Five experiments, involving 265 subjects, were performed with the objective of extending the analysis of response probability as a determinant of the practice effect in tachistoscopic word recognition. The results showed that the response probabilities of words may be manipulated and act as a determinant of the practice effect under certain limited experimental conditions. A more powerful determinant appears to be a general skill in tachistoscopic recognition which improves as a function of the number of stimuli recognized and transfers to the recognition of different stimuli. This skill was examined in the final experiment. The overall results were discussed in terms of both response probability and a general tachistoscopic skill. / Thesis / Doctor of Philosophy (PhD)

Upp till 20% av alla barn drabbas av någon form av läs- och skrivsvårigheter. För kunna utvärdera de interventioner och anpassningar som skolan gör för dessa barn behövs valida och reliabla testinstrument. Studien avser bidra med normeringsdata samt information kring eventuell igenkänningseffekt/övningseffekt för mellanstadieelever avseende ordavkodningstesten A1-A4. Sammanlagt deltog 77 elever från 2 grundskolor. Samtliga deltagande elever genomförde alla fyra ordavkodningstester. Testordningen varierades mellan varje elev. En signifikant skillnad i svårighetsgrad mellan A1, A2, A3 och A4 hittades. A1 visade sig vara signifikant lättare än A2 och A4. Det gick däremot inte att fastställa någon signifikant igenkänningseffekt/övningseffekt. Det förelåg en signifikant resultatskillnad mellan årskurserna 4 - 5 och 4 - 6. Däremot var inte resultatskillnaden mellan årskurs 5 och 6 signifikant. Resultaten antyder en viss skillnad i svårighetsgrad mellan de olika deltesten, vilket påvisar att testen kan behöva justeras något för att kunna användas som parallelltest. / Up to 20% of all children suffer from some variety of reading or writing disability. To be able to evaluate the interventions and adaptations the school makes for these children, valid and reliable test-instruments are needed. This study intends to contribute with standardization data and information about recognition effect and/or practice effect for students in grade 4, 5 and 6, regarding the word decoding tests A1-A4. A total of 77 students from 2 different schools participated. All participating students completed all four word decoding tests. The order of the tests was varied between students. A significant difference in difficulty between A1, A2, A3 and A4 was found. A1 proved to be significantly easier than A2 and A4. It was not possible to determine a significant recognition effect and/or practice effect. There was a significant difference in results between the 4th and 5th grade and the 4th and 6th grade. The difference in results between the 5th and 6th grade was not significant. The results of this study indicate a slight difference in difficulty between the tests, which prompts the need for further adjustment in each subtest for proper use as parallel tests.

Le modèle computo-fonctionnel de la vision de haut niveau de Kosslyn et Koenig (1992) repose sur la dissociation entre la reconnaissance et le traitement spatial de la scène visuelle. En 1987, Kosslyn postula l’existence de deux processus pour le traitement des relations spatiales : un processus catégoriel qui calcule les positions relatives des objets et un processus coordonné qui calcule la distance entre les objets. Des études utilisant le paradigme de présentation en champ visuel divisé ont mis en évidence que l’hémisphère gauche sous-tendrait un traitement catégoriel ; l’hémisphère droit sous-tendrait un traitement coordonné. Cette interaction semblerait valider la dichotomie des deux types de processus.Une revue de la littérature pluridisciplinaire a été menée afin de savoir si ce fait est suffisant pour rejeter l’hypothèse d’un processus unique pour les traitements catégoriels et coordonnés. Entre autres, plusieurs études ont observé un effet de pratique au cours de la réalisation de jugements coordonnés : une diminution de l’intervention de l’hémisphère droit au profit d’une prise en charge progressive de l’hémisphère gauche. De plus, l’avantage de l’hémisphère gauche pour le traitement catégoriel a été rarement observé.Une série de cinq expériences comportementales ont été conduites pour vérifier certains biais expérimentaux qui pourraient expliquer les différences hémisphériques et l’effet de pratique observés. Nos résultats nous ont permis d’avancer des hypothèses axées sur la communication entre les hémisphères et sur un lien entre les processus catégoriels et coordonnés. Une critique du paradigme de présentation en champ visuel divisé et différents modèles d’interaction hémisphérique ont été présentés. Trois expériences ont été menées, afin d’évaluer l’impact des communications hémisphériques dans le traitement des relations spatiales. A la lumière de nos résultats, la dichotomie des processus catégoriels et coordonnés a été discutée. / The computational-functional conception of high-level processing of vision in Kosslyn and Koenig (1992) relies on dissociation between object recognition and spatial processing. In 1987, Kosslyn postulated that two different processes compute spatial-relations: categorical process computes relative position of objects and coordinate process computes the distance between objects. Some studies indicate a left-hemisphere advantage for processing categorical spatial relations and a right-hemisphere advantage for processing coordinate spatial relations. This hemispheric difference is interpreted as an evidence of a dichotomy between these two processes. A pluridisciplinary review was conducted to assure that single process hypothesis is dismissed out. Some studies showed, in a coordinate task, that practice resulted in a decreased right-hemisphere involvement and a concurrent increase in left-hemisphere involvement (i.e., practice effect). Furthermore, the left-hemisphere advantage in categorical was seldom observed. The theoretical aim of the thesis was based on two questions: (1) Are there single or several processes encoding visual spatial relations? (2) How can we interpret this practice effect ?Five experiments were run to verify possible bias which might explain observed hemispheric differences and practice effect. Our results suggested that hemispheric communication might be an important factor in spatial-relation processing.An theoretical investigation of divided visual field paradigm was led and several interhemispheric models were described. Three experiments were conducted to estimate hemispheric communication in spatial-relation process. In the light of our results, separate categorical-coordinate processes hypothesis were discussed.

