, gender and coun-
try), questions about lucid dream recall, vividness of
motor imagery and handedness. Lucid dream fre-
quency was assessed on an 8-point scale (0 –never;
1–less than once a year; 2 –about once a year; 3 –
about 2–4 times a year; 4 –about once a month; 5 –
about 2–3 times a month; 6 –about once a week and
7–several times a week), with a high retest reliability
(r= .89; Stumbrys, Erlacher, & Schredl, 2013). To
ensure a clear understanding of lucid dreaming, a
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.”In order to obtain
units in frequency per month, the scale was recoded
using the class means: 0 →0, 1 →0.042, 2 →0.083,
3→0.25, 4 →1.0, 5 →2.5, 6 →4.0, 7 →18.0 (see
Stumbrys et al., 2013). Further, the participants
filled a revised version of the Vividness of Motor
Imagery Questionnaire (VMIQ-2, Roberts, Callow,
Hardy, Markland, & Bringer, 2008), which assesses
three-factor (internal visual imagery, external visual
imagery and kinesthetic imagery) individual imagery
characteristics on a 5-point scale (ranging from 1 –
perfectly clear and vivid to 5 –no image at all).
VMIQ-2 has demonstrated acceptable factorial
validity, construct validity and concurrent validity
(Roberts et al., 2008). The order in which VMIQ-2
imagery modalities were presented was randomised.
Lastly, the participants filled the Edinburgh
Handedness Inventory –Short Form (EHI-SF,
Veale, 2014), which contains four items for which
the preference in the use of hands is scored on a 5-
point scale (from 1 –always right to 5 –always left).
The modification was shown to have good reliability,
factor score determinacy and correlation with the
original 10-item inventory (Oldfield, 1971).
After filling the initial questionnaire, the partici-
pants were assigned to one of the groups. The LDP
group was assembled from the participants with a
higher lucid dream frequency (2–3 or more lucid
dreams per month). Other participants were put on
the waiting list and randomly assigned to one of the
other groups after the LDP group completed the
experiment. Instructions to the participants were
sent by email. All participants were asked to choose
a time schedule for the experiment so that the time
difference between the evening pre-test and the
morning post-test would be 10 h. The MP and PP
participants were assigned corresponding practice
times (from the bed time) and durations as the
LDP group. Two lucid dreamers practiced the task
in two different dreams during the night, hence two
corresponding participants in MP and PP groups
were also asked to awaken and practice the task
twice during the night (although one PP participant
did only a single awakening). Further, all partici-
pants were asked to set an alarm clock to awaken at
least 30 min before the post-test time, so that their
performance would not be impaired by sleep inertia
(Tassi & Muzet, 2000).
LDP group. The participants could use any techni-
que to induce lucid dreams (cf. Stumbrys, Erlacher,
Schädlich, & Schredl, 2012), with the exception of
drug intake. After becoming lucid in a dream, they
had to start immediately practicing the task (repeat-
ing the memorised sequence) and continue the prac-
tice for as long as possible. The participants were
instructed to do the practice in 30 s (self-estimated)
intervals with 30 s (self-estimated) rest periods in
between. During the 30 s rest periods they were
allowed to apply techniques that prolong lucid
Effectiveness of motor practice in lucid dreams 3
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dreams (e.g. spinning, hand rubbing; LaBerge,
1995).
MP group. Each participant was assigned one exact
practice time and duration from the LDP group. The
participants were asked to awaken 30 min before the
assigned practice time and keep themselves awake dur-
ing this period (to avoid possible effects of sleep iner-
tia). Then they were instructed to close their eyes and
start practicing the task in their mind without moving
their actual fingers during the practice. With their eyes
closed, they had to attempt to imagine themselves
producing the sequence by visualising the movement
of each finger. The participants were asked to try to feel
each movement of their fingers while repeating the
memorised sequence. The practice had to be accom-
plished in 30 s (self-estimated) intervals with 30 s (self-
estimated) rest periods in between.
