Sequence-space Synesthesia Research Articles

Enhanced spatial navigation skills in sequence-space synesthetes

Individuals with sequence-space synesthesia (SSS) perceive sequences like months, days and numbers in certain spatial arrangements. Several cognitive benefits have been associated with SSS, such as enhanced mental rotation, more vivid visual imagery and an advantage in spatial processing. The current study aimed to further investigate these cognitive benefits, focusing on spatial navigation skills, to explore if their enhanced sensitivity to spatial relations is reflected in enhanced navigational performance. Synesthetes were distinguished from controls by means of a questionnaire, a consistency test and drawings. A virtual Morris Water Maze (MWM) task with two allocentric and two egocentric navigation conditions was used to assess spatial navigation abilities. For the allocentric tasks, participants had to use object cues to find a hidden platform and for the egocentric tasks, they had to use their own position as a reference. Results showed that synesthetes performed significantly better compared to controls on the allocentric and egocentric tasks that reflected real life situations more accurately. However, this significant result was only found for the time taken to find the platform and not for the length of the path that was taken. In exploratory analyses, no significant relations were found between task performance and the specific features of the manifestation of each individual's synesthesia. Our hypothesis that synesthetes with the ability to mentally rotate their spatial arrangements would perform better on the allocentric task was not confirmed. Results add to the growing body of literature concerning the cognitive benefits of SSS and are consistent with the possibility that enhanced spatial navigation skills emerge from generally enhanced visuospatial abilities in SSS.

Synesthesia & autistic features in a large family: Evidence for spatial imagery as a common factor

BackgroundAutism and synesthesia are neurodevelopmental conditions associated with variants of perceptual processing. They also share some genetic variants and include a large magnitude of intra-categorical variation: 60 types for synesthesia, as well as a spectrum for autism. In order to investigate the relationship between these two phenomena, we investigated the family of FC, an autistic individual who also possess savant abilities and synesthesia manifestations. MethodAutistic symptoms were assessed for the entire sample of participants entering the study (39 individuals) using the SRS. Participants above threshold were evaluated with standardized diagnostic tools. Synesthesia was explored in the entire participating sample using a self-reported questionnaire. Consistency tests were used for participants who reported synesthetic manifestations. ResultsIn addition to FC, four individuals with ASD were detected. Fifteen participants self-reported synesthesia (15 sequence-space, 4 sound-shape, 4 day-color), among which nine sequence-space synesthetes satisfied the consistency criteria. Two participants possess both autism and synesthesia. ConclusionThis family illustrates the co-segregation of autism and synesthesia. This co-segregation is in favour of a partially overlapping genetic predisposition for both conditions, but also authorizes a large variety of manifestations in both conditions. The high prevalence of sequence-space synesthesia in this family strengthens the previous assumption that this form of synesthesia may be linked to autism. We discuss the potential role of spatial imagery in the development of this form of synesthesia and savant abilities.

Synaesthetes show advantages in savant skill acquisition: Training calendar calculation in sequence-space synaesthesia

Previous research has suggested that synaesthetic experiences may create the foundation for superior skills to emerge of the type found in savant syndrome (e.g., Simner, Mayo, & Spiller, 2009). People with sequence-space synaesthesia experience units of time (e.g., days, months, years) as a pattern in space, either within the mind's eye or as a 3d projection outside of the body. Our study investigates whether sequence-space synaesthesia facilitates the learning of the savant skill known as ‘calendar calculation’ where an individual can give the correct day of the week for any given date (e.g., 18th September 1990 was a Tuesday). Using a novel experimental methodology, we trained a group of sequence-space synaesthetes as well as non-synaesthete controls how to calendar calculate over two weeks with a final calendar calculation test in the third week. We show for the first time that calendar calculation is relatively easy to acquire: following training sessions totalling 1 h participants could select a day, from a set of several thousand, within ∼10 sec and with ∼80% accuracy. Synaesthetes were not found to have improved abilities from the start, but they outperformed controls in our final calendar calculation test. We suggest that sequence-space synaesthesia may have provided an advantage in performing calendar calculation after the opportunity for initial learning had taken place. This supports the notion of synaesthesia as a foundation for superior, and perhaps sometimes savant-like, skills.

The prevalence and cognitive profile of sequence-space synaesthesia.

