Rôle de l’attention lors de la recherche visuelle : mesures électrophysiologiques

Le but principal de cette thèse était de mieux comprendre la relation entre le déploiement de l’attention visuo-spatiale et la réponse lors de la recherche visuelle. Nous avons combiné des mesures de chronométrie mentale (les temps de réponse; TR) et d’électrophysiologie, permettant le suivi du décours temporel des évènements et la séparation des processus en sous-phases. Trois études ont été effectuées. Dans les deux premières études, la N2pc, un potentiel relié à un événement (PRE), a été utilisé comme indice électrophysiologique de l’attention visuelle vers un stimulus latéral lors d’une tâche de recherche visuelle ayant une cible facilement repérable (qui saute aux yeux) parmi des distracteurs. Cette composante est caractérisée, en électrophysiologie, par une plus grande négativité environ 200 ms suivant la présentation de la stimulation aux sites postérieurs et controlatéraux du champ visuel ciblé. Dans la première étude, la relation entre la composante N2pc et la réponse a été examinée. Pour ce faire, les données électrophysiologiques ont été scindées selon le TR médian. La N2pc était plus ample pour les essais et les participants plus rapides comparés à ceux qui étaient plus lents, suggérant qu’un déploiement attentionnel plus efficace (N2pc plus ample) avait accéléré les processus subséquents (TR plus court). Dans l’étude 2, le traitement depuis le moment du déploiement attentionnel jusqu’à la réponse a été élucidé en examinant le déclenchement de la N2pc par rapport à la réponse et non au stimulus (ce qui est plus utilisé dans les paradigmes classiques). Nous avons été les premiers à utiliser la RLpcN (response-locked posterior contralateral negativity), composée de la composante N2pc et la SPCN (une composante suivant la N2pc reflétant le traitement en mémoire visuelle à court terme). Les résultats ont démontré une augmentation du temps entre le début de la RLpcN et la réponse pour les TR plus lents, reflétant un traitement plus long suivant le déploiement de l’attention spatiale. Nous avons par la suite utilisé cette composante (la RLpcN) pour étudier la recherche visuelle difficile (Étude 3), où la cible n’était pas facilement identifiable parmi des distracteurs, à l’aide de manipulations expérimentales modulant la RLpcN, soit le nombre d’items et de réponses possibles. Plus il y avait d’items dans le champ visuel ou de possibilités de réponses, plus longue était la durée entre le début de la RLpcN et la réponse, démontrant ainsi qu’il est possible d’observer l’activité associée avec les processus sous-jacents à ces manipulations lors d’une recherche difficile. En somme, nous avons montré (1) qu’un déploiement attentionnel plus efficace accélère les processus subséquents, (2) que le traitement déterminant les TR se produit, en majorité, suivant le déploiement de l’attention et, enfin, (3) qu’il est possible d’identifier des marqueurs électrophysiologiques de la sélection de la cible ainsi que de la réponse lors d’une recherche difficile. Dans l’ensemble, les résultats des études constituant la présente thèse vont au-delà des études électrophysiologiques de recherche visuelle typiques, qui utilisent généralement des cibles qui sautent aux yeux, et élucident le décours temporel du traitement lors de recherches plus complexes.The overarching thesis was to understand better the relationship between the deployment of visual spatial attention and the eventual response during visual search. We combined mental chronometry with electrophysiological measures, allowing us to track the temporal sequence of events and bisect processing into sub-phases. The two first studies used the N2pc, an event-related potential (ERP) component, as an electrophysiological marker of visual attention to laterally presented stimuli using a pop-out (i.e., the target stands out) visual search task. The N2pc is characterised by an enhanced negativity emerging around 200 ms after the display onset at posterior sites contralateral to the attended visual field. In Study 1, we first evaluated the relationship between the N2pc component and the moment of response. Electrophysiological data were split according to the response time (RT) median. The N2pc was larger for both fast compared with slow trials and participants, suggesting that a more efficient deployment of attention (larger N2pc) sped up downstream processing (shorter RTs). In Study 2, processing from the deployment of attention to the response was elucidated by examining N2pc onset relative to the response instead of to the display onset. We pioneered the use of the RLpcN (response-locked contralateral negativity), composed of the N2pc and the SPCN (a component following the N2pc and reflecting processing of task-relevant stimuli in visual short-term memory). Importantly, more time passed between RLpcN onset and the response for longer RTs, reflecting more processing time following the onset of visual spatial attention. We then used this component to study difficult search (Study 3), where the target was not easily located, using experimental manipulations designed to modulate the RLpcN. We showed that when there were more items present in the visual field or response selection was more difficult, there was a longer duration between RLpcN onset and the response, demonstrating that it is possible to observe activity associated with specific processes during difficult visual search. In summary, we provide evidence that (1) a more efficient deployment of attention speeds up downstream processing, (2) processing determining RTs occurs, in majority, following the deployment of attention, and (3) it is possible to identify electrophysiological markers of target and response selection during difficult search. Together, the results of these experiments go beyond typical electrophysiological experiments of visual search, which use pop-out targets, and elucidate the time course of processing during more complex search

