Enhanced mental rotation ability in time-space synesthesia

Abstract

Time-space synesthesia is a variant of sequence-space synesthesia and involves the involuntary association of months of the year with 2D and 3D spatial forms, such as arcs, circles, and ellipses. Previous studies have revealed conflicting results regarding the association between time-space synesthesia and enhanced spatial processing ability. Here, we tested 15 time-space synesthetes, and 15 non-synesthetic controls matched for age, education, and gender on standard tests of mental rotation ability, spatial working memory, and verbal working memory. Synesthetes performed better than controls on our test of mental rotation, but similarly to controls on tests of spatial and verbal working memory. Results support a dissociation between visuo-spatial imagery and spatial working memory capacity, and suggest time-space synesthesia is associated only with enhanced visuo-spatial imagery. These data are consistent with the time-space connectivity thesis that time-space synesthesia results from enhanced connectivity in the parietal lobe between regions supporting the representation of temporal sequences and those underlying visuo-spatial imagery.

Do sequence-space synaesthetes have better spatial imagery skills? Yes, but there are individual differences

“…A similar effect has previously also been shown in a group of five sequence-space synaesthetes by Simner et al (2009), and in group of 15 sequence-space synaesthetes by Brang et al (2013). Our current study therefore represents the third instantiation of this effect.…”

“…It is already known that levels of intelligence positively 1 There is no evidence of systemaic diference across previous studies in the presence of 2D/3D forms, and the use of 2D/3D rotaion tasks: Simner et al (2009) and Rizza and Price (2012) both used a 3D object rotaion task whereas Brang et al (2013) used a 2D grapheme rotaion. No informaion regarding spaial dimensionality of forms was reported in either Simner et al (2009) or Rizza and Price (2012), although Brang and colleagues concluded that within their sample of synaesthetes (N=117), there was nearly a 50:50 split between those that experienced their forms as 2D or 3D.…”

“…S302). Nonetheless, a more recent study (Brang et al, 2013) subsequently did replicate this effect, by showing that n=15 sequence-space synaesthetes scored significantly more accurately than controls on their own rotation task (for the mental rotation of letters). In the current paper we provide yet another behavioural replication of the advantage of sequence-space synaesthetes in mental rotation, as well as an attempt to understand why Rizza and Price failed to find the effect in their own paper.…”

“…For example, it is possible that projected forms in particular -i.e., those with object-like qualities that are imaged outside the body --could perhaps be somehow more tangible and so more easily manipulated; if so, projector synaesthetes might be more practiced in mental rotation type tasks. Equally, performance on a mental rotation task might be enhanced if the rotation task is congruent to the synaesthetic spatial representation: 3D spatial forms might benefit a 3D mental rotation task (see Brang et al, 2013 for a similar argument 1 ). For both these reasons, we also include these two individual differences in our study and ask how they might predict performance on tests of mental rotation.…”

“…Synaesthetes can also differ in the way their forms are experienced: firstly, forms can occupy either 2D space or 3D space (Brang et al, 2013). A 3D form might extend away from the body horizontally, vertically and laterally, while 2D forms might extend, for example, just in a planar circle.…”