Persuasion through overheard communication by life-like agents
Satoshi V. Suzuki
Seiji Yamada
CISS, IGSSE, Tokyo Institute of Technology National Institute of Informatics
R1–42 4259 Nagatsuta, Midori-ku
2–1–2 Hitotsubashi, Chiyoda
Yokohama 226–8503 JapanTokyo 101–8430 Japan
E-mail: ssv@ntt.dis.titech.ac.jp
E-mail: seiji@nii.ac.jp
Abstract
It is important to investigate influence of life-like agents
which interact with a user since some studies suggest thatlife-like agents can “persuade” people, in other words,
they have potential to change people’s attitude and behavior. In this study, the influence of overheard communication(OC), one of famous persuasion techniques, by life-likeagents toward online shopping Web site users was examined, since the OC by people often changes attitude of receivers. An experiment to compare the effect of OC by twolife-like agents (a persuader agent and a persuadee agent)
with regular communication by one persuader agent wereconducted. The result of this experiment implied that even
the OC by life-like agents could promote Web site users’
online shopping purchase likelihood. Moreover, althoughcorrelation between participants’ attractiveness toward a
persuader agent and purchase likelihood was observed, theOC by life-like agents inhibited influence of participants’negative impression to a persuader agent. These results
suggest the effectiveness of the OC by life-like agents andthe new direction of studies of social response to life-likeagents, from the viewpoints of presence, gaze, and appearance of life-like agents.

1 Introduction
Recently, there is much argument regarding influence ofsocial interaction between users and communication technology as the communication technology prevails into oureveryday life. Among such technology, a life-like agent(embodied conversational agent) [4] has a possibility to interact with a user using rich social cues. Such technology
can be utilized to provide a user with means to smoothly interact with computers, as well as abused to direct a user toa wrong way. Moreover, how much influence the communication technology has toward users is still unclear. Research on the communication technology should reveal its
possibility and the risk of social influence to users.
In particular, a life-like agent has potential to change
a user’s attitude. A life-like agent technology can be oneof “interactive computing systems designed to change peo-

ple’s attitudes and behaviors” [6] with its many modalities.
From the viewpoint of persuasion, such interactive computing systems can let users improve their unfavorable attitude, or drive users to immoral thoughts. In this study, we
approach life-like agent technology from the framework oflife-like agents as social actors [12] applying the theories
established in persuasion studies [15].

We implemented life-like agents on an online shopping
Web site. Recently, in the field of marketing, many online services succeeded in their business with existence of
established customers [7]. This existence can be virtually represented by life-like agents, since the life-like agent
technology can express social cues and presence with its
virtual body [8]. Moreover, people often avoid direct sales
promotion in marketing because such promotion is often
intrusive [7]. If a life-like agent implemented as a clerk
on an online shopping Web site promote its products directly to Web site visitors, they may avoid if the promotion seems intrusive. This intrusiveness derives from not
only a clerk agent’s appearance or messages, but its behavior. To improve this problem, we introduce an agent whichplays a role of a clerk and another agent which plays arole of a customer. Using a clerk agent and a customer
agent enables users to see sales promotion to the customer
agent by the clerk agent. This study investigated the influence of a behavior rule shown in this case to users’ attitude, since there was no study which referred to influenceof such inter-agent interaction to users’ attitude change.

In this article, first we review the studies of social response toward a computer and a life-like agent, and clarify
the problem in the studies of inter-agent interaction. Second, the behavior rule called overheard communication is
introduced and applied to inter-agent interaction. Then,through results of a psychological experiment, the influence and potential of overheard communication by life-likeagents is discussed.

2 Related Works
2.1 Attribution of Action to Each Life-like Agent
It is possible that users unawarely accept computers andlife-like agents as persuasive social existence, because people tend to react to computers and life-like agents as if they
were humans. Many theories of social response to humans proved to be applicable to the relationship between
users and computers, and life-like agents as social existence [12]. Especially, if there are several life-like agentson the screen, users should attribute sources of action toeach life-like agent [8]. Social influence of human-agent
interaction, and users’ perception of inter-agent interaction
should be considered based on attribution of actions foreach life-like agent.

