Categorization in Macaca fascicularis.

Categorization in Macaca fascicularis

Kanthi Arum Widayati

GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2012

STATEMENT LETTER
I hereby declare that dissertation entitled Categorization in Macaca
fascicularis is original result of my own research supervised under advisory
committee and has never been submitted in any form at any institution before. All
information from other authors cited here are mentioned in the text and listed in
the reference at the end part of the dissertation.

Bogor, February 1st, 2012

Kanthi Arum Widayati
Student ID G362070051

ABSTRACT
KANTHI ARUM WIDAYATI. Categorization in Macaca fascicularis.
Supervised by BAMBANG SURYOBROTO, AKICHIKA MIKAMI, ACHMAD
FARAJALLAH.
Categorization is an ability to group individuals or events into different
classes mediated by conceptualized mental images. There are several levels of
categorization and within a taxonomy the levels are nested. At the most concrete
level of categorization, all or most members of the category shared common
physical attributes that differ from other categories. The higher the level of
category, the fewer common attributes between members of the group. In addition
to humans, the ability to categorize has also been proposed in animals. One
example of categorization in animal is species discrimination. Using matching-tosample task, present experiment tested ability of the long-tailed macaque (Macaca
fascicularis) in discriminating dichotomous-stimuli of different animals. The
species has been shown to be able to see photos as representations of real object
so I used facial photos of humans and animals for the stimuli. First, I tested their
ability to classify humans and macaques into separate group. Second, I tested their
ability to discriminate their conspecific from other macaques. And the last, I tested
whether the subjects were able to discriminate non-human animals from humans.
In all of these experiments I found that the subjects showed high performance in
categorizing objects, even when I discarded details of visual informations, such as
color and local shapes. The ability to identify objects with reduced representation
of physical properties means the subjects were able to generalize attributes of
members of the group. This would indicate that the subjects created a higher level
abstraction. On the other hand, in discriminating intrageneric macaque species I
found that they were able to extract uniqueness of each species. More over, I also
found that the subjects were able to put photos of non-human animals that shared
very few similarities in physical percepts into one group. I suggested that the
subjects could create a more abstract concept based on non-percepts relations as a
basis to put the objects into one category. Thus, I concluded that M. fascicularis
were able to perform multiple levels of categorizations.
Key Words: Categorization, Conceptualized mental
discrimination, Macaca fascicularis, Matching-to-sample task

image,

Species

ABSTRAK
KANTHI ARUM WIDAYATI. Kemampuan kategorisasi Macaca
fascicularis. Dibimbing oleh BAMBANG SURYOBROTO, AKICHIKA
MIKAMI, ACHMAD FARAJALLAH.
Kategorisasi adalah kemampuan seseorang untuk mengelompokkan
individu-individu atau kejadian-kejadian ke dalam kelompok yang berbeda.
Kemampuan kategorisasi didukung oleh konsep yang dibentuk di otak. Ada
beberapa tingkat kategorisasi. Pada tingkat yang paling dasar, semua anggota
kelompok memiliki banyak persamaan ciri fisik dibandingkan dengan kelompok
lainnya. Semakin tinggi tingkat kategorisasi, persamaan ciri fisik di antara
anggota kelompok semakin sedikit. Selain manusia, hewan diduga juga memiliki
kemampuan kategorisasi. Salah satu contoh kategorisasi adalah diskriminasi
spesies hewan yang berbeda. Penelitian ini bertujuan untuk mengetahui
kemampuan diskriminasi spesies pada Macaca fascicularis. Monyet ini memiliki
kemampuan untuk melihat foto sebagai representasi dari benda sebenarnya.
Penelitian ini menggunakan stimulus berupa foto-foto wajah dari manusia dan
hewan dengan metode matching-to-sample task. Saya melakukan tiga eksperimen
utama. Pertama, saya ingin menguji apakah M. fascicularis dapat
mengelompokkan manusia dan makaka ke dalam dua kelompok terpisah. Kedua,
saya ingin mengetahui apakah monyet mampu membedakan antara individuindividu spesiesnya dengan individu-individu dari spesies lain. Terakhir, saya
ingin menguji apakah monyet mampu membedakan antara manusia dan hewan
lain non manusia. Hasil penelitian menunjukkan bahwa M. fascicularis mampu
memisahkan dan mengelompokan objek-objek ke dalam kategori yang diujikan
walaupun saya menyingkirkan informasi visual dari stimulus seperti warna dan
bentuk. Kemampuan monyet untuk mengidentifikasi objek berdasarkan sedikitnya
informasi fisik mengindikasikan adanya kemampuan dalam membentuk konsep
yang lebih abstrak. Selain itu, pada eksperimen ke dua, monyet saya berhasil
menemukan ciri-ciri unik dari masing-masing spesies makaka. Saya juga
menemukan bahwa monyet berhasil mengelompokkan foto-foto hewan yang
berbeda secara fisik ke dalam satu kelompok. Saya menduga bahwa monyet
dapat membuat konsep yang lebih abstrak berdasarkan hubungan non-perseptual
sebagai dasar untuk mengelompokkan objek ke dalam satu kategori. Saya
menyimpulkan bahwa dalam mengkategori hewan, M. fascicularis menggunakan
beberapa tingkatan abstraksi.
Key Words: Kategorisasi, Konsep, Diskriminasi spesies, Macaca fascicularis,
Matching-to-sample task

