Proceedings of the 2006 IEEE/RSJ
International Conference on Intelligent Robots and Systems
October 9 - 15, 2006, Beijing, China

Designing simple and effective expressionof robot’s primitive minds to a humanSeiji YAMADA

Takanori KOMATSU

National Institute of Informatics
2-1-2 Hitotsubashi, Chiyoda, Tokyo, 101-8430 JAPAN
Email: seiji@nii.ac.jp

Future University-Hakodate
116-2 Kamedanakano, Hakodate 041-8655 JAPAN
Email: komatsu@fun.ac.jp

Abstract— This paper describes designing expression of robot’s
primitive minds in a simple and effective way. Although expression of robot’s minds like internal states is becoming a major
topic in human-robot interaction, few studies to propose a policy
to design concrete expression. In this paper, we propose thedesign policy, called “SE2PM: Simple Expression to Primitive
Mind”, and fully implement expression of robot’s minds basedon the design policy, then investigate the effectiveness of them.
SE2PM implies that intuitive and simple expression like beepsound from a simple robot (e. g. a mobile robot) is more effective
than complicated behaviors from a complex robot (e. g. a doglike pet robot) in informing its primitive minds to a human.
Thus, in order to investigate the validation of our SE2PM policy,
we implement two robots: a mobile robot based on Mindstorms
with mind expression of beep sound, and a pet robot, AIBO,
with mind expression of complicated behaviors. We also conduct
a psychological experiment with participants to compare the twodifferent expression, and the results eventually support SE2PM
policy.

I. I NTRODUCTION
Home robots like Roomba1 , AIBO2 have started to moveout of robotics laboratories and into people’s homes in recent
years. Almost all of them are for entertainment to a user andthe remaining ones are for a simple home task like roughsweeping by themselves. However home robots for a hometask are expected to rapidly increase from now on because
most of users never require just the entertainment and strongly
need a robot to achieve various home tasks. In this situation,
since a robot often can not achieve such a task by itself, itneeds a way to ask a user to help it. For example, even thoughsweeping is a very simple home task, a robot can not remove
a heavy obstacle like a chair or a table in order to sweep thefloor under it, so a robot would ask user’s help and a user
would have to remove it for the robot.
The significant problem here is how to express the robot’sinternal state to a user. We call such an internal state the robot’s
mind because it may correspond to a human state of mind
in the theory of mind[1]. We consider the expression should
be designed depending on the robot’s appearance because weintuitively think the appearance significantly influences humanimpression and interpretation of robot’s expression. Although
it is a important problem to design how a robot expresses
1 http://www.irobot.com/
2 http://www.sony.net/Products/aibo/

1-4244-0259-X/06/$20.00 ©2006 IEEEand inform its mind to a human depending on the appearance,
few studies on designing robot’s expression in such a way
have been done thus far. We are able to consider one of thesimplest ways to express the mind is to use verbal communication with speech synthesis and it may be independent ofa robot’s appearance. However, such verbal communication
significantly depends on natural language and needs additional
equipment like a speech synthesis module. Hence we focusedon nonverbal communication because psychological researches
also show that nonverbal communication has rich information.
In this paper, we propose a policy to design expression ofrobot’s mind depending on its appearance, called “SE2PM:
Simple Expression to Primitive Minds”, that means that a designer should design simple information with a simple appearance to express primitive robot’s minds. We actually apply thisSE2PM policy to express primitive minds of a robot with an
appearance of a simple mobile robot implemented with LEGO
Mindstorms, and design beep sound as simple expression.
We consider this beep sound is a promising way to express
primitive minds like negative, positive, and neutral because it
was reported to be effective in human-computer interaction[7].
To compare with our proposed expression, we implement a
pet robot, AIBO, which has a complicated appearance andcan express its primitive minds by executing some complex
behaviors with motion, light and sound. We investigate theeffectiveness of SE2PM policy by a psychological experiment
to compare the two robots with participants. Finally we obtain
results to support our SE2PM policy and find out it is avalid policy to design expression of robot’s primitive minds
depending on the appearance.
Different types of social robots have been developed toassist with various tasks in our daily life[11][4]. In general,these robots have a particular appearance that is designed
similar to that of humans or pet animals, i.e., beings thatare familiar to us. Most humans who interact with theserobots notice the familiarity of their appearances, and thismakes it easier for them to communicate with these robots
actively[2]. However, a robot’s appearance should not be thesole focus; designing the robot’s expressed minds to enable
better communication with users is also important. Based on
this concept, Ono and Imai[13] developed an interactive robotthat can express behaviors associated with frustration when it
encounters certain obstacles that interrupt its pathway.

