Speech onset time at home or in the lab: The role of testing environment and experimenter presence.

Psycholinguistic research has become increasingly reliant on online experimentation, making it an attractive approach for studying speech production. However, concerns remain about data quality and participant engagement in online settings. In this preregistered study, we used two tasks-picture naming and reading aloud-to test whether the lexical frequency effect (low-frequency words having shorter speech onset times than high-frequency words) could be reliably detected in the online environment (run at home), both with and without experimenter supervision. Participants completed the same two tasks at home and in the lab. Half of the participants performed both tasks with supervision and the other half unsupervised. In the naming task, all conditions yielded consistent frequency effects (~27-41 ms), comparable to previous online and lab findings. In the reading aloud task, lexical frequency effect emerged in all conditions except for the home-supervised, where the effect was in the expected direction but nonsignificant (~12 ms). Notably, participants were overall faster at home than in the lab (~10 ms), and unsupervised settings yielded the largest effect sizes. This suggests that experimenter presence may inadvertently dampen subtle effects, possibly due to increased self-monitoring or reduced comfort. Such findings indicate the reliability of online platforms for speech production research in psycholinguistics and highlight the nuanced influence of supervision on speech outcomes.