SUMMARY
KANTHI ARUM WIDAYATI. Categorization in Macaca fascicularis.
Supervised by BAMBANG SURYOBROTO, AKICHIKA MIKAMI, ACHMAD
FARAJALLAH.
Categorization is an ability to group individuals or events into different
classes mediated by conceptualized mental image. There are several levels of
categorization and within a taxonomy the levels are nested. At the most concrete
level of categorization, all or most members of the category shared common
physical attributes that differ from other category. The higher the level of
category, the fewer common attributes between members of the group.
In addition to humans, the ability to categorize has also been proposed in
animals. In addition to humans, the ability to categorize has also been proposed
for animals. Being able to identify, visually or otherwise, a new object as a
member of a category is an advantage for animals. It should help them to
distinguish between food or non-food, or to discriminate between species of
animals. This species discrimination is important to prevent hybridization among
species.
Using matching-to-sample task, present experiments tested the ability of
the long-tailed macaque (Macaca fascicularis) in discriminating dichotomousstimuli of different animals. The species has been shown to be able to see photos
as representations of real objects so we used facial photos of humans and animals
for the stimuli. Using operant conditioning method, I trained monkeys to associate
matching to sample stimuli against a distractor stimulus. First, I showed monkeys
a sample stimulus as a reference to be matched. To ensure that the subjects paid
attention to the sample stimulus, they had to touch it and for this they received
reward that they find beneath the stimulus. Next, I presented a matching stimulus
and a distractor stimulus side-by-side. The subjects must choose one of them.
When the subjects chose the matching stimulus, they received a piece of food as a
reward; the response was counted as a correct one. When they chose the distractor,
they did not get any rewards. Subject's motivation for reward warranted the choice
of the matching stimulus. The location of matching and distractor stimuli on the
tray was arranged pseudorandomly. I blocked every 20 trials into one session and
measured their correct rate. If the subject chose the matching stimuli higher than
90% in a session, I interpreted they were able to associate matching to sample
stimuli. Logically, this may be inferred as the subject had developed dichotomic
concepts of matching against distractor. When they showed this competence, they
went to test phase. I expect that monkeys were able to transfer their concept
learned in training phase into new stimuli by showing the same performance in
both baseline and test trials. In the test phases, I introduced new matching and
distractor stimuli and see their response into the stimuli. I did three major
experiment. First, I tested their ability to classify human and macaques into
separate group. Second, I tested their ability to discriminate their conspecific from
other macaques. And the last, I tested whether the subjects able to discriminate
non-human animals from human.
In all of these experiments I found that the subjects showed high
performance in categorizing objects, even when I discarded details of visual
informations, such as color and local features. The ability to identify objects with

reduced representation of physical properties means that the subjects are able to
generalize attributes of members of the group. This would indicate that the
subjects have ability to create a higher level abstraction. On the other hand, in
discriminating intragenic macaque species, I found that they were able to extract
uniqueness of each species. More over, I also found that the subjects able to put
photos of non-primates animals that shared very few similarities in physical
properties into one group. Monkeys may able to create a logical concept such as A
and non-A. I suggest that the subjects could create abstract concepts free from the
physical properties as a basis to put objects into one category. Thus, I conclude
that M. fascicularis are able to perform multiple levels of categorizations.
Key Words: Categorization, Conceptualized mental
discrimination, Macaca fascicularis, Matching-to-sample task

image,

Species

Copyright © 2012. Bogor Agricultural University.
All Rights Reserved
It is prohibited to cite all or a part of this dissertation without referring to
and mentioning the source. Citation is permitted for the purposes of education,
research, scientific paper, report, or critism writing only; and it does not defame
the name and honor of Bogor Agricultural University.
It is prohibited to republish and reproduce all or a part of this dissertation
without permission from Bogor Agricultural University.

Categorization in Macaca fascicularis

KANTHI ARUM WIDAYATI

Dissertation
submitted in partial fulfillment of the requirements for a Doctoral Degree in
Animal Bioscience Major of Graduate School of Bogor Agricultural University

GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2012

Examiners in the Close examination:
1. Dr. Entang Iskandar (Researcher, Primate Research Center, Bogor
Agricultural University)
2. Dr. Yamato Tsuji (Assistant Professor, Primate Research Institute,
Kyoto University, Japan)
Examiners in the Open examination:
1. Prof. Ir. Wasmen Manalu, Ph.D. (Professor of Faculty of Veterinery
Medicine, Bogor Agricultural University)
2. Dr. Harry Susianto (Senior Staff of Faculty of Psychology, University
of Indonesia)

ENDORSEMENT PAGE
Title

: Categorization in Macaca fascicularis

Name

: Kanthi Arum Widayati

Student ID

: G362070051

Major

: Animal Biosciences

Endorsed by,
Supervisory Committee

Dr. Bambang Suryobroto
Chair

Prof. Dr. Akichika Mikami, MD
Member

Dr. Achmad Farajallah
Member

Acknowledged by,

Chair of Major of Animal Biosciences

Dean of Graduate School,

Dr. Bambang Suryobroto

Dr. Ir. Dahrul Syah, M.Sc.Agr.

