Pre-attentive modulation of brain responses to tones in coloured-hearing synesthetes (original) (raw)
Related papers
Time Course of Neural Activity Correlated with Colored-Hearing Synesthesia
Cerebral Cortex, 2007
Synesthesia is defined as the involuntary and automatic perception of a stimulus in 2 or more sensory modalities (i.e., cross-modal linkage). Colored-hearing synesthetes experience colors when hearing tones or spoken utterances. Based on event-related potentials we employed electric brain tomography with high temporal resolution in colored-hearing synesthetes and nonsynesthetic controls during auditory verbal stimulation. The auditoryevoked potentials to words and letters were different between synesthetes and controls at the N1 and P2 components, showing longer latencies and lower amplitudes in synesthetes. The intracerebral sources of these components were estimated with lowresolution brain electromagnetic tomography and revealed stronger activation in synesthetes in left posterior inferior temporal regions, within the color area in the fusiform gyrus (V4), and in orbitofrontal brain regions (ventromedial and lateral). The differences occurred as early as 122 ms after stimulus onset. Our findings replicate and extend earlier reports with functional magnetic resonance imaging and positron emission tomography in colored-hearing synesthesia and contribute new information on the time course in synesthesia demonstrating the fast and possibly automatic processing of this unusual and remarkable phenomenon.
The physiology of coloured hearing A PET activation study of colour-word synaesthesia
Brain, 1995
In a small proportion of the normal population, stimulation in one modality can lead to perceptual experience in another, a phenomenon known as synaesthesia. In the most common form of synaesthesia, hearing a word can result in the experience of colour. We have used the technique of PET, which detects brain activity as changes of regional cerebral blood flow (rCBF), to study the physiology of colour-word synaesthesia in a group of six synaesthete women. During rCBF measurements synaesthetes and six controls were blindfolded and were presented with spoken words or pure tones. Auditory word, but not tone, stimulation triggered synaesthesia in synaesthetes. In both groups word stimulation compared with tone stimulation activated the classical language areas of the perisylvian regions. In synaesthetes, a number of additional visual associative areas, including the posterior inferior temporal cortex and the parieto-occipital junctions, were activated. The former has been implicated in the integration of colour with shape and in verbal tasks which require attention to visual features of objects to which words refer. Synaesthetes also showed activations in the right prefrontal cortex, insula and superior temporal gyrus. By contrast, no significant activity was detected in relatively lower visual areas, including areas VI, V2 and V4. These results suggest that colour-word synaesthesia may result from the activity of brain areas concerned with language and visual feature integration. In the case of colour-word synaesthesia, conscious visual experience appears to occur without activation of the primary visual cortex.
Sound-Colour Synaesthesia: to What Extent Does it Use Cross-Modal Mechanisms Common to us All
Cortex, 2006
This study examines a group of synaesthetes who report colour sensations in response to music and other sounds. Experiment 1 shows that synaesthetes choose more precise colours and are more internally consistent in their choice of colours given a set of sounds of varying pitch, timbre and composition (single notes or dyads) relative to a group of controls. In spite of this difference, both controls and synaesthetes appear to use the same heuristics for matching between auditory and visual domains (e.g., pitch to lightness). We take this as evidence that synaesthesia may recruit some of the mechanisms used in normal cross-modal perception. Experiment 2 establishes that synaesthetic colours are automatically elicited insofar as they give rise to cross-modal Stroop interference. Experiment 3 uses a variant of the cross-modal Posner paradigm in which detection of a lateralised target is enhanced when combined with a non-informative but synaesthetically congruent sound-colour pairing. This suggests that synaesthesia uses the same (or an analogous) mechanism of exogenous cross-modal orienting as normal perception. Overall, the results support the conclusion that this form of synaesthesia recruits some of the same mechanisms used in normal cross-modal perception rather than using direct, privileged pathways between unimodal auditory and unimodal visual areas that are absent in most other adults.
Pathways to seeing music: Enhanced structural connectivity in colored-music synesthesia
NeuroImage, 2013
Synesthesia, a condition in which a stimulus in one sensory modality consistently and automatically triggers concurrent percepts in another modality, provides a window into the neural correlates of cross-modal associations. While research on grapheme-color synesthesia has provided evidence for both hyperconnectivity/hyperbinding and disinhibited feedback as possible underlying mechanisms, less research has explored the neuroanatomical basis of other forms of synesthesia. In the current study we investigated the white matter correlates of colored-music synesthesia. As these synesthetes report seeing colors upon hearing musical sounds, we hypothesized they might show different patterns of connectivity between visual and auditory association areas. We used diffusion tensor imaging to trace the white matter tracts in temporal and occipital lobe regions in 10 synesthetes and 10 matched non-synesthete controls. Results showed that synesthetes possessed different hemispheric patterns of fractional anisotropy, an index of white matter integrity, in the inferior fronto-occipital fasciculus (IFOF), a major white matter pathway that connects visual and auditory association areas to frontal regions. Specifically, white matter integrity within the right IFOF was significantly greater in synesthetes than controls. Furthermore, white matter integrity in synesthetes was correlated with scores on audiovisual tests of the Synesthesia Battery, especially in white matter underlying the right fusiform gyrus. Our findings provide the first evidence of a white matter substrate of colored-music synesthesia, and suggest that enhanced white matter connectivity is involved in enhanced cross-modal associations.
