Synesthesia

Despite the recent surge in research on, and interest in, synesthesia, the mechanism underlying this condition is still unknown. Feedforward mechanisms involving overlapping receptive fields of sensory neurons as well as feedback mechanisms involving a lack of signal disinhibition have been proposed. Here I show that a broad range of studies of developmental synesthesia indicate that the mechanism underlying the phenomenon may involve reinstatement of brain activity in different sensory or cognitive streams in a way that is similar to what (...) happens during memory retrieval of semantically associated items. In the paper’s final sections I look at the relevance of synesthesia research, given the memory model, to our understanding of multisensory perception and common mapping patterns. (shrink)

In her response to my "Seeing as a Non-Experiental Mental State: The Case from Synesthesia and Visual Imagery" Ophelia Deroy presents an argument for an interesting new account of synesthesia. On this account, synesthesia can be thought of as "a perceptual state (e.g. of a letter)" that is "changed or enriched by the incorporation of a conscious mental image (e.g. a color)." I reply that while this is a plausible account of some types of synesthesia, some forms cannot be accounted (...) for this way. (shrink)

We studied the patient JP who has exceptional abilities to draw complex geometrical images by hand and a form of acquired synesthesia for mathematical formulas and objects, which he perceives as geometrical figures. JP sees all smooth curvatures as discrete lines, similarly regardless of scale. We carried out two preliminary investigations to establish the perceptual nature of synesthetic experience and to investigate the neural basis of this phenomenon. In a functional magnetic resonance imaging (fMRI) study, image-inducing formulas produced larger fMRI (...) responses than non-image inducing formulas in the left temporal, parietal and frontal lobes. Thus our main finding is that the activation associated with his experience of complex geometrical images emerging from mathematical formulas is restricted to the left hemisphere. (shrink)

Synesthesia literally means a “union of the senses” whereby two or more of the five senses that are normally experienced separately are involuntarily and automatically joined together in experience. For example, some synesthetes experience a color when they hear a sound, although many instances of synesthesia also occur entirely within the visual sense. In this paper, I first mainly engage critically with Sollberger’s view that there is reason to think that at least some synesthetic experiences can be viewed as truly (...) veridical perceptions, and not as illusions or hallucinations. Among other things, I explore the possibility that many forms of synesthesia can be understood as experiencing what I will call “second-order secondary properties,” that is, experiences of properties of objects induced by the secondary qualities of those objects. In doing so, I shed some light on why synesthesia is typically one-directional and its relation to some psychopathologies such as autism. (shrink)

Linguistic synesthesia refers to crossmodal instances in which expressions in different sensory modalities are combined as in the case of sweet (tast...

It has been repeatedly suggested that synesthesia is intricately connected with unusual ways of exercising one’s mental imagery, although it is not always entirely clear what the exact connection is. My aim is to show that all forms of synesthesia are forms of (often very different kinds of) mental imagery and, further, if we consider synesthesia to be a form of mental imagery, we get significant explanatory benefits, especially concerning less central cases of synesthesia where the inducer is not sensory (...) stimulation. (shrink)

This thesis has, as its primary target, the neo-cartesianism, or property dualism of certain philosophers of mind: David Chalmers, Tim Bayne, and others. All begin with a pre-theoretic commitment to the view that all perceptual states are conscious. They define consciousness by saying that it is synonymous with having ‘qualia’ – a term directed at phenomenal properties which defy reduction to physical states. The thesis argues that this position is challenged by certain neurological conditions, - blindsight, visual form agnosia etc- (...) which we can generalise as ‘dissociations’: conditions in which functions are separated from awareness. The thesis holds that these are examples of unconscious perception, which present the case for a different pre-theoretic position, and a redefinition of concepts used in the vicinity. Insofar as the neo-cartesians recognise the empirical, their inclination to reject the dissociations is challenged with new cases and paradigms which have emerged in recent years. It is contended that the dissociations disrupt Chalmers’ coherence between the phenomenal and the psychological, Bayne’s commitment to the Unity of Consciousness, and Phillips’ campaign against unconscious perception. In addition, synaesthesia is advanced as a problem case for Bayne’s unity contention. I argue that the dissociations are not easily dismissed, and present a real challenge for neo-cartesianism. In exploring this challenge, the thesis contributes to the case for a different philosophy of mind – a Higher Order Thought approach. The notion of unconscious perception – it is contended - much more easily finds an accommodation in HOT theories, so this thesis contributes to existing arguments for that position. HOT theories also have an advantage in being receptive to reduction, in giving a developmental account of consciousness, and in being more open to the accommodation of empirical discoveries. In each respect, there is an advantage over the respective positions taken by Chalmers and Bayne. (shrink)

We often use terms primarily concerned with the description of inanimate objects in order to characterize psychological states or dispositions, without being able to specify the connection between the two uses. I call this inanimation. In this paper, I propose an account of inanimation and of its connection to expressiveness.

