the last couple of years have seen a marked growth of interest in the topic of crossmodal correspondences ( see marks , 2004 ; spence , 2011 , for reviews ) .
crossmodal correspondences have been defined as a tendency for a sensory feature , or attribute , in one modality , either physically present or merely imagined , to be matched ( or associated ) with a sensory feature in another sensory modality ( see parise & spence , in press ; spence , 2012 ) .
crossmodal correspondences have now been documented between pretty much every pair of sensory modalities ( see spence , 2012 ) .
crossmodal correspondences affect behavior in a wide range of experimental paradigms  everything from the redundant target paradigm through to the implicit association test ( see spence , 2011 ) . but how should such phenomena be explained at the computational / neural level ? at the computational level , bayesian coupling priors appear to provide a powerful tool to model the effects of crossmodal correspondences on multisensory integration ( ernst , 2007 ; parise & spence , 2009 ; spence , 2011 ) .
the latest cognitive neuroscience research is now starting to provide answers regarding the time course and cerebral localization of these , often surprising , cross - sensory mappings ( bien , ten oever , goebel , & sack , 2012 ; sadaghiani , maier , & noppeney , 2009 ; seo , et al .
one critical research question in this area concerns whether crossmodal correspondences are all of a kind or whether instead there are different kinds / mechanisms of correspondence at work ( spence , 2011 ) .
one might , for example , want to know whether those correspondences that are based on the internalization of the correlations between stimuli / dimensions present in the environment are represented differently than the semantic correspondences associated with our tendency to use the same terms to describe , for example , certain sounds as having a  high  frequency while at the same time also using the same descriptor when talking about certain elements in a perfume or perhaps wine aroma ( so - called  high notes  ) .
while discriminating between different kinds of crossmodal correspondence has sometimes been possible using behavioral techniques ( gallace & spence , 2006 ) , it is undoubtedly true that more robust insights into the shared vs. distinct mechanism(s ) underlying various examples of crossmodal correspondence are likely to emerge from a better understanding of the neural substrates underpinning these effects . in their latest research ,
2012 ) utilized a simplified version of the psychophysical paradigm developed by parise and spence ( 2009 ) demonstrating enhanced multisensory integration for crossmodally corresponding pairs of auditory and visual stimuli ( small or large circles and low- vs. high - pitched sounds ; with integration being assessed by means of the magnitude of the spatial ventriloquism effect ) . using event - related potentials ( erps ) , bien et al .
( 2012 ) looked for any differences in the pattern of neural activation on those trials where crossmodally congruent vs. incongruent pairs of stimuli were presented .
2010 ) have also demonstrated similar effects when comparing the erps elicited by crossmodally congruent vs. incongruent combinations of abstract visual symbols and orthonasally presented odors ( see also kovic et al . , 2009 ) .
interestingly , the magnitude of the p2 component at parietal recording sites correlated with the effects reported behaviorally in the study of bien et al .
these researchers then used source localization to infer the likely source of this congruency effect as originating in right intraparietal sulcus , a site that was then temporarily lesioned by applying offline transcranial magnetic stimulation ( tms ) .
crucially , this intervention led to the elimination of the effect of crossmodal congruency on participants ' behavioral performance ( not to mention on the erp signal ) .
( 2012 ) builds nicely on the earlier psychophysical research of parise and spence ( 2009 ) while also complementing the results of a study by sadaghiani et al .
( 2009 ) that highlighted differing neural substrates for natural , metaphorical , and linguistic mappings ( or crossmodal correspondences ) . that said , given that bien et al .
( 2012 ) did not fit psychometric curves to their data , it is still an open question whether the effects induced by tms are due to the reduced integration of crossmodally congruent stimulus pairs or else to a horizontal shift in perceptual space . in an earlier tms study by muggleton , tsakanikos ,
walsh , and ward ( 2007 ) , lesioning of right intraparietal cortex using tms knocked out stroop - like interference effects in a group of synesthetic participants . however , before jumping to the conclusion that the same neural substrates may underlie both crossmodal correspondences and synesthesia , it is worth noting that the cortical site targeted in the two studies was actually separated by a few centimeters . of course , the fact that tms was not applied over a control site in the study of bien et al .
( 2012 ) also means that it is not possible to know exactly how specific ( in neural terms ) their tms effects really were .
the temporary lesioning approach to the study of crossmodal correspondences highlighted by bien et al .
( 2012 ) complements previous anecdotal reports that damage to other neighboring regions ( e.g. , the angular gyrus , located within the temporal  parietal  occipital , region ) results in the loss of  the takete  maluma effect  ( see figure 1 ) . in the future ,
our understanding of the mechanism(s ) underlying the many forms of crossmodal correspondence that have been documented behaviorally in recent years ( see parise & spence , in press ; spence , 2011 , 2012 ) are likely to be greatly enriched by further cognitive neuroscience research using techniques such as tms .
indeed , one might even go so far as to consider whether certain coupling priors underpinning crossmodal correspondences ( e.g. , between auditory and visual stimuli ) might not be encoded in the intraparietal sulcus itself ( cf .
better fits with the angular shape shown on the left , whereas the word  maluma  fits better with the rounded shape displayed on the right .
even those individuals from cultures without any written language have been shown to exhibit this effect ( see bremner et al .
the only exceptions to this generalization appear to be those suffering from damage to the angular gyrus ( ramachandran & hubbard , 2003 ) and certain individuals suffering from autism spectrum disorder ( oberman & ramachadran , 2008 ; ramachandran & oberman , 2006 ) .
 in a recent article , n. bien , s. ten oever , r. goebel , and a. t. sack ( 2012 ) used event - related potentials to investigate the consequences of crossmodal correspondences ( the  natural  mapping of features , or dimensions , of experience across sensory modalities ) on the time course of neural information processing . 
 then , by selectively lesioning the right intraparietal cortex using transcranial magnetic stimulation , these researchers went on to demonstrate ( for the first time ) that it is possible to temporarily eliminate the effect of crossmodal congruency on multisensory integration ( specifically on the spatial ventriloquism effect ) . 
 these results are especially exciting given the possibility that the cognitive neuroscience methodology utilized by bien et al . 
 ( 2012 ) holds for dissociating between putatively different kinds of crossmodal correspondence in future research . 
Introduction