Congenital hypothyroidism (CH), a pediatric endocrine condition that results in early thyroid hormone (TH) insufficiency, is associated with visuospatial dysfunction suggestive of selective dorsal visual stream impairment. However, the ventral visual stream has not been adequately investigated in this population and so the effect of early TH insufficiency on development of the two streams had not been clearly established. This thesis used a comprehensive set of neuropsychological and experimental tests to assess higher-order visual functions in children and adolescents with CH compared with typically developing individuals. The results show that while CH is associated with poorer performance on tasks tapping into dorsal stream functions such as judgment of line orientation, spatial localization, three-dimensional block and two-dimensional mental construction, judgment of object location, and mental rotation, performance on typical ventral stream tasks such as identity discrimination, including abstract shapes, faces, and buildings, is relatively unimpaired. Thus this thesis establishes that the dorsal visual stream is selectively vulnerable to TH insufficiency. In addition to the investigating the nature of the higher-order visual problems in CH, this thesis explores the mechanism underlying these problems and assesses whether they result from organizational effects by early TH or activational effects by current TH levels. The data support the organizational mechanism and suggest that prenatal TH insufficiency results in irreversible changes to the dorsal visual stream due to the timing of dorsal stream development, which occurs earlier than ventral stream development and is thus more vulnerable to insult.

Congenital hypothyroidism (CH), a pediatric endocrine condition that results in early thyroid hormone (TH) insufficiency, is associated with visuospatial dysfunction suggestive of selective dorsal visual stream impairment. However, the ventral visual stream has not been adequately investigated in this population and so the effect of early TH insufficiency on development of the two streams had not been clearly established. This thesis used a comprehensive set of neuropsychological and experimental tests to assess higher-order visual functions in children and adolescents with CH compared with typically developing individuals. The results show that while CH is associated with poorer performance on tasks tapping into dorsal stream functions such as judgment of line orientation, spatial localization, three-dimensional block and two-dimensional mental construction, judgment of object location, and mental rotation, performance on typical ventral stream tasks such as identity discrimination, including abstract shapes, faces, and buildings, is relatively unimpaired. Thus this thesis establishes that the dorsal visual stream is selectively vulnerable to TH insufficiency. In addition to the investigating the nature of the higher-order visual problems in CH, this thesis explores the mechanism underlying these problems and assesses whether they result from organizational effects by early TH or activational effects by current TH levels. The data support the organizational mechanism and suggest that prenatal TH insufficiency results in irreversible changes to the dorsal visual stream due to the timing of dorsal stream development, which occurs earlier than ventral stream development and is thus more vulnerable to insult.

<p>This thesis is devoted to understanding and counteracting the primary contributing factor in traffic crashes: inattention. Foremost, it demonstrates the fundamental importance of proactive gaze in the road centre area for action guidance in driving. Inattention is explained with regard to two visual functions (vision-for-action and vision-for-identification), three forms of attentional selection (action-driven-, stimulus-driven-, and goal-directed attention), and two forms of prediction influences (extrapolation-based- and decision-based prediction influences). In Study I an automated eye-movement analysis method was developed for a purpose-built eye-tracking sensor, and was successfully validated. This analysis method was further developed, and several new measures of gaze concentration to the road centre area were created. Study II demonstrated that a sharp decrease in the amount of road centre viewing time is accompanied by a dramatic spatial concentration towards the road centre area in returning gaze during visual tasks. During cognitive tasks, a spatial gaze concentration to road centre is also evident; however contrary to visual tasks, road centre viewing time is increased because the eyes are not directed towards an object within the vehicle. Study III found that gaze concentration measures are highly sensitive to driving task demands as well as to visual and auditory in-vehicle tasks. Gaze concentration to the road centre area was found as driving task complexity increased, as shown in differences between rural curved- and straight sections, between rural and motorway road types, and between simulator and field motorways. Further, when task duration was held constant and the in-vehicle visual task became more difficult, drivers looked less at the road centre area ahead, and looked at the display more often, for longer periods, and for more varied durations. In closing, it is shown how this knowledge can be applied to create in-vehicle attention support functions that counteract the effects of inattention.</p>

This thesis is devoted to understanding and counteracting the primary contributing factor in traffic crashes: inattention. Foremost, it demonstrates the fundamental importance of proactive gaze in the road centre area for action guidance in driving. Inattention is explained with regard to two visual functions (vision-for-action and vision-for-identification), three forms of attentional selection (action-driven-, stimulus-driven-, and goal-directed attention), and two forms of prediction influences (extrapolation-based- and decision-based prediction influences). In Study I an automated eye-movement analysis method was developed for a purpose-built eye-tracking sensor, and was successfully validated. This analysis method was further developed, and several new measures of gaze concentration to the road centre area were created. Study II demonstrated that a sharp decrease in the amount of road centre viewing time is accompanied by a dramatic spatial concentration towards the road centre area in returning gaze during visual tasks. During cognitive tasks, a spatial gaze concentration to road centre is also evident; however contrary to visual tasks, road centre viewing time is increased because the eyes are not directed towards an object within the vehicle. Study III found that gaze concentration measures are highly sensitive to driving task demands as well as to visual and auditory in-vehicle tasks. Gaze concentration to the road centre area was found as driving task complexity increased, as shown in differences between rural curved- and straight sections, between rural and motorway road types, and between simulator and field motorways. Further, when task duration was held constant and the in-vehicle visual task became more difficult, drivers looked less at the road centre area ahead, and looked at the display more often, for longer periods, and for more varied durations. In closing, it is shown how this knowledge can be applied to create in-vehicle attention support functions that counteract the effects of inattention.

