Domestic cats ( Felis catus ) discriminate their names from other words

Abstract

Two of the most common nonhuman animals that interact with humans are domestic dogs (Canis familiaris) and cats (Felis catus). In contrast to dogs, the ability of domestic cats to communicate with humans has not been explored thoroughly. We used a habituation-dishabituation method to investigate whether domestic cats could discriminate human utterances, which consisted of cats’ own names, general nouns, and other cohabiting cats’ names. Cats from ordinary households and from a ‘cat café’ participated in the experiments. Among cats from ordinary households, cats habituated to the serial presentation of four different general nouns or four names of cohabiting cats showed a significant rebound in response to the subsequent presentation of their own names; these cats discriminated their own names from general nouns even when unfamiliar persons uttered them. These results indicate that cats are able to discriminate their own names from other words. There was no difference in discrimination of their own names from general nouns between cats from the cat café and household cats, but café cats did not discriminate their own names from other cohabiting cats’ names. We conclude that cats can discriminate the content of human utterances based on phonemic differences.

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Domestic cats (Felis catus)
discriminate their names from
other words
Atsuko Saito1,2,3, Kazutaka Shinozuka4, Yuki Ito1 & Toshikazu Hasegawa1
Two of the most common nonhuman animals that interact with humans are domestic dogs (Canis
familiaris) and cats (Felis catus). In contrast to dogs, the ability of domestic cats to communicate
with humans has not been explored thoroughly. We used a habituation-dishabituation method to
investigate whether domestic cats could discriminate human utterances, which consisted of cats’ own
names, general nouns, and other cohabiting cats’ names. Cats from ordinary households and from a
‘cat café’ participated in the experiments. Among cats from ordinary households, cats habituated to the
serial presentation of four dierent general nouns or four names of cohabiting cats showed a signicant
rebound in response to the subsequent presentation of their own names; these cats discriminated their
own names from general nouns even when unfamiliar persons uttered them. These results indicate
that cats are able to discriminate their own names from other words. There was no dierence in
discrimination of their own names from general nouns between cats from the cat café and household
cats, but café cats did not discriminate their own names from other cohabiting cats’ names. We
conclude that cats can discriminate the content of human utterances based on phonemic dierences.
Domestic cats (Felis catus) and dogs (Canis familiaris) are the most popular companion animals; worldwide, over
600 million cats live with humans1, and in some countries their number equals or exceeds the number of dogs
(e.g., Japan: dogs: 8,920,000, cats: 9,526,000)2,3. Cats started to cohabit with humans about 9,500 years ago4; their
history of cohabitation with humans is shorter than that of dogs5, and they have been domesticated by natural
selection, not by articial selection6–8. Despite these dierences in their process of domestication compared to
that of dogs, cats too have developed behaviours related to communication with humans; for example, for human
listeners, the vocalisations of domestic cats are more comfortable than those of African wild cats (Felis silvestris
lybica)9. In addition, purring has dierent acoustical components during solicitation of foods than at other times,
and humans perceive such solicitation purrs as more urgent and unpleasant than non-solicitation purrs10. ese
facts clearly indicate that domestic cats have developed the ability to communicate with humans and frequently
do so; Bradshaw8 suggested that this inter-species communicative ability is descended from intra-species com-
municative ability.
Researchers have only recently begun to investigate cats’ ability to communicate with humans. Miklósi et
al. showed that cats are able to use the human pointing gesture as a cue to nd hidden food, similarly to dogs11.
e researchers also suggested that cats do not gaze toward humans when they cannot access food, unlike dogs.
However, a recent study revealed that cats show social referencing behaviour (gazing at human face) when
exposed to a potentially frightening object, and to some extent cats changed their behaviour depending on the
facial expression of their owner (positive or negative)12. Cats in food begging situations can also discriminate the
attentional states of humans who look at and call to them13. In addition, Galvan and Vonk demonstrated that cats
were modestly sensitive to their owner’s emotions14, and other research has indicated that cats’ behaviour is inu-
enced by human mood15,16. Further, cats can discriminate their owner’s voice from a stranger’s17. is research
evidence illustrates that domestic cats have the ability to recognize human gestural, facial, and vocal cues.
