Grapheme-colour synaesthesia is a perceptual experience where graphemes, letters or words evoke a specific colour, which are experienced either as spatially coincident with the grapheme inducer (projector sub-type) or elsewhere, perhaps without a definite spatial location (associator sub-type). Here, we address the question of whether synaesthesia can be rapidly produced using a hypnotic colour suggestion to examine the possibility of ‘hypnotic synaesthesia’, i.e. subjectively experienced colour hallucinations similar to those experienced by projector synaesthetes. We assess the efficacy of this intervention (...) using an “embedded figures” test, in which participants are required to detect a shape (e.g., a square) composed of local graphemic elements. For grapheme-colour synaesthetes, better performance on the task has been linked to a higher proportion of graphemes perceived as coloured. We found no performance benefits on this test when using a hypnotic suggestion, as compared to a no-suggestion control condition. The same result was found when participants were separated according to the degree to which they were susceptible to the suggestion (number of coloured trials perceived). However, we found a relationship between accuracy and subjective reports of colour in those participants who reported a large proportion of coloured trials: trials in which the embedded figure was accurately recognised (relative to trials in which it was not) were associated with reports of more intense colours occupying a greater spatial extent. Collectively, this implies that hypnotic colour was only perceived after shape detection rather than aiding in shape detection via colour-based perceptual grouping. The results suggest that hypnotically induced colours are not directly comparable to synaesthetic ones. (shrink)

Synaesthesia is a heterogeneous phenomenon, even when considering one particular sub-type. The purpose of this study was to design a reliable and valid questionnaire for grapheme-colour synaesthesia that captures this heterogeneity. By the means of a large sample of 628 synaesthetes and a factor analysis, we created the Coloured Letters and Numbers questionnaire with 16 items loading on 4 different factors . These factors were externally validated with tests which are widely used in the field of synaesthesia research. The questionnaire (...) showed good test–retest reliability and construct validity . Our findings are discussed in the light of current theories and new ideas in synaesthesia research. More generally, the questionnaire is a useful tool which can be widely used in synaesthesia research to reveal the influence of individual differences on various performance measures and will be useful in generating new hypotheses. (shrink)

In grapheme-color synesthesia, a number or letter can evoke two different and possibly conflicting color sensations at the same time. In this study, we investigate the relationship between synesthesia and executive control functions. First, no general skill differences were obtained between synesthetes and non-synesthetes in classic executive control paradigms. Furthermore, classic executive control effects did not interact with synesthetic behavioral effects. Third, we found support for our hypothesis that inhibition of a synesthetic color takes effort and time. Finally, individual differences (...) analyses showed no relationship between the two skills; performance on a ‘normal’ Stroop task does not predict performance on a synesthetic Stroop task. Across four studies, the current results consistently show no clear relationship between executive control functions and synesthetic behavioral effects. This raises the question of which mechanisms are at play in synesthetic ‘management’ during the presence of two conflicting sensations. (shrink)

Synesthetes can be distinguished from nonsynesthetes on a variety of experimental tasks because their concurrent synesthetic experiences can affect task performance if these experiences match or conflict with some aspect of the stimulus. Here, we tested grapheme‐color synesthetes and nonsynesthetic control participants using a novel perceptual similarity task to assess whether synesthetes’ concurrent color experiences influence perceived grapheme similarity. Participants iteratively arranged graphemes and, separately, their associated synesthetic colors in a display, such that similar items were placed close together and (...) dissimilar items further apart. The resulting relative inter‐item distances were used to calculate the pair‐wise (dis)similarity between items in the set, and thence to create separate perceptual representational dissimilarity matrices (RDMs) for graphemes and colors, on an individual basis. On the assumption that synesthetes’ similarity judgments for graphemes would be influenced by their concurrent color experiences, we predicted that grapheme and color RDMs would be more strongly correlated for synesthetes than nonsynesthetes. We found that the mean grapheme‐color RDM correlation was indeed significantly higher in synesthetes than nonsynesthetes; in addition, synesthetes’ grapheme‐color RDM correlations were more likely to be individually statistically significant, even after correction for multiple tests, than those of nonsynesthetes. Importantly, synesthetes’ grapheme‐color RDM correlations scaled with the consistency of their grapheme‐color associations as measured by their Synesthesia Battery (SB) scores. By contrast, the relationship between SB scores and grapheme‐color RDM correlations for nonsynesthetes was not significant. Thus, dissimilarity analysis quantitatively distinguished synesthetes from nonsynesthetes, in a way that meaningfully reflects a key aspect of synesthetic experience. (shrink)

