Investigating mental simulation during sentence comprehension in aphantasia.

Aphantasia is a condition in which individuals do not consciously experience visual imagery. There is ongoing debate concerning whether language comprehension involves visual imagery or only unconscious mental simulation (modality-specific perceptual reactivation). To test this directly, we investigated mental simulation during sentence comprehension in a group of individuals with aphantasia. We compared aphantasics to controls on their response time and accuracy on a sentence-picture verification task. In two experiments, participants read sentences (e.g., Melissa's dog was hard to find in the mud) and had to decide whether a subsequently presented image (e.g., a dog) was mentioned in the sentence or not. In Experiment 1 the presented picture could match or mismatch the sentence in terms of the object's implied color, whereas in Experiment 2 the presented picture could match or mismatch the sentence in implied distance (a near versus far away object). In Experiment 1, both controls and aphantasics showed a match effect, suggesting both groups engaged in mental simulation of object color. In contrast to previous work, in Experiment 2 we found no evidence of mental simulation of distance in controls (or aphantasics). Our results are in line with the conclusion that voluntary, conscious visual imagery and involuntary, unconscious mental simulation are separate processes. We interpret the results as evidence for unconscious, involuntary mental simulation during sentence comprehension in aphantasia.