Cognitive dedifferentiation in eidetics and synaesthesia: hunting for the ghost once more

Both synaesthesia and eidetics have a common characteristic of cognitive dedifferentiation. Synaesthesia (e.g. colour-hearing) entails the dedifferentiation of the sensory modalities, while eidetic imagery entails the dedifferentiation of imagery and perception. One can profitably gain by investigating both within the same study. Moreover, some of the same issues have arisen in these, hitherto, separate research literatures. This behoves a common framework for analysis and investigation. We applied a technique previously used for identifying child eidetikers, for screening the adult population, looking at both phenomena in the same sample. After screening, we selected a total of twenty-nine individuals for controlled testing of both phenomena and their variants (structural eidetic imagery, typographic eidetic imagery, colour-hearing synaesthesia, colour-mood synaesthesia). Our participants also completed a number of questionnaires of relevance (absorption, dissociation, and hallucination). We found that the personality trait of absorption underlies the commonality of experience tapped by both typographic and structural eidetic imagery. Furthermore, the latter phenomena were found to have a common pseudohallucinatory experiential base. For subjects scoring relatively high on the absorption scale, there is a negative correlation between structural eidetic imagery and colour-mood synaesthetic differentiation, replicating to a degree results reported earlier.     

What is the relationship between Aphantasia,Synaesthesia and Autism?

For people with aphantasia, visual imagery is absent or markedly impaired. Here, we investigated the relationship between aphantasia and two other neurodevelopmental conditions also linked to imagery differences: synaesthesia, and autism. In Experiment 1a and 1b, we asked whether aphantasia and synaesthesia can co-occur, an important question given that synaesthesia is linked to strong imagery. Taking grapheme-colour synaesthesia as a test case, we found that synaesthesia can be objectively diagnosed in aphantasics, suggesting visual imagery is not necessary for synaesthesia to occur. However, aphantasia influenced the type of synaesthesia experienced (favouring ‘associator’ over ‘projector’ synaesthesia - a distinction tied to the phenomenology of the synaesthetic experience). In Experiment 2, we asked whether aphantasics have traits associated with autism, an important question given that autism – like aphantasia – is linked to weak imagery. We found that aphantasics reported more autistic traits than controls, with weaknesses in imagination and social skills.     

Age Differences and Sex Differences in some Introvertive and Emotional Traits

Two quantitative experiments involving eidetic imagery, performed in 1928–29 on two girls, ages 11 and 15 years, respectively, were repeated in every detail in 1974 on the same two persons. It was found that minor changes (perhaps unreliable) had occurred in the precision of eidetic projection, and that both Ss retained their ability to project a seen circle onto a target square and compare the two for “goodness of fit.”     

Mental imagery and synaesthesia: Is synaesthesia from internally-generated stimuli possible?

Previous studies provide empirical support for the reported colour experience in grapheme-colour synaesthesia by measuring the synaesthetic experience from an externally presented grapheme. The current study explored the synaesthetic experience resulting from a visual mental image of a grapheme. Grapheme-colour synaesthetes (N=6) and matched controls (N=10 per synaesthete) completed a visual mental imagery task that involved visualising a letter and making a size-based decision about it. The background colour that the grapheme was visualised against was manipulated so that it was congruent or incongruent with the synaesthetic colour for the grapheme being visualised. Compared to matched controls, an effect of colour condition was found for four of the six synaesthetes, although importantly the direction of the effect varied between synaesthetes. In addition, a significant effect of group was found, as the synaesthetes were all faster than the matched controls at the imagery task, regardless of background colour. We conclude that there is some support for subjective reports of imagery-induced synaesthesia, but there are important individual differences. These findings are discussed in relation to both the visual imagery and synaesthesia literature.     

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.     

Synaesthesia is associated with enhanced, self-rated visual imagery

Although the condition known as synaesthesia is currently undergoing a scientific resurgence, to date the literature has largely focused on the heterogeneous nature of synaesthesia across individuals. In order to provide a better understanding of synaesthesia, however, general characteristics need to be investigated. Synaesthetic experiences are often described as occurring 'internally' or in the 'mind's eye', which is remarkably similar to how we would describe our experience of visual mental imagery. We assessed the role of visual imagery in synaesthesia by sampling a large group of synaesthetes and found that they report experiencing more vivid mental images than controls. These findings have important implications for our general understanding of synaesthesia and, in particular, emphasize the need to control for visual imagery in behavioural and neuroimaging paradigms.     