PP group. As in the MP group, PP participants were
assigned exact practice times and durations from the
LDP group and asked to awaken 30 min before the
practice time and keep themselves awake during this
period. Then they were instructed to start practicing
the task physically, also in 30 s (self-estimated) inter-
vals with 30 s (self-estimated) rest periods in
between.
Control group. The participants were not asked to do
any practice (only pre-test in the evening and post-
test in the morning).
The experimental night procedure is depicted in
Figure 1. Upon completing the post-test, the parti-
cipants had to fill out a report, indicating their bed
times, and rating their sleep quality of the night on a
4-point scale (1 –very good to 4 –very bad). Three
practice groups were further asked to provide their
practice details. If unsuccessful, participants could
repeat the experiment with a difference sequence
(up to four times).
On one occasion (MP) no results were recorded
for the second post-test interval, whereas in two
other occasions (LDP and MP) the number of
correct sequences produced during one of the pre-
test intervals (in both cases the second interval) was
very low (2 sequences) as compared to the average
performance during the other three test intervals
(16.0 and 13.7 sequences, respectively). To avoid
possible distortions, the data from these intervals
were excluded (thus only a single test interval result
and not the average of the two test intervals were
used).
Statistical analysis
IBM SPSS Statistics 20 software was used for sta-
tistical analysis. One-way ANOVA were performed
to compare the characteristics of the four groups on
interval variables (age, scores on motor imagery
scales), whereas Kruskall–Wallis test was used for
ordinal variables (sleep quality and lucid dream
frequency) and Chi-square for categorical variables
(gender and handedness). Two-way repeated mea-
sures ANOVA were conducted to compare the
performance from pre-test to post-test between
the groups. Differences between the groups were
investigated with post-hoc least significant differ-
ence (LSD) tests. Student t-tests were used to
compare the performance from the pre-test to the
post-test for each individual group. Spearman’srho
correlations were used to check the associations
between changes in performance and potential con-
founding variables: lucid dream frequency and
repeated trials. G*Power 3.1.7 software (Faul,
Erdfelder, Buchner, & Lang, 2009) was used for
calculating effect sizes d. An alpha = .05 signifi-
cance level was employed.
Results
Group characteristics
According to the EHI-SF results, six participants
were considered left-handed and were assigned to
do the motor task with the right hand, whereas the
rest 58 participants were right-handed and per-
formed the task with the left hand. There were no
significant handedness differences between the
groups, as well as differences in motor imagery abil-
ities as measured by VMIQ-2 and reported sleep
quality of the night, although the groups differed in
their lucid dream frequency (Table I). LDP partici-
pants in average had 2.1 ± 1.1 (M ± s) trials.
10 h
≥ 30 min
30 min
MP ControlPP LDP
Morning awakening
Morning post-test
LD induct.
techniques
Evening pre-test
Going to bed
Night practice
Night awakening
Figure 1. Experimental protocol of the four groups.
4T. Stumbrys et al.
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Practice times and durations
A few participants in MP and PP groups slightly
diverged from the original instructions (considering
their exact practice times and durations), but the
conditions were very much similar nevertheless.
The LDP group carried out their practice on average
at 6:07 ± 2:20 h since their bed time (range: 1:20–
9:00), MP at 5:49 ± 2:17 h (range: 1:20–8:40) and
PP at 5:51 ± 2:23 h (range: 1:20–9:00). The LDP
group did 4.2 ± 6.3 blocks of 30 s practice (median:
2; range: 1–22), MP 5.3 ± 6.4 (median: 3; range: 1–
22) and PP 3.8 ± 5.3 (median: 2; range: 1–22).
Three practice groups did not differ in their amount
of practice (F
3,60
= 0.08, P= .927) and duration
(F
3,60
= 0.28, P= .760).
