Cortical and subcortical contributions to state- and strength-based perceptual judgments

peer reviewe

Exploration de l'espace dans la négligence visuelle : Rôle de la mémoire de travail spatiale et de l'attention

Par les questions qu’elle soulève sur la prise de conscience de l’espace qui nous entoure, la négligence spatiale revêt un intérêt particulier dans l’étude et la compréhension de la cognition visuo-spatiale. Auparavant définie comme un trouble de nature principalement attentionnel, la négligence spatiale est aujourd’hui davantage considérée comme pouvant résulter de l’association de troubles cognitifs distincts, parmi lesquels un déficit de la mémoire de travail spatiale. Associés aux déficits attentionnels, ces troubles cognitifs sont non seulement susceptibles d’exacerber la sévérité de la négligence, mais également de participer à la persistance du trouble. Pour cette raison, leur prise en compte tant dans le cadre de l’évaluation que de la prise en charge est donc essentielle. Dans ce contexte, nous avons envisagé notre travail sous deux angles différents, à la fois en considérant l’altération de la mémoire de travail spatiale, mais également la préservation de certains processus attentionnels dans la négligence spatiale. La première partie de cette thèse vise à mieux comprendre l’implication de la mémoire de travail spatiale dans les manifestations comportementales de la négligence. Plus précisément, nous avons étudié le lien entre l’altération de la mémoire de travail spatiale et la tendance des patients à explorer et à traiter de manière répétée les stimuli situés du côté ipsi-lésionnel (Etude 1). Ensuite, partant d’une conception fractionnée de la mémoire de travail visuo-spatiale, nous avons cherché à déterminer dans quelle mesure les patients héminégligents présentaient un déficit spécifique de la composante spatiale séquentielle versus simultanée de la mémoire à court terme, ce qui nous a conduit à explorer l’indépendance de ces deux composantes (Etude 2) ainsi que leur impact fonctionnel sur les manifestations représentationnelles du trouble (Etude 3). La seconde partie de ce travail a pour objectif d’étudier la capacité des patients héminégligents à utiliser les mécanismes d’orientation attentionnelle implicite pour compenser leur défaut d’orientation. Deux études ont été conduites afin d’examiner si l’extraction implicite des régularités statistiques présentes dans l’environnement pouvait permettre aux patients d’orienter plus précisément et plus rapidement leur attention vers le côté contra-lésionnel (Etude 4 et 5)

Different causes explain pathological visual search in spatial neglect

peer reviewedOverview and aim. In visual search tasks, neglect patients tend to explore and repeatedly re-cancel stimuli on the ipsilesional side, as if they did not realize that they had previously examined the rightward location favored by their lateral bias. Re-cancellation behaviors have been related to spatial working memory (SWM) impairment (Husain et al., 2001) but some authors have recently called into question this interpretation (Wansard et al., 2014). Difficulties planning a visual search (Mark et al., 2004) but also abnormal inhibition of return (IOR, Bourgeois et al., 2012) frequently observed in neglect patients could exacerbate neglect behaviors (i.e. omissions and re-cancellations), leading to repetitive searching towards the right side of space. The aim of our study was to investigate the cognitive functions involved in re-cancellation behaviors. Methods. We assessed twenty-nine right-damaged patients suffering from left neglect on experimental tasks evaluating SWM (Corsi Block test), IOR (Bartolomeo et al., 1999), and visual search planning (cancellation task without visual feedback). Results. Results showed that the IOR index and the planification of visual search are the two factors that better explain the re-cancellations behavior, while the measure of SWM significantly predict left omissions. Discussion and conclusion. Re-cancellation behavior cannot be explained by a spatial working memory deficit in neglect patients. In our study, we observed that the lack of IOR and difficulties to plan a visual search observed in neglect patients exacerbate the rightward bias and thus failures to explore the left space. The influence of neglect’s severity and clinical implications of our findings are discussed

What can unilateral neglect tell us about the structure of visuospatial working memory?

Some studies have proposed that deficits in visuospatial working memory (WM) could exacerbate the neglect syndrome, as reflected in the patients’ tendency to repeatedly search through items located on the right, as if they did not realize that they had previously examined the rightward locations favoured by their lateral attentional bias (e.g., Husain et al., 2001). However, we have recently shown that the efficiency level of spatial WM, as evaluated by the Corsi Block test, might not be sufficient to explain perseveration and omission behaviors in neglect patients (Wansard et al., 2014). Moreover, it appears that, until now, research has mostly focused on spatial sequential WM, addressing the study of visuospatial WM through tasks involving the recall of serial order. We will present data suggesting that other subcomponents of visuospatial WM, such as simultaneous-spatial or visual WM (Logie, 1995), could also be involved in the neglect syndrome. We will also present evidence of a double dissociation between the two aspects of visuospatial WM (simultaneous vs sequential) in neglect patients, confirming the dual dimension of visuospatial WM (Wansard et al., 2015)

Developmental Invariance in Implicit Sequence Learning

This study was intended to test the age invariance hypothesis on implicit learning abilities using the serial reaction time paradigm and focusing on the comparison of second-order conditional (SOC) sequences of two different lengths (8 and 12 elements). A total of 128 participants from 4 age groups (4 years, 7 years, 10 years, and adults) were tested. The results showed significant and similar learning effects in 4-, 7-, and 10-year-old children, as well as adults. The learning effect was more pronounced for the 8-element sequence than for the 12-element sequence for all age groups, suggesting that the shorter sequence was better learned than the longer one. In addition, the degree of explicit sequence awareness was comparable between age groups and sequence lengths. These results, showing that 4-year-old children are able to learn 8- and 12-element-long SOC sequences as well as adults, provide further support for the hypothesis that implicit learning abilities are developmentally invariant

Shedding new light on representational neglect: The importance of dissociating visual and spatial components

Over the last decade, many studies have demonstrated that visuospatial working memory (VSWM) can be divided into two subsystems, dealing respectively with spatial and visual information. A similar dissociation has been observed in brain-damaged patients without neglect for mental imagery skills. The first aim of the present study was to examine whether performance dissociations between spatial and visual mental imagery can be observed in unilateral neglect. The second objective was to further investigate the role of spatial and visual working memory subsystems in the mental representation abilities of neglect patients and healthy controls, and their dependence on the nature of the mental imagery tasks performed. The results showed that spatial and visual imagery processes can be selectively impaired in unilateral neglect. Spatial working memory skills were also found to strongly predict spatial imagery score in the two experimental groups. However, contrary to what was observed in healthy controls, visual working memory did not appear to predict performance on visual imagery tasks in neglect patients. Overall, these findings highlight the importance of investigating both visual and spatial components of working memory and mental imagery in neglect patients