Novel tool use does not depend on mechanical reasoning: evidence from apraxia.

A hallmark of human intelligence is the ability to use tools. Yet the cognitive processes supporting this ability remain debated. One contemporary view holds that mechanical reasoning is central for tool use, especially in the case of tools with which we have no prior experience. However, previous support for the role of mechanical reasoning often relies on circular logic, wherein poor performance on novel tool-use tasks is taken as evidence that impaired mechanical reasoning causes tool-use deficits in limb apraxia. To address this limitation, we independently assessed mechanical reasoning and novel tool use in separate tasks in individuals with limb apraxia, and compared their performance to individuals without apraxia. We also examined whether these two abilities are similarly associated with other cognitive abilities including motor imagery, mental rotation of non-body objects, general reasoning, and spatial working memory. Finally, we explored brain-behavior relationships using support vector regression lesion-symptom mapping. Our behavioral and imaging data together showed that mechanical reasoning does not underlie novel tool-use deficits in apraxia. Graphical analysis further revealed that novel tool use and mechanical reasoning loaded onto distinct latent clusters: novel tool use was strongly associated with other praxis abilities yet separable from cognitive abilities that require reasoning and mental simulation, whereas mechanical reasoning was primarily linked to other high-level reasoning abilities but not tool use. These findings challenge the notion that mechanical reasoning is central to tool-use ability, and instead suggest that tool use is more likely to be an intuitive or automatic process.