Pupillometric evidence for perceptual simulation in language comprehension: Sensory and emotional meanings of Japanese adjectives

Previous research has demonstrated that words associated with brightness (e.g., "sun") elicit smaller pupil diameters than those related to darkness (e.g., "night"). The present study aimed to determine whether these language-induced pupillary responses are driven by the luminance of the mentally simulated content-referred to here as <i>sensory interpretation</i>-or by the conceptual brightness linked to the words' emotional valence, termed <i>emotional interpretation</i>. To address this question, we utilized the Japanese adjectives <i>akarui</i> and <i>kurai</i>, which can denote both luminance, as in the noun phrase <i>akarui/kurai gamen</i> ("bright/dark screen"), and emotional valence, as in <i>akarui/kurai seikaku</i> ("cheerful/gloomy personality"). Participants were presented with noun phrases composed of these adjectives and various nouns (<i>akarui/kurai</i> + noun). A significant main effect of the adjective indicated that phrases containing <i>akarui</i> yielded smaller pupil diameters than those containing <i>kurai</i>. Furthermore, although the interaction effect did not reach significance, the adjective effect was observed only when the adjectives conveyed luminance, not when they conveyed emotional valence. These findings suggest that sensory, rather than emotional, interpretation better explains language-induced changes in pupil size. The use of pupillometry as a measure of perceptual simulation offers more direct and compelling evidence in support of the central claim of embodied language theories: that during language comprehension, readers and listeners spontaneously generate sensorimotor simulations of the described content. Future studies are warranted to examine whether these findings extend to sentence- and discourse-level processing, as well as to simulations of information conveyed implicitly or indirectly through language.