Number Representation in Bilinguals. The role of early learning in the Mental Number Line representation

La presente tesis tiene como objetivo el estudio de la matemática bilingüe dentro del ámbito científico de la Cognición Numérica y Bilingüismo. El abordaje de cómo las personas bilingües representan y acceden a la magnitud es actualmente una cuestión de creciente interés que responde a la necesidad de entender el papel que desempeña el lenguaje en la adquisición temprana de las matemáticas. Esa importancia se ve reflejada habitualmente en el contexto de la educación, en donde el aprendizaje de la aritmética y el bilingüismo concurren de forma natural. Dada la importancia que tiene en nuestra sociedad tanto la adquisición de las matemáticas como el aprendizaje de una segunda lengua en edades tempranas, es necesario su estudio y abordaje desde el ámbito de la Neurociencia Cognitiva. Con el fin de entender en mayor profundidad los mecanismos neurocognitivos que subyacen al manejo de los números en las personas bilingües, el presente estudio aborda la cuestión del papel que el aprendizaje temprano de las matemáticas en una de las dos lenguas naturales del bilingüe, tiene en la representación del número. Para ello, se han diseñado tres experimentos utilizando la técnica de electroencefalografía, la cual permite una buena resolución temporal de la actividad neuronal que acompaña a la función cognitiva. Siguiendo la línea de investigación de Salillas y Carreiras (2014) sobre el impacto de la llamada "Lengua de aprendizaje de las matemáticas" (LLmath) en el código básico de la magnitud numérica, este estudio indaga en los efectos que tienen el aprendizaje temprano de las matemáticas en la relación entre número y espacio. Por tanto, el principal objetivo ha sido la investigación de cómo los bilingües activan y recuperan la línea numérica mental cuando la información numérica coincide con la LLmath en comparación con la "Otra Lengua" (OL). Un segundo objetivo se ha centrado en evaluar cómo impactan en la memoria de trabajo la manipulación y retención de la información numérico-espacial cuando ésta se presenta verbalmente en cada una de las dos lenguas (LLmath y OL).The implications of bilingualism in Math Cognition might be particularly visible in social, cultural and educational contexts. The clearest proof is the fact that bilinguals often switch languages when carrying out arithmetic computations such as fact retrieval or even number comparison, regardless of proficiency (Kolers, 1968). Thus, the main assumption is that arithmetic is sensitive to the language in which it was learned or trained (Frenk-Mestre and Vaid, 1993; Spelke and Tsivkin, 2001; Salillas and Wicha, 2012). More recently, we have proposed that this preference for one language has also an impact in the basic numerical magnitude representation. We suggested that the Language of Learning Math (herein LLmath) entails a preferred verbal code also for the most basic numerical knowledge: When bilinguals manage two different wording systems for naming quantity, the system pertaining to LLmath, and not L1, automatically gets activated and modulates the distance effect (Salillas and Carreiras, 2014; Salillas et al., 2015). The present study aims to further investigate the relationship between the LLmath and the evolved magnitude representation that implies an spatial component, the so-called “Mental Number Line” (MNL; Restle, 1970; Deahene, 1992).Given that previous research has provided evidence of the role of language in basic aspects of numerical representation in bilinguals, we aimed to investigate the neural bases of early math learning influence in the MNL representation. For such purpose, we tested a sample of Spanish-Basque bilinguals, equally proficient in both languages. We conducted two experiments based on a visual and an auditory working memory paradigm. It is well-known that specific working memory (WM) resources (e.g. phonological loop, visuospatial sketchpad) have an active role in number processing (Baddeley, 1986; DeStefano and LeFevre, 2004; Hecht, 2002; LeFevre et al., 2005; Raghubar et al., 2010; Seitz and Schumann-Hengsteler, 2000). Working memory entails a number of operations, needed to keep information active, each one related to a transient cognitive stage (encoding, retention, retrieval) (Baddeley, 1984; Friedman and Johnson, 2000). EEG-ERPs methods have been used in previous studies to isolate neural activity associated to the time course in each WM stage (Berti et at., 2000; McEvoy et al., 1998; Ruchkin et al., 1992, 1994, 1997; Shucard et al., 2009). In our study, we measured EEG during a match-to-sample task to investigate numerical-spatial processing signatures as a function of early learning math (LLmath vs Other Language (OL)) during the different WM stages. Participants were instructed to memorize the spatial location of a set of numbers presented visually (Experiment 1) or auditory (Experiment 2) either in the LLmath or in OL, and respond accordingly to a test number. Number-words could be congruent or incongruent with the spatial arrangement of the MNL (small numbers-left side/ large numbers-right side). We manipulated the memory load using 4 or 6 items in parallel versions of visual and auditory match-to-sample tasks (Sternberg task, Sternberg, 1966). This allowed us to better investigate the WM cognitive cost associated to each language during numerical-spatial information management. In general, our study provides neuroimaging evidence supporting different brain mechanisms for LLmath and OL in bilinguals´ MNL representation that agrees with previous findings. The results suggest an important role of language in the access to the MNL consistent with the early math leaning impact hypothesis. Further research should consider the results of this study to further investigate the neural mechanisms and core cognitive processes underlying the bilingual math case in order to enhance development of math competence and optimize learning