1Department of Cognitive and Behavioral Science, Graduate School of Arts and Sciences, the University of Tokyo,
3-8-1 Komaba, Meguro-ku, Tokyo, Japan. 2Department of Childhood Education, Musashino University, 1-1-20
Shinmachi, Nishitokyo-shi, Tokyo, Japan. 3Department of Psychology, Faculty of Human Sciences, Sophia University,
7-1 Kioicho, Chiyoda-ku, Tokyo, Japan. 4RIKEN Center for Brain Science, 2-1 Hirosawa, Wako, Saitama, Japan. Atsuko
Saito and Kazutaka Shinozuka contributed equally. Correspondence and requests for materials should be addressed
to A.S. (email: atsaito@sophia.ac.jp)
Received: 21 June 2016
Accepted: 20 February 2019
Published online: 04 April 2019
Corrected: Author Correction
OPEN
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In contrast to cats, numerous research studies have shown the ability of domestic dogs to communicate with
humans. Dogs are skilful at reading human communicative gestures, such as pointing (reviewed in Miklósi &
Soproni18). Dogs can dierentiate human attentional states19–22 and distinguish human smiling faces from blank
expressions23. ey are also capable of using some human emotional expressions to help them nd hidden food
and fetch objects24,25.
Although the majority of prior studies have focused on visual communication between humans and dogs26,
some studies have investigated the dog’s ability to respond to human vocalisations. For example, the pitch of a
human voice aects dog behaviour27: dogs obey high-pitched voices to a greater extent than low-pitched voices.
Dogs can discriminate expressions of emotion with voice28, and obey a command with angry voice more slowly
than with happy voice. Dogs trained to sit and come in response to tape-recorded commands change their perfor-
mance when the phonemes of commands are changed29. Many dog owners believe their dogs understand about
30 utterances30. Extensively trained dogs are able to dierentiate 200–1000 human words or labels31,32. e ability
to understand human verbal utterances is also shown in other species, such as apes33, dolphins34, and parrots35;
however, whether such an ability exists in domestic cats remains untested.
In the present study, we investigated the ability of domestic cats to discriminate human verbal utterances. Cats
are sensitive to dierences in human voice characteristics17. Some owners insist that their cats can recognize their
own names and words related to food. erefore, we can make the following hypothesis: cats can discriminate
words uttered by humans from other words—especially their own names, because a cat’s name is a salient stim-
ulus as it may be the human utterance most frequently heard by domestic cats (cats kept by humans) and may be
associated with rewards, such as food, petting, and play.
We conducted experiments in cats’ homes, using a habituation-dishabituation method, as in our previous
study17. In general, dogs’ ability to recognize human utterances are tested using command and retrieval tasks31,36.
ese tasks require pre-training, and the training of cats to perform on command would require a lot of eort
and time. On the other hand, habituation-dishabituation method enabled us to measure cats’ natural reactions
during a single visit, without extensive training. To test the hypothesis, we presented four dierent words serially
as habituation stimuli, then presented the cats’ own names as test stimuli. If the cats were habituated to the other
4 words and dishabituated to their own names, a rebound response to the presentation of their own names would
be observed, indicating the ability to discriminate their own names from other words.