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Mori pioneered relationship between a appearance andmovement in a robot with the uncanny valley[10]. His uncanny
valley described a robot becomes more uncanny as it becomes
more similar to a real human. Although the uncanny valley
does not directly imply SE2PM, the basic consideration isclose to it. Duffy also discussed anthropomorphism of a robot
with much insight[3], and he pointed out various important
issues on relationship between anthropomorphism and a robot.
In contrast with their studies, we propose the concrete design
policy to express primitive minds, actually design them andverify the effectiveness.
Matsumoto et al. proposed a “Minimal Design” for interactive agents[9]; that is, agents should only have a minimalist
appearance or express a minimal amount of information tousers. In fact, they applied this minimal design policy indeveloping their interactive robots “Muu”[12] and life-likeagent “Talking Eye” [15]. Moreover, Reeves & Nass showed intheir “Media Equation” studies that anthropomorphized agentsor computers might induce natural behaviors in humans, suchas those that we direct towards other people[14].
Although the policies of minimal design and Media Equation are similar to our hypothesis that a detailed and likableappearance and expressed information are not vital for informing us of primitive minds, they lack a concrete strategy, like“which kinds of appearance should agents have” or “whichkinds of information should agents express to users.” In
contract, our study provides a concrete strategy for designinginteractive agents by clarifying the relationship between theagent’s appearance and its expressed information so that theuser understands these primitive minds.
Kanda et. al[5] investigated human behaviors to humanoid
robots with two different appearances, ASIMO, Robovie,
through a systematic psychological experiment with participant. As results, they found statistical significant difference
in non-verbal behaviors like movement of arms, greeting
motions, not in verbal behaviors. Their results are interesting,however they do not propose any design policy to express
robot’s minds.

Fig. 1. Concept of our hypothesis about the relationship between robot’s
expressed information and its appearance.

of the robot’s primitive minds(Fig. 1). If this hypothesis tosupport SE2PM was shown to be true, various interactive
robots could be developed, ones that can interact naturallywith users without the need for a huge budget to create acomplex and likable appearance for these robots.
III. R EALIZING SE2PM WITH BEEP SOUNDS AND MOBILEROBOT- LIKE APPEARANCE
According to SE2PM, we are able to design actual expression and appearance of a robot for express primitive minds.
In this study, we realize simple expression with beep sounds
and simple appearance with a mobile robot-like appearance.
This realization is based on the following reasons.
Beep sounds: Komatsu[7] showed that people can estimate different primitive minds by means of simple beeplike sounds with different durations and inflections. He
reported the following results.
1) Sounds with decreasing intonation with shorter durations were perceived as a “positive mind.”
2) Sounds with increasing intonation regardless of its
durations were perceived as a “negative mind.”
3) Flat sounds with longer durations were estimated asa “neutral mind.”
These beep sounds were simple but intuitive and effective
information for the user to understand primitive minds.
We applied these beep sounds as expressed informationfrom robots that did not have a life-like appearance andbehaviors.
• Mobile robot-like appearance: Mindstorms is a mobile
robot, thus Mobile robot-like appearance is utilized without additional cost.
•