Effects of practice
All three practice groups had significant improve-
ments from pre-test to post-test in terms of the
number of correct sequences produced, averaged
across two 30 s test intervals, whereas the control
participants had only nonsignificant improvements
(Table II). There was a significant time (pre-test to
post-test; F
1,60
= 50.12, P< .001) but not group
(F
3,60
= 0.48, P= .695) effect. Group × time inter-
action was significant (F
3,60
= 3.43, P= .023), show-
ing that four groups improved differently from the
pre-test to post-test. Post-hoc LSD pair-wise com-
parisons showed significant differences between the
LDP and control group (P= .003), as well as
between the PP and control group (P= .031), but
not between other pairs of the groups. Increases in
performance from pre-test to post-test were not asso-
ciated with lucid dream frequency (rho = .100,
P= .432). Further, no significant association
between changes in performance and the number
of trials (rho =−.473, P= .055) was found in the
LDP group, where most of participants attempted
the experiment more than once. Practice times
(since the bed time) were also not significantly asso-
ciated with changes in performance (rho = .040,
P= .785).
LDP group made on average 5.3 ± 5.2 errors on
the pre-test, MP 5.5 ± 6.7, PP 5.0 ± 8.1 and control
group 8.3 ± 13.0. On the post-test the respective
error rates were 5.6 ± 5.0, 7.1 ± 7.8, 5.7 ± 9.7 and
10.9 ± 13.3. Differences between the two tests were
significant for control group (more errors on the
post-test; t= 3.76, P= .002) but not for practice
groups (LDP: t= 0.23, P= .820; MP: t= 1.63,
P= .125; PP: t= 0.69, P= .504). Overall differences
for the change in the error rate between the four
groups were not significant (F
3,60
= 0.95, P= .423).
Discussion
The present study corroborates the findings of a pilot
study by Erlacher and Schredl (2010) that motor
practice in lucid dreams enhances subsequent per-
formance. All three types of practice lead to signifi-
cant improvements from the pre-test to the post-test,
whereas only a small but not statistically significant
improvement was found in the control (no practice)
group. LDP and PP participants had significantly
higher improvements as compared to the control
group who did only the test and retest. No signifi-
cant differences were found between the three dif-
ferent practices, as well as between the MP and
control group. LDP resulted in highest average
gains (+20%), followed by PP (+17%) and MP
(+12%), however the effect size was highest for PP
(1.57), followed by MP (1.16) and LDP (0.91). All
these effect sizes are considered large (≥0.8) accord-
ing to Cohen (1992).
Before discussing the findings, several methodolo-
gical issues have to be acknowledged. Firstly, the
study was conducted as a field experiment and there-
fore the experimental control was lacking (i.e. only
the test procedure but not the experimental treat-
ment can be controlled by the experimenter online).
For example, it is possible that some participants did
not adhere to the instructions correctly. Although
instructions sent to the participants were written as
clearly as possible, in a few cases the participants
slightly diverged (e.g. by awakening for practice at a
slightly different time, by doing a somewhat different
number of practice intervals, or by forgetting to do
rest periods during LDP). To have a better experi-
mental control, sleep laboratory studies are
Table II. Effects of practice on motor task performance (number of correct sequences averaged across two 30 s periods per test).
Pre-test Post-test T-test
MsSEM M sSEM Change in % T PEffect size
Lucid dream practice 17.1 4.1 1.00 20.5 4.7 1.14 +20% 3.75 .001 0.91
Mental practice 15.4 4.9 1.27 17.3 5.6 1.45 +12% 4.46 <.001 1.16
Physical practice 16.2 5.8 1.45 18.9 6.4 1.60 +17% 6.25 <.001 1.57
Control (no practice) 17.1 6.8 1.70 17.9 7.7 1.93 +5% 1.56 .070 0.39
Note: One-tailed T-tests were used.
Effectiveness of motor practice in lucid dreams 5
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recommended where actions in lucid dreams can be
monitored by using eye movements (cf. Erlacher
et al., 2014). Yet such sleep laboratory studies are
always affected by small sample sizes (limited usually
only to a few successful participants), because it is
very difficult to recruit proficient lucid dreamers. In
the general population, only 5% of people have at
least one lucid dream a week (Schredl & Erlacher,
2011), which is necessary for sleep laboratory stu-
dies, often restricted only to a few nights. The big-
gest advantage of online field experiments is that
they allow the recruitment of participants from all
over the world (e.g., 21 lucid dreamers who com-
pleted the present study represented 11 different
countries) and therefore samples can be much
higher. Secondly, the assignment to the experimental
groups was not completely randomised, as the LDP
group was selected by lucid dream frequency.