We conducted four experiments to test the hypothesis. In Experiment 1, we investigated whether cats can dis-
criminate their own names from general nouns with the same length and accents as their own names. If cats can
discriminate their own names from other words by using phonetic characteristics other than length of or accent
of stimuli, cats habituated to the other 4 words should show dishabituation when hearing their own names. e
test cats were living either with no other cats or with a small number of other cats. In this experiment, although
we equalized the familiarity of the nouns, the relative familiarity of names and other nouns was markedly dif-
ferent, that is, cats heard their own names more frequently than other nouns. erefore, cats discriminated their
own names depending both on phonetic characteristics and on familiarity. In Experiment 2, we investigated cats’
ability to discriminate their own names from other cats’ names, by using cats living with 4 or more other cats. It
can be assumed that the test cats were exposed to the other cats’ names as well as their own names; stimuli were
prepared using cohabiting cats’ names. en, in Experiment 3, we examined eects of multiple-cat living envi-
ronments on discrimination of general nouns and cats’ own names, similar to Experiment 1. In Experiments 2
and 3, we tested cats both from ordinary households and from a ‘cat café’, a business establishment where visitors
can freely interact with cats. In Experiments 1 to 3, stimuli used cats’ owners’ own voices, because they exhibit a
marked response to their owner’s voice17. However, this leaves open the possibility that cats can discriminate their
own names only when their owners utter them. us, in Experiment 4, we tested whether cats can discriminate
their own names from general nouns even when unfamiliar persons utter them; if they showed discrimination
ability in this experiment, we would take them to recognize their own names based on common phonetic char-
acteristics in human verbal utterances.
Results
Behaviour score. e upper panels of Fig.1 summarise the cats’ responses to the stimuli, as scored by the
experimenter. rough all the experiments, more than half of the cats responded to voice stimuli by moving
their ears and heads; fewer than 10% of the cats demonstrated vocalisation, tail movement, and displacement.
is trend did not dier contingent on whether stimuli were nouns, other cats’ names, or tested cats’ own names.
Fisher’s exact test revealed that number of cats which showed orienting response (moving ear and/or moving
head) were signicantly higher than which showed communicative response (vocalization and/or tail movement)
in all trials from Experiment 1 to 4 (Supplementary TableS1).
e total scores (Fig.1 lower panels) were moderately correlated with the average response magnitude eval-
uated by the raters, as shown in the next section (Spearman’s rank correlation, ρ = 0.70, P < 0.001; ρ = 0.61,
P < 0.001; ρ = 0.64, P < 0.001, ρ = 0.60, P < 0.001 for Experiments 1, 2, 3, and 4, respectively). us, the raters’
evaluations of the response magnitudes might have partly depended on the number of simultaneously occurring
responses by the cats.
Response magnitude. In Experiment 1, the raters’ evaluations revealed that eleven out of the 16 test cats
decreased their average response magnitude from noun 1 to noun 4. ese cats were considered to have suc-
cessfully habituated to the general nouns vocalised by the owners. en, nine out of the eleven habituated cats
increased their response magnitude from noun 4 to their own name. Group-level analysis using a generalized
linear mixed model (GLMM) revealed a signicant eect of stimulus category (F(1,10) = 11.18, P = 0.007),
indicating eleven habituated cats signicantly increased in response magnitude from noun 4 to their own name
(t(10) = −3.34, P = 0.007, Fig.2a). us, habituated cats dishabituated when they heard their own names.
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In Experiment 2, 15 out of the 34 test cats decreased average response magnitude from name 1 to name 4, and
were considered to have successfully habituated to stimuli consisting of the names of other cohabiting cats. e
ratio of successfully habituated cats was dierent between the ordinary households and the cat café (ordinary
households: 6 out of 24, cat café: 9 out of 10; χ2 = 9.60, df = 1, P = 0.002). Although the ratio of successfully habit-
uated cats from ordinary households is very low, we analysed the data from these six cats because of methodolog-
ical restriction. We added housing environment (ordinary households or cat café) as a xed eect for group-level
analysis. GLMM revealed a signicant eect of interaction (stimulus category * environment; F(1,13) = 8.26,
P = 0.013). All six habituated cats from ordinary households increased their response magnitudes from name
Figure 1. Response style to vocal stimuli in overall cats. Upper panels: Behaviour observed in response to voice
stimuli and the percentage of cats that expressed each behaviour in (a) Experiment 1, (b) Experiment 2, (c)
Experiment 3, and (d) Experiment 4. Black solid lines indicate orienting response. Black dashed lines indicate
communicative response. Gray solid lines indicate displacement. Lower panels: Mean total behavioural scores
for all cats in (a) Experiment 1, (b) Experiment 2, (c) Experiment 3, and (d) Experiment 4. Error bars indicate
SEs.