II. SE2PM: D ESIGN POLICY TO EXPRESS ROBOT ’ S
PRIMITIVE MINDS TO A HUMAN

We propose a policy to design expression of robot’s minds
depending on the appearance, called “SE2PM: Simple Expression to Primitive Mind”. SE2PM means that a designer should
design simple information from a robot with a simple (e.g.
robot-like) appearance to express its primitive minds. On theother hand, this policy is based on the following hypothesis
about the relationship between the robot’s appearance and its
expressed information on the user’s understanding of primitiveminds: A robot with a human-like or animal-like appearance
expressing complex and likable actions or behaviors is more
confusing for users and is not really effective for conveying primitive minds. On the other hand, an agent with amore typical robot appearance conveying subtle expression[8],which show simple but intuitive information that can be more
readily understood, is much more effective for informing users

IV. E XPERIMENT
A. Overview
As already mentioned, our SE2PM hypothesized that a robot
with a typical robot appearance expressing simple but intuitive
information regarding primitive minds is much more effectively to users. We then conducted a psychological experiment
to investigate this hypothesis.

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Fig. 2. Three robots utilized in this experiment: AIBO, Mindstorms, and PC(from left to right).

1) Expressing Minds: We focused on the following threeprimitive minds as primitive and important ones for a user:
negative, positive, and neutral. These three minds correspondto a valence value that is the basic dimension of complex
emotions or affect[14]. These minds were briefly explained tothe participants so that they would have a rough idea of how
to recognize the minds.
• Positive Mind: Agreement, e.g., acceptance.
• Negative Mind: Disagreement, e.g., surprising, doubting.
• Neutral Mind: Hesitation, e.g., being lost for words.
These three primitive minds and interpretations were thesame as the ones used in Komatsu’s former study[7].
2) Appearance of robots: We utilized the following two
robots as robots in our experiment. One was AIBO (ESR7, SONY corporation). It is a robot that has a detailed andanimal-like appearance and behaviors. The other was Mindstorms (Robotic Invention System 2.0, LEGO cooperation). It
is an robot that has a typical robotic appearance like “Star
Wars’ R2D2.” AIBO is one of the most famous consumer pet
robots, and Mindstorms consists of LEGO blocks and Microcomputer modules. The user can then determine their preferredrobot appearance by using various types of LEGO blocks. In
addition, for a control, we utilized a normal laptop computer(Let’s Note, W2 CF-W2DW6AXR, Panasonic corporation)that was utilized to express beep sounds in the former study[7].
The reason we utilized this laptop computer (PC) as a control
was that it has a non-robot-like appearance compared withother robots (AIBO and Mindstorms). Fig. 2 shows the actual
appearance of these three robots. They were nearly the samesize.
3) Expressed Information: For expressing primitive minds
to users, AIBO expresses already prepared dog-like behaviors,
and Mindstorms and the PC express the beep sounds that were
utilized in Komatsu’s former study[7].
• Expressing information of AIBO: SONY prepared utility
software called the “AIBO entertainment player” forAIBO users, which offers about 80 basic preset motions,like “cheer up” and “good morning.” Among these motions, we chose the following six motions (two motions
for each mind) that were similar to typical dog-likebehaviors and accorded them with three primitive minds.
– Positive Mind: “Happy 1” (wagging her tail cheerfully), “Happy 3” (blinking face LED expresses
smiling face)– Negative Mind: “Angry 1” (howling action), “Unhappy 1” (moving her tail cheerlessly)– Neutral Mind: “Incline her head”, “Wondering”(looking doubtful while moving her tail flatly)• Expressing information of Mindstorms and PC: The
following six beep sounds (two sounds for each mind)
showed higher interpretation rates (more than 80%) in
the former study in each of the minds.
– Positive Mind: Two beep sounds with decreasing
intonation (One is a duration of 189ms and a decreasing transition range in the F0 value between theonset and endpoint of 125Hz; the other is a durationof 418ms and a decreasing transition range of 125Hz)– Negative Mind: Two beep sounds with increasing
intonation (One is a duration of 189ms and anincreasing transition range of 125Hz; the other is aduration of 819ms and an increasing transition rangeof 125Hz)– Neutral Mind: Two beep sounds with a flat intonation(One is a duration of 639ms; the other is a durationof 819ms)
These sounds were triangle waves generated by soundauthoring software called “Cool Edit 2000,” and they havethe same F0 average of 131Hz.
Just before AIBO expressed these behaviors to participants,
the experimenter said “Ready” to them, and then AIBO started
expressing the selected behaviors. Before Mindstorms expressed these sounds, the experimenter started moving Mindstorms backward by about 5 cm and then forward by about thesame distance. And before the PC expressed its sounds, theexperimenter flashed its display. These actions were meant totell the participants that the “stimulus is about to be expressed.”
B. Participants
The participants were 18 Japanese university students (12men and 6 women with a mean age of 21.2 years). All
participants were not familiar with AIBO, Mindstorms, andother robots in general.
C. Experimental procedure
First, the experimenter gave participants the following instructions: “the purpose of this experiment is to evaluate thethree robots by means of a questionnaire. Specifically, theserobots express certain information that includes one of threeprimitive minds (positive, negative, and neutral), and yourtasks in this experiment are to answer “which kinds of mind
were included with the expressed information,” and to tell us
your impression of these robots in the questionnaire.”2616