Neuropsychological impairment following cardiopulmonary bypass (CPB) remains a serious consequence of otherwise successful surgery. The incidence of neuropsychological decline is poorly understood due to varied measurement intervals, and perhaps more importantly the use of unreliable detection and classification methods. The reported incidence varies considerably, ranging anywhere from 30% to 90% of subjects. While the nature of this impairment has not been fully elucidated, recent evidence suggests that microembolism during surgery may be the principal causative agent of postoperative cerebral dysfunction. The work described in this thesis investigates one possible source of microembolism leading to postoperative decline, namely thromboembolism arising from excessive activation of the haemostatic mechanism. Crucial to the accurate detection of significant decline in individual patients, this work also focuses on the development and use of meaningful criteria to be used when describing change in neuropsychological performance measures. The strong haemostatic activation during CPB is controlled by heparin anticoagulation. The clinical performance of the Hepcon heparin-monitoring instrument was compared to the activated clotting time (ACT), which is used in most cardiac centres. An analysis of samples from 42 elective coronary artery bypass grafting (CABG) patients shows that the ACT does not detect the significant decline in heparin concentration seen upon connection to CPB, in comparison to the Hepcon. The Hepcon appears to be in satisfactory agreement with laboratory anti-Xa analysis of heparin concentration, with the mean difference for the Hepcon at -0.46 U/ml, and the limits of agreement +/- 1.12 U/ml. Further analysis shows that that for 95% of cases, the Hepcon will give values that are between 0.53 and 1.27 times the value for anti-Xa. The loss of relationship between ACT and heparin concentration was further investigated by converting ACT values to heparin concentration. The results provide data on the degree of prolongation in ACT times brought about by factors associated with CPB. A methodology is presented by which users can adjust for the loss of relationship between ACT and heparin. This work also demonstrates that under normal usage of the ACT, the user may obtain values up to 3 times appropriate for the plasma heparin concentration. The computer-administered neuropsychological testing tool (the MicroCog) was validated using 40 age-matched control subjects. Using a two-week interval, the summary score correlation coefficients ranged from .49 to .84, with all scores demonstrating significant practice effects. Also presented are retest normative data that may be used to determine significant change in a homogeneous sample using both reliable change and regression models of analysis. The performance of four different models of change analysis was then analysed using data from the clinical group. The regression technique of analysis was shown to be the most useful prediction model as it provides correction for both practice effects and regression toward the mean in each individual. A novel statistical rationale is presented for the choice of criteria in the identification of patients that may be defined as overall impaired when using a battery of test scores. When using one-tailed prediction models for decline, the binomial distribution of scores was shown to be a useful descriptive statistic providing an estimate of change due to chance. When applied to a suitable selection of scores that minimise shared variance, a value +/- 20% of test scores used was demonstrated to be a rational cut-off for an individual to be classified as impaired. Using this methodology, 32.7% of patients were identified as significantly deteriorated in neuropsychological test function immediately prior to discharge from hospital. Patient age was shown to be a significant predictor of neuropsychological decline following CPB. No significant relationship was identified between thrombin generation and neuropsychological change scores, however problems with patient recruitment and retention limited the statistical power of this study. An intriguing relationship with heparin concentration was noted that might warrant further investigation. This work highlights the complex nature of post-bypass neuropsychological dysfunction and the complexities in assessing decline. The regression-based model was shown to be highly useful in the analysis of data from a suitably validated neuropsychological testing tool. The argument that no suitable criterion exists for the identification of patients as overall impaired has been challenged with the development of a rational cut-off based on the likely distribution of change scores across a series. The work presented here confirms the need for standardised testing methods based on sound statistical criteria. This work also highlights the problems associated with current methods for monitoring anticoagulation therapy during bypass surgery. Methodology is presented that allows adjustment of ACT results to account for CPB-induced prolongation of clotting times. Current techniques for heparin monitoring overestimate heparin levels on bypass by up to threefold, which may predispose to subclinical coagulation and increased delivery of protamine.

