The language of mental images: Characterizing hippocampal contributions to imageable word use during event construction
Accumulating evidence suggests that the hippocampus plays a critical role in the creative and flexible use of language. For example, amnesic patients with hippocampal damage produce less coherent and cohesive verbal discourse when constructing narratives about the past, present, and future. A recent study by Hilverman and colleagues (2017) found that amnesic patients with hippocampal damage also use less imageable words during narrative construction compared to healthy controls. These results suggest that in addition to supporting language use at the discourse level, the hippocampus also influences the quality of language at the single word level. However, the generalizability of these results to different types of language production tasks and the relationship to patients broader impairments in episodic memory have yet to be examined. In the current study, we investigated whether amnesic patients with hippocampal damage produce less imageable words compared to healthy controls in two different types of language production tasks. In Experiment 1, participants constructed narratives about events depicted in visually presented pictures (picture narratives). In Experiment 2, participants constructed verbal narratives about remembered events from the past or simulated events in the future (past/future narratives). Across all types of narratives, patients produced words that were rated as having similar levels of imageability compared to controls. Importantly, this was the case both in patients picture narratives, which did not require generating details from long-term memory and were matched to controls with respect to narrative content, and in patients narratives about past/future events, which required generating details from long-term memory and which were reduced in narrative content compared to those of controls. These results reveal that the hippocampus is not necessary for the use of imageable representations at the linguistic level, and that hippocampal contributions to imageable word use are independent of hippocampal contributions to episodic memory.