Effects of Diversity and Neuropsychological Performance in an NFL Cohort

Objective: The aim of this study was to examine the effect of ethnicity on neuropsychological test performance by comparing scores of white and black former NFL athletes on each subtest of the WMS. Participants and Methods: Data was derived from a de-identified database in South Florida consisting of 63 former NFL white (n=28, 44.4%) and black (n=35, 55.6%) athletes (Mage= 50.38; SD= 11.57). Participants completed the following subtests of the WMS: Logical Memory I and II, Verbal Paired Associates I and II, and Visual Reproduction I and II. Results: A One-Way ANOVA yielded significant effect between ethnicity and performance on several subtests from the WMS-IV. Black athletes had significantly lower scores compared to white athletes on Logical Memory II: F(1,61) = 4.667, p= .035, Verbal Paired Associates I: F(1,61) = 4.536, p = .037, Verbal Paired Associates: II F(1,61) = 4.677, p = .034, and Visual Reproduction I: F(1,61) = 6.562, p = .013. Conclusions: Results suggest significant differences exist between white and black athletes on neuropsychological test performance, necessitating the need for proper normative samples for each ethnic group. It is possible the differences found can be explained by the psychometric properties of the assessment and possibility of a non-representative sample for minorities, or simply individual differences. Previous literature has found white individuals to outperform African-Americans on verbal and non-verbal cognitive tasks after controlling for socioeconomic and other demographic variables (Manly & Jacobs, 2002). This highlights the need for future investigators to identify cultural factors and evaluate how ethnicity specifically plays a role on neuropsychological test performance. Notably, differences between ethnic groups can have significant implications when evaluating a sample of former athletes for cognitive impairment, as these results suggest retired NFL minorities may be more impaired compared to retired NFL white athletes

Distinguishing Performance on Tests of Executive Functions Between Those with Depression and Anxiety

Objective: To see if there are differences in executive functions between those diagnosed with Major Depressive Disorder (MDD) and those with Generalized Anxiety Disorder (GAD).Participants and Methods: The data were chosen from a de-identified database at a neuropsychological clinic in South Florida. The sample used was adults diagnosed with MDD (n=75) and GAD (n=71) and who had taken the Halstead Category Test, Trail Making Test, Stroop Test, and the Wisconsin Card Sorting Test. Age (M=32.97, SD=11.75), gender (56.7% female), and race (52.7% White) did not differ between groups. IQ did not differ but education did (MDD=13.41 years, SD=2.45; GAD=15.11 years, SD=2.40), so it was ran as a covariate in the analyses. Six ANCOVAs were run separately with diagnosis being held as the fixed factor and executive function test scores held as dependent variables. Results: The MDD group only performed worse on the Category Test than the GAD group ([1,132]=4.022, p\u3c .05). Even though both WCST scores used were significantly different between the two groups, both analyses failed Levene’s test of Equality of Error Variances, so the data were not interpreted. Conclusions: Due to previous findings that those diagnosed with MDD perform worse on tests of executive function than normal controls (Veiel, 1997), this study wanted to compare executive function performance between those diagnosed with MDD and those with another common psychological disorder. The fact that these two groups only differed on the Category Test shows that there may not be much of a difference in executive function deficits between those with MDD and GAD. That being said, not being able to interpret the scores on the WCST test due to a lack of homogeneity of variance indicates that a larger sample size is needed to compare these two types of patients, as significant differences may be found. The results of this specific study, however, could mean that the Category Test could be used in assisting the diagnosis of a MDD patient