This review provides a commentary on coloured-hearing arising on hearing music: music-colour synaesthesia. Although traditionally explained by the hyperconnectivity theory (Ramachandran & Hubbard, 2001a) and the disinhibited feedback theory (Grossenbacher & Lovelace, 2001) as a purely perceptual phenomenon, the review of eight coloured-hearing neuroimaging studies shows that it may not be assumed that these explanations are directly translatable to music-colour synaesthesia. The concept of 'ideaesthesia' (Nikolić, 2009) and the role of conceptual and semantic inducers challenge the likelihood of a single (...) mechanism underlying the cause of synaesthesia and argue for a move away from a purely sensory to sensory explanation. Finally, music-colour synaesthesia forms a challenge for established philosophical theories and the position of synaesthesia is considered within the larger context of musical qualia. (shrink)

What do different concepts like true lie, bad luck, honest thief, old news, spacetime, glocalisation, symplexity, sustainable development, constant change, soft law, substantive due process, pure law, bureaucratic efficiency and global justice have in common? What connections do they share with innumerable paradoxes, like the ones of happiness, of time, globalisation, sex, and of free will and fate? Law in the Time of Oxymora provides answers to these conundrums by critically comparing the apparent rise in recent years of the use (...) of rhetorical figures called "essentially oxymoronic concepts" in the areas of art, science and law. Albeit to varying degrees, these concepts share the quality of giving expression to apparent contradictions. Through this quality, they also challenge the scientific paradigm rooted in the dualist thinking and binary logic that is traditionally used in the West, as opposed to the East, where a paradoxical mode of thinking and fuzzy logic are said to have been cultivated. Following a review of oxymora and paradoxes in art and various scientific writings, hundreds of 'hard cases' featuring oxymora and a comprehensive review of the legal literature are discussed, revealing evidence suggesting that the present scientific paradigm of dualism alone will no longer be able to tackle the challenges arising from increasing diversity and complexity coupled with an apparent acceleration of change. Law in the Time of Oxymora reaches the surprising conclusion that essentially oxymoronic concepts may inaugurate a new era of cognition involving the ways the senses interact and how we reason, think and make decisions in law and in life. (shrink)

Synaesthesia is a strange sensory blending: synaesthetes report experiences of colours or tastes associated with particular sounds or words. This volume presents new essays by scientists and philosophers exploring what such cases can tell us about the nature of perception and its boundaries with illusion and imagination.

We can discern two opposing viewpoints regarding synesthesia. According to the first, it is an oddity, an outlier, or a disordered condition. According to the second, synesthesia is pervasive, driving creativity, metaphor, or language itself. Which is it? Ultimately, I favor the first perspective, according to which cross-sensory synesthesia is an outlying condition. But the second perspective is not wholly misguided. My discussion has three lessons. First, synesthesia is just one of a variety of effects in which one sense modality (...) causally impacts and reshapes experience associated with another. These effects are utterly common. However, due to their unfamiliarity, and to their conflict with a widespread conception of the role of the senses in perception and perceptual experience, until recently they have been surprising. Second, synesthesia nevertheless must be distinguished from other inter-modal effects that lead to misperception, such as crossmodal illusions. Third, synesthesia also may be distinguished from the potentially much broader class of synesthetic effects, which could be common across the population and within individuals. (shrink)

Studies have shown that both serotonin and glutamate receptor systems play a crucial role in the mechanisms underlying drug-induced synesthesia. The specific nature of these mechanisms, however, continues to remain elusive. Here we propose two distinct hypotheses for how synesthesia triggered by hallucinogens in the serotonin-agonist family may occur. One hypothesis is that the drug-induced destabilization of thalamic projections via GABAergic neuronal circuits from sensory areas leads to a disruption of low-level, spontaneous integration of multisensory stimuli. This sort of integration (...) regularly occurs when spatial and temporal attributes match. Destabilization of feedback loops, however, can result in incongruent experiences or binding of random thalamus activation with sensory input in a particular sensory modality. The second hypothesis builds on embodied cognition, cases in which visual images of external stimuli activate task-related neural regions. On this proposal, binding processes that do not normally generate awareness become accessible to consciousness as a result of decreased attentional discrimination among incoming stimuli. (shrink)

