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Music preference in degus (Octodon degus): Analysis with Chilean folk music

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Most nonhuman animals do not show selective preference for types of music, but researchers have typically employed only Western classical music in such studies. Thus, there has been bias in music choice. Degus (Octodon degus), originally from the mountain areas of Chile, have highly developed vocal communication. Here, we examined music preference of degus using not only Western classical music (music composed by Bach and Stravinsky), but also South American folk music (Chilean and Peruvian). The degus preferred the South American music to the Western classical music but did not show selective preference between the two Western classical music choices. Furthermore, the degus preferred the Chilean to the Peruvian music to some extent. In the second experiment, we examined preference for music vs. silence. Degus overall showed a preference for Chilean music over silence, but preferred silence over Western music. The present results indicate that the previous negative data for musical preference in nonhuman animals may be due to biased music selection (Krause, 2012). Our results suggest the possibility that the soundscape of an environment influences folk music created by native peoples living there and the auditory preference of other resident animals there.
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ABC 2018, 5(2):201208
Animal Behavior and Cognition https://doi.org/10.26451/abc.05.02.02.2018
©Attribution 3.0 Unported (CC BY 3.0)
Music Preference in Degus (Octodon degus): Analysis with
Chilean Folk Music
Shigeru Watanabe1*, Katharina Braun2, Maria Mensch2, and Henning Scheich3
1 Keio University, Minato-ku, Mita 2-15-45,Tokyo Japan
2 Otto Von Guericke University, Magdeburg, Germany
3 Leibniz Institute for Neurobiology
*Corresponding author (Email: swat@flet.keio.ac.jp)
Citation Watanabe, S., Braun, K., Mensch, M., & Scheich, H. (2018). Music preference in degus (Octodon
degus): Analysis with Chilean folk music. Animal Behavior and Cognition, 5(2), 201208.
https://doi.org/10.26451/abc.05.02.02.2018
Abstract Most nonhuman animals do not show selective preference for types of music, but researchers have
typically employed only Western classical music in such studies. Thus, there has been bias in music choice. Degus
(Octodon degus), originally from the mountain areas of Chile, have highly developed vocal communication. Here,
we examined music preference of degus using not only Western classical music (music composed by Bach and
Stravinsky), but also South American folk music (Chilean and Peruvian). The degus preferred the South American
music to the Western classical music but did not show selective preference between the two Western classical music
choices. Furthermore, the degus preferred the Chilean to the Peruvian music to some extent. In the second
experiment, we examined preference for music vs. silence. Degus overall showed a preference for Chilean music
over silence, but preferred silence over Western music. The present results indicate that the previous negative data
for musical preference in nonhuman animals may be due to biased music selection (Krause, 2012). Our results
suggest the possibility that the soundscape of an environment influences folk music created by native peoples living
there and the auditory preference of other resident animals there.
Keywords Degu, Music preference, Chilean music, Reinforcement
Hearing music often causes a pleasurable experience in humans, but nonhuman animals do not
display such pleasure (see review by Watanabe 2012, 2015). Therefore, the reinforcing property (or
pleasure) of music has been concluded to be a human-specific trait (McDermott & Hauser, 2004). We
have, however, demonstrated that Java sparrowsLonchura oryzivorashow a selective preference for
particular music (Watanabe & Nemoto, 1998). Although the reinforcing property of music has not been
thoroughly examined, humans and songbirds (Java sparrows) appear to be exceptional species for
showing preferences for particular types of music (Gess, 2007). Most of the relevant published studies
have failed to demonstrate any reinforcing effect of music in primates. Chimpanzees (Pan troglodytes,
Howell, Schwandt, Fritz, Roeder, & Nelson, 2003), gorillas (Gorilla gorilla gorilla, Wells, Coleman, &
Challis, 2006), the common marmoset (Callithrix jacchus) and cotton-top tamarin (Saguinus oedipus,
McDermott & Hauser, 2004, 2007), rats (Rattus norvegicus, Otsuka, Yanagi, & Watanabe, 2009), pigeons
(Columba livia, Watanabe, Suzuki, & Yamazaki, 2009) and goldfish (Carassius auratus, Shinozuka,
Ono, & Watanabe, 2013) did not show musical preference.
