Consistency in synesthetic experience to vowels and consonants: Five case studies

The present study attempted to specify the actual degree of consistency in synesthetic experience in two synesthetes and three non-synesthetes. By comparing colour chip selections, and size and density ratings, to the same set of stimulus letters on separate occasions, it was found that the synesthetic subjects showed a high consistency in responding over a short (24 hours) as well as a long (one year) time span. In comparison, the non-synesthetic subjects demonstrated less consistent responding when retested after 24 hours. However, the differences between the two groups were smaller than expected. Consistency to vowels and consonants was compared, and it was found that consistency to consonants was comparable to, or even higher than, vowel consistency in all subjects.     

Synesthetic grapheme-color percepts exist for newly encountered Hebrew,Devanagari, Armenian and Cyrillic graphemes

Grapheme-color synesthetes experience color, not physically present, when viewing symbols. Synesthetes cannot remember learning these associations. Must synesthetic percepts be formed during a sensitive period? Can they form later and be consistent? What determines their nature? We tested grapheme-color synesthete, MC2, before, during and after she studied Hindi abroad. We investigated whether novel graphemes elicited synesthetic percepts, changed with familiarity, and/or benefited from phonemic information. MC2 reported color percepts to novel Devanagari and Hebrew graphemes. MC2 monitored these percepts over 6 months in a Hindi-speaking environment. MC2 and synesthete DN, reported synesthetic percepts for Armenian graphemes, or Cyrillic graphemes + phonemes over time. Synesthetes, not controls, reported color percepts for novel graphemes that gained consistency over time. Phonemic information did not enhance consistency. Thus, synesthetes can form and consolidate percepts to novel graphemes as adults. These percepts may depend on pre-existing grapheme-color relationships but they can flexibly shift with familiarity.     

Tasty non-words and neighbours: The cognitive roots of lexical-gustatory synaesthesia

For lexical-gustatory synaesthetes, words trigger automatic, associated food sensations (e.g., for JB, the word slope tastes of over-ripe melon). Our study tests two claims about this unusual condition: that synaesthetic tastes are associated with abstract levels of word representation (concepts/lemmas), and that the first tastes to crystallise in early development are those triggered by food-names (e.g., apple tastes of apple; Simner & Ward, 2006). This concept/lemma-based proposal is difficult to immediately reconcile with the finding that non-words may also generate tastes (Ward, Simner, & Auyeung, 2005), since non-words have no concept/lemma representations. We manipulated the characteristics of non-words to provide three types of evidence that non-word tastes in fact stem from real word neighbours: Non-words with neighbours (e.g., keach) are more likely to generate tastes than those with no neighbours (e.g., vilps); pseudo-homophone non-words that are orthographically close to real words (e.g., peeple) are more likely to generate tastes than those that are more distant (baybee); and finally, the tastes of non-words are less consistent, and less intense, than those of real words. Additionally, we test the hypothesis that synaesthetic tastes develop initially from food-names by showing that non-words are more intensely flavoured if they are homophonic with food-names (e.g., toffie) versus non-foods (e.g., peeple). From this we conclude that synaesthetic tastes develop from food-names, and that tasty non-words do not challenge a concept/lemma-based account of lexical-gustatory synaesthesia.     

Synaesthesia in a logographic language: the colouring of Chinese characters and Pinyin/Bopomo spellings

Studies of linguistic synaesthesias in English have shown a range of fine-grained language mechanisms governing the associations between colours on the one hand, and graphemes, phonemes and words on the other. However, virtually nothing is known about how synaesthetic colouring might operate in non-alphabetic systems. The current study shows how synaesthetic speakers of Mandarin Chinese come to colour the logographic units of their language. Both native and non-native Chinese speakers experienced synaesthetic colours for characters, and for words spelled in the Chinese spelling systems of Pinyin and Bopomo. We assessed the influences of lexical tone and Pinyin/Bopomo spelling and showed that synaesthetic colours are assigned to Chinese words in a non-random fashion. Our data show that Chinese-speaking synaesthetes with very different native languages can exhibit both differences and similarities in the ways in which they come to colour their Chinese words.     

Consistency and strength of grapheme-color associations are separable aspects of synesthetic experience

Consistency of synesthetic associations over time is a widely used test of synesthesia. Since many studies suggest that consistency is not a completely reliable feature, we compared the consistency and strength of synesthetes’ grapheme-color associations. Consistency was measured by scores on the Synesthesia Battery and by the Euclidean distance in color space for the specific graphemes tested for each participant. Strength was measured by congruency magnitudes on the Implicit Association Test. The strength of associations was substantially greater for synesthetes than non-synesthetes, suggesting that this is a novel, objective marker of synesthesia. Although, intuitively, strong associations should also be consistent, consistency and strength were uncorrelated, indicating that they are likely independent, at least for grapheme-color synesthesia. These findings have implications for our understanding of synesthesia and for estimates of its prevalence since synesthetes who experience strong, but inconsistent, associations may not be identified by tests that focus solely on consistency.     

