It's not all about looks: The role of object shape in parietal representations of manual tools

The ability to build and expertly manipulate manual tools sets humans apart from other animals. Watching images of manual tools has been shown to elicit a distinct pattern of neural activity in a network of parietal areas, assumingly because tools entail a potential for action—a unique feature related to their functional use and not shared with other manipulable objects. However, a question has been raised whether this selectivity reflects a processing of low-level visual properties—such as elongated shape that is idiosyncratic to most tool-objects—rather than action-specific features. To address this question, we created and behaviourally validated a stimulus set that dissociates objects that are manipulable and nonmanipulable, as well as objects with different degrees of body extension property (tools and non-tools), while controlling for object shape and low-level image properties. We tested the encoding of action-related features by investigating neural representations in two parietal regions of interest (intraparietal sulcus and superior parietal lobule) using functional MRI. Univariate differences between tools and non-tools were not observed when controlling for visual properties, but strong evidence for the action account was nevertheless revealed when using a multivariate approach. Overall, this study provides further evidence that the representational content in the dorsal visual stream reflects encoding of action-specific properties.