Watanabe et al. 202
One common bias in the design of music preference experiments is the choice of music. Nearly
all previous studies, including our own, have presented animals with Western classical music. Ritvo and
MacDonald (2016) examined musical preference in the Sumatran orangutan (Pongo abelli). They
presented orangutans with different kinds of music, including non-Western music (Mongolian Tuva throat
singing). However, all of them showed a preference for silence over music or showed no clear preference.
Mingle, Eppley, Campbell, Hall, and de Waal (2014) presented traditional African music to chimpanzees
and observed that the animals moved closer to the sound source when African music was broadcast.
These results suggest the possibility of preference for native folk music in the animals habitat over
Western (non-habitat) music in nonhuman animals. Snowdon and Teie (2010) produced music composed
with characteristics of animal vocalization and observed that tamarins preferred such music over human
music. Snowdon, Teie, and Savage (2015) created species-appropriate music and found that cats preferred
the music over human-appropriate music.
The degu, a so-called “singing rat” of the Andes, is a rodent that originates in the mountainous
areas of Chile. They have more than 15 sounds (Long, 2007). This species is considered suitable for
musical preference studies for several reasons. First, they have highly developed auditory communication,
which makes auditory stimuli important information for them. Second, their hearing range is similar to
that of humans (Braun, Kremz, Wetzel, Wagner, & Poeggel, 2003), which suggests that human-made
music would be suitable for their auditory sensation. Here, we tested the music preference of degus using
Western music and South American folk music.
Experiment 1: Preference Among Western, Chilean, and Peruvian Music
Method
Subjects. The 42 male degus (Octogon degus) used in this study were bred in our colony
(Institute of Biology, Otto von Guericke University, Magdeburg). Animals were group-caged in wire
cages (51 × 42 × 68 cm) in air-conditioned rooms with an average temperature of 22°C, under artificial
light/dark cycle (12h/12h). Fresh water, food pellets and vegetables were available ad libitum. The
experiment was carried out across five years (2013 - 2017). The age of animals ranged from one to three
years. We used 12 animals for the preference tests with Western music, ten animals for the preference
tests with Chilean and Western music, ten animals for the preference tests with Chilean, Peruvian and
Western music, and ten animals for the music vs. silence experiment. We used experimentally naïve
animals in each year. The experimental protocols were conducted according to the German guidelines for
the care and the use of animals in laboratory research (§8, Abs.1, 25.05.1998), and all experiments were
performed in accordance with the European Communities Council Directive of November 1986
(86/609/EEC).
Apparatus. The experimental chamber was a 120 × 39 × 70 cm white box (Figure 1) with
separate speakers at each end. Two photo-sensors connected to each speaker (one at 3 cm and the other at
16 cm from the speaker) were affixed to the sidewalls of the chamber. Two music sticks (Intenso MP3
player) continuously played music but the relay circuit connected to the photo-sensors (either one at 3 cm
or one at 16 cm) could switch on the output of the music sticks to a speaker only when the animal crossed
one of the photo-sensors paths. A start box (31 × 31 × 31 cm) with a guillotine door was connected to the
chamber. Behavior of the subjects was recorded through a video camera (WV-CP480, Panasonic) above
the experimental chamber and analyzed after the test using the EthoVision software. The chamber was
divided into three areas, namely the left, central and right areas. The start box opened into the central area.
The left and right areas (20 cm from the each speaker) were the approximate space in which the subjects
could hear the music.
Stimuli. The two Western classical music pieces used were the Toccata and Fugue in D minor
(BWV 565) (J. S. Bach), which is played by pipe organ, and The Rite of Spring (I. Stravinsky), which is
played by orchestra. The Chilean music was “Gracias a la Vida” played with charango (stringed
instrument) by Ethnophonic Ensemble and the Peruvian music was “El condor pasa” played with quena
Watanabe et al. 203
(traditional flute). The reason that we selected these pieces by Bach and Stravinsky is that we had used
them in previous animal experiments (Otsuka et al, 2009; Shinozuka et al., 2013; Watanabe et al., 2009;
Watanabe & Nemoto, 1998), thus allowing us to compare the results with our previous experiments. As
for the Chilean and Peruvian music, we selected these particular pieces for two reasons. First, the music is
played with folk instruments, and not Western instruments. Second, in searching for Chilean and Peruvian
music on the Internet, these pieces were often retrieved, suggesting that they are relatively common
pieces. Because the length of the music pieces differed markedly due to the different types of music, we
recorded 20 s clips from each piece into a music stick MP3 player. These sounds were repeatedly played,
but animals could hear the sound only when they stayed in the music areas and crossed the sensors. The
loudness at the photo-sensor was 5870 dB for the Toccata and Fugue, 5971 dB for The Rite of Spring,
60–69 dB for “Gracias a la Vida” and 60–70 dB for “El condor pasa.Thus, there were no systematic
differences in loudness between the music types.