Consistency of synesthetic association varies with grapheme familiarity: A longitudinal study of grapheme-color synesthesia

Grapheme-color synesthesia is a condition in which the visual perception of letters or numbers induces a specific color sensation. The consistency of grapheme-color association has been considered as a fundamental characteristic of synesthesia. However, recent studies have indicated that this association can change across the adult lifespan, and it has become necessary to investigate the factors behind the changes within each synesthete. We conducted a longitudinal study of Japanese adult synesthetes to investigate long-term (5–8 years) changes in color responses to 300 graphemes (alphanumeric and Japanese characters). Graphemes with lower long-term consistency of synesthetic association also tended to have lower short-term consistency, indicating that grapheme-color association's consistency is determined for each grapheme. Further, less familiar graphemes had less consistent associations with their synesthetic colors. These findings suggest that a stronger grapheme-color association is formed for more familiar graphemes, leading to the consolidation of synesthetic color for such graphemes.     

Spatial cueing in time–space synesthetes: An event-related brain potential study

Some people report that they consistently and involuntarily associate time events, such as months of the year, with specific spatial locations; a condition referred to as time–space synesthesia. The present study investigated the manner in which such synesthetic time–space associations affect visuo-spatial attention via an endogenous cuing paradigm. Reaction times and ERPs were recorded as 12 time–space synesthetes and 12 control participants did a peripheral target detection task, cued by three different types of centrally presented cues: arrows pointing left or right, direction words “left” or “right”, and month names associated with either the left or the right side of the synesthete’s mental calendar (e.g., “October” or “May”). Cues were followed by probes on the left or right side of the screen, and participants responded to the probes with button presses. Behavioral and ERP data suggested that for synesthetes, month words functioned more effectively as cues to direct attention in space. In synesthetes but not controls, a comparison of ERPs to probes cued by months revealed effects of cue validity on the P3b component peaking 370 ms post-onset and on the subsequent positive slow wave (pSW) observed 600–900 ms post-onset (both larger for invalid probes). No effects of cue validity were observed on early visual potentials (N1) for probes cued by months. The findings suggest that in these time–space synesthetes cue validity influenced post-perceptual processes, such as stimulus evaluation and categorization, with no evidence for enhanced visual processing.     

Synesthesia and number cognition in children

Grapheme-color synesthesia, when achromatic digits evoke an experience of a specific color (photisms), has been shown to be consistent, involuntary, and linked with number concept in adults, yet there have been no comparable investigations with children. We present a systematic study of grapheme-color synesthesia in children aged between 7 and 15 years. Here we show that such children (but not children with phoneme-color synesthesia) experience involuntary difficulties in numerical tasks when digits are presented in colors incongruent with their photisms. Synesthesia in children may thus have important consequences for certain aspects of numerical cognition.     

Musical space synesthesia: Automatic,explicit and conceptual connections between musical stimuli and space

In musical–space synesthesia, musical pitches are perceived as having a spatially defined array. Previous studies showed that symbolic inducers (e.g., numbers, months) can modulate response according to the inducer’s relative position on the synesthetic spatial form. In the current study we tested two musical–space synesthetes and a group of matched controls on three different tasks: musical–space mapping, spatial cue detection and a spatial Stroop-like task. In the free mapping task, both synesthetes exhibited a diagonal organization of musical pitch tones rising from bottom left to the top right. This organization was found to be consistent over time. In the subsequent tasks, synesthetes were asked to ignore an auditory or visually presented musical pitch (irrelevant information) and respond to a visual target (i.e., an asterisk) on the screen (relevant information). Compatibility between musical pitch and the target’s spatial location was manipulated to be compatible or incompatible with the synesthetes’ spatial representations. In the spatial cue detection task participants had to press the space key immediately upon detecting the target. In the Stroop-like task, they had to reach the target by using a mouse cursor. In both tasks, synesthetes’ performance was modulated by the compatibility between irrelevant and relevant spatial information. Specifically, the target’s spatial location conflicted with the spatial information triggered by the irrelevant musical stimulus. These results reveal that for musical–space synesthetes, musical information automatically orients attention according to their specific spatial musical-forms. The present study demonstrates the genuineness of musical–space synesthesia by revealing its two hallmarks—automaticity and consistency. In addition, our results challenge previous findings regarding an implicit vertical representation for pitch tones in non-synesthete musicians.     

Beyond visual imagery: How modality-specific is enhanced mental imagery in synesthesia?

Synesthesia based in visual modalities has been associated with reports of vivid visual imagery. We extend this finding to consider whether other forms of synesthesia are also associated with enhanced imagery, and whether this enhancement reflects the modality of synesthesia. We used self-report imagery measures across multiple sensory modalities, comparing synesthetes’ responses (with a variety of forms of synesthesia) to those of non-synesthete matched controls. Synesthetes reported higher levels of visual, auditory, gustatory, olfactory and tactile imagery and a greater level of imagery use. Furthermore, their reported enhanced imagery is restricted to the modalities involved in the individual’s synesthesia. There was also a relationship between the number of forms of synesthesia an individual has, and the reported vividness of their imagery, highlighting the need for future research to consider the impact of multiple forms of synesthesia. We also recommend the use of behavioral measures to validate these self-report findings.