We introduce a distinction between cortical dominance andcortical deference, and apply it to various examples ofneural plasticity in which input is rerouted intermodally orintramodally to nonstandard cortical targets. In some cases butnot others, cortical activity `defers’ to the nonstandard sourcesof input. We ask why, consider some possible explanations, andpropose a dynamic sensorimotor hypothesis. We believe that thisdistinction is important and worthy of further study, bothphilosophical and empirical, whether or not our hypothesis turnsout to be correct. In particular, the question of how the distinction should be explained is linked to explanatory gapissues for consciousness. Comparative and absolute explanatorygaps should be distinguished: why does neural activity in aparticular area of cortex have this qualitative expressionrather than that, and why does it have any qualitativeexpression at all? We use the dominance/deference distinction toaddress the comparative gaps, both intermodal and intramodal (notthe absolute gap). We do so not by inward scrutiny but rather by expanding our gaze to include relations between brain, body and environment.

Key words: consciousness, cortical deference, cortical dominance, dynamic sensorimotor contingencies, explanatory gaps, neural plasticity, perceptual adaptation, phantom limbs, synaesthesia.

People with synaesthesia have additional perceptual experiences, which are automatically and consistently triggered by specific inducing stimuli. Synaesthesia therefore offers a unique window into the neurocognitive mechanisms underlying conscious perception. A long-standing question in synaesthesia research is whether it is possible to artificially induce non-synaesthetic individuals to have synaesthesia-like experiences. Although synaesthesia is widely considered a congenital condition, increasing evidence points to the potential of a variety of approaches to induce synaesthesia-like experiences, even in adulthood. Here, we summarize a range of methods for artificially inducing synaesthesia-like experiences, comparing the resulting experiences to the key hallmarks of natural synaesthesia which include consistency, automaticity and a lack of ‘perceptual presence’. We conclude that a number of aspects of synaesthesia can be artificially induced in non-synaesthetes. These data suggest the involvement of developmental and/or learning components in the acquisition of synaesthesia, and they extend previous reports of perceptual plasticity leading to dramatic changes in perceptual phenomenology in adults.

Key words: perception, plasticity, consciousness, training, phenomenology, synaesthesia.