Psychology (Functional Area: Brain, Behaviour & Cognitive Science)

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Open Access
Visuomotor Learning and Proprioception Across Development
(2023-03-28) Clayton, Holly Ann; Henriques, Denise
Being able to adapt our motor repertoire to novel contexts is crucial for completing even the simplest daily tasks. This can be examined in visuomotor adaptation paradigms where the motor system is challenged to compensate for changes in vision, such as learning to reach to targets on a screen with a misaligned hand-cursor, which our brains do through trial-and-error. A motor command is sent to the arm and a prediction of the outcome is sent back into the brain. This prediction is compared with sensory feedback from proprioceptors and is thought to generate one of the error signals that drives motor learning. This begs the question of whether adaptation processes might differ across development if proprioception is less reliable, as proprioceptive impairments have been found to occur alongside normal aging (children and older adults differ from young adults) and in several neurological disorders. Proprioception is suspected to be impaired in Ehlers-Danlos syndrome (EDS), a group of inherited connective tissue diseases where the most common symptoms are joint hypermobility and chronic pain. In Chapter 2 I explored sensitivity of hand proprioception in EDS as a function of disease severity. In Chapter 3 I further explored proprioceptive sensitivity in EDS by comparing patients’ estimates of hand position to those of controls, and changes in their estimates after participants underwent visuomotor adaptation. Finally, in Chapter 4, I examined whether visuomotor adaptation differs across the lifespan, by looking at several characteristics of learning and comparing them across groups of children, young adults, and older adults that I tested in familiar settings. Together, these findings provide further insight into how the sensorimotor system functions under special developmental circumstances, such as with connective tissue disease, or during early/late stages of life.
Open Access
Differentiating Visual Search Efficiencies for Symmetry Type and Texture Regularity
(2023-03-28) Moreau, Rachel Carmen Earleen; Kohler, Peter
Symmetry is believed to be a fundamental gestalt that aides in our day-to-day ability to interact with the visual world. The goal of this thesis was to investigate the differential processing of types of symmetry when embedded in texture or when viewed as individual objects. Across four experiments, I used the behavioural paradigm of the visual search task to measure processing efficiency across types of symmetry and texture regularity. I used stimuli called “wallpaper groups” which allowed for manipulations of symmetry type while holding constant low and midlevel visual cues. My results indicated that reflection symmetry was processed more efficiently than rotation symmetry and when these symmetries are embedded in a regular texture, they are processed more efficiently than not. The results of this research extend previous findings across behavioural psychology and visual neuroscience.
Open Access
Sex and Sexual Orientation Differences in Perceptual and Cognitive Processing
(2023-03-28) Andrinopoulos, Katerina Deanna; Steeves, Jennifer
Sex differences have been found in some visual perception and cognitive abilities, and male and female brains have been shown to have differences in functional activation. These abilities include mental rotation, face recognition and face detection. One way to measure mental rotation is by using the mental rotation task (MRT), with males outperforming females (Voyer, 2011). Face perception tasks show differences favouring females (McBain et al., 2009; Brewster et al., 2012). Same-sex attracted males tend to perform at the level of females in face recognition ability (Brewster et al., 2012). This thesis seeks to further examine the effect sexual orientation has on these visual and perceptual abilities that have previously shown sex differences. A male advantage was found for mental rotation ability, with heterosexual males outperforming heterosexual females. Within the same-sex attracted groups, this difference was not found, with same-sex attracted females performing at the level of same-sex attracted males.
Open Access
Effects of the Brain Derived Neurotrophic Factor Val66met Polymorphism on the Structural and Functional Architecture of the Human Brain
(2022-12-14) Alba Suarez, Vicente Alejandro; Stevens, Dale
Brain Derived Neurotrophic Factor (BDNF) is an important neurotrophin enabling synaptogenesis at the dendrites of neurons. Several studies have implicated the Val66Met single nucleotide polymorphism of the BDNF gene as a factor affecting cortical thickness and resting-state functional connectivity (RSFC) of the human brain. In this thesis, I investigated the effects of Val66Met on cortical thickness and RSFC among individual cortical regions and at the level of large-scale functional networks in all genotype groups (Val/Val, Val/Met, Met/Met, and Met carriers). Cutting-edge techniques were used to individually localize anatomical and functional brain regions in a large sample of healthy young adults from the Human Connectome Project. A comprehensive series of analyses revealed no significant group differences in cortical thickness or RSFC across the brain. These results suggest that, contrary to previous reports, the Met allele does not confer differences in structural or functional integrity of the healthy young adult brain.