People with sequence-space synaesthesia visualize sequential concepts such as numbers and time as an ordered pattern extending through space. Unlike other types of synaesthesia, there is no generally agreed objective method for diagnosing this variant or separating it from potentially related aspects of cognition. We use a recently-developed spatial consistency test together with a novel questionnaire on naïve samples and estimate the prevalence of sequence-space synaesthesia to be around 8.1% (Study 1) to 12.8% (Study 2). We validate our test by showing that participants classified as having sequence-space synaesthesia perform differently on lab-based tasks. They show a spatial Stroop-like interference response, they show enhanced detection of low visibility Gabor stimuli, they report more use of visual imagery, and improved memory for certain types of public events. We suggest that sequence-space synaesthesia develops from a particular neurocognitive profile linked both to greater visual imagery and enhanced visual perception.

Ignoring Irrelevant Information: Enhanced Intermodal Attention in Synaesthetes.

Despite the fact that synaesthetes experience additional percepts during their inducer-concurrent associations that are often unrelated or irrelevant to their daily activities, they appear to be relatively unaffected by this potentially distracting information. This might suggest that synaesthetes are particularly good at ignoring irrelevant perceptual information coming from different sensory modalities. To investigate this hypothesis, the performance of a group of synaesthetes was compared to that of a matched non-synaesthete group in two different conflict tasks aimed at assessing participants' abilities to ignore irrelevant information. In order to match the sensory modality of the task-irrelevant distractors (vision) with participants' synaesthetic attentional filtering experience, we tested only synaesthetes experiencing at least one synaesthesia subtype triggering visual concurrents (e.g., grapheme-colour synaesthesia or sequence-space synaesthesia). Synaesthetes and controls performed a classic flanker task (FT) and a visuo-tactile cross-modal congruency task (CCT) in which they had to attend to tactile targets while ignoring visual distractors. While no differences were observed between synaesthetes and controls in the FT, synaesthetes showed reduced interference by the irrelevant distractors of the CCT. These findings provide the first direct evidence that synaesthetes might be more efficient than non-synaesthetes at dissociating conflicting information from different sensory modalities when the irrelevant modality correlates with their synaesthetic concurrent modality (here vision).

What spatial coordinate defines color-space synesthesia?

Synesthesia is characterized by the association between different stimuli modalities. For example, in sequence-space synesthesia, numbers, weekdays, months, and musical tones are visualized in specific spatial locations. Although sequence-space synesthesia tends to co-occur with other types of synesthesia (e.g., grapheme-color), our knowledge about how these individuals represent space is still limited. A central issue for understanding spatial processing refers to the coordinate system used to represent spatial locations. We report on a space-color synesthete (N.W.) who vividly experiences colors in specific spatial locations. We used a task where N.W. and control subjects were required to report the location of a gray square relative to a colored square. The color of the square was task-irrelevant. Participants responded to the following trial types: (1) central trials, where one stimulus appeared on the left and the other on the right side of fixation, and (2) relative location trials, where both stimuli appeared either on the left or on the right side of fixation. Results showed that the color of the target had a strong impact on N.W.’s responses on both trial types, but not on the controls’ responses. These results show that the spatial representation underlying N.W.’s synesthetic experience is automatic and sensitive to the relative location of objects.

The sensitivity and specificity of a diagnostic test of sequence-space synesthesia.

People with sequence-space synesthesia (SSS) report stable visuo-spatial forms corresponding to numbers, days, and months (amongst others). This type of synesthesia has intrigued scientists for over 130 years but the lack of an agreed upon tool for assessing it has held back research on this phenomenon. The present study builds on previous tests by measuring the consistency of spatial locations that is known to discriminate controls from synesthetes. We document, for the first time, the sensitivity and specificity of such a test and suggest a diagnostic cut-off point for discriminating between the groups based on the area bounded by different placement attempts with the same item.Electronic supplementary materialThe online version of this article (doi:10.3758/s13428-015-0656-2) contains supplementary material, which is available to authorized users.

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

People with sequence-space synaesthesia perceive sequences (e.g. numbers, months, letters) as spatially extended forms. Here, we ask whether sequence-space synaesthetes have advantages in visuo-spatial skills such as mental rotation. Previous studies addressing this question have produced mixed results with some showing mental rotation advantages (Simner et al. in Cortex 45:1246-1260, 2009; Brang et al. in Cogn Process, 2013), but one that did not (Rizza and Price in Cogn Process 13:299-303, 2012). We tested this hypothesis again with a new group of sequence-space synaesthetes, and we also tested a range of individual differences that might have caused this conflict across previous studies. Specifically, we tested: years of education, visual imagery ability, nature of forms (2D or 3D representation of sequences), number of forms (e.g. for months, days, numbers), and tendency to project sequences into external space versus the mind's eye. We found yet again that synaesthetes had enhanced abilities in mental rotation compared to controls, but that one individual difference in synaesthetes (the ability to project forms into space) was especially linked to performance. We also found that synaesthetes self-reported higher visual imagery than controls (Price in Cortex 45:1229-1245, 2009; Mann et al. in Conscious Cognit 18:619-627, 2009; Rizza and Price 2012). Overall, our data support previous studies showing superior imagery reports (Price 2009) and mental rotation (Simner et al. 2009; Brang et al. 2013) in sequence-space synaesthetes, and we suggest that one previous failure to replicate (Rizza and Price 2012) might be explained by individual differences among synaesthetes recruited for testing.