Figure 2. Mean magnitude of responses to each voice in habituated cats in (a) Experiment 1, (b) Experiment
2, (c) Experiment 3, and (d) Experiment 4. Error bars indicate SEs. Asterisks indicate signicant dierences
(P < 0.05).
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4 to their own names. Post-hoc analysis revealed that response magnitudes to stimuli for cats’ own names were
signicantly higher than those for name 4 in these six habituated cats (t(13) = −3.43, P = 0.005, Fig.2b). In con-
trast, only three out of nine habituated cats from the cat café increased their response magnitudes from name 4 to
their own name. e response magnitudes to cats’ own names did not dier from those to name 4 in these nine
habituated cats (t(13) = 0.35, P = 0.732, Fig.2b). Signicantly higher response was also seen in household cats
compared to café cats in response to own name (t (20.24) = −2.39, P = 0.027), but not in response to noun 4 (t
(20.24) = 0.38, P = 0.705, Fig.2b).
In Experiment 3, following the results of Experiment 2, we again included the environment as a xed eect.
Fourteen out of the 20 household cats decreased average response magnitude from noun 1 to noun 4. Seven out
of nine café cats decreased average response magnitude from noun 1 to noun 4. ese cats were considered to
have successfully habituated to the stimuli consisting of spoken nouns. In contrast to Experiment 2, interaction
of stimulus category * environment was not signicant (F (1,19) = 1.52, P = 0.233). A nal model only included
the eect of stimulus category (F (1,20) = 6.05, P = 0.023). irteen out of the 21 habituated cats increased their
response magnitude from noun 4 to their own name. e response magnitude to cats’ own names was signif-
icantly higher from that to noun 4 in these 21 habituated cats (t(20) = −2.46, P = 0.023, Fig.2c). us, these
habituated cats dishabituated when they heard their own names.
In Experiment 4, the raters’ evaluations revealed that 20 out of the 33 test cats decreased their average response
magnitude from noun 1 to noun 4; these cats were considered to have successfully habituated to the general nouns
vocalised by unfamiliar persons. en, 13 out of the 20 habituated cats increased their response magnitude from
noun 4 to their own name. Group-level analysis revealed a signicant eect of stimulus category in twenty habit-
uated cats (F(1,19) = 4.41, P = 0.049), who dishabituated signicantly when they heard their own name uttered
by an unfamiliar person as compared to noun 4 (t(19) = −2.10, P = 0.049, Fig.2d).
We also analysed habituated cats’ sum of behaviour score (total score) to test whether number of responses
simultaneously elicited in response to a vocal stimulus increased from trial 4 (noun or other cat’s name) to trial
5 (test cat’s name). However, unlike response magnitude, signicant increase in the total score was not observed
except for Experiment 2 (Supplementary Fig.S1). is result suggests that qualitative analysis of behaviour with
present/absent manner is less sensitive to detect dishabituation. It is conrmed that eectiveness of quantitative
analysis with the response magnitude coded by blind raters.
Discussion
In Experiments 1, 3, and 4, cats that habituated to general nouns with the same length and accent as their own
names dishabituated to their own names. is was true both when their owner’s voice was presented (Experiments
1 and 3) and when the unfamiliar person’s voice was presented (Experiment 4), in spite of the fact that cats distin-
guish owners’ voices from unfamiliar persons’ voices17. ese results show that cats can identify their own names
from other words that consisted of the same number of mora but with dierent phonemes when they are uttered
both by familiar person and by unfamiliar person. e results of Experiment 2 suggest that cats from ordinary
households discriminate their own names from those of cohabiting cats but that cats from a cat café may not.