Figure 1. Schematic of the preference test. The smaller box is the start box. The dashed lines indicate the area in which the
animals could hear the music.
Procedure. The procedure consisted of adaptation and preference test phases. During the
adaptation phase the animals were placed in a start box for two minutes then released into the test
chamber and allowed to move freely around the chamber for five minutes with no auditory stimuli.
Testing started on the day after adaptation. The subjects were placed in the start box for 2 min
and then released into the chamber. They were allowed to move around the chamber for 10 min, during
which the two speakers presented them with the two different types of music whenever they activated the
photo-sensors. For half of the subjects, one music piece was presented from the left speaker and the other
music piece from the right speaker. This orientation was reversed for the remaining subjects. We carried
out preference testing twice a day, at 9:00 in the morning and at 14:00 in the afternoon. The music at each
speaker was reversed in the afternoon session. Thus, each animal received a particular stimulus from both
the right and left speakers in one day to neutralize possible side preference.
Statistical Analysis. We used time spent (s) within 20 cm from each speaker as an index of
preference and employed two-tailed paired t-tests to assess the results from each preference experiment.
In the South American folk and Western music comparison, data from the South American vs. Bach and
the South American vs. Stravinsky tests were integrated. The difference in the time spent in each music
area, 20 cm from the end wall, from the chance level (i.e., 100 s) was also examined using a one-sample t-
test.
Watanabe et al. 204
Results
Figure 2A shows the results of the Western music preference test. The subjects were placed in a
rectangular experimental chamber in which a speaker was fixed at each end wall (see Figure 1). Photo-
sensors activated each speaker to broadcast one of the two music choices when the animal was in close
proximity. We measured the time spent near each speaker during a 10 min period to detect preference
between the two music choices. The first test compared two different Western music pieces, Toccata and
Fugue in D minor (BWV 565) by J. S. Bach and The Rite of Spring by I. Stravinsky. As shown in Figure
2A, the subjects did not show a particular preference for either classical style. The two-tailed paired t-test
showed no significant difference in time spent at the two sites (t(11) = 0.11, p = .91, 95% CI [-64.93,
58.53]). One animal consistently stayed more than 60% of the total time in the music areas at the right
music area. A one-sample t-test revealed no significant difference from the chance level in the time spent
in the Bach area (t(11) = 0.49, p = .64, 95% CI 95% [-52.24, 81.54]) or in the Stravinsky area (t(11) =
0.59, p = .56, 95% CI [-48.27, 83.96]). Thus, degus did not show selective preference for either Western
music style.
Figure 2. Musical preference in Degus (Experiment 1). A) Degus did not show selective preference for Bach or Stravinsky.
Degus preferred Chilean folk music to the Western music (B) and also preferred Peruvian folk music to the Western music (C).
D) They also preferred the Chilean to the Peruvian music. The broken line indicates chance level time spent in each music area.
Vertical bars indicate SE. *p < .05, **p < .01.
Watanabe et al. 205
The second test examined preference between the Chilean folk instrumental music piece “Gracias
a la Vida” and each of the two Western music pieces (Figure 2B). There was a significant difference in
time spent near the Chilean and either of the Western music pieces (two-tailed paired t-test, t(18) = 2.14,
p = .04, 95% CI [1.51, 177.56]). There was a significant difference from the chance level in time spent in
the Chilean area (t(18) = 2.89, p = .01, 95% CI [25.50, 160.74]), but no significant difference in time
spent in the Western area (t(18) = 0.19, p = .85, 95% CI [-34.50, 41.67]). Thus, the degus displayed
preference for Chilean folk music over Western classical music.