TABLE I
Q UESTIONNAIRE ON IMPRESSIONS OF ROBOT

Fig. 3.

Average No. of correct answers.

Q1: Did you understand the robot’s minds?
Q2: Was the expressed information easily understandable?
Q3: Did you enjoy the way that the robot expressed its information?
Q4: Do you think that this robot can be part of our daily life?
Q5: Do you think that this robot has emotions?
Q6: Do you think that you can communicate effectively with thisrobot?

Experimental settings.

18
16
14
12
10
8
6
4
2
0
AIBO
Fig. 5.

Fig. 4.

Actual experimental scene (a participant facing AIBO).

The experimenter locating behind the partition used a wireless LAN to make AIBO express its behaviors in front ofparticipants. To make Mindstorms express its beep sounds,
the experimenter played the sounds on a computer besidehim, and then the sounds were transmitted as an FM radio
wave. The FM radio tuner loaded on Mindstorms received
this radio wave and played the received sounds to participants.
For the PC, the experimenter remotely controlled it by meansof “Real VNC remote access system,” and he started playing
the beep sounds at the appropriate time. The set up of theexperiment is depicted in Fig. 3. Fig.4 is a photograph of theactual conditions in the experiment. A participant is facing
AIBO.
When the robots expressed the behaviors or sounds toparticipants, the display placed in front of them simultaneously
showed the following questions, “Did you feel that [***] wasthis robot’s mind based on this presented information?”; [***]
was the randomly selected mind among the three primitiveminds. Participants were asked to answer YES or NO on

Mindstorms

PC

Average numbers of correct answers for each robot.

the questionnaire. Specifically, each participant went through18 trials (6 parts of information x 3 minds) for each robot.
The order of presentation for the stimulus-question pairs wascounterbalanced, and all participants were assumed to havecontingent tendencies for judging each of the trials.
After finishing 18 trials with one robot, the participants wereasked to fill in a questionnaire about their impressions of theserobots. The questions are shown in table 1. After filling in thisquestionnaire, another 18 trials were conducted with the next
robot, and then again with the last one. Thus, all participants
worked with all three robots. The orders of robots (AIBO,
Mindstorms, and PC) was also counterbalanced.
V. R ESULTS
A. Can participants estimate the robot’s mind correctly?
The average number of correct answers (within 18 trials)
was calculated for each robot to determine whether or not theparticipants could estimate the robot’s minds correctly. The
results were that participants got an average of 8.50 answers
correct with AIBO, 14.33 with Mindstorms, and 13.78 answers
with the PC (5).
The results of an ANOVA showed significant differences
between these three robots (F (2, 52) = 39.71, p < .01(∗∗)),
and an LSD test revealed that significant differences existed
between AIBO and Mindstorms and between AIBO and thePC (M se = 4.6987, 5%level). Although the Mindstorms had
a higher numbers of correct answers than the PC, no significant
difference was found.

