Document Type

Thesis

Date of Degree Completion

Spring 2026

Degree Name

Master of Science (MS)

Department

Primate Behavior

Committee Chair

Mary Lee Jensvold

Second Committee Member

Mary Radeke

Third Committee Member

John B. Mulcahy

Abstract

Turn-taking occurs in spoken and signed human conversations. Interactions in both spoken and signed languages are characterized by a systematic back-and-forth exchange that minimizes gaps and overlaps. This study utilized an archival Conversational Video Database to analyze 256 American Sign Language (ASL) turn transitions between two cross-fostered chimpanzees (Pan troglodytes), Moja and Tatu, and their human caregivers. Using ELAN software, turns were annotated for movement phases: preparation, stroke, hold, and retraction. Because the stroke is the lexically meaningful part of the sign, we predicted less overlap during the stroke and more during the other phases. We first investigated the timing of overlap between chimpanzee and human turns. We found a mean stroke to stroke latency of 623.02 ms for chimpanzees and 1,134.62 ms for humans which was not statistically significant.  We noted individual differences between the chimpanzees. 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). The chimpanzees overlapped 28.75% of the time and humans 18.46%. We next explored patterns in the types of phases that overlapped between partners. Both chimpanzees tended not to sign when the human partner was in the stroke phase, significantly avoiding simultaneous strokes. Holds in human signed conversations tend to be a space for overlap, and a similar pattern appeared for the chimpanzees. These findings demonstrate that chimpanzee turn-taking follows the one-at-a-time principle, which appears in the structural timing of human signers and wild chimpanzee populations.

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Available for download on Saturday, June 28, 2031

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