Abstract
Several cortical areas respond selectively to images of tools (e.g., hammers, paint-brushes) relative to other kinds of objects (e.g., clocks, shoes). What drives these responses? Tools have elongated shapes and are more likely to have motor associations, but an under-explored yet core property is that they exert causal effects on the environment. We hypothesized that tool-selective areas should respond to novel objects to the extent that these objects also exert causal effects. We used animations to imbue novel objects with causal properties by varying the temporal order of events: ‘causer’ objects moved before the appearance of an environmental event (e.g., stars appearing), while ‘reactor’ objects moved afterwards. Shapes were counterbalanced across conditions. In addition, the objects’ movements were either self-generated or initiated by an animated hand. Participants memorized the animations associated with each object, then viewed pictures of the objects during fMRI. In a separate localizer, responses to images of real-world tools (e.g., hammers) were contrasted to non-tool objects (e.g., clocks) to identify tool-selective lateral temporal (LOTC) and inferior parietal (IPL) areas. The reverse contrast was used to identify a non-tool-selective parahippocampal (PHC) area. We found that tool-selective LOTC responded more to causers than reactors (both self- and hand- initiated), and this causality effect was significantly stronger than in non-tool-selective PHC. Effects were robust even in the most tool-selective LOTC voxels. No effects were found in IPL. We suggest that LOTC has a preference for objects with causal effects, and this preference can emerge as a result of learning about event relations involving those objects.