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2) Relationship B: AIBO received a higher evaluation compared with the PC: This relationship was observed in Q1 “Didyou understand the robot’s minds?” The only significant tendency was between AIBO and the PC (F (2, 51) = 3.16, p <.10(+), M se = 0.7265, 5%level). However, the average number of correct answers for the PC’s responses was significantly
higher than that for AIBO, and it was nearly the same as thatof Mindstorms. Thus, a significant gap was evident between
the effectiveness of the actual function (informing participantsof the robot’s minds) and the participants’ impressions of therobots.

AIBO
Mindstorms
PC

5

Average scores.

4
3
2
1
0
Q1

Fig. 6.

Q2

Q3

Q4

Q5

Q6

Average scores for each question in questionnaire.

From these results, it is evident that using Mindstorms or a
PC is a much more effective method of informing participantsof a robot’s minds compared with AIBO. Thus, these results
support our hypothesis of SE2PM, which is, a robot witha typical robot appearance expressing simple but intuitive
information regarding primitive minds is much more effectively
to users than a robot that has a life-like appearance expressing
more complex and likable behaviors. Although some concerns
remain as to whether our hypothesis of SE2PM will stand up
to further scientific analysis in an experiment, these results to
support SE2PM will likely have a significant impact on the
traditional design policy, which attempts to make the robot’s
appearance similar to those of humans or pets.

3) Relationship C: Order of preference in the evaluation
was AIBO, Mindstorms, and PC: This relationship was observed in Q5 “Do you think that this robot has emotions?” andQ6 “Do you think that you can communicate with this robot?”Specifically, significant differences were evident between thesethree robots (Q5: F (2, 51) = 23.64, p < .01(∗∗), M se =0.7614, 5%level, Q6: F (2, 51) = 14.56, p < .01(∗∗), M se =0.7492, 5%level). Here, AIBO received the highest evaluation,
just as in relationship A. Moreover, Mindstorms received ahigher evaluation than the PC.
4) Relationship D: No differences between the three robots:
This relationship was observed in Q2 “Was the expressed
information easily understandable?” (F (2, 51) = 1.04, n.s.).
Here, although AIBO received higher evaluations on mostquestions, there were no significant differences between the
robots.

VI. D ISCUSSION
A. Coverage of SE2PM

B. Subjective impressions of these robots
We investigated the impressions users had of these robots
by means of a questionnaire that was completed for eachof the robots after the trials. Our investigation involved theuse of an ANOVA of each of the aforementioned questions,which were answered using a six point likert scale (With lower
points indicating poorer assessment: one point was the worst
assessment, and six points was the best).
The average scores in evaluating the different robots foreach question are depicted in Fig.6. AIBO had the highest
evaluations, and the PC had the lowest. However, the results of
the ANOVA determined that four different relationships were
present between the three robots.
1) Relationship A: AIBO received the highest overall evaluation: This relationship was observed in Q3 “Did you enjoy
the way that the robot expressed its information?” and Q4“Do you think that this robot can be part of our daily
life?” Specifically, there were significant differences between
AIBO and Mindstorms and between AIBO and the PC (Q3:
F (2, 51) = 10.33, p < .01(∗∗), M se = 1.3845, 5%level, Q4:
F (2, 51) = 4.38, p < .05(∗), M se = 1.2298, 5%level). These
results stem from the fact that AIBO is already well known
as a sophisticated robot for entertainment purposes.