Improvements in performance, however, were not
associated with lucid dream frequency. Further, a
number of participants who registered for the experi-
ment did not complete it. Participation in the study
was quite demanding for MP and PP participants, as
they had to awaken at a certain time during the night
and wait for half an hour before starting to practice.
Lucid dreamers could have had an additional stress
“to be successful”(i.e. to be able to have a lucid
dream and practice the task in it). Thus, this might
have resulted that only certain (e.g. highly moti-
vated) individuals completed the study, and there-
fore the findings should be interpreted cautious.
Thirdly, most participants in the LDP group and a
few participants in the other practice groups did the
experiment a few times (up to four). While each time
a different sequence was used, there is a possibility
that some transfer (positive or negative) in learning
had occurred. The possibility to have a task which
could be repeatable with a different variation was
important to increase the chances of success for
lucid dreamers –for example, out of 21 lucid drea-
mers who completed the study, only 6 were success-
ful on their first trial. Yet multiple trials did not seem
to influence the performance: No significant associa-
tion was found between the changes in performance
and the number of trials in LDP group. The trend,
in fact, was negative: Further trials were associated
with lesser performance improvements. Fourthly,
practice times and durations for all practice condi-
tions were derived from the lucid dreamers’esti-
mates of time, which might be somewhat
inaccurate. For example, lucid dreamers and parti-
cipants in the two other intervention groups might
have considerably deviated in their actual practice
times and durations. Sleep laboratory research, how-
ever, demonstrated that time in dreams is perceived
very similarly as to when awake and while motor
actions might take longer times in lucid dreams,
this difference exists only for absolute but not for
relative durations, which is crucial for motor skill
learning (Erlacher et al., 2014). Under- and over-
estimations of motor imagery durations also happen
during MP (Guillot & Collet, 2005b; Guillot et al.,
2012). In this study, participants in all three practice
groups were asked to estimate their practice
durations.
As in the previous study (Erlacher & Schredl, 2010),
LDP was found to improve subsequent performance
in wakefulness. This group had the highest gains but
the lowest effect size, which suggests that its effects
might be more variable. The previous study (Erlacher
& Schredl, 2010) with a different –aiming –task found
higher improvements (+43% for LDP and +88% for
PP), but the reanalysis of the data showed that effect
sizes for practices were similar (LDP: 1.24; PP: 1.32)
and the effects of PP showed greater variability than of
LDP. Considering the results of the two studies
together, LDP appears to be similar or slightly less
effective than PP. The comparison with MP is some-
what less clear. LDP showed significantly greater
improvements as compared to control group, whereas
MP did not significantly differ from any of groups.
LDP resulted in somewhat higher performance gains
as compared to MP, yet somewhat lower effect size,
which might be considered a better indicator of
improvement than the percentage gains taking into
account fairly large standard deviations (Table II).
Previous studies with similar finger-tapping tasks
have shown that MP improves performance and the
gains are similar or slightly lower as compared to PP
(e.g. Debarnot, Creveaux, Collet, Doyon, & Guillot,
2009; Nyberg, Eriksson, Larsson, & Marklund, 2006).
The present study corroborates those findings and
suggests that the effectiveness of LDP might be similar
to the effectiveness of MP, however more research is
needed.