Hearing words and seeing colours: an experimental investigation of a case of synaesthesia

A case of 'chromatic-lexical' (colour-word) synaesthesia is described, and its genuineness confirmed using the criterion of stable cross-modality imagery across time. The synaesthesia could not be accounted for by a memory hypothesis, nor was it associated with any psychiatric condition. Further analysis did not identify any semantic relationship between real words and colours, but the colours of nonwords were determined by the colours of the individual letters. Numbers also had their own stable colours. The experience of synaesthesia was triggered by other auditory stimuli, but most strongly by words. Cortical electrophysiological recording failed to reveal any abnormalities. An unusual organisation of modalities in the brain is postulated to account for the phenomenon.     

The neural basis of illusory gustatory sensations: two rare cases of lexical-gustatory synaesthesia

Lexical-gustatory synaesthesia is a rare phenomenon in which the individual experiences flavour sensations when they read, hear, or imagine words. In this study, we provide insight into the neural basis of this form of synaesthesia using functional neuroimaging. Words known to evoke pleasant, neutral, and unpleasant synaesthetic tastes and synaesthetically tasteless words were presented to two lexical-gustatory synaesthetes, during fMRI scanning. Ten non-synaesthetic participants were also scanned on the same list of words. The synaesthetic brain displayed a different pattern of activity to words when compared to the non-synaesthetes, with insula activation related to viewing words that elicited tastes that have an associated emotional valence (i.e., pleasant or unpleasant tastes). The subjective intensity of the synaesthesia was correlated with activity in the medial parietal lobes (precuneus/retrosplenial cortex), which are implicated in polymodal imagery and self-directed thought. This region has also previously been activated in studies of lexical-colour synaesthesia, suggesting its role may not be limited to the type of synaesthesia explored here.     

Synaesthesia: learned or lost?

The question why synaesthesia, an atypical binding within or between modalities, occurs is both enduring and important. Two explanations have been provided: (1) a congenital explanation: we are all born as synaesthetes but most of us subsequently lose the experience due to brain development; (2) a learning explanation: synaesthesia is related to some learning process during childhood. Three recent studies provide conflicting support for these explanations. Two studies supported the idea that synaesthesia is learned by showing that the frequency of everyday language implicitly modulates the synaesthetic experience. Another study argued that synaesthesia reflects basic, innate magnitude representations. In this paper we reassess these points of view, and show that it is possible for both to be valid. These findings are integrated into an interactive specialization account of development in order to explain the neuronal mechanism underlying synaesthesia.     

Intervention in Creativity With Children Aged 10 and 11 Years: Impact of a Play Program on Verbal and Graphic–Figural Creativity

The three way links between creativity, mental illness and synaesthesia have been rarely investigated empirically, despite anecdotal evidence and the insights into creativity such relationships may uncover. The extent to which creativity is predicted by obsessive-compulsive disorder (OCD) and synaesthesia was explored. 210 participants completed a survey measuring the three variables. Statistically significant, moderate effect sizes were found for all pairs of scale correlations when using a proposed ‘Creative Absorption’ (CA) measure as the indication of creativity. Despite all three variables being significantly correlated with each other, and both OCD and synaesthesia being significant predictors of CA, synaesthesia and creativity displayed the strongest relationship.     

Time–space synaesthesia – A cognitive advantage?

Is synaesthesia cognitively useful? Individuals with time–space synaesthesia experience time units (such as months of the year) as idiosyncratic spatial forms, and report that these forms aid them in mentally organising their time. In the present study, we hypothesised that time–space synaesthesia would facilitate performance on a time-related cognitive task. Synaesthetes were not specifically recruited for participation; instead, likelihood of time–space synaesthesia was assessed on a continuous scale based on participants’ responses during a semi-structured interview. Participants performed a month-manipulation task, which involved naming every second month or every third month in reverse-chronological order, beginning and ending with a target month. Using hierarchical multiple regression, we found that time–space synaesthesia corresponded with faster performance on both versions of the task. We propose that time–space synaesthesia may expedite the cognitive manipulation of time-based information. Our results also indicate that synaesthesia is far less unusual than widely believed.     

