Non-informative vision enhances tactile acuity: A systematic review and meta-analysis.

BACKGROUND Individual experimental data suggest that visual input during tactile stimulation enhances tactile appreciation - whether this finding is replicated across studies and across body sites is unknown. OBJECTIVE To determine the available evidence as to whether non-informative vision of the body has an effect on tactile acuity. METHODS Studies that assessed tactile acuity with vision of the body, compared to vision of a neutral object or vision occluded, were systematically identified and reviewed. Seven relevant electronic databases were searched from their inception to April 2014. Risk of bias was assessed using adapted criteria from the Cochrane Handbook. Effect sizes were calculated using mean differences in a random effects model. RESULTS Ten studies were included. All were randomized, within subject, controlled trials published in English (total n=232 participants), with low to moderate risk of bias. Despite the diversity of protocols and outcome measures used, eight of the studies reported improvements in tactile acuity when vision of the relevant body part (predominantly the hand) was available. Meta-analysis revealed statistically significant findings from grating orientation tests (p=0.002, SMD 3.31, 95% CI 1.24-5.39), demonstrating a positive effect of vision of the body. No significant effect was found for other sensory tests or for other body parts, such as the back, and statistical heterogeneity was high. CONCLUSIONS This review provides confirmatory evidence for a visual enhancement effect for tactile acuity for body parts where vision has a plausible functional linkage - further studies are required to elaborate on the mechanisms for multi-modal processing of sensory stimuli.