Cortical representations of auditory and tactile perceptual decisions

Perceptual decision making is the process that makes a rich environment manageable by compartmentalizing stimuli into various categories. Parietal cortex is involved in many tasks that require perceptual decisions. While much work in both the human and monkey domains has investigated processes related to visual decision making in the frontal and parietal lobes in a predominantly unimodal fashion, relatively little research has explored auditory and tactile perceptual decisions. As such, we wanted to know whether these regions also play a role in auditory and tactile decision making and to what extent information therein may be represented supramodally. Using functional magnetic resonance imaging and a paradigm requiring human participants to categorize auditory and tactile frequency-modulated sweeps, we sought to disentangle motor confounds and minimize linguistic processing from the perceptual decisions that participants made. We ran a series of experiments that utilized whole-brain multivariate pattern analysis implemented via linear discriminant analysis classification in order to detect cortical representations of such potentially supramodal information. Ultimately, we showed that learned categories were best decoded within the right parietal lobe and the medial frontal gyrus, supramodal representations of “up- vs. down-sweeps” were localized to the left parietal-temporal-occipital junction, and, most consequentially, cross-modality decoding of category membership was strongest in the left posterior insula and precuneus. Given our choice of paradigm, such results appear to demonstrate that the information representations in the posterior insula and precuneus are independent of motor and language processing and instead reflect supramodal or modality-free mechanisms that underlie the categorization process.