Examination date: January 25 th 2012

Graduation date:

PREFACE
The title of this dissertation is Categorization in Macaca fascicularis. The
experiment took place in the Laboratory of Zoology Departement of Biology
Faculty of Mathematics and Natural Sciences Bogor Agricultural University,
Bogor and Primate Research Institute, Kyoto University, Japan.
I want to send my gratitude to Dr. Bambang Suryobroto, Dr. Achmad
Farajallah and Prof. Dr. Akichika Mikami, MD as author’s advisors; to Mr. Adi
Surahman, Mrs. Ani and Mr. Mamat for taking care of the monkeys. To all
individuals with their unique personality in Zoo Corner (Dr. Tetri Widiyani, Sarah
Nila, S.Si, Puji Rianti, M.Si, Islamul Hadi, M.Si, Eneng Nunuz R, S.Si, Elda Irma
Kawulur, M.Si, Andi Darmawan, M.Si) for great discussion and their supports for
the experiments.
I also want to send my appreciation to Dr. Yamato Tsuji from Primate
Research Institute, Kyoto University, Dr. Harry Susianto from Faculty of
Psychology, University of Indonesia, Dr. Entang Iskandar from Primate Research
Center, Bogor Agricultural University and Prof. Wasmen Manalu, PhD from
Faculty of Veterinary Medicine, Bogor Agricultural University for improving the
dissertation.
I also want to send my gratitude to Dra. Taruni Sri Prawasti.M.Si, Dr.
Dedy Duryadi Solihin, Tri Heru Widarto, M.Sc, Dr. Dyah Perwitasari, Dr. Rika
Raffiudin, Dr. Tri Atmowidi, Msi for their support during the study.
I deeply send my gratitude to Yayasan SDM IPTEK HABIBIE CENTER
for the scholarship for academic year 2008/2009 and 2009/2010. I also want to
send my appreciation to program SANDWICH LIKE from Directorate General of
Higher Education which gave me financial support when I work in Primate
Research Institute, Kyoto University, Japan.
I also want to appreciate and gives love to Ucok, Sukhoi and Kerok for
their great performances.
Bogor, February 1st 2012

Kanthi Arum Widayati

CURRICULUM VITAE
Author was born in Bogor on 29th of September 1982 as the first child of
four from the parent, Hidayat Banjaransari and Sri Wilujeng.
In 1999, author graduated from SMUN 3 Bogor and enrolled the
Department of Biology, Faculty of Mathematics and Natural Science, Bogor
Agricultural University and graduated in 2004. At the same year, author enrolled
in the Graduate School, Study Program of Biology, Bogor Agricultural University.
In 2007, author enrolled her Doctoral Course at Bogor Agricultural University,
majoring in Animal Bioscience. In 2007, author officially accepted as a staff in the
Department of Biology, Bogor Agricultural University.

CONTENTS
Page
LIST OF FIGURES....................................................................................

xiv

APPENDIX …...........................................................................................

xiv

INTRODUCTION ….................................................................................

1

LITERATURE STUDY..............................................................................

3

Categorization in Human ................................................................

3

Categorization in Animal................................................................

3

Operant Conditioning Behavior.......................................................

5

METHODS................................................................................................

6

Subjects............................................................................................

6

Apparatus........................................................................................

6

Stimuli and Procedure.....................................................................

7

a. Human vs Macaques................................................................

10

b. Macaca fascicularis vs Other Macaques................................

11

c. Human vs Non-Human...........................................................

12

Data Analysis...................................................................................

13

RESULTS..................................................................................................

14

Human vs Macaques.........................................................................

14

Macaca fascicularis vs Other Macaques........................................

18

Human vs Non-human.....................................................................

20

DISCUSSION...........................................................................................

22

CONCLUSION..........................................................................................

27

REFERENCES.........................................................................................

28

LIST OF FIGURES
Page
1 Schematic diagram of operant conditioning match-to-sample task of
the experiment in baseline (a) and test trials (b).....................................

8

2 Example of stimuli used for Human vs Macaques experiment...............

9

3 Example of stimuli used for Human vs Non-Human experiment …......

13

4 Monkeys performances in categorizing human and monkeys in color
stimuli.....................................................................................................

15

5 Monkeys performances in categorizing human and monkeys using
black and white stimuli...........................................................................

16

6 Monkeys performances in categorizing human and monkeys using
resized stimuli.........................................................................................

16

7 Monkeys performances in categorizing human and monkeys using
black and white blurred stimuli...............................................................

17

8 Monkeys performances in categorizing human and monkeys using
resized, blurred, black and white stimuli................................................

17

9 Monkeys performances in categorizing conspecific and other monkeys
using colored stimuli..............................................................................

19

10 Monkeys performances in categorizing conspecific and other
monkeys using black and white stimuli................................................

19

11 Monkeys performances in categorizing human and non-human using
colored and black and white stimuli........................................................