Human brain mapping, 2018
Auditory-visual (AV) synesthesia is a rare phenomenon in which an auditory stimulus induces a "concurrent" color sensation. Current neurophysiological models of synesthesia mainly hypothesize "hyperconnected" and "hyperactivated" brains, but differ in the directionality of signal transmission. The two-stage model proposes bottom-up signal transmission from inducer- to concurrent- to higher-order brain areas, whereas the disinhibited feedback model postulates top-down signal transmission from inducer- to higher-order- to concurrent brain areas. To test the different models of synesthesia, we estimated local current density, directed and undirected connectivity patterns in the intracranial space during 2 min of resting-state (RS) EEG in 11 AV synesthetes and 11 nonsynesthetes. AV synesthetes demonstrated increased parietal theta, alpha, and lower beta current density compared to nonsynesthetes. Furthermore, AV synesthetes were characterized by increased t...
Synaesthesia lost and found: Two cases of person- and music-colour synaesthesia
2016
Synaesthesia is a developmental condition involving cross-communication between sensory modalities or substreams whereby an inducer (e.g. a sound) automatically evokes a concurrent percept in another modality (e.g. a colour). Whether this condition arises due to atypical structural connectivity (e.g., between normally unconnected cortical areas) or altered neurochemistry remains a central question. We report the exceptional cases of two synaesthetes – subjects AB and CD – both of whom experience coloured auras around individuals, as well as coloured perceptions in response to music. Both subjects have, in recent years, suffered a complete loss or reduction of their synaesthetic experiences, one (AB) through successive head traumas, including a lightning strike, followed by a number of medications, and the other (CD) while taking anxiolytic medications. Using semi-structured interviews and data from the Synaesthesia Battery and a colourpicker task, we characterise the phenomenologica...
Speed and Consistency of Sound-Color Association in a Colored-Hearing Test
Synesthesia is the phenomenon in which the stimulation of one sensory modality results in perception in another modality, namely, unstimulated modality. Colored hearing is a synesthesia in which sound stimulation induces visual color perception. The current research investigated the speed and consistency of sound-color association in a colored-hearing test by using a color search task. The results showed that the reaction time (RT) of the colored-hearing group was faster than that of the control group. We also found that the colors selected by the colored-hearing group were more consistent than those selected by the control group. These findings suggested that in colored-hearing synesthetes, automatic and consistent sound-color association occurs in the perceptual stage of processing.
Functional magnetic resonance imaging of synesthesia: activation of V4/V8 by spoken words
Nature Neuroscience, 2002
In synesthesia, a stimulus in one sensory modality triggers, involuntarily and automatically, a sensation in another: thus, in 'colored hearing' , hearing words induces sensations of color 1 . Positron-emission tomography (PET) has shown in colored-hearing synesthetes the activation by speech of regions of visual association cortex not activated in controls, without significant activation of lower visual areas, including areas V1, V2 or V4/V8 (ref. 2). If synesthetic color experience is similar to true color percepts, however, one can more specifically predict activation of the human 'color center ' , called V4 (refs. 3, 4) or V8 (ref. 5). Using the greater spatial resolution and sensitivity of fMRI, we tested this prediction by comparing brain activation patterns elicited by spoken words versus tones in synesthetes and controls. We also determined whether primary visual cortex (areas V1 and V2) was active during colored-hearing synesthesia. Lack of V1/V2 activity would suggest the generation of conscious visual percepts without contribution from primary visual cortex 6-8 . Specifically, we compared the activation pattern in synesthetes hearing words to those observed in response to seen colors both in a group of non-synesthetes for whom the latter data were already 9 available (Experiment 1) and, in a within-subject design, in synesthetes themselves (Experiment 2). To control for the possibility that synesthetes might have an unusual topography of the visual areas, we also compared the regions activated by seen colors in these subjects and in non-synesthetes. In Experiment 3, we investigated whether normal subjects imagining colors show activation of a similar kind to that observed when synesthetes spontaneously