SYNAESTHESIA is a neurological condition in which there is a merging of the senses, so that activity in one sensory modality elicits sensations in another. Although first described by Francis Galton in the 1880s, little was known about this condition until recently. A rennaissance in synaesthesia research began about a decade ago; since then, three previously unrecognized forms of the condition have been described, and hypotheses for how it arises have been put forward.
Two new studies now provide some insight into time-space synaesthesia, the least researched of all the forms of this fascinating condition. One is a case study of an individual whose time-space synaesthesia has an apparently unique characteristic. The second demonstrates that time-space synaesthetes are superior to non-synaesthetes in some cognitive abilities, and suggests that time-space synaesthesia may underly the savant-like abilities of people with hyperthymestic (or “super-memory”) syndrome.
Time-space synaesthesia is a form of visuo-spatial synaesthesia in which individuals experience units of time – such as hours, days, or months – as occupying specific locations in space relative to their own body. These associations are highly specific and are experienced consistently. For example, one synaesthete described her experience as follows: “When someone mentions a year, I see the oval with myself at the very bottom, Christmas day to be precise. As soon as a month is given, I see exactly where that month is on the oval. As I move through the year, I am very aware of my place on the oval at the current time, and the direction I am moving in.”
Michelle Jarick of the Synaesthesia Research Group at the University of Waterloo in Ontario and her colleagues describe the case of an individual whose time-space synaesthesia has a previously undescribed feature. Like other time-space synaesthetes, the 21-year-old individual, known as L, experiences the time of day and the months of the year as being represented in the space around her body. She experiences the hours of the day in the form of a large “clock face”, and her mental calender consists of a giant number “7″, which extends for approximately 1 meter around her waist, and on which the months of the year are arranged.
Uniquely though, L’s mental vantage point changes depending on whether she sees or hears the time unit. When presented visually with the name of a month, she reports seeing the giant 7 as if she was standing in its crux, with the month of April directly in front of her. From this perspective, she experiences January, February and March to her left, May and June to her right, and the rest of the months of the year, which form the tail of the 7, running along her right side and behind her.
When she hears or thinks about the name of a month, L still experiences the months as being arranged in the same way, but perceives them from a different vantage point, as if she had walked around the arm of the 7. From this perspective, January, February and March are to her right, while May and June are to her left, and the remaining months extend forward on her left. She also reports similar changes in vantage point when she sees or hears the hours of the day. (The diagram on the right shows a “bird’s eye view” of the vantage points associated with vision (V) and hearing (A).)
To verify L’s reported experiences objectively, the researchers used a spatial cueing paradigm, in which a visual month cue was presented to the centre of her field of vision, followed by a target square presented to the left or right of the cue. They predicted that the visual cues would trigger shifts in her spatial attention that affect the time she takes to detect and respond to the target squares. For example, if presented with a visual cue for the month of January, this should orient her attention to the left, making her detect targets presented to the left quicker than those presented to the right. By contrast, an auditory cue for the same month should shift her attention to the right.
L’s performance on this task was compared with that of ten non-synaesthetic controls. The visual month cues were presented on a computer monitor for 600 milliseconds each, followed by a target square. The participants were asked to press a button as soon as they detected the presence of the target. As predicted, following visual cues of the first three months, L detected targets presented to the left significantly quicker than those presented to the right. Similarly, cues presented to the right were detected more quickly following visual presentations of the later months. For cues presented aurally, the opposite cueing pattern was observed. However, none of these effects was observed in the non-synaesthetic participants.
L’s calender is a purely mental space, generated by her brain. Yet, as this study shows, there is a strong correspondence between this imagined space and spaces in the real world. One can explore real external spaces from multiple vantage points, and these characteristics seem to apply also to L’s mentally generated calender. The study also shows that time-space synaesthesia can bias visual perception and affect behaviour accordingly – L could not process the time units without biasing her visual attention towards the corresponding location in the space around her. As a result, her reaction times to the targets presented in the appropriate region of external space became quicker.
Julia Simner of the University of Edinburgh and her colleagues provide further evidence that the visual, spatial and temporal abilities of time-space synaesthetes are superior to those of non-synaesthetes. They recruited ten time-space synaesthetes, and compared their performance on eight different tasks to those of non-synaesthetic controls. The synaesthetes were able to recall the dates of autobiographical, cultural and world political events more accurately than the non-synaesthetic controls. They also out-performed the controls in tasks involving the manipulation of objects in three-dimensional space, the recognition of 3D objects from 2D silhouette representations, non-verbal visual short-term memory, and mental rotation of 2D drawings of 3D objects.
The authors argue that time-space synaesthesia may underly hyperthymestic syndrome. Individuals with this syndrome have an exceptional autobiographical memory, and can recall life events, as well as other events which coincided with them, in remarkable detail. These recollections are, according to one hyperthymestic, “non-stop, uncontrollable and automatic“. The first documented case of hyperthymestic syndrome, a woman referred to in the literature as A.J., reported that her prodigious memory was at least partly due to an ability to mentally map time in space. Her super memory therefore appears to be closely linked to what Simner’s group assume to be time-space synaesthesia
Two of the synaesthetes studied by Simner and her colleagues spontaneously reported having exceptional memories for dates and events. This suggests that there are parallels between time-space synaesthesia and hyperthymestic syndrome. It also raises the possibility that all time-space synaesthetes have hyperthymestic syndrome, but this is not the case. Time-space synaesthesia may be necessary, but not sufficient, for hyperthymesia, and could possibly lie at the heart of the condition.
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Jarick, M., et al. (2009). A different outlook on time: Visual and auditory month names elicit different mental vantage points for a time-space synaesthete. Cortex 45: 1217-1228. DOI: 10.1016/j.cortex.2009.05.014.
Simner, J., et al. (2009). A foundation for savantism? Visuo-spatial synaesthetes present with cognitive benefits. Cortex 45: 1246-1260. DOI: 10.1016/j.cortex.2009.07.007.