Large language models (LLMs) have revolutionized natural language generation across various applications. Although LLMs are highly capable in many domains, they sometimes produce responses that lack coherence or fail to align with conversational norms such as turn-taking, or providing relevant acknowledgments. Conversational LLMs are widely used, but evaluation often misses pragmatic aspects of dialogue. In this paper, we evaluate how LLM-generated dialogue compares to human conversation through the lens of dialogue acts, the functional building blocks of interaction. Using the Switchboard Dialogue Act (SwDA) corpus, we prompt two widely used open-source models, Llama 2 and Mistral, to generate responses under varying context lengths. We then automatically annotate the dialogue acts of both model and human responses with a BERT classifier and compare their distributions. Our experimental findings reveal that the distribution of dialogue acts generated by these models differs significantly from the distribution of dialogue acts in human conversation, indicating an area for improvement. Perplexity analysis further highlights that certain dialogue acts like Acknowledge (Backchannel) are harder for models to predict. While preliminary, this study demonstrates the value of dialogue act analysis as a diagnostic tool for human-LLM interaction, highlighting both current limitations and directions for improvement.

During conversations, people align to one another over time, by using similar words, concepts, and syntax. This helps form a shared understanding of the conversational content and is associated with increased engagement and satisfaction. It also affects conversation outcomes: e.g., when talking to language learners, an above normal level of linguistic alignment of parents or language teachers is correlated with faster language acquisition. These benefits make human-like alignment an important property of dialogue systems, which has often been overlooked by the NLP community. In order to fill this gap, we ask: (RQ1) Due to the importance for engagement and satisfaction, to what degree do state-of-the-art dialogue systems align to adult users? (RQ2) With a potential application to child language acquisition in mind, do systems, similar to parents, show high levels of alignment during conversations with children? Our experiments show that ChatGPT aligns to adults at roughly human levels, while Llama2 shows elevated alignment. However, when responding to a child, both systems’ alignment is below human levels.