Impact of early blindness on the spatial distribution of attention and rhythm perception : a psychophysical and brain imaging approach

Vision is our dominant sense to apprehend the environment. How does a blind person compensate for this lack of information? The present thesis addresses this question in two domains: the distribution of auditory attention in the surrounding space and rhythm and beat processing. We demonstrated that early blind individuals have improved sound detection abilities in both frontal and peripheral spaces. However, the improvement was bigger for the peripheral space than the frontal one. In rhythm perception, we demonstrated, for the first time, the presence of improved beat asynchrony detection abilities in early blind individuals as well as a different profile of brain activity in several frontal areas during rhythm and beat perception in this population. All these behavioural and neural changes could be caused by an increased reliance on the preserved modalities and are informative about the type of brain plasticity that takes place following early blindness.(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 201

Does visual experience influence the spatial distribution of auditory attention?

Sighted individuals are less accurate and slower to localize sounds coming from the peripheral space than sounds coming from the frontal space. This specific bias in favour of the frontal auditory space seems reduced in early blind individuals, who are particularly better than sighted individuals at localizing sounds coming from the peripheral space. Currently, it is not clear to what extent this bias in the auditory space is a general phenomenon or if it applies only to spatial processing (i.e. sound localization). In our approach we compared the performance of early blind participants with that of sighted subjects during a frequency discrimination task with sounds originating either from frontal or peripheral locations. Results showed that early blind participants discriminated faster than sighted subjects both peripheral and frontal sounds. In addition, sighted subjects were faster at discriminating frontal sounds than peripheral ones, whereas early blind participants showed equal discrimination speed for frontal and peripheral sounds. We conclude that the spatial bias observed in sighted subjects reflects an unbalance in the spatial distribution of auditory attention resources that is induced by visual experience

Improved beat asynchrony detection in early blind individuals.

Although early blind (EB) individuals are thought to have a better musical sense than sighted subjects, no study has investigated the musical rhythm and beat processing abilities in EB individuals. Using an adaptive 'up and down' procedure, we measured the beat asynchrony detection threshold and the duration discrimination threshold, in the auditory and vibrotactile modalities in both EB and sighted control (SC) subjects matched for age, gender, and musical experience. We observed that EB subjects were better than SC in the beat asynchrony detection task; that is, they showed lower thresholds than SC, both in the auditory and in the vibrotactile modalities. In addition, EB subjects had a lower threshold than SC for duration discrimination in the vibrotactile modality only. These improved beat asynchrony detection abilities may contribute to the known excellent musical abilities often observed in many blind subjects

Finger agnosia and acalculia: Neglected issues

Objective: Finger agnosia refers to the inability to discriminate one's fingers and is frequently associated with acalculia in the Gerstmann syndrome. This co-occurence of symptoms has been related to the helping role of fingers for counting but the cognitive components involved in finger agnosia remain poorly documented. This study investigates the effect of attention allocation on finger agnosia. Method: PM, a 54-year-old patient with a right parietal lesion, showed signs of neglect and difficulties for calculating and recognizing his fingers. In addition to the neuropsychological examination, we measured speed and accuracy in tasks that required PM to move a finger in response to its name or to mentally solve addition and subtraction problems. His performance was compared to the performance of healthy participants matched for age and education. Results: The neuropsychological examination evidenced left neglect and difficulties to discriminate fingers of the left hand in tasks that put high demands on attention allocation. Finger recognition was slower for the left than for the right hand when the two hands were tested in the same block of trials, whereas no difference was observed when they were tested in separate blocks. In arithmetic tasks, PM took more time to solve subtraction than addition problems. Conclusions: We conclude that, in the present case, finger agnosia is contingent on a spatial attention deficit. To account for the specific deficit of the patient in subtraction, we propose that subtracting a number involves shifting attention leftward on a visuospatial medium where numbers are represented from left to right

Syndrome d’Asperger avec Haut Potentiel Intellectuel : le camouflage à l’origine des diagnostics tardifs ?

