Hierarchy, Context, and Modulation Use in Chimpanzee-to-Chimpanzee Interactions Alexis Erickson* Project Mentor(s): Mary Lee Jensvold, PhD Chimpanzees are highly social primates, using vocal and gestural forms of communication in various contexts. Considering their relation to humans, their language capacities are of interest. In the 1960s, an infant chimpanzee, Washoe, was raised like a Deaf human child and acquired signs of American Sign Language. In the 1970s, four additional chimpanzees, Tatu, Dar, Loulis, and Moja also acquired signs from human caregivers. Loulis learned signs from Washoe and was the first non-human to learn a language from another non-human. The chimpanzees acquired signs in patterns that resembled human children, including modulation of signs. Caregivers at Central Washington University used sign logs to document all aspects of signed interactions by the chimpanzees when they lived on campus. Researchers also determined the dominance hierarchy of the social group, and it was as follows: Washoe and Loulis were high-ranking, Dar and Tatu were middle-ranking, and Moja was low-ranking (Sanz et al., 1996; Hayashida et al., 2002). The current study explored the dominance hierarchy, contexts, and modulation use in chimpanzee-to-chimpanzee interactions. Emphatic modulations, followed by directional modulations, occurred the most across signers, ranks, and contexts. Washoe signed and modulated the most, while Moja signed and modulated the least. The most modulations were produced in reassurance contexts, and the least were produced in discipline contexts. These findings offer a new perspective toward the language capacities of chimpanzees and their behaviors across contexts. Presentation Type: Oral Presentation (May 20, 9:30am–5:00pm) Keywords: sign language, modulation, hierarchy, behavioral context, chimpanzee SOURCE Form ID: 161 Turn-taking occurs in spoken and signed human conversations. It also appears across various taxa and language. Chimpanzees ( Pan troglodytes ) engage in turn-taking in gestural interactions and signed conversations (Badihi et al., 2024; Hartmann, 2011; Rossano, 2013). This study investigates the timing of conversational exchanges between signing chimpanzees, Moja and Tatu, and human interlocutors using archival video recordings of their unstructured conversations with human caregivers. This research focuses on the latency between turn transitions. An analysis of 256 transitions revealed similar mean latency of 623.02 ms for chimpanzees and 1,134.62 ms for humans. A t-test showed this difference was not significant t (250.59) = -1.82, p = .069, d = -0.23, 95% CI [-0.47, 0.02] with a small effect size. Density plots showed primary peaks for both species near 0 ms, which is a nearly simultaneous transitions. Both groups were predominantly non-overlapping; 62.70% of chimpanzee and 76.92% of human responses occurred after the partner’s stroke ended. Individual differences also appeared. Tatu had a shorter mean latency (422.83 ms; range: 7,000 to 9,400 ms) and a broader response range compared to Moja (1,164.71 ms; range: -600 to 4,800 ms). These results indicate that both species operate under a similar turn-taking system adapted to minimize gaps and overlaps between turns. Presentation Type: Pre-Recorded Presentation (https://www.youtube.com/@cwusource5518) Keywords: ASL Conversations, Turn Transitions, Chimpanzee-Human Conversations, Turn Taking, Latency SOURCE Form ID: 119 Turn Taking in Chimpanzee-Human Signed Conversations Candice Mendez*; Nève Djevalikian-Couture; Mary Lee Jensvold, PhD Project Mentor(s): Mary Lee Jensvold, PhD
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