From the results of all experiments, it thus appears that at least cats living in ordinary households can distinguish
their own names from general words and names of other cats. is is the rst experimental evidence showing cats’
ability to understand human verbal utterances.
How can we explain this ability and behaviour on the part of the cats? eir own names must be one of the
most-heard human utterances by cats. If they have no meaning, frequently experienced stimuli should be habitu-
ated and not elicit reaction from cats. However, the results of our experiment were to the contrary; thus, the asso-
ciation between hearing their names and receiving rewards or punishments might aect the behaviour of cats.
is implies that cats’ names can be associated with rewards, such as food, petting, and play, or with punishments,
such as taking them to a veterinary clinic or to a bath. Sometimes, owners who keep multiple cats will call all of
their cats’ names at the same time. In that situation, a cat may associate both its own name and those of cohabiting
cats with reward. ese situations could explain the results of Experiment 2: the ratio of ordinary household cats
that successfully habituated to names of other cohabiting cats was very low (6 out of 24). ere is a possibility
that cats housed with other multiple cats may associate other cats’ names with rewarding or unpleasant events.
However, in some situations, for example, when the owner wishes to take it to a veterinary clinic, or to pet a cat,
they may call only one cat’s name. Taking them to clinic should be a stressor. Petting could be rewarding to the
cat37, although depending on the cats’ personality, it could also be a stressor38. ese situations would facilitate a
cat’s learning to discriminate its own name from those of other cats.
If cats associate their own name with rewards or stressors, it is reasonable to think that they react to their
name. In these experiments, cats responded to owner vocalisation not with communicative behaviour (vocal-
isation and tail moving)39 but just with orienting behaviour (ear moving and head moving)40. is tendency
replicated that reported in our previous study17. is may be caused by the dierence between the situation where
we conducted the experiments and the natural situation. In normal reward or stress situations, name calling by
owners may elicit more dynamic, or communicative reaction from cats.
Next, we consider the results from the cat café. e café cats did not discriminate their own names from the
names of cohabiting cats, though their performance in the discrimination of their own names from general nouns
did not dier from that of ordinary household cats. e social environment may explain this dierence in results.
Many dierent humans visit cat cafés, and since the cats’ names are listed in cafés, visitors can call the names of
the cats. However, the way names are called may vary by visitor (e.g., intonation may vary); such a condition may
hinder cats in discriminating their name from those of other cats. Or, café cats may hear their name mentioned
along with other cat names frequently without accurate reward discrimination by visitors. For example, if a visitor
calls cat A, but cat B approaches to the visitor and cat B gets petting and treats instead of cat A. ese situations
would make name discrimination less relevant for these cats. Additionally, the number of cohabiting cats may
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have aected the results. Usually, the number of cats in a cat café is greater than the number in an ordinary house-
hold. Further, because we conducted the experiment in only one cat café, we cannot assure their generalisability
or reach a denitive conclusion.
Nevertheless, this study has demonstrated that cats can discriminate human utterances based on phonemic
dierences. Although such discrimination is acquired without explicit discrimination training, instead emerging
from the patterns of natural daily communication between humans and cats, we may utilise this ability positively
for cats’ quality of life. For example, perhaps we can get cats to learn that dangerous objects or places are referred
to by specic utterances. is work has shed new light on the ability of cats to communicate with humans; further
clarifying cats’ abilities with respect to cat–human communication will potentially enhance the welfare of both
humans and cats.
Methods
Subjects. In Experiment 1, the participants were 16 domestic cats (8 males and 8 females; age range: 1–11
years, mean age: 3.69 years, SD = 3.01) living with 11 families (three male and eight female owners), each of whom
lived with 2 or fewer other cats. By breed, there were 12 mongrels, two Scottish Folds, an American Shorthair, and
a Himalayan. Fieen of the cats had begun to live with their owner within one year of birth, and one cat when it
was 5 years old. Fieen of the cats were neutered (one female was not).
