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Santani Teng, Radoslaw Cichy, Dimitrios Pantazis, Aude Oliva; Tracking tactile braille brain responses in space and time. Journal of Vision 2018;18(10):1225. doi: https://doi.org/10.1167/18.10.1225.
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© ARVO (1962-2015); The Authors (2016-present)
When read by blind individuals, tactile braille characters undergo a cascade of transformations over space, time, and representational format. This processing stream is known to recruit typically visual cortical regions as it changes somatosensory dot patterns to semantically meaningful representations. To elucidate the poorly understood spatiotemporal, as well as representational, dynamics of this reorganized functional network, we applied multivariate decoding and representational similarity analysis to magnetoencephalography (MEG) recordings of blind participants' brain responses to braille letters presented to the finger pads. Following previous work suggesting largely idiosyncratic patterns in a sample of braille readers, we presented single alphabetical braille letters in random order during MEG recording of early-blind, braille-proficient individuals in multiple sessions. Subjects performed a 1-back task in which they passively read presented letters and responded via button press to occasional repeated trials, which we excluded from further analysis. To increase the spatial specificity of the signal, we extracted left and right sensorimotor, early "visual" (EVC), and fusiform regions of interest (ROIs) from individual MRI anatomical scans. We then used MVPA to decode letter identity pairwise over time and construct a representational dissimilarity matrix (RDM) of pairwise relationships between letter signals for each time point. Earliest and strongest decoding signals were found specific to the sensorimotor ROIs contralateral to the stimulated finger. EVC and fusiform ROIs showed later onsets and noisier, more sustained representations. Early representational patterns as operationalized by model RDMs are consistent with a sensitivity to low-level letter complexity (e.g., number of dots) in somatosensory cortex, while later representations in downstream ROIs exhibited weaker adherence to this scheme. Our results offer a window into the sensory-to-semantic transformation of braille stimuli as well as a model for investigating the dynamics of crossmodal plasticity in sensory loss generally.
Meeting abstract presented at VSS 2018
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