Figure 2C shows the results of the third test in which we compared the Peruvian folk instrumental
music piece “El condor pasa” to each of the two Western music pieces. There was a significant difference
in time spent near the Peruvian music vs. the Western music pieces (two-tailed paired, t-test t(18) = 2.60,
p = .02, 95% CI [26.03, 244.06]). There was a significant difference in time spent in the Peruvian area
from chance (t(18) = 2.76, p = .02, 95% CI [28.54, 209.68]), but no significant difference for time spent
in the Western area (t(18) = 0.92, p = .37, 95% CI [-52.27, 20.39]). Thus, degus displayed preference for
Peruvian music over Western music.
The last test compared the response to the Peruvian and Chilean Instrumental folk music used in
the previous test (Figure 2D). There was a significant difference in time spent near the Chilean and
Peruvian music (two-tailed paired t-test, t(10) = 2.48, p = .03, 95% CI [13.85, 254.25]). There was a
significant difference from the chance level in time spent in the Chilean area (t(9) = 3.41, p = .01, 95% CI
[37.18, 183.95]) but no significant difference in time spent in the Peruvian area (t(9) = 0.64, p = .54, 95%
CI [-54.54, 97.86]). Thus, degus appeared to display preference for Chilean music over Peruvian music to
some extent.
Experiment 2: Preference Between Music and Silence
Experiment 1 demonstrated degus’ selective preference for different types of music, revealing
that they stayed in the Chilean or Peruvian music areas longer than they did in the Western music areas.
In addition, they stayed at the Chilean or Peruvian music areas longer than would be expected by chance,
suggesting that they preferred this music rather than that they stayed in those areas in order to escape from
the Western music. To confirm this preference, Experiment 2 compared time spent in a music area with
that in an area without music. The same apparatus and music as used in Experiment 1 were employed in
this study. Subjects were ten experimentally naïve male degus less than one year old. The procedure was
identical to that in Experiment 1, except that one of the music areas did not present music. Because there
were four different music pieces, each subject underwent eight tests.
Results were analyzed in three different ways. The first is comparison of time spent in the music
area with that in the area without music with a paired t-test. The time spent in the music area was
compared with the chance level staying time (i.e., 100 s) using a one-sample t-test. Finally, time spent in
each music area was analyzed by one-way ANOVA and Shaffer’s modified sequential rejective
Bonferroni procedure.
Results
Figure 3 presents the results. There was a significant difference in time spent between the Chilean
music and silence areas (t(9) = 2.80, p = .02, 95% CI [11.60, 110.06]), between the Bach and silence areas
(t(9) =2.80, p < .02, 95% CI [11.60, 110.06]), and between the Stravinsky and silence areas (t(9) = 2.84, p
= .02, 95% CI [-98.94, -11.28]). However, there was no significant difference between the Peruvian
music and silence areas (t(9) = 1.25, p = .24, 95% CI [-48.60, 168.95]). The degus preferred the Chilean
music to silence, but preferred silence to Bach or Stravinsky. They also showed no selective preference
for Peruvian music or silence.
When comparing time spent with the chance level (100 s), we found a significant difference from
the chance level in time spent in the Chilean music area (t(9) = 3.49, p = .007, 95% CI [17.11, 79.95]),
Bach area (t(9) = -4.47, p = .002, 95% CI [-59.10, -25.74]), and Peruvian area (t(9) = -2.481, p = .03, 95%
Watanabe et al. 206
Figure 3. Music preference to silence (Experiment 2). Dark bars indicate time spent in music area and open bars those in the
silence area. Broken line indicates chance level time spent in music area. Vertical bars indicate SE. *p < .05, **p < .01.
CI [-40.03, -16.06]). However, time spent in the Stravinsky area did not significantly differ from the
chance level (t(9) = -1.87, p = .09, 95% CI [-12.76, 136.89]).
One-way ANOVA of time spent in the music areas revealed a significant effect of the music (F
(3, 39) = 6.45, p = .002). Shaffer’s modified Bonferroni procedure gave a significant difference between
Chilean and Bach (t(9) = 6.49, p = .0001) or Stravinsky (t(9) = 4.43, p = .002), and between Peruvian and
Bach (t(9) = 2.45, p = .04) or between Peruvian and Stravinsky (t(9) = 2.74, p = .02). There was no
significant difference between Chilean and Peruvian (t(9) = 0.37, p = .72) or between Bach and
Stravinsky (t(9) = .87, p = .41). Thus, the degus preferred Chilean and Peruvian music to the Western
music.