In response to Fred Adams and Charlotte Shreve’s (2016) paper entitled “What Can Synesthesia Teach Us about Higher Order Theories of Consciousness?”, previously published in Symposion, I argue that H.O.T. theory does have the resources to account for synesthesia and the specific worries that they advance in their paper, such as the relationship between concepts and experience and the ability to handle instances of ‘pop-out’ experiences.

The phenomenon of synesthesia has undergone an invigoration of research interest and empirical progress over the past decade. Studies investigating the cognitive mechanisms underlying synesthesia have yielded insight into neural processes behind such cognitive operations as attention, memory, spatial phenomenology and inter-modal processes. However, the structural and functional mechanisms underlying synesthesia still remain contentious and hypothetical. The first section of the present paper reviews recent research on grapheme-color synesthesia, one of the most common forms of synesthesia, and addresses the ongoing (...) debate concerning the role of selective attention in eliciting synesthetic experience. Drawing on conclusions of the first half, the paper’s second half examines the various models proposed to explain the cognitive mechanisms behind grapheme-color synesthesia, and discusses the explanatory virtues of a new model suggesting that grapheme-color synesthesia is grounded in memory. The last section offers an examination of some of the broader philosophical implications of synesthesia. (shrink)

Grapheme-colour synaesthetes experience unusual colour percepts when they encounter letters and/or digits. Studies of English-speaking grapheme-colour synaesthetes have shown that synaesthetic colours are sometimes triggered by rule-based linguistic mechanisms . In contrast, little is known about synaesthesia in logographic languages such as Chinese. The current study shows the mechanisms by which synaesthetic speakers of Chinese colour their language. One hypothesis is that Chinese characters might be coloured by their constituent morphological units, known as radicals, and we tested this by eliciting (...) synaesthetic colours for characters while manipulating features of the radicals within them. We found that both the function and position of radicals influence the nature of the synaesthetic colour generated. Our data show that in Chinese, as in English, synaesthetic colours are influenced by systematic rules, rather than by random associations, and that these rules are based on existing psycholinguistic mechanisms of language processing. (shrink)

Synaesthesia is an excellent model for understanding perceptual binding in the human brain. Current evidence suggests that if synaesthetic colour is bound, it is through the same attention-dependent integration of feature maps that occurs in other forms of binding. synaesthetic colour arises after the point that separate wavelengths blend in normal colour vision, which creates a perceptual paradox where synaesthetic and print colour can appear bound to a single location without blending. If a letter is printed in a colour that (...) is different from the synaesthetic colour it induces, the two hues will activate different hue-selective maps allowing for dual representation of colour, but if synaesthetic and print colours are the same/similar they will co-activate the same hue-selective map and create an amplified colour signal. Studies suggest that the parietal cortex plays a key role in this binding of synaesthetic and/or print colour to shape. (shrink)

Synaesthesia is a neurodevelopmental condition characterised by anomalous sensory perceptions and associated alterations in cognitive function. This chapter summarises what is known about the familial transmission of synaesthesia and its genetic underpinnings. Early familiality studies showed evidence for a strong genetic predisposition, a highly skewed female: male ratio, and an absence of male-to-male transmission. These patterns supported an early hypothesis of a single-gene X-linked dominant mode of inheritance with male lethality. Subsequent analyses in larger samples indicated that the mode of (...) inheritance was likely to be more complex, with both the strong female skew and absence of male-to-male transmission brought into question. We review in detail the first whole genome linkage scan for auditory-visual synaesthesia and a subsequent family linkage study on coloured sequence synaesthesia. Together these results suggest linkage to five chromosomes but give no support for linkage to the X-chromosome. We discuss candidate genes within these regions and potential implications for the aetiology of synaesthesia. We also discuss the implications of these pioneering genome scans for our understanding of synaesthesia and of how different synaesthetic phenotypes may arise from different genetic predispositions interacting with other genes and with the environment. (shrink)