21

APPENDIX
Page
1 Monkeys performance in Human vs Macaques experiments..................

32

2 Monkeys performance in M. fascicularis vs other Macaques
experiments.............................................................................................

34

3 Monkeys performances in Human vs Non-Human experiments............

35

4 Test of the similarity of the monkey performances between baseline
and test trials …......................................................................................

36

1

INTRODUCTION

We live in a world full of ever-changing objects. It is impossible for us to
memorize each and every new individuals we encountered. Our brain need to have
an ability to deal with infinite informations that is continuously coming from the
surrounding environment. One way to overcome the memory storage constraint is
to represent factual objects as conceptualized mental images. A concept concludes
a lot of informations that had been collected at the time we perceive the object and
abstracts them to assist the process of grouping individuals or events into different
categories (Rosch et al. 1976). These categories reduce the number of bits of
information to manageable classes. There are several levels of categorization and
within a taxonomy the levels are nested (Rosch et al. 1976). At the most concrete
level of categorization, all or most members of the category shared common
physical attributes that differ from other category. The higher the level of
category, the fewer common attributes between members of the group.
In addition to humans, the ability to categorize has also been proposed in
the animals. Being able to identify, visually or otherwise, a new object as a
member of a category is an advantage for the animals. It should help them to
distinguish between food or non-food, and to discriminate between species of
animal. This species discrimination is important to prevent hybridization among
species (Yoshikubo 1985, Fujita 1987, Fujita and Watanabe 1995, Fujita et al.
1997).
Present experiment aims to test the ability of species discrimination by
primates. I did three major experiments. First, I tested whether the monkeys were
able to categorize monkey individuals as a class against human individuals as
another class. Second, I tested whether they were able to discriminate their
conspecific from other macaque species. Third, I tested their ability to categorize
non primate animal as non-human class against human individuals as human
class. Previous studies showed that monkeys were able to see photos as
representations of real objects (Kyes et al. 1982). I therefore used photos of
various humans, monkeys and other animals as stimuli to infer their categorization

2
ability. The stimuli consisted of information on physical properties of the object.
The physical properties represented in photos may be modified in many ways to
alter the amount of information in the stimuli. These modified photos provide a
way to deduce levels of categorization of the monkey. Some experiments found
that the monkeys look to their conspecific longer than to non-conspecific so they
used duration of visual fixation to indicate this discriminative capability (Demaria
and Thierry 1988, Fujita 1993, Fujita and Watanabe 1995, Fujita et al. 1997).
However, although counting the fixation time is easy to be described
quantitatively, it is uncertain as to what the reaction time measures. For instance,
the longer the time could represent two facts; the monkeys likes the picture in the
stimuli, or it can be the opposite. In fact, in agonistic bouts, the amonkeys tend to
look longer to their opponent (de Waal et al. 1976). Thus, the reaction time may
better be interpreted as a measure for the attention of the monkeys and may not
carry information about species discrimination. Moreover, it is not clear whether
the monkeys are truly able to distinguish between species or their familiarity with
their own species due to experience in their life history made them see conspecific
longer. Instead of counting fixation time of each stimulus, present experiment test
their categorization ability in discriminating dichotomous-stimuli of two different
classes of animal.

3

LITERATURE STUDY

Categorization in Humans
Categorization is the ability to put an object to a group based on some
internal representations of the group (Rosch et al. 1976). The ability to categorize
objects and events and extending this behavior to new instances is fundamental to
many human activities. I sort the objects and events around us into categories,
while still being able to recognize some or all of the individuals. In general,
categorization could be divided into two levels (Behl-Chadha 1996). If the
detected physical properties of the individuals within a category are mostly
similar, we call it as basic level of abstraction (Rosch et al. 1976). For example;
we could put Asians, Africans and Caucasians into one group; that is a human
group. If the connection between members of one category is not only based on
perceptual similarity but more on relations between concepts, we call it as abstract
level of categorization (Mervis and Rosch 1975). For example, we can put rice,
bread and fruit into the food or edible group and put a chair, a plane and a soap
into the non-food group. Although it is basically divided into two levels, the
relation between each class often overlap and sometimes it is very difficult to
differentiate between classes. These levels of categorization are basic to
understand language, number and social relationship with other humans. This
ability obviously needs memory, learning and reasoning.
In humans, categorizing behavior was predicted to start at infantile age.
Quinn (1993, 2002) found that the 3-4 month old infants attended to natural
objects as though they belong to groups of basic level. The experiments used the
preferential looking procedure and measure the looking time of the pictures. The
infants tended to look at the picture of a new categories for longer period of time.
Their ability was regarded as in the basic-level of categorization.