Open Access
Perceived Depth in Virtual and Physical Environments
(2022-12-14) Hartle, Brittney Ann; Wilcox, Laurie
Theoretically, stereopsis provides accurate depth information if information regarding absolute distance is accurate and reliable. However, assessments of stereopsis often report depth distortions, particularly for virtual stimuli. These distortions are often attributed to misestimates of viewing distance caused by limited distance cues and/or the presence of conflicts between ocular distance cues in virtual displays. To understand how these factors contribute to depth distortions, I conducted a series of experiments in which depth was estimated under a range of viewing conditions and cue combinations. In the first series (Chapter 2), I evaluated if conflicts between oculomotor distance cues drive depth underconstancy observed in virtual environments by comparing judgments of virtual and physical objects. The results showed that depth judgments of physical stimuli were accurate and exhibited depth constancy, but judgments of virtual stimuli failed to achieve depth constancy. This failure was due in part to the presence of the vergence-accommodation conflict. Further, prior experience with each environment had a profound effect on depth judgments, e.g., performance in virtual environments was enhanced by limited exposure to a similar task using physical objects. In Chapter 3, I assessed if limitations of virtual environments contributed to previous failures of linear combination models to account for the integration of stereopsis and motion cues. I measured the perceived depth of virtual and physical objects defined by motion parallax, binocular disparity, or their combination. Accuracy was remarkedly similar for both environments, but estimates were more precise when depth was defined by binocular disparity than motion parallax. A linear combination model did not adequately describe performance in either physical or virtual conditions. In Chapter 4, I evaluated if reaching to virtual objects provides distance information that can be used to scale stereopsis using an interactive ring game. Brief experience reaching to virtual objects improved the accuracy and scaling of subsequent depth judgements. Overall, experience with physical objects or reaching-in-depth enhanced performance on tasks dependent on distance perception. To fully understand how binocular depth perception is used to interact with objects in the real world, it is important to assess these cues in a rich, full-cue natural scenes.
Open Access
The Effect of Frequent Cannabis Use on the Main Components of Executive Functioning
(2022-12-14) Al-Bayati, Assel; Henriques, Denise
The legalization of recreational cannabis use in Canada has raised many questions regarding its immediate and sustained effect on performance of various critical daily tasks (e.g., driving). To investigate the sustained effect, we created an online battery of tasks that assess the main components of executive functioning that are involved in all aspects of daily activities. The performance of healthy, young frequent cannabis users, infrequent users, and non-users was compared. Selective visual attention, response inhibition, visuospatial working memory, and cognitive flexibility and set shifting ability was analyzed. No meaningful differences in performance were found on any of the measures of executive functioning components between frequent users, infrequent users, and non-users. Additionally, secondary analyses in frequent users on the effect of sex, last occasion of cannabis use, age of cannabis-use onset, length of cannabis use (years), and reason for cannabis use (medical or recreational) on executive functioning performance are also reported.
Open Access
The Impact Of Color on Response Inhibition
(2022-12-14) Asare, Gifty; Fallah, Mazyar
Response inhibition is an important cognitive function that affects decision-making and action selection. Impairments in it occur in neurodegenerative diseases therefore, ways to support response inhibition are important for quality of life. One possibility is the use of color, as color has been shown to modulate inhibitory processes. The overall objective of this work was to determine the prefrontal networks underlying response inhibition that can be modulated through an automatic attentional process such as color. A series of three studies were performed whereby young adults performed a stop-signal task (SST) or a Go/No-go task (GNGT) with colored stimuli. In our first study, the SST, a reactive response inhibition task, was performed to determine whether the effect of color on response inhibition was due to color opponency, attentional color hierarchy, or visual associations. We found that while red stop signals produced faster response inhibition compared to green, blue and yellow stop signals did not differ from each other. This pattern of results was not consistent with color opponency or the attentional color hierarchy of red > green > yellow > blue. Therefore, red facilitating and green impairing response inhibition suggested that response inhibition was modulated by visual color associations where red means stop and green means go. In our second study, we tested if the color modulations between red and green extended beyond countermanding to more general inhibitory control by using a proactive response inhibition task, the GNGT. Indeed, participants were more successful on red in comparison to green No-go trials. Based on these results, a modified accumulator model and putative neural circuitry of color modulation response inhibition was proposed. In our third study, event-related potentials (ERPs) were recorded while participants performed a GNGT to test the putative underlying neural network. While the P300 was not modulated by color, we observed reduced N200 amplitudes and earlier N200 latencies over the prefrontal areas proposed in study 2 in response to red No-go stimuli over green, yellow, and blue. The increased accuracy was argued to be an advantage conferred by learned and evolutionary associations to the colour red. The decreased N200 amplitudes suggested reduced conflict on No-go trials with red No-go stimuli compared to other colours. These findings bring us a step closer to mapping out the differential colour modulated neural circuitry involved in response inhibition and such research will help pave the way for efficient decision-making and staving off cognitive decline.