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. (shrink)

Synaesthesia has an emotional side. Many synaesthetes have a sense of certainty about the reality and accuracy of their experiences. Consequently, when their synaesthesia is mimicked in real life these synaeshtetes report a positive emotion whereas when the opposite is true, they experience discomfort. Synaesthesia can also be induced by emotions, and emotions can also be the synaesthetic experience. Here we review the research on these types of synaesthesia and study the current evidence for the true nature of these emotions (...) associated to synesthetic perceptions as studied in grapheme-colour synaesthesia. We begin by presenting evidence of how they can be measured in a laboratory setting and proceed to report studies showing that emotions are automatically activated and can vary in degree as a function of certain factors. We lastly review a study showing that these emerging emotions can be so strong and vivid that they can influence attitudes towards otherwise neutral stimuli. We conclude by presenting a model that could account for the findings reported here. (shrink)

Synaesthesia's Renaissance comments on attitudes and developments in synaesthesia research during the 20th century, focusing in particular on the last three decades when the greatest change took place. During the last century, reaction to the phenomenon varied by group. Synesthetes were gratified to learn that their experience was bona fide and had a scientific name. Laypersons were fascinated and clamored to know more. Well-known psychologists published on it early in the century, but then academia became hostile. After 1940 synesthesia was (...) dismissed as merely subjective and unsuited to respectable scientific inquiry. For decades critics insisted that synesthesia was neither a real perception nor a brain phenomenon. Though put to rest by century's end, an attitude of disbelief can still be encountered. (shrink)

This chapter considers the possible origins of the associations reported by synaesthetes, especially coloured graphemes. There are two well-documented cases where the origins of coloured letters or numbers are known; one from coloured fridge magnets, one from a jigsaw puzzle. While some synaesthetes report beliefs about the origin of their colours, most would say they have been the same as long as they can remember. Statistical analysis of large groups of synaesthetes indicates more consistency of colours than would be expected (...) by chance: 'A' is often red, 'D' is often brown, while 'I' and 'O' are typically white or black. A systematic study could find no evidence for a common origin, such as alphabet teaching books, for these colours. However, when required to suggest a colour for 'A', non-synaesthetes also tend to choose red. Overall, common synaesthetic colours and those chosen by non-synaesthetes agree more than would be expected by chance. This agreement might be mediated by a relationship between the frequency of occurrence of letters and the frequency of colour names; there is also a relationship between numbers and luminance, such that lower numbers tend to be brighter than later ones. Studies of pre-lingual toddlers have shown they tend to associate angular shapes, such as 'X' and 'Z', with black, and non-angular ones, such as 'I' and 'O', with white. There is also evidence that letters that are learned early are associated with simpler colour concepts. (shrink)

Synaesthesia is a neurological condition in which a sensory or cognitive stimulus consistently co-activates another sensory/cognitive quality in addition to its usual qualities. For example, synaesthetes might see colours when they read words. Coloured language is one of the most common and most studied types of synaesthesia. The processes that govern the associations of colours and language have been linked to the mechanisms underlying the processing of language more generally. This chapter reviews evidence from current psycholinguistic synaesthesia research in Chinese, (...) focusing in particular on how synaesthetic colouring works in Chinese characters, the basic writing units in Chinese. I consider this in relation to the psycholinguistic processes of character recognition. This chapter reviews evidence for the following facts: that synaesthetic colouring of Chinese characters is a genuine phenomenon in the Chinese population and may affect as many as 1 in 100 in the Chinese population, with a non-significant difference across the sexes that the colouring of characters is rule-based and influenced by a number of linguistic factors; and that synaesthetic colouring can transfer across Chinese and English in bilinguals. These findings are discussed in relation to native versus non-native Chinese synaesthetes, and to the Chinese versus English systems. (shrink)

We begin this chapter with a review of the history of synaesthesia and a comparison of what we consider to be either genuine or inauthentic manifestations of the phenomenon. Next, we describe the creation and development of synaesthetic consistency tests and explore reasons why assessing consistency became the most widely used method of confirming the genuineness of synaesthesia. We then consider methodologies that demonstrate synaesthesia's authenticity by capitalizing on properties other than consistency. Finally, we discuss how together, consistency tests and (...) other methodologies are helping researchers determine prevalence and elucidate the mechanisms of synaesthesia. (shrink)