Categorization in Animal
The field of research on the ability of animals to categorize objects was
opened by the pioneering study of Herrnstein and Loveland (1964). They showed

4
that the pigeon were able to sort photographs on the basis of whether the image
contained human being or not. It means the pigeon were able to make a class of
human and a class of non-human, which is the definition of categorization. Since
then, several studies have demonstrated categorization in other animals, most of
them used primates as models (ex: Tanaka 2001, Jitsumori and Matsuzawa 1991,
Santos 2000). Some of the researches aimed to know whether categorization
processes in the animal is based on similar processess compare to human (ex:
Farbe-Thorpe 2003, Freedman et al. 2002,2003, Hampson et al. 2004). In other
case, some studies wanted to find out the levels of categorization that could be
performed by the animals (ex: Tanaka 2000, Jitsumori and Matsuzawa 1991,
Santos 2000, Inoue et al. 2008, Vonk & McDonald 2002; Vonk & McDonald
2004). In both cases, the studies used photos of biologically significant objects,
such food vs non food, animals vs non-animals, and the last is own species vs
non-own species or species discrimination (Tanaka 2001, Jitsumori and
Matsuzawa 1991, Santos 2000, Inoue et al. 2008, Fujita et al 1995, 1997, Vonk &
McDonald 2002; Vonk & McDonald 2004).
Species discrimination is important to prevent hybridization among species
(Yoshikubo 1985, Fujita 1995, Fujita et al. 1997). Some studies were conducted to
find out which part of the body are really important to identify and categorize the
species. Those studies found that face provide information about species, sex, age
and emotion of an individual (Pascalis and Bachevalier 1988, Tomonaga 2007).
Fujita et al. (1995) demonstrated that Sulawesi macaques performed basic level of
categorization in identifying their conspecific. The stimuli used in that experiment
were photos of monkey presented sequentially. By counting the fixation time of
each stimulus, they found that the Sulawesi macaques see their conspecific longer
than non-conspecific. Thus, the photos carry specific information which could be
categorized by conspecific or non-conspecific (Fujita et al. 1995, Pascalis and
Bachevalier 1988, Tomonaga 2007). However, although the fixation time is easy
to be described quantitatively, it is difficult to draw conclusion from it. For
example, the longer reaction time could mean that monkey likes the picture in the
stimuli, or it could be the opposite. In fact, in agonistic bout, the monkeys tend to

5
look longer to his/her opponents (de Waal et al. 1976).
Looking at previous work in primates, there are some data on
categorization in great apes, M. mulatta, M. fuscata and Sulawesi macaques but
not really in long-tailed macaques (M. fascicularis). A few studies showed that M.
fascicularis were able to see photos as a representations of the real objects (Dasser
1987, Kyes et al. 1982). More over, some studies also found that those monkeys
were able to identify individual within species (Dasser 1987), read facial
expression from the drawing and could discriminate between drawings of some
bodies of old world primate species (Dittrich 1994). However, there were no
direct experiment to infer the level of categorization in this species.

Operant Conditioning Behavior
In this experiment, I used the operant conditioning methods which refers to
process in which the frequency of occurrence of the particular type of behavior
was modified by the consequences of the behavior (Reynolds 1975). In operant
conditioning, the behavior (called operant) came from animal motivation to
response to a given stimulus. The stimulus used in operant conditioning is
discriminative. In this particular experiment, monkeys were trained to choose a
specific stimulus (the plus stimulus, S+) from another alternative to get a reward.
If they choose the other (the minus stimulus, S-), they would not get any rewards.
The behavior to choose a specific card is an operant. The reward is the
consequences of the behavior and it should increase animal motivation to choose
the plus stimulus. The specific task in this operant conditioning method is
matching to sample (Miller et al. 1996) with photographs of human, macaques
and other animals as stimuli.

6

METHODS
Subjects
The subjects were two adult M. fascicularis males, named Ucok and
Sukhoi and one female named Kerok. Ucok were born in Pangandaran National
Park, with present age at least 19 years old. Kerok and Sukhoi were born in
Department of Biology, Bogor Agricultural University with ages are 14 and 9
years old, respectively. Both male monkeys were maintained at the Department of
Biology of Bogor Agricultural University. The female monkey was maintained at
Primate Research Institute, Kyoto University. They were reared in individual
cages and tested in the same cage. Experiments were conducted according to the
Guide for the Care and Use of Laboratory Animals by the National Institute of
Health, U.S.A. (1985), and the Guide for the Care and Use of Laboratory Primates
by the Primate Research Institute, Kyoto University (1986, 2002). The training
phases were held about two years for Ucok and one year for Sukhoi and two
months for Kerok depended on the ability of learning of the monkeys. The test
phase was conducted for few months for all monkeys.

Apparatus
A modified version of the Wisconsin General Test Apparatus (WGTA) was
used for the presentation of stimuli to the macaques. The apparatus used consisted
of a horizontal tray containing three shallow food-wells mounted on a portable
shelf. A sample stimulus and a matching stimulus were placed over the food-wells
so that they always associated with a food reward beneath. When setting up the
food reward between trials, an opaque screen was placed between the cage and the
experimenter to prevent animals from seeing the process. The eye of the
experimenter was covered with sunglasses, so the monkey could not use eye
direction of the experimenter as cue to find the matching stimulus. To control the
animal’s motivation level, animals were deprived of food after 5 pm until the next
morning before the day of a training session or a test session. Foods were
provided either during or after the experiments.