Discussion
The present results are the first demonstration of a music style preference in degus. The degus
prefer South American folk instrumental music to Western music. They did not show selective preference
for either Western music style, but showed preference for Chilean music over Peruvian.
Because the degus preferred the Chilean music not only to the Western music but also to the
silence, it seems clear that they actively preferred the Chilean music and that their selection was not the
result of trying to escape from the Western music, which had an aversive effect on them. The lack of a
preference for Western music in degus accords with previous research on other animal species, with the
exception of songbirds. It is interesting that the degus avoided the Western music. In a previous
experiment with Java sparrows, some birds showed an avoidance of Stravinsky but a preference for Bach
(Watanabe & Nemoto, 1998). They also preferred silence over Stravinsky. Chimpanzees preferred
African and Indian music (Mingle et al., 2014), but did not show a preference for Japanese music. It is,
however, premature to conclude that these data reveal their general preferences. Furthermore, Sumatran
Watanabe et al. 207
orangutans did not show a preference for Mongolian Tuva throat singing over Western music (Ritvo &
MacDonald, 2016), but because orangutans are not Mongolian animals and the researchers did not
examine Sumatran music, it remains unclear whether orangutans prefer native folk music in Sumatra over
Western music.
We have to point out three possible factors in the present experiments. First, we used degus of
different ages (ranging from one to three years) but did not find any systematic differences according to
age. Second, all of the subjects in the present study were male. Although both males and females
produced a variety of sounds and there are no sex differences in the role of singer and receiver (a
phenomenon found in songbirds), it is still possible that degus show sexually dimorphic vocalization. For
example, Wied’s black-tufted-ear marmosets (Callithrix kuhlii) showed sex-dependent variations in
vocalization (Smith, Birnie, Lane, & French, 2009). Thus, it is possible that female degus showed
different musical preferences. Third, side preference might affect the results. Consistent preference for
one side might result in no apparent preference for music. In one sense, strong side preference indicates
absence of music preference or overshadowing weak music preference by the side preference. We found
only one subject showing a consistent side preference in Experiment 1 and no subjects showed more than
60% side preference in Experiment 2. Thus, the side preference did not affect the results.
Because music is a quite complex stimulus, the present experiments cannot clarify which aspect
of the music has reinforcing properties. It is also premature to conclude that the degus prefer Chilean
music “in general” or that they dislike Western music “in general, but the present results display the
presence of musical preference in degus. One possible explanation for the preference of degus for South
American folk music is based on their complex auditory communication. However, in contrast to Java
sparrows that also have complex auditory communication, the degus’ preference appears to be restricted
to the South American music as far as we know.
Physical properties of the environment produce a particular soundscape (biophony and
geophony). Development of folk music by native peoples may be influenced by the sound scape of their
living area, and nonhuman animals living in that area may have similarly developed preference for the
particular acoustic stimuli based on the sound scape. Biomusicologists investigate the links between
acoustic configurations in nature and the evolution of human music (Wallin, Bjorn, & Brown, 2001). For
example, similarities between the sounds of the Dzanga-Santgha rain forest to music of the Ba’Aka
people (Sarno, 1996), as well as the influence of the rhythms and melodies of rain striking vegetation and
traditional music of the Yamanomi (Krause, 2012) are pointed out. Although the explanation of degus'
musical preference in terms of biophony is speculative, the present study may suggest that some animals
may prefer human music produced by people who share the biophony and geophony with such animals.
Acknowledgements
This research was supported by Japan Society for the Promotion of Science (25118001), German
Science Foundation DFG (SFB 779) and the German-Israeli Science Foundation (#1114-101.4/2010).
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... American folk music over Western classical music; moreover, they did not show a preference between two Western classical music choices (Watanabe et al., 2018). Although some species have shown a preference for these non-Western music styles, more research is needed to understand if different acoustic patterns predict preferences in other species. ...
... Because all three gorillas showed a lack of preference for piano sounds, we replaced this category of sound in the last four phases with drum sounds. We anticipated the gorillas would enjoy these sounds due to their tendency to drum on their own chests or on objects in their environment to produce drumming sounds, and because some animals prefer sounds and music from their natural environments (Mingle et al., 2014;Watanabe et al., 2018). However, the drum sounds were chosen at similarly low levels as the piano sound in the previous phases. ...
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