Saccades to both vision and touch are modified following adaptation but cross-modal transfers are asymmetrical

Adaptation of reactive saccades (RS), made toward the sudden appearance of stimuli in our environment, is a plastic mechanism thought to occur at the motor level of saccade generation. As saccadic oculomotor commands integrate multisensory information in the parietal cortex and superior colliculus, adaptation of RS should occur not only toward visual but also tactile targets. In addition, saccadic adaptation in one modality (vision or touch) should transfer cross-modally. To test these predictions, we used the double-step target paradigm to adapt rightward saccades made at two different eccentricities toward the participants' index and middle fingers, identified either visually (experiment 1) or tactually (experiment 2). In each experiment, the rate of adaptation induced for the adapted modality and the rate of adaptation transfer to the nonadapted modality were compared with that measured in a control (no adaptation) session. Results revealed that touch-triggered RS can be adapted as well as visually triggered ones. Moreover, the transfer pattern was asymmetric: visual saccadic adaptation transferred fully to tactile saccades, whereas tactile saccadic adaptation, despite full generalization to nonadapted fingers, transferred only partially to visual saccades. These findings disclose that in the case of tactile saccades, adaptation can be elicited in the absence of postsaccadic visual feedback. In addition, the asymmetric adaptation transfer across sensory modalities suggests that the adaptation locus for tactile saccades may occur in part upstream of the final motor pathway common to all saccades. These findings bring new insights both on the functional loci(us) and on the error signals of RS adaptation.