abstract: The present study explores the role of motion in the perception of form from dynamic occlusion, employing color to help isolate the contributions of both visual pathways. Although the cells that respond to color cues in the environment usually feed into the ventral stream, humans can perceive motion based on chromatic cues. The current study was designed to use grey, green, and red stimuli to successively limit the amount of information available to the dorsal stream pathway, while providing roughly equal information to the ventral system. Twenty-one participants identified shapes that were presented in grey, green, and red and were defined by dynamic occlusion. The shapes were then presented again in a static condition where the maximum occlusions were presented as before, but without motion. Results showed an interaction between the motion and static conditions in that when the speed of presentation increased, performance in the motion conditions became significantly less accurate than in the static conditions. The grey and green motion conditions crossed static performance at the same point, whereas the red motion condition crossed at a much slower speed. These data are consistent with a model of neural processing in which the main visual systems share information. Moreover, they support the notion that presenting stimuli in specific colors may help isolate perceptual pathways for scientific investigation. Given the potential for chromatic cues to target specific visual systems in the performance of dynamic object recognition, exploring these perceptual parameters may help our understanding of human visual processing. / Dissertation/Thesis / M.A. Psychology 2011

Due to various shortcomings of the visual system, some visual stimuli can only be identified with 100% accuracy if they are shown for a certain amount of time. This time can be measured using the Inspection Time (IT) paradigm. In an IT task, a “pi” figure with differing leg lengths is typically presented briefly (e.g., 20-200 ms) and is then immediately masked to prevent retinal afterimages. Participants are subsequently required to choose which of the two legs was longer. The objective of this task is to determine the shortest amount of time the pi figure needs to be shown for it to be perceived with 80% accuracy. Given that visual processing has been shown to be altered during and /or prior to a movement, the present experiment sought to test how the requirement to perform a motor task affected IT. Twenty-eight participants took part in the experiment, which was comprised of three conditions: no-movement (NM), peak velocity (PV), and foreperiod (FP). In the NM condition, participants grasped a manipulandum and engaged in the IT paradigm. At the end of every trial, participants verbally stated which leg they believed was longest. In the PV condition participants made a rapid movement to a target, and the IT stimulus was presented when their limb reached peak velocity. Finally in the FP condition the IT stimulus was presented during foreperiod (FP). In all three conditions the IT stimulus was randomly presented from between 15-105 ms (in 15 ms increments) and masked for 400 ms. Results showed no significant differences on the IT task between the NM and FP conditions, suggesting no visual upregulation during foreperiod. However, IT performance was significantly poorer in the PV condition in comparison to both the NM and FP condition, suggesting a visual downregulation at that particular movement kinematic.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

L’objectif de ces travaux a été d’étudier, à partir des potentiels évoqués, l’implication des voies ventrale (qui sous-tend le traitement expert de l’écrit) et dorsale (qui sous-tend des processus phonologiques et attentionnels) lors de la reconnaissance visuelle des mots chez des adultes dyslexiques. Les spécificités des sujets dyslexiques ont été isolées en les comparant à deux groupes contrôles, appariés sur : l’âge (i.e., des lecteurs experts) et sur le niveau de lecture (i.e., des mauvais lecteurs). Les résultats montrent des déficits du traitement expert de l’écrit, phonologiques et de la détection du conflit spécifiques aux sujets dyslexiques. Nos données montrent aussi des déficits du traitement expert des mots familiers et d’orientation de l’attention communs aux sujets dyslexiques et mauvais lecteurs. Les résultats sont discutés dans le cadre du modèle LCD, de la théorie du mapping phonologique et d’une implication précoce de l’orientation attentionnelle dans la lecture. / The aim of this project was to examine with event related potentials ventral (involved in expertise for print) and dorsal (involved in phonological and attentional processes) pathways implication in visual word recognition in dyslexic adults. The specificity of dyslexics was determined by comparing them to age-matched controls (i.e., expert readers) and reading-level matched controls (i.e., poor readers). Results showed impaired expertise for print, decoding abilities and conflict detection which were specific to dyslexics. Our data also revealed impaired expertise for familiar words and attention orienting in both dyslexics and poor readers. Results are discussed in the context of the LCD model, the phonological mapping theory and an early involvement of attention orienting in reading.