2.2 Persuasion by Life-like AgentsSome studies of life-like agents as “social persuaders”
already exist, however, there is still no study which focuses on the social influence of existence of inter-agent
interaction. Moon [10] examined the social influence of
intimacy between a user and a computer through the exchange of personal information, and she found that such intimacy contributed a user’s attitude change. She considered
only human-computer interaction, and there is no argument about influence from other social existence. Besides,André et al. [1] claimed the effect of inter-agent interaction in implementation of online car dealer agent system,
but they did not argue how effective inter-agent interaction was. Moreover, Katagiri, Takahashi and Takeuchi [8]insisted that authorizing a life-like agent by other agent
could grab a user’s attention stronger than non-authorizing
situation. Their study compared two inter-agent interaction styles, not existence of inter-agent interaction and absence of inter-agent interaction, and they did not mention
the social influence by inter-agent interaction. Therefore,
the influence of existence of inter-agent interaction toward
a user’s attitude change was investigated in this study.

2.3 Influence of gaze by a life-like agent
Among social cues that a user should perceive from alife-like agent, where the agent gaze plays a very importantrole in human-agent interaction. As people pay attention
to someone’s eyes when interacting with him/her [2], theagent’s “eyes” imply social meanings toward the user [12].
Although Reeves and Nass [12] claimed that the agent
should gaze the user in front of a display since it would
be the “etiquette” which the agent should obey, in somesituation, the agent’s direct gaze toward the user may seem
somehow imposing for him/her. In addition, especially ifthere is inter-agent interaction, it is natural that two or moreagents talk with gazing at each other. For these reasons, theinfluence of the agent’s direction of gaze to distinguish towhom the agent talk was considered.

3 Overheard Communication by Life-like
Agents3.1

Overheard Communication as a Persuasion
TechniqueSuppose you hear the reputation of a movie in which
you are not so much interesting in these two situations:
1. Your friend directly told to you that the movie wasvery interesting and you must watch it (as seen in Figure 1).
2. You overheard that someone told to another one thatthe movie was very interesting and he/she must watch
it (as seen in Figure 2).
In some cases, the message from your friend may seem
intrusive since your friend directly told you such a pushy
message in situation 1. On the contrary, in situation 2, you
may have interests in the movie because you did not receive
someone’s message directly and the message did not seemso intrusive. The persuasion style shown in situation 2, thata persuader tell another one the message, without tellingthe “true” persuadee, is known as overheard communication (OC) in persuasion studies [14, 15]. In this study, thepersuasion style that a persuader directly tell the persuadee
the message, represented in situation 1, is called regularcommunication (RC). In addition, a life-like agent which
behaves as a persuader is called a persuader agent (previously mentioned as a “clerk agent”), and a persuadee agent(previously mentioned as a “customer agent”) represents alife-like agent persuaded by a persuader agent in the situation of OC by life-like agents.
Why does OC function well? There should be two reasons:• When people make a decision about something, they
may often take others’ action and opinion into account [5]. For example, when people go to an amusement park, many of them should avoid riding a ridewith no other visitors. In this case, the existence ofother visitors should be a criterion whether the ridein this amusement park is enjoyable or not. Suchdecision-making influenced by others’ behavior isseen in many other situations since the others’ behavior often works as one of important norm among people.
• In persuasive communication, where a persuader
gazes when persuading others should affect the persuadees’ attitude change [2]. If a persuader talks topersuadees without gazing them, they should not beable to regard a persuader’s message that this message is to persuade them. Then, how much persuadees
change their attitude should depend on where a persuader is gazing when he/she persuades.

You must watch that movie because it was very interesting.

Persuader

You must watch that movie because it was very interesting.

The persuader directly
gazes at the persuadee.

It sounds good.
I’d like to see
it.

Persuader

Another one

The persuader does notgaze at the persuadee, butgazes at another one.
Persuadee

Persuadee

Really? I’m unwilling towatch it...

Really?
out...

I should check it

Figure 1. An example of regular communica-

Figure 2. An example of overheard commu-

tionnication

3.2 Application to Life-like Agents
Considering the influence of human-agent interaction
and inter-agent interaction, and the effect of OC-style persuasive communication, we implemented OC by life-likeagents in the following manner:• Let both the persuader agent and the persuadee agent
appear on the screen, because users will perceive thattwo distinguishable social actors exist and each ofthem behave at their own thought.
• The persuader agent always tell the persuadee agent a
message, because users will perceive the message ofthe persuader agent with distinguishing whom the persuader agent tell the message by where the persuader
agent gazes.

