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PhD Defence Alix de Dieuleveult

a simple interception task used as diagnostic tool of multisensory integration problems in aging

Alix de Dieuleveult is a PhD student in the research group Human Media Interaction. Her supervisor is prof.dr. J.B.F. van Erp from the Faculty of Electrical Engineering, Mathematics and Computer Science.

To be able to live independently, older adults (OA) need to properly integrate sensory information from their environment in order to perform the activities of daily living (ADL). It is known that the aging process leading to ADL difficulties starts with the degradation of brain regions that are highly associated with MSI. Therefore, the diagnostic of changes in performance in MSI tasks may be a more sensitive and earlier predictor for future ADL difficulties than unisensory tasks. If a reliable relation between the decline in MSI and the performance of the ADL can be shown, a measure of MSI may be used as an early diagnostic and/or predictive tool for ADL problems in individual OA. This thesis aims to develop this clinically useful diagnostic tool. This could allow clinicians to develop personalized interventions with the aim to help OA to maintain their quality of life and stay independent. In order to have a broad view of what had already been done in the past, we first performed a systematic review on the different tests available in the literature that have been used to measure MSI in OA. In this review, we showed that aging influences sensory integration. OA appear to benefit more from multisensory enrichment in their environment than younger adults (YA). However, there is also some evidence that OA have trouble ignoring clearly irrelevant or unreliable sensory information; they use all environmental information even when it is disrupted or non-informative (distractors). The addition of a secondary task tends to decrease task performance more strongly in OA than in YA. We used the results of the systematic review to develop our task. Participants had to intercept disappearing targets moving downwards on a screen while the background was moving horizontally to the left or to the right creating an illusion of motion of the target. We added two additional conditions (dual tasks) to the baseline where participants had to stand on a foam (perturbing the proprioceptive and vestibular inputs) or keep track of the number of two types of tones while doing the interception task (cognitive load). We used this task in three different experiments. Overall, OA without any problem to perform ADL tend to have a larger effect of the illusion as compared to YA. However, when studying OA with a range of ADL difficulties, we discovered that they showed three different patterns of illusion effect: a (large) illusion effect (‘over integration’ pattern), a reverse illusion effect (‘dragged by the background’ pattern) and no illusion effect (‘minimal use of visual information’ pattern). These observations allowed us to develop a transitional model of the aging process happening in our task. Using different setups, we have shown as well that our task alone can predict the results of ADL-related clinical pretests measuring issues in sensorimotor systems that contribute to postural control, ADL issues, functional change of transitional movements, survival rates and life expectancy. Therefore, our results indicate that the interception task may ultimately be relevant for clinical practice. Although further research would be necessary, this thesis was a first step towards the development of a clinical tool that could assist the diagnosis of MSI issues in OA individually and predict the onset of problems in ADL.