In Experiment 2, 34 domestic cats (16 males and 18 females) each of which was living with 4 or more other
cats, participated. Twenty-four cats were owned by four families and the remaining 10 were part of a ‘cat café’, a
business establishment where visitors can freely interact with cats. e cats had six female owners (two owners
were members of the same household). Of the 34 cats, there were 24 mongrels, three LaPerms, a Devon Rex, a
Somali, a Scottish Fold, an American Curl, a LaPerm Shorthair, a Tonkinese, and a Munchkin. eir ages ranged
from 0.5 to 10 years (mean age: 5.51 years, SD = 2.95), and the ages when they began to live with their owners
ranged from birth to 36 months aer birth. All cats were neutered.
In Experiment 3, participants were 29 domestic cats (16 males and 13 females) living with 4 or more other
cats. ey were kept by three families and one cat café, which had four female owners; of the 29 cats, 9 were from
the cat café. Breeds were 21 mongrels, three LaPerms, a Scottish Fold, an American Curl, a LaPerm Shorthair,
a Tonkinese, and a Munchkin. eir ages ranged from 1 to 11 years (mean age: 6.48 years, SD = 3.29). e ages
when they began to live with their owners ranged from birth to 36 months aer birth. All cats were neutered. Of
these 29 cats, 26 cats participated in Experiment 2. Interval between Experiment 2 and 3 was at least 2 weeks.
In Experiment 4, participants were 33 domestic cats (14 males and 19 females) living with from 0 to 5 other
cats. Of them, 30 cats were kept in 21 families (2 male and 19 female owners) and 3 cats were kept in univer-
sity laboratories. Of the 33 cats, 24 were mongrels, two LaPerms, two American Shorthair, a Scottish Fold, a
Himalayan, a Russian Blue, a Norwegian Forest Cat, and a Bengal. eir ages ranged from 1 to 17 years (mean
age: 6.48 years, SD = 4.14), and the ages when they began to live with their owners ranged from one month
to 36 months aer birth. All cats were neutered, excepting one female. Of these 33 cats, 3 had participated in
Experiment 1 and 5 had participated in Experiments 2 and 3. Experiment 4 was conducted about 3 years aer
Experiment 3. In all experiments, all cats were indoor only except one, and cats were not subjected to food dep-
rivation during the study period. Detailed information is presented in the electronic Supplementary Material
(TablesS2–S5).
Apparatus and Stimuli. Before the experiments began, for each cat, ve sound stimuli consisting of human
voice were recorded. One stimulus consisted of a human calling the cat’s name. e other four stimuli consisted of
a human vocalising four dierent general nouns (Experiments 1, 3, and 4) or four names of other cats living with
the test cats (Experiment 2). For Experiments 1, 2, and 3, the stimuli were recorded by the owners of the tested
cats. For Experiment 4, the stimuli were recorded by two women unfamiliar to the tested cats. Each owner was
instructed to vocalise the cat’s names as he/she normally would; if the owner usually called the cat by a nickname
instead of its real name, the nickname was used. In Experiments 1, 3, and 4, four dierent general Japanese nouns
were selected from the list of Matsumoto41; all nouns had the same level of familiarity and were emotionally neu-
tral. e numbers of moras and accents in the nouns were the same as in the cat’s name. Speakers were instructed
to vocalise the nouns with the same intonation and manner as they vocalised the cats’ names. In Experiment 2,
four of the other cohabiting cats’ names were recorded similarly to the test cats’ names. e orders of presentation
of general nouns and cohabiting cats’ names were pseudo-randomized.
