Late-Breaking Papers (Poster Session)

HAI ’18, December 15–18, 2018, Southampton, United Kingdom

Subjective Speech Can Be Useful for Persuasive Virtual Humans
Executing Distinctiveness to Increase the Virtual Humans’ Trustworthiness and Persuasion EffectTetsuya Matsui

Seiji Yamada

National Institute of Informatics, The Graduate University
for Advanced Studies (SOKENDAI)
Chiyoda-ku, Tokyo
seiji@nii.ac.jp

Seikei university
Musashino-shi, Tokyo
t-matsui@st.seikei.ac.jp

distinctiveness as the difference in persuasion strategy for a given
topic. Kelley’s covariation model suggested that distinctiveness isthe main factor of attribution [2][3]. Bohner et al. showed thatspeakers who responded positively every time regardless of thetopic or their own principles were less likely to be trusted [1]. Thisfinding demonstrates that distinctive speech has a bigger effectthan non-distinctive speech, and distinctiveness can be perceived
when the manner of speaking is changed for different topics. In
this research, we aimed to equip VHs with distinctiveness so as toincrease their trustworthiness and motivate users to buy.
We express distinctiveness as the difference in persuasion strategy, namely, subjective persuasion and objective persuasion. Ourhypothesis is as follows:“PRVAs that make recommendations subjectively when talking about topics they prefer are more strongly
trusted and increase users’ motivation to buy more compared withother PRVAs". To verify this hypothesis, we defined two kinds ofstrategy and performed experiments using both.

ABSTRACTIn this work, we developed virtual humans (VH) designed to persuade users. We introduce the notion of distinctiveness of topics
and define two kinds of persuasion strategies: "objective persuasion", which aims to persuade with only objective sentences andno expression, and "subjective persuasion", which aims to persuadewith only subjective sentences and smiles and gestures. We performed experiments in which a VH recommended trips under twoconditions. In condition 1, the VH recommended a topic that she
preferred using subjective persuasion and another topic using objective persuasion. In condition 2, she recommended a topic that she
preferred using objective persuasion and another topic using subjective persuasion. Results showed the VH in condition 1 increased
the buying motivation of participants.

CCS CONCEPTS• Human-centered computing → HCI theory, concepts, andmodels;

2To express distinctiveness, we defined two kinds of persuasion
strategy: “objective persuasion" and “subjective persuasion." Objective persuasion means persuasion that is constructed with only
objective sentences, for example, “This restaurant opened in 1922."
Subjective persuasion means persuasion that is constructed with
only normative propositions, i.e., propositions that are composedof subjective sentences, for example, “This meal is very delicious."
We also specified the facial expressions and gestures that go alongwith each strategy. For only subjective persuasion, VHs smile anduse hand gestures to express positive emotion. Prior works haveshown that VHs and robots can effectively express their emotions
to users by means of hand gestures [8][4][6].
The experiments were performed under two conditions. In all
experiments, participants watched movies in which a PRVA recommends a trip to Sapporo, a popular Japanese sightseeing city. Afterwatching the movies, participants answered questionnaires. The
PRVA recommended sightseeing spots first and then local delicacies second. Before starting recommendations, the PRVA gave aself-introduction that included the phrase “I like to eat local delicacies on trips." This is the PRVA’s declaration of a preference. We
constructed all movies with MMDAgent, a toolkit for constructing
virtual agent conversation systems, executed by the Nagoya Institute of Technology1 . Figure 1 shows an example of the process flowof one trial in the experiment and the virtual human we used.
In condition 1, the “discriminable condition," the PRVA recommended a sightseeing spot by using objective persuasion and local delicacies by using subjective persuasion. In condition 2, theKEYWORDS
Virtual human, Virtual agent, Persuasion technology, Anthropomorphic agent, Trust, Product recommendation virtual agent (PRVA)ACM Reference Format:
Tetsuya Matsui and Seiji Yamada. 2018. Subjective Speech Can Be Useful for Persuasive Virtual Humans: Executing Distinctiveness to Increase
the Virtual Humans’ Trustworthiness and Persuasion Effect. In 6th International Conference on Human-Agent Interaction (HAI ’18), December 15–18, 2018, Southampton, United Kingdom, Jennifer B. Sartor, Theo D’Hondt,and Wolfgang De Meuter (Eds.). ACM, New York, NY, USA, 2 pages. https://doi.org/10.1145/3284432.3287178

1EXPERIMENTAL DESIGNINTRODUCTION

One of the applications of virtual humans (VHs), which are anthropomorphic virtual agents, is to persuade people. For example, theproduct recommendation virtual agent (PRVA) is a virtual agent
that persuades users to purchase products [5]. In this paper, we
propose a method for increasing the persuasion effect of VHs.
We introduce the notion of the distinctiveness of topics, whichcomes from prior research in social psychology. Here, we define
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HAI ’18, December 15–18, 2018, Southampton, United Kingdom© 2018 Copyright held by the owner/author(s).
ACM ISBN 978-1-4503-5953-5/18/12.
https://doi.org/10.1145/3284432.3287178

1 http://www.mmdagent.jp/336

Late-Breaking Papers (Poster Session)

