Metamodal Coupling of Vibrotactile and Auditory Speech Processing Systems Through Matched Stimulus Representations

Summary It has been postulated the brain is organized by “metamodal”, sensory-independent cortical modules implementing particular computations. Yet, evidence for this theory has been variable. We hypothesized that effective metamodal engagement requires not only an abstract, “cognitive” congruence between cross-modal stimuli but also a congruence between neural representations. To test this hypothesis, we trained participants to recognize vibrotactile versions of auditory words using two encoding schemes. The vocoded approach preserved the dynamics and representational similarities of auditory speech while the token-based approach used an abstract phoneme-based code. Although both groups learned the vibrotactile word recognition task, only in the vocoded group did trained vibrotactile stimuli recruit the auditory speech network and lead to increased coupling between somatosensory and auditory speech areas. In contrast, the token-based encoding appeared to rely on paired-associate learning. Thus, matching neural input representations is a critical factor for assessing and leveraging the metamodal potential of cortical modules.