7
Stimuli and Procedure
I assessed the ability of M. fascicularis in categorizing objects by
conducting three experiments. First, Human vs Macaques experiment, aimed to
test the ability of M. fascicularis in categorizing monkeys and humans into two
different conceptual classes. Second, M. fascicularis vs Other Macaques
experiment, to test the ability of M. fascicularis in categorizing conspecific
differently from M. mulatta or M. fuscata. And the last one, Human vs Non
Human experiment, to test the ability of M. fascicularis in categorizing various
kinds of animal differently from human.
Fujita et al. (1995) demonstrated the ability of species discrimination of
Sulawesi macaques using photos as stimuli. Other studies of categorization also
used photos (Demaria and Thierry 1988, Fujita 1993, Fujita and Watanabe 1995,
Fujita et al. 1997) but those former studies did not control feature of the photos so
it is difficult to delineate which component of the photo provides informations to
do categorization. Each species of the animal possess distinctive non-facial,
physical features; for instance, posture and proportion of legs which may or may
not be present at the photo frames. For that reason, I used facial photos and
controlled the background color by changing it into green. Because of limitation
of visual fixation time to infer species discrimination as noted in Introduction,
present experiments tested their categorization ability based on dichotomic
discrimination of one species against other. To do this, I employed match-tosample task that often were used in working memory experiments (Miller et al.
1996, Rao et al. 1997) and later to study categorization experiments (Freedman et
al. 2002; Hampson et al. 2004; Inoue et al. 2008; Tanaka 2001). Using operant
conditioning method, at first, the monkeys were trained to respond only to
particular stimulus, not based on previous experience in their life. Every trial
consisted of two presentations. The first presentation shows sample stimulus, and
the second matching and distractor stimuli side by side. The sample and matching
stimuli always belonged to a same category that dichotomically differ to the
distractor (Figure 1). I assumed that each stimulus was independent from each
other so a stimulus could be defined as a matching stimulus in one trial and could

8
be a distractor in other trial depended to the sample stimulus.
I trained the monkeys to associate sample and matching stimuli against
distractor stimulus. First, I showed the monkeys a sample stimulus as reference to
be matched (Figure 1a). To ensure that the subjects paid attention to the sample
stimulus, they had to touch the sample stimulus and for this they received reward
that they may find beneath the stimulus. Next, I presented side-by-side matching
and distractor stimuli which one had to be chosen by the subjects. When the
subjects chose the matching stimulus, they received food as a reward; the
response was counted as a correct one. When they chose the distractor, they did
not get any rewards. Subject's motivation for reward warranted the choice of the
matching stimulus. I repeated the trials consecutively with inter-trial intervals for
about 30 second. The location of matching and distractor stimuli on the tray was
arranged pseudorandomly. I blocked every 20 trials into one session and measured
their correct rate. If the subjects chose the matching stimuli higher than 90% in a

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session, it means they were able to associate matching to sample stimuli. Then I
introduced a set of new photographs of the same human and the same monkey. I
repeated this training until the same criterion was reached (90% correct rate in 3
continuous sessions). After the monkey cleared the criterion of third set, I
introduced the photographs of a different human and a different monkey. This
procedure was repeated for six set of new humans and monkeys. After the monkey
cleared all of these training phases, I started the test session. At this stage,
logically, this may be inferred as the subjects had developed dichotomic concepts
of matching against distractor. When they showed this competence, they went to
test phase (see below for details) where the matching photos were new ones. If the
subjects were able to transfer the learned concept to novel stimuli, it proved that
they could categorize.

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a. Human vs Macaques
In this experiment, I assessed categorization ability of M. fascicularis to
discriminate monkeys from humans using facial features. Both primates possess
distinctive physical features, notably different shape of face and the presence of
hair in the monkey's face which is absent from human. These distinctions would
allow us to safely infer the discriminative ability on the different conceptual class
of human and monkey. For monkey category, I used photos of both sexes of three
species of macaques, those were M. fascicularis, M. mulatta and M. fuscata. For
human category, I used female and male photos. Some of the female heads were
covered by scarf. Nevertheless, all pictures showed the whole face.
For training phase, sample and matching stimuli were the same and
monkey's stimuli were always M. fascicularis (see Figure 2b and 2d). For
practical reason, I used 90% correct rate as threshold to infer subject's competence
in discriminating human from monkey categories. Furthermore, to make sure they
have achieved this ability, they have to show it in three successive sessions.
To test if a subject could apply the learned concept of human and monkeys
to new individuals, I changed the pictures of matching stimulus with different
individuals that belonged to the same category as the sample stimuli (eg. Figure
2c , 2e, 2g); for example, if the sample stimulus is monkey b then the matching
stimulus is monkey d. The subject should compare the novel matching stimulus to
the available distractor. If the subject associate the sample and the differentpicture of matching stimuli, I may infer that they put those two pictures into one
class that dichotomically differs from the class of distractor. This would evidenced
they transfer the human and monkey concepts to novel stimuli. This would prove
their categorization ability. For practical reason, the test sessions consisted of
baseline and test trials in certain proportion. In the baseline trials, the stimuli is the
same as in training trials so this would provide a reference to compare the test
trials.
The stimulus photos give subjects various informations about color and
shape of each species. Thus, I expected that subjects used informations from
detailed physical properties of sample and matching stimuli to perform basic level