4 Psychological Experiment
4.1 Experimental Design and Prediction
In this study, we suppose two conditions for the psychological experiment. When a persuader agent explainscharacteristics of items, in the RC condition, it gazes toward a user in front of the screen; on the other hand, itgazes toward a persuadee agent in the OC condition. Considering the argument above, the OC by two life-like agentsshould promote a user’s attitude change more than the RC
by a life-like agent. Additionally, the OC by a persuader
agent should emphasize its attractiveness, and expertness
and reliability of information which it provides more thanthe RC by it. Then, considering these hypotheses above,
the following predictions should be determined:

P1 Participants in the OC condition will evaluate the pur-chase likelihood of items higher than those in the RC
condition.
P2 Participants in the OC condition will evaluate the per-suader agent’s attractiveness and reliability of information which it provides higher than those in the RC
condition.

4.2

Procedure

Valid experimental data were collected from 24
Japanese participants (19 males and 5 females). The participants consisted of undergraduate students, graduate students, and office workers. Their age ranged from 19 to
29. They were randomly assigned to either RC condition
or OC condition. Each condition contained equal participants. They had been using PC, e-mail, and WWW for 3
years at least, and 21 participants had used online shopping
services at least once.
Participants are offered to look at the explanation of
items by a persuader agent on an online shopping WWWsite with a note PC (Sony VAIO PCG-SR9G/K, 10.400
XGA display, OS: Windows2000). In the RC condition,
the persuader agent introduced items directly gazing at participants (Figure 4); in the OC condition, a persuadee agent
appeared on the screen and the persuader agent introduced
items gazing at the persuadee agent (Figure 5). The same
item explanation phrases by the persuader agent were usedin both condition. To preserve natural conversation context, the persuadee agent gave short responses to the persuader agent for each item explanation phrase in the OC
condition. As introduction of each item ended, participantsFigure 3. Interface to present an item and ask purchase likelihood of the item used in the experiment

Figure 4. Explanation of characteristics of an item in RC

Figure 5. Explanation of characteristics of an item in OC

condition

condition

answered how much he/she want to purchase this item by a
10-point likert scale. The evaluation of purchase likelihoodfor the items which the participants had already possessed
were omitted for analysis. The price of the items was considered so that the participant could afford to buy the item
if he/she wanted it.
The behavior of the agents were implemented with Microsoft Agent via JScript on Microsoft Internet Explorer,
and the answers of participants were collected via CGI
written in Ruby. For all participants, the agent “James1 ”
played a role of the persuader, and the agent “Cosmy2 ”
played a role of the persuadee. These agents did not change
their roles among participants, and the other agents withdifferent appearance were not used in this experiment. Thisis because it is difficult to handle what difference in char-acteristics of the agent’s appearance would influence in theexperiment if the different agent appearances were used.
Instead, after the evaluation of purchase likelihood for 15
items, participants answered the questionnaire about attractiveness of the persuader agent. The attractiveness wasevaluated on a 10-point likert scale for four adjectives:kind, friendly, useful, and likable. Also, participants wereasked to answer the question with a 10-point scale about
expertness (extensiveness, expertness), and reliability (reliable, objective, fair) of the goods information that thepersuader agent offered. About the choice of these adjectives, we considered the result of other studies [9, 10].
After reporting the impression of this experiment, participants were debriefed, thanked for their participation, anddismissed. It took around 30 minutes to finish the experiment for each participant.

1 This agent is available at http://www.cantoche.com/
english/gallery/msagent.htm.
2 This agent is available at http://www2.mic.atr.co.jp/
agent/.

4.3

Result of Experiment

Mean and standard deviation values of all variables inthis experiment were shown in Table 1.

Table 1. Mean (standard deviation in parentheses) values of measured variables for each condition and results of statistical tests
RC cond.
OC cond.
t-value
Effect Size

Purchase likelihood scores(n = 12)(n = 12)(d.f. = 22) (ES)4.127 (1.348)

5.421 (0.664)

2.984∗∗ F

1.166

RC cond.

OC cond.

RC cond.

OC cond.

