Co-speech gesture is ubiquitous in everyday conversation, facilitating comprehension, learning, and memory. Information is often provided uniquely in the gesture modality and this information is integrated with speech, affecting the listener’s comprehension and memory of a message. Despite the robust evidence that gesture supports learning, the memory mechanisms that support this learning are unclear. The current study investigates the ability of patients with hippocampal damage to integrate and retain information from co-speech gesture.
Four patients with bilateral hippocampal lesions, four patients with damage to the ventral medial prefrontal cortex, and 17 healthy comparisons watched videos of a storyteller narrating four stories with gestures. Some of the gestures provided redundant information to the speech signal and some provided supplementary information that was unique. The participants retold the story immediately after, thirty-minutes after, and four weeks later. Co-speech gesture integration was measured by the proportion of words changed as a result of seeing a supplementary gesture. Memory retention for the stories was measured by the number of story features mentioned during each retelling.
The patients with hippocampal amnesia were successful at integrating speech and gesture information immediately after hearing the story but did not show a benefit in memory for gestured features after delays. Though the hippocampus has previously been thought to be critical for relational memory, this finding suggests that the integration of speech and gesture may be mediated by other cognitive mechanisms.