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of categorization. To test whether the subjects has levels of abstraction, I extended
the experiment to see whether the subjects would still have the ability to identify
objects if the informations on the physical properties of the stimuli were reduced.
For this reason, I deviced extended experiments that stripped off certain visual
information from the stimuli. First, I took color off the photos and presented it in
black and white. In the next step, I tried to test whether size of the stimuli could
affect the performance of the subjects in categorizing humans differently from
monkeys. I thought that altering the size of the photos would also perspectively
change the shape of the figures. I reduced the size of the stimuli to one quarter of
the original and showed it to monkeys. In this case, I tested them using pairs of
photos of colored human and M. fascicularis. I continued the test by giving the
subjects the blurred, black and white, original size photos of human and
macaques. These photo manipulations aimed to test whether the subjects could
categorize human differently from monkeys though the stimuli lack informations
about color and shape. In my last attempt to ascertain whether the subjects could
categorize human differently from macaques, I reduced the size of the black and
white, blurred photos of human and monkeys to one quarter of the original size.
The complete and modified physical properties of the photo stimulate the varied
amount of information perceived on the objects. Thus, by comparing subject's
responds to the stimuli, I may interpret their level of categorization. In total, I
used 82 photos as the stimuli for the test.

b. Macaca fascicularis vs Other Macaques
In this experiment, I assessed categorization ability of M. fascicularis to
discriminate their own species from other species of macaques. In this
experiment, I used several facial photos of M. fascicularis, M. mulatta and M.
fuscata. I did this in two conditions, that is in color and black and white.
After the first experiment of Human v Macaques, I assured that monkeys
have mastered to do maching-to-sample task. In this intra-generic experiment I
used two paradigms, that is, M. fascicularis vs M. mulatta and M. fascicularis vs
M. fuscata. Since those macaques shared almost similar facial feature, I wondered

12
whether subjects were able to find the difference between each species and use it
to group them into separate class. In test phase, I changed the pictures of matching
stimulus with different individuals that belonged to the same species. Same as the
first experiment, the test session consisted of certain proportion of baseline and
test trials. In baseline trials of both paradigms, the photos of matching stimuli
were the same to sample stimuli. In total, we used 40 photos as the stimuli for the
test.

c. Human vs Non-Human
In this experiment, I assessed categorization ability of M. fascicularis to
discriminate various kinds of animals from human using facial features. In this
experiment, I used several photos of human (see the first experiment) and nonprimate animals, such as mammals, reptiles and amphibians (Figure 3). I
wondered whether subjects were able to ignore the physical difference of various
animals and creating a new class, that is non-human group. As in the second
experiment, I did this in color and black and white. In test trials, I changed the
pictures of matching stimulus with different individuals that belonged to the same
category as the sample stimuli; for example, if the sample stimulus was monkey
2b then the matching stimulus was animal 3a. The subjects should compare the
novel matching stimulus to the available distractor. If the subjects could associate
the sample and the different-picture of matching stimuli, I may infer that they put
those two pictures into one class that dichotomically differs from the class of
distractor. This would mean they are able to categorize non-human animals
differently from human. The baseline stimuli were the same stimuli used in
Human vs Macaques experiment (see Figure 2). In total, I used 68 photos as the
stimuli for the test.

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Data Analysis
In this experiment, monkeys have to respond to particular stimuli. I
defined the response of monkeys as correct when they choose matching stimulus,
and false when they choose distractor stimulus. This binomial responses was
dependent on stimuli presented in baseline and test trials; I therefore treat baseline
and test trials as independent variables and the effect of individuals in the analysis
as random effect. Thus, I used Generalized Linear Mixed Model (GLMM,
Venables and Ripley 2002) using R software version 2.10.1 (R Development Core
Team 2010) to analyze the discrete, binomial data.
In test phase, I also conducted several baseline trials using stimuli that
used in training phase and test trials using new stimuli. I expect that monkeys
were able to transfer their concept learned in training phase into new stimuli by
showing the same performance in both baseline and test trials. For that reason,
using GlmmPQL, I compare their results in both trials.

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RESULTS
Human vs Macaques
As mentioned before, this experiment aimed to test the ability of monkeys
in categorizing monkeys and humans into two different conceptual classes. The
two classes were presented dichotomously as matching and distractor stimuli. In
baseline trials, the photos of matching stimuli were the same to sample stimuli. As
expected, in this trials all subjects could associate matching to sample stimuli.
They showed high performance of choosing the correct stimuli at the proportion
around 90% of the trials. Because the matching stimuli were always of a different
category to the distractor stimuli, it might mean they developed different and
mutually exclusive concepts of human and monkeys. These results provided a
reference to test whether subjects could transfer the newly developed mental
concepts to identify new individuals. I did this by changing the matching stimulus
with pictures of different humans and different kinds of monkeys. In this test, I
found that all subjects associate sample stimuli to new individuals of matching
stimuli (Figure 4, Appendix 1, Appendix 4). This same result to baseline
(glmmPQL, p=0.15; Venables and Ripley 2002) would indicate that the subjects
were able to correctly identify new individuals as members of its own class or of
human class. This would mean that monkeys categorized humans differently from
monkeys.
Since the stimuli used in the above experiment contained information on
physical properties (that is, shape and color) of the objects, I suggested that the
subjects used those properties to create a concept (see Discussion for detailed). I
was wondering whether the subjects would still have the ability to identify objects
if the informations of the physical properties were reduced. I expected that the
subjects will be able to gain informations from the stimuli with a reduced physical
properties and combine them with previous concepts they learned before and this
would lead them to create higher level of abstraction. For this reason, I deviced
three experiments that stripped off certain visual information from the stimuli.