No description available.

La façon dont une information se répète au cours du temps a une influence sur la façon dont nous nous souviendrons de cette information. Les recherches en psychologie ont mis en évidence l’effet de pratique distribuée, selon lequel on retient mieux les informations qui se répètent avec des intervalles inter-répétitions longs que celles qui se répètent avec des intervalles courts. Nos travaux ont porté spécifiquement sur les situations où l’information se répète sur plusieurs jours, et nous avons comparé l’efficacité relative de différents types d’agencement temporel des répétitions. Un agencement uniforme consiste en des répétitions se produisant à intervalles réguliers, un agencement expansif en des répétitions se produisant selon des intervalles de plus en plus espacés, et un agencement contractant en des répétitions se produisant selon des intervalles de plus en plus rapprochés. Les Expériences 1 et 2 consistaient en une phase d’apprentissage d’une semaine et ont révélé la supériorité des agencements expansif et uniforme après un délai de rétention de deux jours. L’Expérience 3 consistait en une phase d’apprentissage de deux semaines, et les sujets étaient ensuite testés lors de trois délais de rétention différents (2, 6 ou 13 jours). La supériorité de l’agencement expansif sur les deux autres agencements est apparue progressivement, suggérant que les différents agencements induisaient des taux d’oubli différents. Nous avons également tenté de tester différentes théories explicatives des effets de l’agencement temporel des répétitions sur la mémorisation, en particulier les théories de la variabilité de l’encodage (Expérience 4) et de la récupération en phase d’étude (Expérience 2). Les résultats observés tendent à confirmer la théorie de la récupération en phase d’étude. Nous insistons sur l’importance de la prise en compte des apports des autres disciplines des sciences cognitives dans l’étude de l’effet de pratique distribuée. / How information is repeated over time determines future recollection of this information. Studies in psychology revealed a distributed practice effect, that is, one retains information better when its occurrences are separated by long lags rather than by short lags. Our studies focused specifically on cases in which items were repeated upon several days. We compared the efficiency of three different temporal schedules of repetitions: A uniform schedule that consisted in repetitions occurring with equal intervals, an expanding schedule that consisted in repetitions occurring with longer and longer intervals, and a contracting schedule that consisted in repetitions occurring with shorter and shorter intervals. In Experiments 1 and 2, the learning phase lasted one week and the retention interval lasted two days. It was shown that the expanding and uniform schedules were more efficient than the contracting schedule. In Experiment 3, the learning phase lasted two weeks and the retention interval lasted 2, 6, or 13 days. It was shown that the superiority of the expanding schedule over the other two schedules appeared gradually when the retention interval increased, suggesting that different schedules yielded different forgetting rates. We also tried to test major theories of the distributed practice effect, such as the encoding variability (Experiment 4) and the study-phase retrieval (Experiment 2) theories. Our results appeared to be consistent with the study-phase retrieval theory. We concluded our dissertation by emphasizing the importance of considering findings from other areas in cognitive science–especially neuroscience and computer science–in the study of the distributed practice effect.

