Investigating Grounded Conceptualization: Stimulus-Response Compatibility for Tool Handles Is Due to Spatial Attention

Brain imaging research shows that viewing tools activates regions of the cortex implicated in performing actions with that tool. Grounded (or embodied) theories of cognition propose that this activity reflects the activation of motor representations that are constitutive of the object concept. Behaviorally, participants respond faster with the hand that is aligned with the handle of an object. This stimulus-response compatibility (SRC) effect is often taken as evidence supporting the hypothesis that motor representations are activated in response to the visual presentation of tools during conceptual processing. To test this hypothesis, we trained participants to use a set of novel tools (manipulation group) or to report spatial information about the tools (spatial group) in preparation for a Martian archeological dig. We investigated compatibility effects in a conceptual judgment task and a visual discrimination task. Compatibility effects were observed for both groups regardless of experience. These effects were predicted by the salient parts of objects specified by task demands and not by motor experience with the objects. This result provides evidence that compatibility effects with tools reflect a general stimulus-response compatibly effect due to visual attention. Public Significance Statement When we judge pictures of tools, we tend to be faster at responding with our hand that is on the same side of space as the handle. This has led some researchers to suggest that seeing tools automatically activates motor programs in the brain that are used to interact with the tools. The other explanation is that humans are just generally better at reaching toward the location of their attention. We trained "Martian archeologists" to either (a) use a new set of tools or (b) explain how they are stored when not in use. It turns out that both groups were faster at responding with a hand that is on the same side of attention. This rules out the idea that motor activations contribute to the phenomena and shows that the attention account is sufficient to explain it.