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First, I took color off from the photos and presented it in black and white. I found
that the subject's performance in both baseline and test phases were the same
(glmmPQL, p=0.19) (Figure 5, Appendix 1). This result indicates that even
without color, the subjects categorized humans differently from monkeys.
In the next step, I tested whether size of the stimuli could affect the
performance of the subjects in categorizing humans differently from monkeys. I
thought that altering the size of the photos would also perspectively change the
shape of the figures. I reduced the size of the stimuli to one quarter of the original
and showed it to monkeys. In this case, I tested them using pairs of photos of
colored human and M. fascicularis. I found that the subject's performance in both
baseline and test phase were the same (glmmPQL, p=0.85)(Figure 6, Appendix 1,
Appendix 4). It means the subjects did not affected by the reduction in size of the
stimuli.

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17

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I continued the test by giving the subjects the blurred and black and white original
size photos of human and macaques. These photo manipulations tested whether
the subjects could categorize human differently from monkeys though the stimuli
lack informations about color and shape. I found that the subjects were able to
categorize human separately from monkeys. Their performance in both baseline
and test phases were the same (glmmPQL, p=0.53) (Figure 7, Appendix 1,
Appendix 4).
In my last attempt to find out whether the subjects could categorize human
differently from macaques, I reduced the size of the black and white, blurred
photos of human and monkeys to one quarter of the original size. I found that
even in a condition lacking important physical informations, such as color, shape
and size, their performance in both baseline and test phases were the same
(glmmPQL, p=0.57) (Figure 8, Appendix 1, Appendix 4). It means that the
subjects could categorize human differently from monkeys. Overall, by seeing the
high performance of the subjects when tested by the manipulated stimuli, I
concluded that they were able to develop higher level of abstraction based on
available concepts they have learned before.

Macaca fascicularis vs other macaques
This experiment aimed to test the ability of monkeys in categorizing M.
fascicularis differently from other macaque species. In this experiment I used two
paradigms, that is, M. fascicularis vs M.mulatta and M. fascicularis vs M. fuscata.
In baseline trials of both paradigms, the photos of matching stimuli were the same
to sample stimuli. Thus, all subjects could associate matching to sample stimuli at
around 90% of trials. Similar with human vs macaques experiment, the matching
stimuli were always of a different category to the distractor stimuli, so this result
might mean they developed different and mutually exclusive concepts between
M. fascicularis and the other macaques; that is M. mulatta and M. fuscata. This
result provided a reference to test whether the subjects could use the developed
concepts of M. mulatta to identify new individuals of the species; the same also
true for M. fuscata. I did this by changing the matching stimulus with pictures of

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different individual of monkeys. I found that all subjects associate sample
stimulus to new individuals of matching stimuli (Figure 9, Appendix 2, Appendix
4). This same result to baseline (glmmPQL, p=1) indicate that the subjects were
able to correctly identify new individuals as members of their respective class.
This would mean that the subjects categorized M. fascicularis differently from the
two other macaque species.
As in the first experiment, I ascertained this categorization ability by
taking color off the photos used in the stimuli and presented it in black and white
color. I found that all subjects associate sample stimulus to black and white
version of the matching stimuli (Figure 10, Appendix 2, Appendix 4). This same
result to baseline (glmmPQL, p=1) would indicate that even without color, the
subjects could also categorize M. fascicularis differently from other macaques.

Human vs Non-Human
This experiment aimed to test ability of monkeys in categorizing human
differently from non-primate animals. In this experiment, I used several photos of
human and non-primate animals, such as mammals, birds and reptiles and
amphibians. I tested the subjects using both color and black and white photos. For
baseline trials, I used same photos of human and M. fascicularis that used in
baseline trials of Human vs Macaques experiment. I found that the subjects did
high performance in test trials, similar to that in baseline trials (glmmPQL, p=0.65
for colored stimuli and p=0.70 for black and white stimuli) (Figure 11, Appendix
3, Appendix 4). It means that they were able to maintain concept of human and
developed new concept about non-human.

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DISCUSSION

Fujita and his coworkers (1993, 1995, 1997) found that monkeys see their
conspecific longer compared to other species, and this were thought to lead to
species discrimination. His works using various kinds of pictures of macaques
give us an insight into how monkey learn to categorize via species discrimination.
However, the methods that he used could be doubted; for example, there were
several interpretation for how monkeys see conspecific in longer duration. First,
the longer reaction time might mean that monkey's attention varied in response to
different pictures regardless of their species membership. Second, they were
mostly wild born so they have already familiar with their own species since
opportunities to learn facial properties of memb

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