How the motor aspect of speaking influences the blink rate

Brych, Mareike; Murali, Supriya; Händel, Barbara · 2021 · Crossref

DOI: 10.1371/journal.pone.0258322

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Summary

This study investigates the specific factors driving the increased blink rate observed during conversation, aiming to disentangle the roles of motor activity, cognitive load, and auditory input. While it is well-established that blink rates rise during social interaction compared to rest, the underlying mechanisms remain unclear. The authors hypothesized that complex facial motor movements, rather than cognitive demands or auditory feedback, are the primary drivers of this increase. This distinction is clinically significant, as blink rate is often used as a neurological indicator for conditions like Parkinson’s disease and as a marker for cognitive load; if speaking inherently increases blinking via motor pathways, such metrics could be confounded. To test this, the researchers conducted a series of experiments with 30 participants, utilizing eye-tracking technology to record blink rates while minimizing visual and social influences. The experimental design isolated specific variables through distinct tasks: "normal talking" (full speech), "talking inside the head" (cognitive load without motor output), "talking without sound" (motor output without auditory feedback), isolated lip movements (sucking a lollipop), isolated jaw movements (chewing gum), and passive listening to recorded monologues. Statistical analyses, including repeated measures ANOVAs and Bayesian inference, compared blink rates across these conditions against baseline rest periods. The results demonstrated that neither cognitive processes alone nor auditory input significantly altered blink rates compared to rest. Specifically, "talking inside the head" yielded blink rates statistically indistinguishable from baseline, and listening to either one’s own voice or another person’s did not significantly increase blinking relative to rest. In contrast, motor activity had a pronounced effect. "Talking without sound" significantly increased blink rates, nearly matching the rate observed during normal vocalized speech. Furthermore, isolated complex facial movements, such as sucking on a lollipop, also significantly elevated blink rates compared to baseline, whereas simple jaw movements from gum chewing did not reach statistical significance. The study concludes that complex facial motor movements associated with speech production are the primary cause of increased blink rates during conversation. The findings suggest that the anatomical proximity of facial and eyelid muscles facilitates this motor coupling. This has important implications for clinical and experimental psychology: blink rates measured during patient interviews or verbal tasks may reflect motor activity rather than cognitive state or neurological pathology. Consequently, researchers and clinicians should exercise caution when interpreting blink rate data collected during speaking, as the motor aspect of speech introduces a substantial confounding variable.

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• signaling behavior