3 4 5 6 7 8

Mean value of attractiveness scores

10
8
6
4
0

2

6
0

2

4

8

10

Attractiveness of the persuader agent 5.729 (1.760) 6.521 (1.694) 1.123
0.439
Expertness of the goods information
5.167 (1.710) 6.000 (1.989) 1.101
0.430
Reliability of the goods information
4.944 (1.613) 5.472 (1.696) 0.781
0.305
FFor the significant difference of variances between the two conditions, the t-value by Welch test∗∗
: p < .01
was shown here (d.f. = 16.04).

R

R

2

10
8
6
4
RC cond.

OC cond.

Figure 8. Mean value of ex- Figure 9. Mean value of relipertness scores

5

6chase likelihood scores and attractiveness scores0
OC cond.

4

Figure 10. Correlation between pur-

2

6

8

10

tractiveness scores

4
20
RC cond.

3

Mean value of purchase likelihoodscoresFigure 6. Mean value of pur- Figure 7. Mean value of atchase likelihood scores

OR
O OO
ORRO
R
O
R
R
R
O
O
O
R: RC cond.
R
O
O: OC cond.
RR

ability scoresFirst of all, as Figure 6 indicates, the mean value ofpurchase likelihood scores in OC condition was significantly higher than that of RC condition. Since the difference of variance between these two variables was significant (F(11, 11) = 4.124, two-tailed p < .05), Welch
test was applied to confirming the significant difference between the mean values of them. As a result, the significant
difference between them observed (t(16.04) = 2.984, twotailed p < .01, ES = 1.166). Thus, the result supported theprediction P1.
However, there was no significant difference between
the two condition in the scores regarding impression toward the persuader agent and the goods information. De-

spite Figure 7–9 represents all of these scores (attractiveness, expertness, and reliability) in the OC condition exceeded those in the RC condition, according to the resultof two-tailed t-tests, significant difference between the two
conditions did not appear in these three scores, as shown in
Table 1. Then, the prediction P2 was rejected by the result.
Nevertheless, between the score of attractiveness andthe score of purchase likelihood for each participant, there
was a significant positive correlation. A scatter diagramin Figure 10 indicated positive correlations between these
two scores with respect to each condition. The values ofPearson’s product-moment correlation coefficient and thesignificance test of these values proved there were significant correlations between the two scores for each condition (in RC condition, r = .505, t(10) = 1.851, two-tailed
p < .10, and in OC condition, r = .615, t(10) = 2.463,
two-tailed p < .05).

5

Discussion

5.1

The Influence of OC by Life-like AgentsThe result shown in section 4.3 suggested that the OC
induced a user’s purchase likelihood of products on online
shopping Web site more than the RC. This result impliedthat life-like agents could play a role of a clerk and anothercustomer virtually. To analyze why the OC by life-likeagents succeeded in the experiment, there seem to be two
reasons, as expected:
1. In the OC, the persuader agent gazed at the persuadee
agent when explaining feature of items and nevergazed at the user.
2. In the OC, the persuadee agent existed on the screen.
The gaze of the persuader agent could be perceived asa important social cue to participants. In fact, one participant in OC condition reported: “It is good to see theconversation between two agents from the viewpoint of a
stranger, since it may feel annoying if one agent directly
talks to me.” In addition, the existence of the persuadee
agent could serve as a criterion for participants to consider
whether they should buy the items or not. There were twoparticipants who answered that he/she took the behavior of
the persuadee agent into consideration. This fact suggeststhat the influence of the existence of the persuadee agent
could not be ignored.
As for the impression of a persuader agent, there wasno significant difference between the OC condition and the
RC condition in three scores of impression. However, thescores of attractiveness is significantly correlated with thescores of purchase likelihood. This result indicated theinfluence of physical appearance of a persuader agent because we used the persuader agent with same appearance inboth the RC condition and the OC condition. Fogg [6] argued physical appearance of life-like agents as a importantfactor of persuasion of a user by life-like agents, and someparticipants answered that the persuader agents used in thisexperiment looked “too strong” or “not so cute.” However, considering Figure 10, participants’ negative evaluation of attractiveness of the persuader agent was affectedto their purchase likelihood in the RC condition. On theother hand, in the OC condition, despite some participants
poorly evaluated the attractiveness of the persuader agent,
they evaluated purchase likelihood not lower than several
participants in the RC condition.
Then, it is still difficult to control many attributes in appearance of life-like agents, however, the result suggeststhat the OC by life-like agents can suppress the influenceof negative impression of a persuader agent. What appearance is suitable should be dependent on what situation the
OC by life-like agents is applied, and who interacts withthe persuader agent. Moreover, it is often hard since we
can hardly target various users’ preference on appearanceof life-like agents. Therefore, we can expect that the OC
by life-like agents warrant the attitude change of users toa certain level even if there may be lots of factors which
affect users badly.