Induced Cross-Modal Synaesthetic Experience Without Abnormal Neuronal Connections

ABSTRACT— Are the kinds of abnormal cross-modal interactions seen in synaesthesia or following brain damage due to hyperconnectivity between or within brain areas, or are they a result of lack of inhibition? This question is highly contested. Here we show that posthypnotic suggestion induces abnormal cross-modal experience similar to that observed in congenital grapheme-color synaesthesia. Given the short time frame of the experiment, it is unlikely that new cortical connections were established, so we conclude that synaesthesia can result from disinhibition between brain areas.     

Familial patterns and the origins of individual differences in synaesthesia

The term synaesthesia has been applied to a range of different sensory-perceptual and cognitive experiences, yet how these experiences are related to each other is not well understood. Not only are there disparate types of synaesthesia, but even within types there are vast individual differences in the way that stimuli induce synaesthesia and in the subjective synaesthetic experience. An investigation of the inheritance patterns of different types of synaesthesia is likely to elucidate whether a single underlying mechanism can explain all types. This study is the first to systematically survey all types of synaesthesia within a familial framework. We recruited 53 synaesthetes and 42% of these probands reported a first-degree relative with synaesthesia. We then directly contacted as many first-degree relatives as possible and collected complete data on synaesthetic status for all family members for 17 families. We found that different types of synaesthesia can occur within the same family and that the qualitative nature of the experience can differ between family members. Our findings strongly indicate that various types of synaesthesia are fundamentally related at the genetic level, but that the explicit associations and the individual differences between synaesthetes are influenced by other factors. Synaesthesia thus provides a good model to explore the interplay of all these factors in the development of cognitive traits in general.     

Brain areas involved in synaesthesia: a review

Despite a recent upsurge of research, much remains unknown about the neurobiological mechanisms underlying synaesthesia. By integrating results obtained so far in Magnetic Resonance Imaging (MRI) studies, this contribution sheds light on the role of particular brain regions in synaesthetic experiences. First, in accordance with its sensory nature, it seems that the sensory brain areas corresponding to the type of synaesthetic experience are activated. Synaesthetic colour experiences can activate colour regions in occipito-temporal cortex, but this is not necessarily restricted to V4. Furthermore, sensory and motor brain regions have been obtained that extend beyond the particular type of synaesthesia studied. Second, differences in experimental setup, number and type of synaesthetes tested, and method to delineate regions of interest may help explain inconsistent results obtained in the BOLD-MRI (Blood Oxygen Level Dependent functional MRI) studies. Third, an overview of obtained results shows that a network of brain areas rather than a single brain region underlies synaesthesia. Six brain regions of overlapping results emerge, these regions are in sensory and motor regions as well as 'higher level' regions in parietal and frontal lobe. We propose that these regions are related to three different cognitive processes inherently part of synaesthesia; the sensory processes, the (attentional) 'binding' processes, and cognitive control processes. Finally, we discuss how these functional and structural brain properties might relate to the development of synaesthesia. In particular, we believe this relationship is better understood by separating the question what underlies the presence of synaesthesia ('trait') from what determines particular synaesthetic associations ('type').     

Searching for Shereshevskii: what is superior about the memory of synaesthetes?

Some individuals with superior memory, such as the mnemonist Shereshevskii (Luria, 1968), are known to have synaesthesia. However, the extent to which superior memory is a general characteristic of synaesthesia is unknown, as is the precise cognitive mechanism by which synaesthesia affects memory. This study demonstrates that synaesthetes tend to report subjectively better than average memory and that these reports are borne out with objective testing. Synaesthetes experiencing colours for words show better memory than matched controls for stimuli that induce synaesthesia (word lists) relative to stimuli that do not (an abstract figure). However, memory advantages are not limited to material that elicits synaesthesia because synaesthetes demonstrate enhanced memory for colour per se (which does not induce a synaesthetic response). Our results suggest that the memory enhancement found in synaesthetes is related to an enhanced retention of colour in both synaesthetic and nonsynaesthetic situations. Furthermore, this may account for the fact that synaesthetic associations, once formed, remain highly consistent.     

