This dimension had quite general effects on both oculomotor and somatosensory measures together. The number of participants in our study is too small to explore   the factors underlying these correlations, though it does allow us to test specific models of vestibular-somatosensory interaction suggested by the aggregation approach, using confirmatory  , as opposed to exploratory   analyses. To find more test alternative models of this interaction, we next created structural equation models of specific patterns of vestibular-somatosensory interaction using SAS PROC CALIS. In such modelling, better-fitting models have higher probability values associated with chi-squared statistics (inability to

show difference of data from model predictions). They also have lower values of Akaike’s Information Criterion (AIC), which is adjusted for parsimony. A first model with a single latent factor influencing all somatosensory and all

vestibular measures provided the best fit [ χ(5)2=3.32, p   = .67, AIC = −6.77]. Interestingly, this latent factor had much lower loading for pointing (standardised weight .11) than for either oculomotor (slow-phase .33, fast-phase −.48) or somatosensory measures (touch 1.22, pain −.43). Goodness of fit was reduced for a two factor model in which touch NVP-BGJ398 mw and pain measures were linked to one latent factor and the three vestibular measures to another [ χ(4)2 = 3.22, p = .52, AIC = −4.78]. Finally, a model in which touch, pain and vestibular measures reflected three separate factors failed to converge. Thus, these methods confirmed a direct link between vestibular system activation and somatosensory perception.

Since the CVS procedure itself could induce changes in general arousal levels, which might in turn influence perception, we performed an additional time-course analyses, considering the interval between irrigation and touch Aspartate or pain threshold measures. We reasoned that these arousal effects would most probably be linked to the unusual sensations of irrigation itself, and any brief subsequent experience of vertigo, and would therefore be short-lived. Any arousal effects would decrease over the five successive blocks of touch or pain threshold estimation. A linear trend analysis showed no time-related changes across the five blocks of the Post-CVS condition in any of the dependent variables (touch left hand: p = .991; touch right hand: p = .900; pain left hand: p = .804 and pain right hand: p = .699) ( Fig. 2C). Moreover, a further ANOVA using block number as an additional factor showed no significant differences between any of the five blocks after Bonferroni correction for multiple comparisons (all p > .05 corrected). Vestibular input reduces the detection threshold of faint tactile stimuli delivered to either hand. Intriguingly, CVS also dramatically increases the threshold for detecting pain. Again, the modulation affects both the ipsilateral and contralateral hand.