There should arise one question: what if the user noticed the existence behind the agents who operate it (e.g.
programmer, Web site administrator, etc.)? Considering
the study of Sundar and Nass [13] regarding perception ofsource of information by users, it seems hard for users tokeep paying attention to the existence behind the agents
since it is natural and easy for them to consider the behavior of the agents themselves while they are interactingwith agents. As it is difficult to follow both the story andthe making process of an animation movie simultaneously
when we watch it, thinking the existence behind the agents
when watching their behavior should be tiring for users.
Then, in most cases, users accept behavior of the agents
without taking into account the existence behind them.

5.2

The Potential of Application of OC

In the OC by life-like agents, the social cue of a persuader agent’s gaze was functioned in the experiment.
However, there are still few studies which focus on thefunction of a body of a life-like agent. Thus, the influence of non-verbal social cues triggered by the appearance
and behavior of life-like agents is not clear so far. This influence should not only apply to human-agent interaction,
but to human-robot interaction. If we hope that technology
pervade many aspects of our life, we should emphasize thesocial aspect of human-agent interaction.
Since all the participants of the experiment in this study
are Japanese, the influence of OC may partly derive from
cultural factors. However, Godin [7] showed examples of
ineffectiveness of intrusive marketing in the United States,
thus, the problem of intrusiveness in marketing regards
users beyond countries. The result of the experiment indicates that the OC by life-like agents can hinder such intrusiveness with avoiding directing the persuader agent’s
gaze toward a user.
Besides, we did not mention the interactivity between auser and agents. First, this study does not consider the influence of the difference of a reaction by a persuadee agent
since we focus on the existence of inter-agent interaction.
Some persuasion studies reveal that the negative reaction ofothers toward a persuader gave people negative impression(for example, Axsom et al. [3]). The valence of reaction ofa persuadee agent can influence the decision of users, andshould be considered in future works. In addition, if a user
has interacted with agents before the OC, the user can be
influenced with the history of interaction by the agents [8].
Then, in the future, the influence of the history of interaction to the user should be considered with regard to relation
between the interactivity with the agents and the influenceof OC by the agents.
We dealed novel media and information for most of participants in the experiment in this study. In such environment that people do not get accustomed, they tend to rely

on the superficial information rather than the content of information [11]. This means if the content of information
is known to users well, users may take the content of information into consideration more than the social cues of
the agents. How much the users understand the content of
information can be the important factor of persuasion withagents, and should be one of unignorable issues afterward.
If we utilize life-like agents as social actors to persuade
users, we should pay attention to whether we deceive users
or not. The result of the experiment revealed how strong
the OC by life-like agent affected toward the attitude ofusers. Even though the message provided by a persuader
agent contains unfavorable information, users may overlook the problem underlying the message if they “overheard” it. We should provide other means for users to examine the reliability of information to prevent users fromdeception.

[4] J. Cassell, J. Sullivan, S. Prevost, and E. Churchill, editors.
Embodied Conversational Agents. MIT Press, Cambridge,
MA, 2000.

6 Conclusion[10] Y. Moon. Intimate exchanges: Using computers to elicit
self-disclosure from consumers. Journal of Consumer Research, 26:323–339, Mar. 2000.

In this study, we discussed the influence and potentialof overheard communication by life-like agents. Particularly, it is pointed out that existence of the persuadee agent
and the direction of the persuader agent’s gaze played an
important role in the overheard communication by life-likeagents. From the stance of social responses of users to lifelike agents, the way to utilize life-like agents for the voluntary attitude change of users should be explored in the
future.
Since the result of this study was obtained under controlled environment, it is hard to immediately apply the
discussion in this study to other situations. Nonetheless,this study could suggest the potential of life-like agentsbased on social interaction with a user and its embodied
characteristics.

Acknowledgments
We would like to express our gratitude for those who
participate the experiment in this study, and those who cooperate in recruiting the participants. Also, we would liketo thank to Dr. Kazuhiro Ueda in University of Tokyo for
his valuable advice on the idea of the experiment.

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