Both lucid dream and wakeful MPs are cognitive
rehearsals with a representation of the body without
overt physical movements and both seem to some
extent to share the same neural mechanisms that
produce actual movements (Decety, 1996; Erlacher
& Schredl, 2008b), supporting the notion of func-
tional equivalence (Jeannerod, 2001). Thus, lucidly
dreamed and imagined movements would have simi-
lar functional outcomes with actual physical move-
ments, allowing motor learning to occur. A recent
functional magnetic resonance imaging/near-infra-
red spectroscopy study showed that brain activity in
the sensorimotor cortex is similar during imagined
and lucidly dreamed movement (Dresler et al.,
2011). The perception in lucid dreams, however,
seems to be much closer to actual perception and
both are quite distinct from imagination (LaBerge &
Zimbardo, 2000). In lucid dreams the simulation is
experienced as real (not just existing in imagination)
6T. Stumbrys et al.
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and therefore it has been suggested that LDP should
be more effective than MP performed in wakeful
imagination (Tholey, 1990). The present study,
however, did not show a clear difference between
the two types of practice.
All three types of practice increased performance
speed without compromising accuracy –the error
rate did not significantly differ between the two
tests, which is consistent with previous research (cf.
Walker et al., 2002). Only the control group showed
a significant increase in the error rate, which perhaps
might be linked to changes in motivation (i.e. less
motivated to retake the same test without any prac-
tice in between). A finger-tapping study by Debarnot
et al. (2009), for example, also found somewhat
increased error rate during the retest, although the
difference did not reach significance.
In comparison with the earlier study (Erlacher &
Schredl, 2010), this study involved a larger sample
and practice times were matched. In the previous
study, the PP group accomplished practice in the
evening, whereas lucid dreamers practiced at some
later point at night. Sleep memory consolidation
research shows that improvements in performance
seem to be associated with various sleep parameters,
such as a higher amount of rapid eye movement
(REM) sleep (Fischer, Hallschmid, Elsner, & Born,
2002) or a greater proportion of time spent in Stage
2 sleep (Walker et al., 2002). Therefore, the PP
group might have had an advantage in the previous
study. In this study, the practice times were
matched. PP and MP participants had a small dis-
advantage to awaken at night and wait 30 min before
starting their practice. The LDP group, however,
also had to awaken after a lucid dream (to write
down the dream) and several lucid dreamers indi-
cated that they used Wake-up-Back-To-Bed method
for lucid dream induction, which requires to awaken
at night and stay awake for some time (cf. Stumbrys
et al., 2012). Thus, the conditions were comparable
and the awakenings did not seem to significantly
disturb the sleep –all groups rated their subjective
sleep quality similarly. While there are some indica-
tions that the brain seems to be more active during
lucid as compared to non-lucid REM sleep (Dresler
et al., 2012; Voss, Holzmann, Tuin, & Hobson,
2009), there appears to be no evidence in the litera-
ture about negative effects of frequent lucid dream-
ing on sleep quality.
In summary, the present study corroborates the
findings that motor practice in lucid dreams
improves subsequent performance in wakefulness.
No significant differences were found when compar-
ing the effectiveness of LDP to PP and MP in wake-
fulness. While further research with more complex
skills is very much needed, current research with
simple motor skills, such as finger-tapping or coin-
tossing, shows that LDP gives an additional oppor-
tunity to athletes to practice specific sport skills dur-
ing the night time when physiologically asleep. LDP
provides a more realistic simulation of the waking
environment than MP (cf. LaBerge & Zimbardo,
2000; Tholey, 1990) and could be alternatively
used when an athlete is injured, unable to practice
physically or actions are dangerous. LDP may be
more beneficial for those athletes who have lucid
dreams more often but lack vivid wakeful imagina-
tion. While only a limited number of athletes have
lucid dreams on a frequent basis (Erlacher et al.,
2011–2012), there is a wide range of techniques
that can be used for lucid dream induction
(Stumbrys et al., 2012), yet none of them has been
verified to induce lucid dreams reliably and consis-
tently. This is one the main challenges facing lucid
dream research. Future studies should establish reli-
able techniques for lucid dream induction and exam-
ine the effects of LDP in controllable sleep
laboratory conditions.
Acknowledgement
The authors would like to thank Laurens Van Keer
from Snoozon.com for developing the online finger-
tapping application.
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