A foundation for savantism? Visuo-spatial synaesthetes present with cognitive benefits

Individuals with ‘time–space’ synaesthesia have conscious awareness of mappings between time and space (e.g., they may see months arranged in an ellipse, or years as columns or spirals). These mappings exist in the 3D space around the body or in a virtual space within the mind's eye. Our study shows that these extra-ordinary mappings derive from, or give rise to, superior abilities in the two domains linked by this cross-modal phenomenon (i.e., abilities relating to time, and visualised space). We tested ten time–space synaesthetes with a battery of temporal and visual/spatial tests. Our temporal battery (the Edinburgh [Public and Autobiographical] Events Battery – EEB) assessed both autobiographical and non-autobiographical memory for events. Our visual/spatial tests assessed the ability to manipulate real or imagined objects in 3D space (the Three Dimensional Constructional Praxis test; Visual Object and Space Perception Battery, University of Southern California Mental Rotation Test) as well as assessing visual memory recall (Visual Patterns Test – VPT). Synaesthetes' performance was superior to the control population in every assessment, but was not superior in tasks that do not draw upon abilities related to their mental calendars. Our paper discusses the implications of this temporal–spatial advantage as it relates to normal processing, synaesthetic processing, and to the savant-like condition of hyperthymestic syndrome (Parker et al., 2006).