HAI ’18, December 15–18, 2018, Southampton, United Kingdom

Figure 1: Process flow and VH used in the experiments.
Figure 2
Average of ISS and recommendation effect scores ofeach condition“reverse-discriminable condition," the PRVA recommended the sightseeing spot by using subjective persuasion and local delicacies
by using objective persuasion. We used this condition to confirm
whether only executing distinctiveness was ineffective, i.e., thatconsistency in declaring a preference is also important. We hypothesized that the recommendation effect (buying motivation) on
participants in condition 1 would be higher than in condition 2.
The questionnaires that participants were asked to fill out after
watching the movies included the Interpersonal Solidarity Scale(ISS) and one additional question. The ISS is a scale that measurespersonal trust toward a particular person [7]. It contains 20 questions that participants were asked to answer on a seven-point Likert
scale. The additional question was “Do you want to go on a trip toSapporo, like the PRVA recommended?" We used this question tocalculate the “recommendation effect." The participants answered
this question on a seven-point Likert scale, the same as the ISS.
We also asked them two additional questions about the movies toensure that they had watched the whole thing. Participants whoanswered with the same number five times in a row were excluded
as noise. We also excluded participants who did not answer thequestions about completing the movies correctly.
For condition 1, we recruited 84 participants, 62 of whom remained after noise exclusion. There were 34 males and 28 females
ranging in age from 22 to 71 years for an average of 42.6 (SD =9.9). For condition 2, we recruited 130 participants, 64 of whom
remained after noise exclusion. There were 36 males and 28 females
ranging in age from 24 to 61 years for an average of 41.8 (SD =8.5). All participants were recruited from Yahoo Crowd Sourcing2
and paid 50 yen (about 45 US cents) as a reward. All trials wereconducted on the Web.

3

the recommendations about trips than in condition 2. This result isin good agreement with our hypothesis.

4CONCLUSION

We proposed a method for increasing the persuasion effect of VHs,specifically, PRVAs. In this method, the distinctiveness of topics is
an important notion. We defined distinctiveness as the difference inpersuasion strategy and defined two kinds of persuasion: “objectivepersuasion" and “subjective persuasion." To verify this hypothesis,
we performed experiments under two conditions. In condition 1, thePRVA used subjective persuasion when she spoke about a topic thatshe preferred and used objective persuasion when she spoke aboutother things. In condition 2, the PRVA used objective persuasion
when she spoke about a topic that she preferred and used subjective
persuasion when she spoke about other things. The results showedthat the participants in condition 1 had increased motivation to buy
compared with condition 2. This supports our hypothesis.

ACKNOWLEDGMENTS
This research was partially supported by JSPS KAKENHI “CognitiveInteraction Design" (No. 32626118005).

REFERENCES[1] Gerd Bohner, Elisabeth Frank, and Hans-Peter Erb. [n. d.]. Heuristic processing ofdistinctiveness information in minority and majority influence. European Journalof Social Psychology 28, 5 ([n. d.]), 855–860.
[2] Beryl Hesketh. 1984. Attribution theory and unemployment: Kelley’s covariation
model, self-esteem, and locus of control. Journal of Vocational Behavior 24, 1 (1984),94–109.
[3] Harold H Kelley. 1967. Attribution theory in social psychology.. In Nebraska
symposium on motivation.
[4] Tetsuya Matsui and Seiji Yamada. 2016. Building trust in prvas by user inner statetransition through agent state transition. In Proceedings of the Fourth International
Conference on Human Agent Interaction. 111–114.
[5] Lingyun Qiu and Izak Benbasat. 2009. Evaluating anthropomorphic productrecommendation agents: A social relationship perspective to designing information systems. Journal of Management Information Systems 25, 4 (2009), 145–182.
https://doi.org/10.2753/MIS0742-1222250405[6] Jason Tsai, Emma Bowring, Stacy Marsella, Wendy Wood, and Milind Tambe. 2012.
A study of emotional contagion with virtual characters. In International Conferenceon Intelligent Virtual Agents. Springer, 81–88.
[7] Lawrence R Wheeless. 1978. A follow-up study of the relationships among trust,disclosure, and interpersonal solidarity. Human Communication Research 4, 2(1978), 143–157. https://doi.org/10.1111/j.1468-2958.1978.tb00604.x[8] Junchao Xu, Joost Broekens, Koen Hindriks, and Mark A Neerincx. 2014. Robot
mood is contagious: Effects of robot body language in the imitation game. In
Proceedings of the 2014 International Conference on Autonomous Agents and Multiagent Systems. 973–980.

RESULT AND DISCUSSION

Fig. 1 shows the average of the ISS and recommendation effectscores. We conducted a t-test between the two conditions. There
were no significant differences in ISS [t(124) = 1.56, p = 0.121], andthere were significant differences in recommendation effect score(p< 0.05)[t(124) = 2.19, p = 0.030].
In Fig. 2 there are no significant differences in ISS. This meansthat being trusted is not always important to increase the recommendation effect. Also, there were significant differences in recommendation effect. The results suggest that distinctiveness thatconsists of declaring a preference can increase the recommendation
effect. The participants in condition 1 were more likely to accept
2 https://crowdsourcing.yahoo.co.jp/337