Event-related potential evidence for the use of external coordinates in the preparation of tactile attention by the early blind.

Recent studies have suggested that visual experience in childhood is crucial for the automatic activation of an external spatial reference frame in tactile perception. These findings are largely based on behavioural work, with limited exploration using event-related potentials (ERPs). The present study examined the role of external spatial frameworks on tactile perception by recording ERP correlates of both preparatory processes and somatosensory processing during a tactile attention task for a group of early blind participants and age-matched sighted controls who carried out the task in darkness. Participants had to shift attention to one hand or the other as indicated by an auditory cue presented at the start of each trial, in order to detect infrequent tactile targets delivered to the attended hand. Spatial information about the external environment was acquired in advance during tactile exploration of the testing booth. ERPs measured during the cue-target interval indicated a conflict between anatomical and external spatial reference frames for both early blind and sighted participants, as marked by the delayed onset of the anterior directing attention negativity, although the delay was more pronounced in the sighted. A delay was also observed, irrespective of visual experience, on the onset of attentional modulations of somatosensory ERPs elicited by tactile stimuli. Although these results confirm that neither concurrent nor developmental vision is necessary for the default use of an external spatial framework in tactile attention, they suggest that the relative impact of an external vs. an anatomical spatial coordinate system may be affected by visual experience.