Un grand défi des cliniciens dans le domaine des commotions cérébrales est de déterminer le moment où l’athlète est prêt à retourner au jeu. Pour guider cette décision, plusieurs ont recours à l’évaluation cognitive pour accompagner l’évaluation des symptômes de l’athlète. Toutefois, plusieurs études appuient la nécessité de développer des tâches cognitives plus raffinées avec des propriétés psychométriques adéquates. Par ailleurs, une étude récente montre que des déficits cognitifs sont exacerbés par l’exercice physique chez 27,7 % des athlètes ayant reçu l’autorisation médicale de retourner au jeu et montrant des résultats normaux à l’état de repos, suggérant une récupération incomplète. Le but de cette thèse consiste en l’élaboration d’un outil, valide et accessible, pour évaluer la disposition d’un athlète à retourner au jeu à la suite d’une commotion, ainsi que pour évaluer les déficits à long terme (c.-à-d., plus de six mois) associés à la blessure. Cet outil comprend un protocole d’exercice standardisé (20 minutes à 80 % de la fréquence maximale théorique sur vélo) et une tâche cognitive, appelée la tâche d’alternance. Dans l’article I, nous avons examiné les propriétés psychométriques de la tâche cognitive. Les résultats suggèrent que la tâche d’alternance est une mesure valide des fonctions exécutives et montre une bonne fidélité test-retest. Ils indiquent aussi que les coûts d’alternance, traditionnellement calculés pour isoler les différentes composantes des fonctions exécutives, ne montrent pas d’aussi bonnes propriétés psychométriques que les variables primaires (vitesse de réaction, précision des réponses et score d’efficacité inverse). Dans l’article II, nous avons mesuré l’effet de pratique associé à la passation répétée de la tâche à des intervalles de 48 heures, dans le but de répliquer l’administration en série de cette tâche lors du suivi post-commotion. Les résultats indiquent que la performance s’améliore durant les trois premières passations de la tâche et que l’utilisation d’une version alternative ne permet pas d’éliminer l’effet de pratique. Dans l’article III, nous avons déterminé que notre outil détenait la capacité de détecter des déficits cognitifs chez des athlètes ayant réussi le protocole de retour au jeu de Zurich. Spécifiquement, notre outil a permis de créer trois sous-groupes : 80 % des athlètes qui ne montrent aucun déficit ; 20 % des athlètes qui montrent des déficits cognitifs au repos sur la tâche d’alternance ; 10 % des athlètes qui montrent des déficits seulement après l’exercice. Ainsi, lorsqu’utilisés ensemble, la tâche d’alternance et le protocole d’exercice permettent de détecter des déficits chez jusqu’à 30 % des athlètes, qui sont pourtant considérés comme rétablis. Dans l’article IV, nous avons montré que notre outil peut détecter les déficits persistants associés à la commotion. Alors qu’au repos aucun déficit n’est observé, l’évaluation post-exercice révèle des déficits chez 20 % des athlètes avec un historique de commotions. En somme, nos résultats soutiennent l’utilisation de notre outil pour l’évaluation du retour au jeu. Les résultats de cette thèse réaffirment la nécessité de changer la norme pour l’évaluation de la commotion. Sur la base des résultats actuels, l’utilisation de tâches cognitives valides et sensibles aux effets de la commotion au-delà de la phase symptomatique, associée à un protocole d’exercice, devrait devenir l’étalon-or. / Concussion is especially hard to detect because clinicians must rely on self-reported symptoms to diagnose the injury and to determine when an athlete is ready to safely return to play (RTP). To guide the latter decision, many use cognitive testing. However, several studies indicate the need to develop more refined cognitive tasks, with better psychometric properties than those currently used to assess concussion. Another option would be to perform the psychometric validation of experimental tasks frequently used in research settings. Further, a recent study suggests that physical exercise can reveal deficits that were not perceptible at rest in one in four athletes, thus indicating incomplete recovery in a significant minority of the concussed athletes. Accordingly, this dissertation aimed to develop a valid and easily accessible tool to assess the readiness of recently concussed athletes to safely return to play, as well as to assess deficits in the protracted phase of the recovery. The tool includes a standardized exercise protocol (20-min on an ergocycle at 80% theoretical maximum heart rate) and a cognitive task (color-shape switch task). In the first manuscript, we examined the construct validity and the test-retest reliability of the switch task. The results suggest that the switch task is a valid measure of executive functions that shows an adequate test-retest reliability. The results also suggest that the switch costs, which are traditionally computed to isolate the different components of executive functions, do not show as good psychometric properties as primary variables do (i.e., reaction time, accuracy, and inverse efficiency score). In the second manuscript, we measured the practice effect associated with serial administration of the switch task. The results indicate that the performance improves during the first three assessments when the task is completed every 48 hours. Also, they do not support the use of alternative versions of the task in order to eliminate the practice effect as it is still present. In the third manuscript, we determined that our tool has the requisite sensitivity for detecting cognitive deficits in recently concussed athletes who had successfully completed the RTP protocol. Specifically, our tool detected deficits in 20% of athletes when the switch task is completed at rest and in an additional 10% when it is completed post-exercise. Thus, our tool can detect deficits in up to 30% of athletes who had received their medical clearance to RTP. In the 4th manuscript, we showed that our tool can detect persistent deficits stemming from sports concussion. The post-exercise testing showed deficits in 20% of athletes, deficits that were not detected at rest. Thus, the use of an acute bout of aerobic exercise may increase the sensitivity of the cognitive testing. The results herein support the use of the switch task, before and after an acute bout of exercise of moderate intensity. Moreover, they reaffirm the necessity to change the standard for assessing sports concussion. Indeed, based on the current results, the use of valid and reliable cognitive tasks, sensitive to the effects of concussion beyond the symptomatic phase, in combination with an exercise protocol, should become the gold standard.