Can Tracking Representationalism Make Sense of Synesthesia?

Synesthesia is a neurological phenomenon in which a single stimulus typically associated with one sensory modality automatically and involuntarily produces sensations not typically associated with that modality. I argue that synesthesia elucidates how two naturalistic theories of representation and phenomenal experience conflict. Strong representationalism holds that what an experience is like is determined by the experience’s representational content. Informational semantics holds that representational content is determined by causal co-variation between a representation and an external object or property. I argue that according to informational semantics, synesthetes and normal perceivers represent the same content in different ways. However, according to strong representationalism, two experiences with the same content must be represented in the same way. Therefore, if strong representationalists want to account for synesthesia, they cannot hold onto informational semantics as a theory of mental content

The brain of synesthetes

Synesthesia is a fascinating phenomenon in which a particular perception induces a concurrent perception resulting in a kind of double perception. This phenomenon has received considerable attraction in the last 15years by neuroscientists and cognitive psychologists. Here I will summarize and discuss some of the main findings and ideas from this research. First, I will discuss the main neurophysiological models trying to explain this extraordinary phenomenon. Secondly, I will describe the findings trying to delineate the time course of synesthetic perception in relation to the associated neurophysiological models. Finally, current findings reporting specific and general neuroanatomical features of the synesthete's brain will be discussed. These findings will be integrated into the current models about the neurophysiological underpinnings of synesthesia

Automatic letter-colour associations in non-synaesthetes and their relation to grapheme-colour synaesthesia

Although grapheme-colour synaesthesia is a well-characterized phenomenon in which achromatic letters and/or digits involuntarily trigger specific colour sensations, its underlying mechanisms remain unresolved. Models diverge on a central question: whether triggered sensations reflect (i) an overdeveloped capacity in normal cross-modal processing (i.e., sharing characteristics with the general population), or rather (ii) qualitatively deviant processing (i.e., unique to a few individuals). We here address this question on several fronts: first, with adult synaesthesia-trainees and second with congenital grapheme-colour synaesthetes. In Chapter 3, we investigate whether synaesthesia-like (automatic) letter-colour associations may be learned by non- synaesthetes into adulthood. To this end, we developed a learning paradigm that aimed to implicitly train such associations while keeping participants naïve as to the end-goal of the experiments (i.e., the formation of letter-colour associations), thus mimicking the learning conditions of acquired grapheme- colour synaesthesia (Hancock, 2006; Witthoft & Winawer, 2006). In two experiments, we found evidence for significant binding of colours to letters by non-synaesthetes. These learned associations showed synaesthesia-like characteristics despite an absence of conscious, colour concurrents, correlating with individual performance on synaesthetic Stroop-tasks (experiment 1), and modulated by the colour-opponency effect (experiment 2) (Nikolic, Lichti, & Singer, 2007), suggesting formation on a perceptual (rather than conceptual) level. In Chapter 4, we probed the nature of these learned, synaesthesia-like associations by investigating the brain areas involved in their formation. Using transcranial Direct Current Stimulation to interfere with two distinct brain regions, we found an enhancement of letter-colour learning in adult trainees following dlPFC-stimulation, suggesting a role for the prefrontal cortex in the release of binding processes. In Chapter 5, we attempt to integrate our results from synaesthesia-learners with the neural mechanisms of grapheme-colour synaesthesia, as assessed in six congenital synaesthetes using novel techniques in magnetoencephalography. While our results may not support the existence of a “synaesthesia continuum,” we propose that they still relate to synaesthesia in a meaningful way

The immune hypothesis of synesthesia

No abstract available

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

Learning partial grapheme synaesthesia

Synaesthesia is a variation of normal human perception. A grapheme synaesthete, for example, can experience extra sensations, such as colours when seeing letters and/or numbers. Synaesthetic ability is commonly developed at an early age, and is linked to a genetic pre-disposition; however, there is a learnt component, as one must also learn to read and write to develop grapheme synaesthesia. To explore the extent to which synaesthesia can be learnt, a training method was employed, which was first used by Colizoli, Murre and Rouw (2012). In order to learn their own coloured letters a group of non-synaesthetic individuals read colour books, which are free eBooks reproduced to have four letters consistently appear in colour. Before and after reading, the participants completed a modified Stroop-design based on Mills (1999), which was used to measure if they had learnt the two key characteristics of synaesthesia, namely an involuntary and automatic reaction to letters. Both the colour reading (n=15) and control (n=6) groups did not have a significant involuntary reaction to letters. However, it was found that the participants had significantly more automatic reactions to letters. This included the control group, who did not read in colour, which suggests that merely completing the modified Stroop test is enough to learn the automatic characteristic of grapheme synaesthesia.PsychologyM.A. (Psychology

Intrinsic functional brain networks in health and disease

6 Introduction   6  6.1   Imaging  cognitive  processes  with  functional  magnetic  resonance  imaging   7  6.2   Imaging  the  brain’s  resting  state   8  6.3   Intrinsic  connectivity  networks  in  the  resting  state   9  6.4   Investigating  modulations  and  plasticity  of  intrinsic  connectivity  networks   12 7 Paper  1:   Towards  discovery  science  of  human  brain  function  (PNAS  2010)   14 8 Paper  2:   Repeated  pain  induces  adaptations  of  intrinsic  brain  activity  to  reflect  past  and  predict future pain  (Neuroimage  2011)   30 9 Paper  3:   Intrinsic  network  connectivity  reflects  consistency  of  synesthetic  experience

Reduced Visual and Frontal Cortex Activation During Visual Working Memory in Grapheme-Color Synaesthetes Relative to Young and Older Adults

The sensory recruitment model envisages visual working memory (VWM) as an emergent property that is encoded and maintained in sensory (visual) regions. The model implies that enhanced sensory-perceptual functions, as in synaesthesia, entail a dedicated VWM-system, showing reduced visual cortex activity as a result of neural specificity. By contrast, sensory-perceptual decline, as in old age, is expected to show enhanced visual cortex activity as a result of neural broadening. To test this model, young grapheme-color synaesthetes, older adults and young controls engaged in a delayed pair-associative retrieval and a delayed matching-to-sample task, consisting of achromatic fractal stimuli that do not induce synaesthesia. While a previous analysis of this dataset (Pfeifer et al., 2016) has focused on cued retrieval and recognition of pair-associates (i.e., long-term memory), the current study focuses on visual working memory and considers, for the first time, the crucial delay period in which no visual stimuli are present, but working memory processes are engaged. Participants were trained to criterion and demonstrated comparable behavioral performance on VWM tasks. Whole-brain and region-of-interest-analyses revealed significantly lower activity in synaesthetes’ middle frontal gyrus and visual regions (cuneus, inferior temporal cortex), respectively, suggesting greater neural efficiency relative to young and older adults in both tasks. The results support the sensory recruitment model and can explain age and individual WM-differences based on neural specificity in visual cortex