Not all synesthetes are alike: spatial vs. visual dimensions of sequence-space synesthesia.

Sequence-space synesthesia (SSS) is a common condition in which ordinal sequences such as months, numbers or the letters of the alphabet are perceived to occupy spatial locations in the mind's eye or peripersonal or extrapersonal space (e.g., Price and Mentzoni, 2008; Jonas and Jarick, 2013). For example, thinking about a month may elicit the visuospatial impression of a circular arrangement of the months, or hearing a numeral may elicit a specifically shaped number line. These “spatial forms” are typically thought to be consistent over time within an individual (e.g., Smilek et al., 2007), though they can actually evolve (Price and Pearson, 2013; Gould et al., 2014; Price, 2014; see also Simner, 2012; Meier et al., 2014). They are also idiosyncratic, with synesthetes reporting many different shapes of varying complexity (Galton, 1880; Phillips, 1897) that are experienced outside the body (i.e., projected) or in the mind's eye (i.e., associated; Dixon et al., 2004; Smilek et al., 2007; Ward et al., 2007). SSS can vary along several dimensions, including the projector-associator distinction, automaticity, visual salience, and type of spatial transformation that can be applied to the spatial form (e.g., Price, 2013; Price and Mattingley, 2013). Since SSS could be considered a variety of visuospatial mental imagery, these individual differences may reflect known fractionation of imagery processes and skills (Price, 2013; Price and Pearson, 2013). However, a thorough and empirically grounded taxonomy for individual differences in SSS is missing (Price, 2014). We explore here a possible systematization for one area of these individual differences—the visual and spatial qualities of SSS. We further suggest this can help to classify synesthetes as experimental participants and perhaps explain some inconsistencies in published data.

An extended case study on the phenomenology of sequence-space synesthesia.

Investigation of synesthesia phenomenology in adults is needed to constrain accounts of developmental trajectories of this trait. We report an extended phenomenological investigation of sequence-space synesthesia in a single case (AB). We used the Elicitation Interview (EI) method to facilitate repeated exploration of AB's synesthetic experience. During an EI the subject's attention is selectively guided by the interviewer in order to reveal precise details about the experience. Detailed analysis of the resulting 9 h of interview transcripts provided a comprehensive description of AB's synesthetic experience, including several novel observations. For example, we describe a specific spatial reference frame (a “mental room”) in which AB's concurrents occur, and which overlays his perception of the real world (the “physical room”). AB is able to switch his attention voluntarily between this mental room and the physical room. Exemplifying the EI method, some of our observations were previously unknown even to AB. For example, AB initially reported to experience concurrents following visual presentation, yet we determined that in the majority of cases the concurrent followed an internal verbalization of the inducer, indicating an auditory component to sequence-space synesthesia. This finding is congruent with typical rehearsal of inducer sequences during development, implicating cross-modal interactions between auditory and visual systems in the genesis of this synesthetic form. To our knowledge, this paper describes the first application of an EI to synesthesia, and the first systematic longitudinal investigation of the first-person experience of synesthesia since the re-emergence of interest in this topic in the 1980's. These descriptions move beyond rudimentary graphical or spatial representations of the synesthetic spatial form, thereby providing new targets for neurobehavioral analysis.

Insights from introspection: a commentary on Gould et al. (2014), "An extended case study on the phenomenology of spatial form synaesthesia".

Insights from introspection: a commentary on Gould et al. (2014), "An extended case study on the phenomenology of spatial form synaesthesia".

Enhanced mental rotation ability in time-space synesthesia

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.