We recorded the vocalisations with a handheld digital audio recorder (ZOOM H2 Handy Recorder) in WAV
format; the sampling rate was 44100 Hz with 16-bit quantisation. e sound stimuli were adjusted to the same
volume level using sound editing soware (Adobe Soundbooth CS4 or Adobe Audition CS6). During the exper-
iment, the handheld recorder was used to present the stimuli through a speaker (Sony SRS-Z100), which was
hidden from the test cat. e distance between the test cat and the speaker was about 3 m, and the volume of
the voices was approximately 65 dB at 3 m from the speaker. A video camera (Sanyo DNX-CA9 or Panasonic
HX-WA20) placed in front of the test cats recorded their reactions during the playback of the stimuli.
For Experiment 1, 3, and 4, the discriminant analysis was performed to conrm that there was no implicit
dierence in acoustic characteristics between noun and name stimuli. Vocal stimuli for cats which showed dis-
habituation (habituated cats with increasing response magnitude from noun 4 to own name: N = 9, 13, and 13
in Experiment 1, 3, and 4, respectively) were selected for analysis. Six acoustic parameters were extracted from
each vocal stimulus by using Praat 6.0.43 soware: total duration (sec), mean pitch (Hz), f1 (Hz), f2 (Hz), f3
(Hz), and mean intensity (dB). en the discriminant analysis was applied with IBM SPSS Statistics 21. Above
acoustic parameters were set as independent variables, and type of stimulus (noun or name) was set as a group.
As a result of the analysis, high values of Wilks lambda were obtained (Experiment 1, Wilks lambda = 0.930,
χ2 = 2.884, df = 6, P = 0.823; Experiment 3, Wilks lambda = 0.821, χ2 = 11.866, df = 6, P = 0.065; Experiment 4,
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Wilks lambda = 0.979, χ2 = 1.294, df = 6, P = 0.972), indicating that it was dicult to discriminate between noun
and name stimuli by using implicit acoustical characteristics as a cue.
Procedure. Experiments 1, 2, and 3 were conducted from December 2012 to November 2013; Experiment
4 was conducted from September 2016 to April 2017. All experiments were held in each owner’s home or in the
cat café, wherever the particular cats lived. e experimenter waited until cats were calm before beginning the
experiment. During the experiment, the owners were out of their cat’s sight. We used a habituation-dishabituation
procedure in which prepared stimuli were played serially with a 15-s inter-stimulus interval (ISI); the order of
presentation was word 1, word 2, word 3, word 4, and test cat’s name. e number of habituation stimuli and the
ISI were improved versions of those used in a previous study17. Cats’ responses to the stimuli were expected to
decrease during the presentation of words 1 through 4 due to habituation; then, if the cats could discriminate
their own names from the other words, responses were expected to increase again when their own names were
presented, due to dishabituation. e experiment lasted around 1.5 minutes. During presentation, the test cat
was not actively isolated from cohabiting cats, to keep the test cat’s behaviour natural. ere was no need for any
interruption in the experimental sessions due to cohabiting cats’ behaviour.
All procedures related to animal care and experimentation in our research adhered to the ‘Guidelines for
the treatment of animals in behavioural research and teaching’ as published by the Association for the Study
of Animal Behaviour in Animal Behaviour 71, 245–253 (2006) and to the ethical guidelines of the University
of Tokyo. e study was approved by the Animal Experiments Committee of the Graduate School of Arts and
Sciences of the University of Tokyo and by the Animal Experiments Committee of Musashino University.
Behavioural analysis. Video-recordings of cats’ responses were trimmed to show from 5 s before stimulus
onset to 10 s aer stimulus oset, using Adobe Premiere CS6. Vocalisation of the words and cats’ names in the
clips was masked by pure tones to facilitate blind evaluation of the clips. In total, 80, 170, 145, and 165 clips were
created for Experiments 1, 2, 3, and 4, respectively.
