Abstract
Visuo-motor adaptation to optical prisms displacing the visual scene (prism adaptation, PA) is a method used for investigating visuo-motor plasticity in healthy individuals and, in clinical settings, for the rehabilitation of unilateral spatial neglect. In the standard paradigm, the adaptation phase involves repeated pointings to visual targets, while wearing optical prisms displacing the visual scene laterally. Here we explored differences in PA, and its aftereffects (AEs), as related to the sensory modality of the target. Visual, auditory, and multisensory – audio-visual – targets in the adaptation phase were used, while participants wore prisms displacing the visual field rightward by 10°. Proprioceptive, visual, visual-proprioceptive, auditory-proprioceptive straight-ahead shifts were measured. Pointing to auditory and to audio-visual targets in the adaptation phase produces proprioceptive, visual-proprioceptive, and auditory-proprioceptive AEs, as the typical visual targets did. This finding reveals that cross-modal plasticity effects involve both the auditory and the visual modality, and their interactions (Experiment 1). Even a shortened PA phase, requiring only 24 pointings to visual and audio-visual targets (Experiment 2), is sufficient to bring about AEs, as compared to the standard 92-pointings procedure. Finally, pointings to auditory targets cause AEs, although PA with a reduced number of pointings (24) to auditory targets brings about smaller AEs, as compared to the 92-pointings procedure (Experiment 3). Together, results from the three experiments extend to the auditory modality the sensorimotor plasticity underlying the typical AEs produced by PA to visual targets. Importantly, PA to auditory targets appears characterized by less accurate pointings and error correction, suggesting that the auditory component of the PA process may be less central to the building up of the AEs, than the sensorimotor pointing activity per se. These findings highlight both the effectiveness of a reduced number of pointings for bringing about AEs, and the possibility of inducing PA with auditory targets, which may be used as a compensatory route in patients with visual deficits.
Highlights
Prism adaptation (PA) is a technique that, through the use of goggles fitted with prismatic lenses inducing a lateral displacement of the visual field, allows to investigate short-term sensorimotor neuroplasticity in healthy participants (Redding et al, 2005)
Post hoc comparisons for the main effect of target modality showed that the pointing movements toward visual and audio-visual targets were more deviated to the right, as compared to those to auditory targets
The ANOVA on the visual test did not show any significant main effect or interaction [modality: F(2,46) = 0.48, p = 0.62; time: F(1,23) = 0.72, p = 0.41; modality by time: F(2,46) = 0.80, p = 0.45]. These findings demonstrate that PA, obtained by repeated visuo-motor pointings to targets in the visual, auditory, or audio-visual modalities, brings about comparable amounts of AEs in the proprioceptive, auditory-proprioceptive, and visualproprioceptive straight-ahead tests
Summary
Prism adaptation (PA) is a technique that, through the use of goggles fitted with prismatic lenses inducing a lateral displacement of the visual field, allows to investigate short-term sensorimotor neuroplasticity in healthy participants (Redding et al, 2005). Once the prisms are removed, the participants’ pointing movements are still deviated, but in the opposite direction of the previous visual displacement (‘after-effects’). Given the rehabilitative potential of PA (for reviews on USN and PA see Barrett et al, 2012; Newport and Schenk, 2012; Jacquin-Courtois et al, 2013), the need of a systematic investigation of this technique has been pointed out, in order to determine the optimal parameters for its clinical application, such as, for instance, the number of adaptation sessions, the type of visuo-motor activity, the magnitude of the prismatic displacement, the exposure duration, or the number of targets during exposure (for a comprehensive review of these issues see Jacquin-Courtois et al, 2013)
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