Determinants of synesthetic color choice for the Japanese logographic script, Kanji, were studied. The study investigated how synesthetic colors for Kanji characters, which are usually acquired later in life than other types of graphemes in Japanese language , are influenced by linguistic properties such as phonology, orthography, and meaning. Of central interest was a hypothesized generalization process from synesthetic colors for graphemes, learned prior to acquisition of Kanji, to Kanji characters learned later. Results revealed that color choices for Kanji characters (...) depend on meaning and phonological information. Some results suggested that colors are generalized from Hiragana characters and Arabic digits to Kanji characters via phonology and meaning, respectively. Little influence of orthographic information was observed. The findings and approach of this study contributes to a clarification of the mechanism underlying grapheme-color synesthesia, especially in terms of its relationship to normal language processing. (shrink)

The concept of informational encapsulation has been important in promoting a view of the mind that has dominated cognitive science. Multisensory phenomena, such as synaesthesia, have been used as evidence for challenging this view. The main objective of this paper is to provide a more detailed understanding of the nature of such a challenge by examining the two types of grapheme–colour synaesthesia, projectors and associators. It is argued that the phenomena under consideration exemplify partial encapsulation failure and that it is (...) expressed in three forms: intramodal, intermodal, and top-down. Additional support for these claims is provided by considering some evidence on synaesthetic-like experiences in relation to the continuity thesis. (shrink)

The apparent dichotomy between qualitative versus quantitative dimensions in science intersects with the domain of several disciplines, as well as different research fields within one and the same discipline. The perception of qualitative as “poor quantitative,” however, is methodologically unsustainable, because there are perfectly rigorous ways to conduct qualitative research. A somehow different question is whether a science of qualities per se is possible: that is, whether a science of appearances can be devised, what its observables are, and its methodological (...) implications. The article deals with this last issue, and especially from the point of view of experimental phenomenology. The weakness of the current approach to perception is discussed, and an alternative view that goes beyond veridicalism is presented. The analysis tackles crucial issues such as color and spatial appearances, the qualitative dimension of perceived depth, and the role of visual meaningful gestalten as information tools for the survival of living beings in the environment. If developed, a science of the qualitative dimensions of appearances may contribute to revising the ecological theory of perception by making its natural semantics more explicit. (shrink)

Recent research on synesthesia has focused on how the condition may depend on selective attention, but there is a lack of consensus on whether selective attention is required to bind colors to their grapheme inducers. In the present study, we used a novel change detection paradigm to examine whether synesthetic colors guide the subject’s attention to the location of the inducer or whether selective attention is required to act as a unique feature during visual search. If synesthetic experiences are elicited (...) by inducers without selective attention, then a target that is distinct from the distractors by virtue of its unique synesthetic color should capture attention. This should lead to efficiency in the search that is analogous to the efficiency in searches involving unique display colors. If, however, an inducer does not elicit a synesthetic color until the subject selectively attends to it, then the search should be as inefficient as for control subjects. We found that, not only does synesthesia not provide an advantage in complicated visual search tasks, it offers a slight disadvantage, supporting the re-entrant processing hypothesis about the mechanism underlying synesthesia. (shrink)

Despite some principal similarities, there is no systematic comparison between the different types of synesthesia . This comprehensive review compares the three principal types of synesthesia and focuses on their phenomenological features and their relation to different etiological models. Implications of this comparison for the validity of the different etiological models are discussed.Comparison of the three forms of synesthesia show many more differences than similarities. This is in contrast to their representation in the literature, where they are discussed in many (...) respects as being virtually similar. Noteworthy is the much broader spectrum and intensity with the typical drug-induced synesthesias compared to genuine and acquired synesthesias. A major implication of the phenomenological comparison in regard to the etiological models is that genuine and acquired synesthesias point to morphological substrates, while drug-induced synesthesia appears to be based on functional changes of brain activity. (shrink)

Determinants of synesthetic color choice for Japanese phonetic characters were studied in six Japanese synesthetes. The study used Hiragana and Katakana characters, which represent the same set of syllables although their visual forms are dissimilar. From a palette of 138 colors, synesthetes selected a color corresponding to each character. Results revealed that synesthetic color choices for Hiragana characters and those for their Katakana counterparts were remarkably consistent, indicating that color selection depended on character-related sounds and not visual form. This Hiragana–Katakana (...) invariance cannot be regarded as the same phenomenon as letter case invariance, usually reported for English grapheme-color synesthesia, because Hiragana and Katakana characters have different identities whereas upper and lower case letters have the same identity. This involvement of phonology suggests that cross-activation between an inducer brain region and that of the concurrent area in grapheme-color synesthesia is mediated by higher order cortical processing areas. (shrink)