## 3 Materials and Methods  
### Talk to Kotaro: A Web Crowdsourcing Experiment  
To create a data set of how people respond to different phonetic and prosodic choices in gibberish speech, the web-based crowdsourcing experiment \"Talk to Kotaro\" was conducted between 1 October 2021 to 31 March 2023. The experiment was approved by Tokyo University of Agriculture and Technology Ethics Committee (approval number 210801-0321 and experiment extension request approval number 220306-0321). All participants had to read an online consent form and the experiment instructions and had to click a consent button, which was deemed an acceptable means of obtaining consent by University of Agriculture and Technology Ethics Committee.  
In the \"Talk to Kotaro\" experiment, research volunteers talked as long as they wanted to a cartoon avatar of the robot [PERSON], which responded with IPA-based gibberish speech. The website, developed using JavaScript (client-side) and Python (server-side), required volunteers to register a profile with personal information, which was used to evaluate the impact of gender, age, nationality, native language, etc., on the average response of a given group of people. In addition, the platform recorded the audio of what the volunteers said to assess their emotional state before listening to [PERSON]'s response. Video of the volunteers' facial expressions as they listened to the [PERSON] response was recorded. To avoid the need for voice activity detection (VAD), the platform required volunteers to press a button (bottom left button shown in Figure 2) before speaking and press it again after they finished speaking, allowing [PERSON] to respond. This cycle would repeat as long as a volunteer wanted; the most prolific volunteer contributed 201 conversations, about 23.4% of all the data in the experiment. When volunteers felt they had talked enough, they could either close the experiment web page tab or click the logout button (top left button in Figure 2). If they chose to click the logout button, they were redirected to a 10-question Likert scale questionnaire about their experience. Answering the questionnaire was optional, and 22 of the 37 participants chose to do so.  
The experiment was designed with the goal of obtaining the immediate emotional changed caused by the GS patterns of the robot avatar in a open-ended conversational setting, trying not to introduce many distraction factors, such as having a very expressive conversational agent or a lively background of the web page. The experiment was performed during the height of COVID-19 pandemic restriction, and thus, it had to be held online, since having research subjects in the laboratory without wearing face masks would be impossible. However, such exceptional measures also had the benefit of allowing research subjects from all over the world to participate in the experiment. The decision of having a screen-based embodied conversational agent was taken in order to simulate the experience of talking to a social robot without requiring any special hardware by volunteers, such as VR or AR googles, trading off some of the realism of the task for ease of participation.  
[PERSON]'s IPA-based gibberish speech was transformed into voice by using the eSpeak [45] speech synthesizer, which was chosen because it is open-source, can receive ASCII-IPA input, and allows for control of the prosody of generated speech. Algorithm 1, described in Section 3.1.1, was used to select the phones to be used in [PERSON]'s speech. As for the prosody, the three chosen parameters--speed, pitch, and volume--were randomly chosen between 80-450 words per minute (speed), 10-200% (volume), and 0-99 (arbitrary unit, pitch). Some participants reported a feeling of alienation when the ECA suddenly changed its voice pitch, making them feel like they were not talking to the same person.