We conducted two kinds of analyses to investigate the cats’ response styles and magnitudes, as in our previous
study17. e rst analysis describes response style. One of the experimenters (KS) observed the clips of each cat
in random order and classied the cat’s responses to the stimuli into ve categories: ear moving, head moving,
vocalising, tail moving, and displacement; each category is described in Table1. ese categories cover orienting
responses (ear moving and head moving)40 and communicative responses (vocalising and tail moving)39. Each
category was scored separately as 0 (absent) or 1 (present) for each clip, to determine the proportion of cats show-
ing each response in each presentation trial. en, the summed score was calculated as the total score for each
clip, to enable examination of the correlation between the numbers of categories occurring simultaneously and
response magnitude rated by blind raters (described in the next section). To check for reliability, the other exper-
imenter (AS) observed a random selection of one-fourth of the clips and scored the cats’ behaviours. e indices
of concordance were 0.75 for ear moving, 0.81 for head moving, 0.99 for vocalising, 0.97 for tail moving, and 0.99
for displacement (κ = 0.76, P < 0.001 for overall observation).
e second analysis was conducted to examine response magnitude. Raters who were blind to the stimuli and
their presentation order scored each cat’s responses in the clips, which were presented in random order within
each test cat. In Experiment 1, there were ten blind raters (6 men and 4 women; mean age = 21.7 years), whereas
in Experiment 2 and 3 there were six blind raters (all women; mean age = 27.5 years), and in Experiment 4, nine
blind raters (one man and 8 women; mean age = 22.9 years). e raters were instructed to compare each cat’s
behaviours before and aer the presentation of each stimulus and rate the magnitude of the cat’s responses to the
stimuli from 0 (no response) to 3 (marked response). Kendall’s coecient of concordance showed signicant,
moderate concordance among the raters (W = 0.73, df = 79, P < 0.001; W = 0.73, df = 169, P < 0.001; W = 0.65,
df = 144, P < 0.001, W = 0.55, df = 164, P < 0.001 for Experiments 1, 2 3, and 4, respectively).
Mean response magnitude was calculated for each video clip and used for subsequent analysis. GLMM was
applied using the lme4 package version 1.1–13 on R soware version 3.4.1. Stimulus category (Experiment
1; noun 4 v. own name, Experiment 2; other cat’s name 4 v. own name, Experiment 3; noun 4 v. own name,
Experiment 4; noun 4 v. own name) was set as a xed eect. Environment (ordinary households v. cat café) and
interaction of stimulus category * environment were also set as xed eects for Experiments 2 and 3. Subjects
were set as a random eect. Gaussian distribution with identity link function was specied for lmer function.
en, post-hoc analysis was conducted using the step function in the lmerTest package version 2.0–33; the step
function reduced non-signicant xed eects and determined a nal model. e random eect (subjects) was
manually kept regardless of signicance, to control pseudo-replication.
Data Availability
e data supporting this article are included in Supplementary Electronic Information.
Category Description
Ear moving Any change in ear(s) angle from ear root
Head moving Any change in head angle at the neck
Vocalising Any vocalisation
Tail moving Any movement of tail between its root and tip
Displacement More than one step of displacement of both
hind paws in any direction
Table 1. Descriptions of categories for behavioural scores.
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Acknowledgements
We wish thank the owners of the cats and Marsa Smith (cat café). We also thank Saho Takagi, Minori Arahori,
and Hitomi Chijiiwa for helping with data collection, Hiroki Koda for helping with auditory stimulus analysis. A.
Saito and T. Hasegawa were granted funding by Kakenhi (No. 25118003). A. Saito was supported with Incentive
Allowance for Dissemination of Individual Research Results by Sophia University.
Author Contributions
A.S., Y.I. and T.H. conceived and designed the experiments. A.S., K.S. and Y.I. performed the experiments and
analysed the behavioural data. K.S. conducted statistical analysis. A.S. and K.S. prepared the manuscript. K.S.
analysed auditory stimuli. A.S. and T.H. organized the research project. All the authors read and approved the
nal manuscript.
Additional Information
Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-019-40616-4.
Competing Interests: e authors declare no competing interests.
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