We conducted psychological experiment to verify the effectiveness of SE2PM design policy, and the results eventually
supported SE2PM. However these results are concerned withjust case studies and just one example of various SE2PM
realizations. Hence we need to discuss the coverage of theexperimental results.
We consider the generality as to the following. First theresults in this work show a concrete example that SE2PMbased robot design outperformed conventional one, with lifelike and complicated appearance and expression, in expressing
primitive minds. This also shows that another direction to
design effective social robot without expensive appearance andactuators.
Second, by developing various simple expression based on
SE2PM under a fixed robot-like appearance, the coverage ofSE2PM can spread more an more. For example, we also
developed and investigated a motion-based method to inform auser of robot’s minds (e.g. a trouble with the front obstacle)[6].
In the work, a simple back-and-forth behavior of a robot with asimple mobile robot’s appearance are shown effective. We canutilize this behavior as simple expression and extend simple
expression of SE2PM.

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B. What will the gap between user’s impressions and mind
estimation cause?
The results of the experiment clarified that the evaluationsof AIBO in the questionnaires were mostly higher than thoseof the other robots. However the average number of correct
answers in interpreting AIBO’s basic behaviors were significantly lower. At a glance, the first set of results indicates that
AIBO is an appropriate robot for communicating with users.
However, these superiorities are derived from its well-designed
appearance as a commercial product or from participants’superficial impressions, such as “AIBO is a famous, cute,and clever pet robot,” not from the fact that its behaviors areeasily understandable. Yet, a serious gap has been demonstrated between the high evaluation participants gave AIBO
and its inability to inform participants of its primitive minds.
Specifically, the results of Q1 in table 1 are an obvious pieceof evidence for this gap; AIBO received its highest evaluationon Q1 “Did you understand the robot’s minds?” even thoughmost participants perceived AIBO’s expressed information
incorrectly. If these participants continued interacting withthis robot, they would eventually notice the gap between its
behavior and appearance, and then this gap might disappoint
the participants and cause them to lose interest in communicating with it further. They would say something to the effectthat “This robot looks very cute, but its behaviors are notreally understandable...” An indication of this can be observedin the results of Q2 “Was the expressed information easily
understandable?” No significant difference existed between thethree robots on this item.
Mindstorms, the other robot used in our test, received alower evaluation from participants. However, the average number of correct answers was significantly higher; that is, Mindstorms was better at informing participants of their primitiveminds. If participants continuously communicated with it, theymight notice that its behavior was more understandable, andsubsequently, they might have a better subjective impressionof the robot.
C. Influence of robot’s appearance on users
In our experiment, Mindstorms and the PC expressed thesame information (beep sounds) so that we could investigate
the effects of the robots’ appearance on the user’s impressions
and on their ability to estimate the robot’s primitive minds.
In regards to estimating primitive minds, the average number of correct answers to Mindstorms’ expression was somewhat higher than that to PC’s ones. However, the differences were not significant. The participants’ impressions of
Mindstorms were significantly higher on the following twoquestions related to the participants’ emotions: Q5 “Do you
think that this robot has emotions?” and Q6 “Do you thinkthat you can communicate with this robot?” These results werecaused by the familiarity with the Mindstorms’ robot-like appearance, compared with the PC, which did not have a robotlike appearance. However, this does not automatically meanthat pursuing a familiar appearance increased the evaluationsof participants.

VII. C ONCLUSIONS
Various kinds of social robots have been developed to assist
us with different tasks in our daily life. One of the mostimportant issues in these studies is how to express the robot’s
primitive minds to a user for communication between them.
This issue is strongly related to the robots’ expressed information and its appearance. However few studies have investigated
the relationship between these. Most studies applied humanlike or animal-like appearance in the robots. In this paper, we
proposed design policy of robot’s expression of its primitiveminds, SE2PM: Simple Expression to Primitive Mind, thatmeans that a designer should design simple information witha simple appearance to express robot’s primitive minds. To realize expression based on SE2PM, we designed mobile robotlike robot, Mindstorms, with simple beep sound. We conducteda psychological experiment to clarify effectiveness of SE2PM
by using AIBO entertainment robots with likely behaviors
and Mindstorms with beep sounds as simple expression. The
results of our experiment supported SE2PM. Based on theseresults, we are able to create a design policy for simple andeffective robots to interact with users.
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