Somatosensory Involvement in the Conceptual Representation of Objects
The involvement of the sensorimotor system in visual object processing is at the forefront of cognitive neuroscience research. Since the discovery of the mirror neuron system, a plethora of research has been dedicated to understanding how action influences cognition. Of particular interest to the current work is the way in which two-dimensional objects are represented in the human brain. Embodied cognition theories assert that the sensorimotor system plays a large (if not entire) role in the conceptual representation of objects. Interestingly, however, although somatosensation provides the first means of acquiring information from our environments and thus is integral to the development of conceptual representation, research has generally focused on motor system contributions to object processing. Therefore, this series of experiments will focus on unravelling the relationship between the somatosensory system and object processing. To do this, we employed two different priming paradigms, one in which vibratory stimulation served as a prime and an object picture as the target (Experiments 1 to 4), and the other where the object was the prime and the vibration the target (reverse priming task; Experiments 5 and 6). In Experiments 1 to 3, the participant was required to indicate how they would interact with the presented object (i.e., a semantic generation task). Results from Experiments 1 and 2 showed that object processing of graspable objects could be facilitated by a vibratory hand prime, compared to non-graspable objects (Experiment 1) and objects with foot related action affordances (Experiment 2), both of which showed no priming effects. Experiment 3 used a vibratory foot prime to investigate whether the priming effects in Experiments 1 and 2 were due semantic matching effects, such that drawing attention to a modality serves to enhance processing of objects related to that modality, and found no evidence to support this account. Experiment 4 assessed the degree to which sensorimotor representations are automatically activated using an object-naming paradigm, which showed no somatosensory priming effects, and thus no evidence for automatic somatosensory involvement. Experiment 5 utilized the reverse priming task (described above), and found evidence for faster somatosensory detection when primed with a hand object, providing converging evidence of a reciprocal relationship between the somatosensory system and object processing. Finally, Experiment 6 examined whether the results from Experiment 5 were due to matching effects (similar to Experiment 3), and found no evidence for this account. Taken together, our research provides corroborative, converging evidence that semantic knowledge about how one interacts with manipulable objects involves sensorimotor representations in the somatosensory system. This supports theories of embodied cognition and the mirror neuron system, and extends them from the motor domain to accommodate somatosensory influences, opening a new window into exploration of how touch may be incorporated into these theories. Implications for models of the mirror neuron system, and future directions for localizing these effects using neuroimaging are discussed.
Somatosensory priming, object processing, embodied cognition
Master of Arts (M.A.)