ERP investigations into the effects of gaze and spatial attention on the processing of tactile events

Previous research demonstrated that directing one’s gaze at a body part reduces detection speed (e.g., Tipper et al., 1998) and enhances the processing (Forster and Eimer, 2005) of tactile stimuli presented at the gazed location. Interestingly, gaze-dependent modulation of somatosensory evoked potentials (SEPs), are very similar to those observed in previous studies of tactile spatial attention. This might indicate that manipulating gaze direction activates the same mechanisms that are responsible for the covert orienting of spatial attention in touch. To investigate this possibility, gaze direction and sustained tactile attention were orthogonally manipulated in the present study. In different blocks of trials, participants focused their attention on the left or right hand while gazing to the attended or to the unattended hand while they had to respond to infrequent tactile targets presented to the attended hand. Analyses of the SEPs elicited by tactile non-target stimuli demonstrate that gaze and attention influence different stages of tactile processing. While gaze is able to modulate tactile processing already 50 ms after stimulus onset, attentional SEP modulations are only observed beyond 110 ms post-stimulus. This dissociation in the timing and therefore the associated locus of the effects of gaze and attention on somatosensory processing reveals that the effect of gaze on tactile processing is independent of tactile attention.