The Effect of Ethnicity on Neuropsychological Test Performance of Former NFL Athletes

Objective: To investigate the effect of ethnicity on neuropsychological test performance by specifically exploring differences between white and black former NFL athletes on subtests of the WAIS-IV. Participants and Methods: Data was derived from a de-identified database in Florida consisting of 63 former NFL athletes (Mage=50.38; SD=11.57); 28 white and 35 black. Participants completed the following subtests of the WAIS-IV: Block Design, Similarities, Digit Span, Matrix Reasoning, Arithmetic, Symbol Search, Visual Puzzles, Coding, and Cancellation. Results: One-Way ANOVA yielded a significant effect between ethnicity and performance on several subtests. Black athletes had significantly lower scaled scores than white athletes on Block Design F(1,61)=14.266, p\u3c.001, Similarities F(1,61)=5.904, p=.018, Digit Span F(1,61)=8.985, p=.004, Arithmetic F(1,61)=16.07, p\u3c.001 and Visual Puzzles F(1,61)=16.682, p\u3c .001. No effect of ethnicity was seen on performance of Matrix Reasoning F(1,61)=2.937, p=.092, Symbol Search F(1,61)=3.619, p=.062, Coding F(1,61)=3.032, p=.087 or Cancellation F(1,61)=2.289, p=.136. Conclusions: Results reveal significant differences between white and black athletes on all subtests of the WAIS-IV but those from the Processing Speed Scale and Matrix Reasoning. These findings align with previous literature that found white individuals to outperform African-Americans on verbal and non-verbal tasks after controlling for socioeconomic and demographic variables (Manly & Jacobs, 2002). These differences may also be a reflection of the WAIS-IV’s psychometric properties and it is significant to consider the normative sample used may not be appropriate for African-Americans. This study highlights the need for future research to identify how ethnicity specifically influences performance, sheds light on the importance of considering cultural factors when interpreting test results, and serves as a call to action to further understand how and why minorities may not be accurately represented in neuropsychological testing

Regional Cerebral Blood Flow Patterns in Children vs. Adults with ADHD Combined and Inattentive Types: A SPECT Study

Objective: The current study sought to determine whether ADHD Combined Type (ADHD-C) and ADHD Primarily Inattentive Type (ADHD-PI) showed differential regional cerebral blood flow (rCBF) patterns in children vs. adults. Participants and Methods: The overall sample (N=1484) was effectively split into four groups: adults with ADHD-PI (n=519), adults with ADHD-C (n=405), children with ADHD-PI (n=192), children with ADHD-C (n=368). All participants were void of bipolar, schizophrenia, autism, neurocognitive disorders, and TBI. The data were collected from a de-identified archival database of individuals who underwent SPECT scans at rest. Results: Using αConclusions: Overall, the current study suggested that children may show rCBF differences between different ADHD subtypes, but adults may not. The current study did not find significance in any of the 17 brain regions examined when comparing adults with ADHD-C to adults with ADHD-PI. All significant findings were attributed to the children with ADHD-C group showing aberrant blood flow rate than at least one other group. Previous research has supported that the differentiation of these subtypes as distinctive disorders is difficult to make in adults (Sobanski et al., 2006). Other research has indicated the potential of imaging techniques to differentiate the two in children (Al-Amin, Zinchenko, & Geyer, 2018). The current findings support nuanced ways in which rCBF patterns of ADHD-C and ADHD-PI differ between children and adults

Feedback Coding for Efficient Interactive Machine Learning

When training machine learning systems, the most basic scenario consists of the learning algorithm operating on a fixed batch of data, provided in its entirety before training. However, there are a large number of applications where there lies a choice in which data points are selected for labeling, and where this choice can be made “on the fly” after each selected data point is labeled. In such interactive machine learning (IML) systems, it is possible to train a model with far fewer labels than would be required with random sampling. In this thesis, we identify and model query structures in IML to develop direct information maximization solutions as well as approximations that allow for computationally efficient query selection. To do so, we frame IML as a feedback communications problem and directly apply principles and tools from coding theory to design and analyze new interaction selection algorithms. First, we directly apply a recently developed feedback coding scheme to sequential human-computer interaction systems. We then identify simplifying query structures to develop approximate methods for efficient, informative query selection in interactive ordinal embedding construction and preference learning systems. Finally, we combine the direct application of feedback coding with approximate information maximization to design and analyze a general active learning algorithm, which we study in detail for logistic regression.Ph.D