Searching for Shereshevskii: What is superior about the memory of synaesthetes?

Some individuals with superior memory, such as the mnemonist Shereshevskii (Luria, 1968), are known to have synaesthesia. However, the extent to which superior memory is a general characteristic of synaesthesia is unknown, as is the precise cognitive mechanism by which synaesthesia affects memory. This study demonstrates that synaesthetes tend to report subjectively better than average memory and that these reports are borne out with objective testing. Synaesthetes experiencing colours for words show better memory than matched controls for stimuli that induce synaesthesia (word lists) relative to stimuli that do not (an abstract figure). However, memory advantages are not limited to material that elicits synaesthesia because synaesthetes demonstrate enhanced memory for colour per se (which does not induce a synaesthetic response). Our results suggest that the memory enhancement found in synaesthetes is related to an enhanced retention of colour in both synaesthetic and nonsynaesthetic situations. Furthermore, this may account for the fact that synaesthetic associations, once formed, remain highly consistent.     

Can synaesthesia research inform cognitive science?

The renaissance of synaesthesia research has produced many insights regarding the aetiology and mechanisms that might underlie this intriguing phenomenon, which abnormally binds features between and within modalities. Synaesthesia is interesting in its own right, but whether it contributes to our knowledge of neurocognitive systems that underlie non-synaesthete experience is an open question. In this review, we show that results from the field of synaesthesia can constrain cognitive theories in numerical cognition, automaticity, crossmodal interaction and awareness. Therefore, research of synaesthesia provides a unique window into other domains of cognitive neuroscience. We conclude that the study of synaesthesia could advance our understanding of the normal and abnormal human brain and cognition.     

Psychophysiological evidence for the genuineness of swimming-style colour synaesthesia

Recently, swimming-style colour synaesthesia was introduced as a new form of synaesthesia. A synaesthetic Stroop test was used to establish its genuineness. Since Stroop interference can occur for any type of overlearned association, in the present study we used a modified Stroop test and psychophysiological synaesthetic conditioning to further establish the genuineness of this form of synaesthesia. We compared the performance of a swimming-style colour synaesthete and a control who was trained on swimming-style colour associations. Our results showed that behavioural aspects of swimming-style colour synaesthesia can be mimicked in a trained control. Importantly, however, our results showed a psychophysiological conditioning effect for the synaesthete only. We discuss the theoretical relevance of swimming-style colour synaesthesia according to different models of synaesthesia. We conclude that swimming-style colour synaesthesia is a genuine form of synaesthesia, can be mimicked behaviourally in non-synaesthetes, and is best explained by a re-entrant feedback model.     

Die Fakta leiten alle Eidetik. Zu Husserls Begriff des materialen Apriori

The paper provides a reconstruction of the notion of material Apriori while exhibiting the anti-Kantian inspiration and factual grounding thereof. The attempt is made to show that a non-formal Apriori obtains because the sensuous has a normative character; further, that the difference between material and formal eidetic laws is rooted in the difference between sensuous contents, given in experience, and intellectual contents, originating in activities of judgement. The material Apriori is not independent of all experience, since it is grounded on sensuous eidetic contents and thus depends on the latter’s givenness and characteristics. It is thanks precisely to this ,contingency‘ that it has an ontological significance.     

Redefining synaesthesia?

In a thought-provoking paper, Simner (2012) highlights and criticizes a number of assumptions concerning synaesthesia. She specifically takes issue with the following assumptions: (1) synaesthesia is strictly a sensory-perceptual phenomenon; (2) consistency of inducer-concurrent pairs is the gold standard for establishing the authenticity of an individual's synaesthesia; and (3) synaesthesia is not heterogeneous. In the wake of this critique, Simner advances a working definition of synaesthesia as a neurological hyper-association that aims to be more inclusive of its variants. We are very sympathetic to Simner's approach and believe that it raises important points that will advance our understanding of synaesthesia. Here we supplement, and sometimes challenge, some of these ideas.