Mirror-touch and ticker tape experiences in synesthesia

A fundamental question in the field of synesthesia is whether it is associated with other cognitive phenomena. The current study examined synesthesia's connections with phenomenal traits of mirror-touch and ticker tape experiences, as well as the representation of the three phenomena in the population, across gender and domain of work/study. Mirror-touch is the automatic, involuntary experience of tactile sensation on one's own body when others are being touched. For example, seeing another person's arm being stroked can evoke physical touch sensation on one's own arm. Ticker tape is the automatic visualization of spoken words or thoughts, such as a teleprompter. For example, when spoken to, a ticker taper might see mentally the spoken words displayed in front of his face or as coming out of the speaker's mouth. To explore synesthesia's associations with these phenomena, a diverse group (n = 3743) was systematically recruited from eight universities and one public museum in France to complete an online screening. Of the 1017 eligible respondents, synesthetes (across all subtypes) reported higher rates of mirror-touch and ticker tape than non-synesthetes, suggesting that synesthesia is associated with these phenomenal traits. However, effect sizes were small and we could not rule out that response bias influenced these associations. Mirror-touch and ticker tape were independent. No differences were found across gender or domain of work and study in prevalence of synesthesia, mirror-touch or ticker tape. The prevalence of ticker tape, unknown so far, was estimated at about 7%, an intermediate rate between estimates of grapheme-color (2–4%) and sequence-space synesthesia (9–14%). Within synesthesia, grapheme-personification, also called ordinal-linguistic personification (OLP) was the most common subtype and was estimated around 12%. Co-occurences of the different types of synesthesia were higher than chance, though at the level of small effect sizes.

Do you see what I hear? Vantage point preference and visual dominance in a time-space synaesthete

Time-space synaesthetes “see” time units organized in a spatial form. While the structure might be invariant for most synaesthetes, the perspective by which some view their calendar is somewhat flexible. One well-studied synaesthete L adopts different viewpoints for months seen vs. heard. Interestingly, L claims to prefer her auditory perspective, even though the month names are represented visually upside down. To verify this, we used a spatial-cueing task that included audiovisual month cues. These cues were either congruent with L's preferred “auditory” viewpoint (auditory-only and auditory + month inverted) or incongruent (upright visual-only and auditory + month upright). Our prediction was that L would show enhanced cueing effects (larger response time difference between valid and invalid targets) following the audiovisual congruent cues since both elicit the “preferred” auditory perspective. Also, when faced with conflicting cues, we predicted L would choose the preferred auditory perspective over the visual perspective. As we expected, L did show enhanced cueing effects following the audiovisual congruent cues that corresponded with her preferred auditory perspective, but that the visual perspective dominated when L was faced with both viewpoints simultaneously. The results are discussed with relation to the reification hypothesis of sequence space synaesthesia (Eagleman, 2009).

Do sequence-space synaesthetes have better spatial imagery skills? Maybe not

Sequence-space synaesthesia is a type of visuo-spatial imagery in which numbers or calendar units are experienced to occupy locations in space. Previous studies have claimed that these synaesthetes (1) have stronger self-reported visual (but not spatial) imagery and (2) perform unusually well on mental rotation tasks that are usually taken to reflect spatial (but not visual) imagery. To further investigate whether this form of synaesthesia is related to spatial imagery, we compared synaesthetes to controls on the Object Spatial Imagery Questionnaire, a paper folding test and a mental rotation task. The synaesthetes did not differ from controls in self-reported spatial imagery, but showed a strong trend to report better visual imagery, replicating previously reported data patterns. Consistent with this, their paper folding and mental rotation performance was no better than controls. We also confirmed that, in our pooled sample, performance on both these tasks was positively correlated with self-reported spatial imagery. We suggest our data are more consistent with the view that sequence-space synaesthesia is related to visual than to spatial imagery, and we suggest reasons why previous studies may have found superior mental rotation performance.

Visuo‐spatial representations of the alphabet in synaesthetes and non‐synaesthetes

Visuo-spatial representations of the alphabet (so-called 'alphabet forms') may be as common as other types of sequence-space synaesthesia, but little is known about them or the way they relate to implicit spatial associations in the general population. In the first study, we describe the characteristics of a large sample of alphabet forms visualized by synaesthetes. They most often run from left to right and have salient features (e.g., bends, breaks) at particular points in the sequence that correspond to chunks in the 'Alphabet Song' and at the alphabet mid-point. The Alphabet Song chunking suggests that the visuo-spatial characteristics are derived, at least in part, from those of the verbal sequence learned earlier in life. However, these synaesthetes are no faster at locating points in the sequence (e.g., what comes before/after letter X?) than controls. They tend to be more spatially consistent (measured by eye tracking) and letters can act as attentional cues to left/right space in synaesthetes with alphabet forms (measured by saccades), but not in non-synaesthetes. This attentional cueing suggests dissociation between numbers (which reliably act as attentional cues in synaesthetes and non-synaesthetes) and letters (which act as attentional cues in synaesthetes only).