OBJECTIFS : Dans notre Centre de référence des troubles du spectre Autistique, nous rencontrons des jeunes présentant à la fois un Syndrome d’Asperger et un profil intellectuel de type haut potentiel. L’objectif de cet article est d’ouvrir une réflexion sur le diagnostic tardif chez ces patients et d’analyser les raisons qui y mènent. MÉTHODE : Nous avons réalisé une étude rétrospective basée sur l’analyse des dossiers cliniques de patients âgés de 8 à 18 ans et présentant à la fois un diagnostic de Syndrome d’Asperger et un profil de Haut Potentiel Intellectuel, ayant bénéficié d’un bilan diagnostique dans notre service. Au départ des dossiers des patients, nous avons identifié plusieurs éléments : motif de la demande, personnes demandeuses, éventuels diagnostics antérieurs, signes cliniques de Troubles du Spectre Autistique. RÉSULTATS : Nous avons étudié une population de 17 jeunes. Les résultats nous permettent de repérer que les caractéristiques autistiques et les difficultés des patients sont plus facilement identifiables dans le contexte de l’ADOS et dans les observations libres que durant les autres épreuves standardisées. Nous notons également l’importance de l’intuition et l’expérience clinique. DISCUSSION : Nous proposons d’étendre la notion de stratégies de camouflage, initialement appliquée aux femmes avec un Syndrome d’Asperger, aux enfants et adolescents présentant à la fois un Syndrome d’Asperger et un Haut Potentiel Intellectuel. Le Haut Potentiel Intellectuel offrirait à ces jeunes la possibilité de compenser ou masquer certaines inaptitudes. CONCLUSION : Cette étude nous permet d’expliquer en partie les diagnostics tardifs de Syndrome d’Asperger avec Haut Potentiel Intellectuel par l’existence chez ces jeunes de stratégies de camouflages qui pourraient être d’autant plus performantes que ces jeunes présentent une intelligence supérieure à la moyenne.[Asperger Syndrome with High Intellectual Potential: Camouflage as a factor in late diagnosis?] BACKGROUND: The mission of our “Centre de référence des troubles du spectre autistique” is to evaluate children and adolescents for whom there is a suspicion of autistic spectrum disorder through a multidisciplinary diagnostic assessment. We encounter cases of patients presenting both Asperger syndrome and High Intellectual Potential. Those patients are frequently older than the norm. The objectives of our study are to understand the reasons leading to a late diagnosis for these patients and to question the value of giving such a diagnosis to children aged from eight to 18 years old. METHODS: We carried out a retrospective study based on the analysis of clinical files from patients presenting both AS and HIP, aged between eight and 18 years old. These patients were all previously seen in our center for a multidisciplinary diagnostic assessment. We analyzed several items from their clinical reports, such as the moment of and the motivation for the assessment; the person(s) asking for the assessment; the possible previous diagnosis; the evident and subtle characteristics of Asperger syndrome present in the speech, neuropsychological, and psychological (ADOS and projective tests) evaluations; psychomotricity; IQ score; the patients’ integration into their peer groups; and the possible associated psychiatric issues. RESULTS: We examined the files of 17 subjects presenting both Asperger syndrome and High Intellectual Potential profiles, aged between eight and 18 years old. The results show that autistic traits are more easily observed during the ADOS test and the informal assessments rather than during the other standardized analysis. We also noticed the importance of the clinical intuition and experience of the examiner. DISCUSSION: We propose to extend the notion of “camouflage” strategies, previously used to describe women with Asperger syndrome, to children and adolescents presenting both an Asperger syndrome and a High Intellectual Potential profile. Their particularly high IQ could allow these patients to compensate for or to hide some of their impairments. CONCLUSION: The results seem to confirm our hypothesis, which is that thanks to their high intellectual functioning, patients presenting both AS and HIP profiles manage to compensate for or to camouflage some of their difficulties related to social adaptation and communication. Therefore, their impairment appears more subtle, leading to a late diagnosis. The quality of these camouflage strategies could depend on a high IQ score. For the future, it would be interesting to compare these results to a population of patients with AS and a normal IQ, in order to more clearly perceive the impact of IQ on camouflage strategies

Perception of rhythm through auditory, vibro-tactile and visual stimulations: an fMRI study

Recent studies reported an involvement of motor/premotor brain areas during the perception of rhythm and beat in audition. However, little is known about the neural network of beat perception through non-auditory modalities. Here we used functional magnetic resonance imaging with auditory, vibro-tactile and visual rhythmic sequences in order to highlight the modality-specific areas involved in beat perception. We contrasted the brain activity changes in 20 healthy volunteers exposed to rhythmic sequences with a beat and control sequences without a beat. Results showed a recruitment of premotor cortex, supplementary motor area (SMA) and basal ganglia during beat sequences compared to rest in all three modalities. Beat sequences compared to no-beat sequences elicited the selective recruitment of the putamen and the SMA in the three sensory modalities, although to a lesser extent in vision. We conclude that the putamen and the SMA play a role in the prediction ability of a regular temporal pattern, although this seems less pronounced in vision compared to audition and to the vibro-tactile sensory modality

Right occipital cortex activation correlates with superior odor processing performance in the early blind.

Using functional magnetic resonance imaging (fMRI) in ten early blind humans, we found robust occipital activation during two odor-processing tasks (discrimination or categorization of fruit and flower odors), as well as during control auditory-verbal conditions (discrimination or categorization of fruit and flower names). We also found evidence for reorganization and specialization of the ventral part of the occipital cortex, with dissociation according to stimulus modality: the right fusiform gyrus was most activated during olfactory conditions while part of the left ventral lateral occipital complex showed a preference for auditory-verbal processing. Only little occipital activation was found in sighted subjects, but the same right-olfactory/left-auditory-verbal hemispheric lateralization was found overall in their brain. This difference between the groups was mirrored by superior performance of the blind in various odor-processing tasks. Moreover, the level of right fusiform gyrus activation during the olfactory conditions was highly correlated with individual scores in a variety of odor recognition tests, indicating that the additional occipital activation may play a functional role in odor processing