Open Access
Atypical Lateralization of Language and Face Processing in Autism Spectrum Disorder
(2022-08-08) Solomon-Harris, Lily Marissa; Stevens, Dale
Autism spectrum disorder (ASD) is characterized by persistent deficits in communication and social interaction, as well as repetitive behaviours and restricted interests. Language and face processing are areas of domain-specific dysfunction impacting social interaction in ASD. Brain function associated with these cognitive domains is typically lateralized across the cerebral hemispheres, such that language and face processing are dominant within the left and right hemispheres, respectively. Furthermore, the degree of lateralization is related to behavioural proficiency in both domains. Converging evidence suggests that the development of lateralization in these separate domains is typically interrelated. Neuroimaging literature demonstrates reduced leftward lateralization of language in ASD, but the existing literature on face processing is inconsistent. Mixed findings are partly due to discrepancies in how regions of interest (ROIs) are localized for neuroimaging analyses. The present work aims to test the hypothesis that ASD is related to atypical lateralization of both language and face processing. First, a quantitative fMRI meta-analysis was conducted to resolve inconsistencies in the literature by identifying the most reliable, concordant patterns of differences in language and face processing in the brain associated with ASD across previous fMRI studies. The findings of the meta-analysis were then used to inform a rigorous analysis of category-related brain activation using individually localized ROIs and task-related fMRI data. However, the question remains regarding whether brain activation differences demonstrate a sustained, fundamental difference in the way language and faces are processed in the brain, rather than reflecting moment-to-moment differences in attention to these stimuli, motivating the final analysis of intrinsic functional connectivity between category-related brain regions. The findings from the meta-analysis, task-related fMRI analyses, and RSFC analysis of intrinsic functional connectivity converged, demonstrating that ASD is indeed related to reduced functional specialization and hemispheric lateralization of both language and face processing, particularly in posterior lateral temporal cortex. This is an important contribution to the mixed existing literature, and further demonstrates the importance of individual ROI localization when studying neurodiverse populations. Atypical development of hemispheric asymmetry for language and face processing in posterior lateral temporal cortex might be a fundamental factor underlying the behavioural presentation of ASD.
Open Access
Understanding Lightness and Brightness in Different Media
(2022-03-03) Patel, Jaykishan Yogeshbhai; Murray, Richard F.
This thesis aimed to study how lightness and brightness perception relate to each other. We used a simple task to study whether observers perceive lightness and brightness to be different percepts and what cues they use to make these judgments. In Experiment 1, we used a custom-built apparatus to present two reflectance patches, each with independent illuminance. In the lightness and brightness conditions, observers judged which patch had a higher reflectance or luminance, respectively. In Experiment 2, we repeated the same procedure using a computer rendering of the apparatus on a monitor. Finally, we simulated computational models of lightness and brightness to evaluate their performance with respect to observer performance. We conclude that (a) lightness and brightness judgments are more similar than expected from previous work, (b) brightness is nothing like an estimate of luminance, and (c) current computational models can fail on even simple lightness and brightness judgments.
Open Access
A Novel Neurorehabilitation Model Designed to Examine the Neural Plasticity Involved in Disease
(2022-03-03) Bearss, Karolina Anna; DeSouza, Joseph FX
Parkinson's disease (PD) is a progressive neurodegenerative disorder that that is most often characterised for its motor impairments. However, people with PD (PwPD) often experience a range of mental health and non-motor issues alongside their physical symptoms. Exercise has shown to positively impact and improve PD motor symptoms, less research observations have been shown in PD mental health and non-motor symptoms. Dance is a great form of exercise which provides both aerobic and anaerobic movements. Dance is constantly changing providing a creative outlet, dance provides flexibility and balance/coordination, develops social skills thereby improving mental health, and lastly dance with music combination allows this form of exercise to be unique in that it encompasses a multisensory component that exercise alone cannot provide. My dissertation aims to understand how dance impacts PD motor, non-motor symptoms and if the changes are associated to specific brain related alterations. Using behavioral, motor and EEG approaches, I will present three separate experiments to test the effects of dance on people with PD by first studying the potential impacts of dance on short-term behavioral changes in PwPD and their overall Quality of Life (QoL) after a 12-week dance intervention. Second I will present a novel examination of the interaction of dance on both behavioural measures and electroencephalography (EEG) activity before and after the short-term (1.25 hour) course of a single dance class. The third study is a novel examination of the interaction of dance on the progression of both behavioural measures and non-motor symptoms over the long-term course of participating in multiple dance classes over a 3-year period of time. Finally, EEG activity changes over the long-term course of participating in multiple dance classes over a 3-year period of time is presented. The results of these studies strengthen the idea of dance being an alternative or additional therapy for PwPD and also provides putative neuroplastic changes in the diseased brain.
Open Access
Explicit Attention to Allocentric Landmarks Improves Memory-Guided Reaching
(2021-11-15) Musa, Lina; Crawford, John Douglas
The presence of an allocentric landmark can have both explicit (instruction-dependent) and implicit influences on reaching performance However, it is not known how the instruction itself (to rely either on egocentric versus allocentric cues) influences memory-guided reaching. Here, 13 participants performed a task with two instruction conditions (egocentric vs. allocentric), but with similar sensory and motor conditions. In the allocentric condition, participants were instructed to remember the initial location of the target relative to a landmark, and to reach relative to a shifted landmark. In the egocentric condition, participants were instructed to ignore the landmark and point toward the remembered location of the target. The allocentric instructions yielded significantly more accurate pointing than the egocentric instruction, despite identical visual and motor conditions and regardless of the final pointing side. This suggests that explicit attention to a visual landmark better recruits allocentric coding mechanisms that can augment implicit egocentric visuomotor transformations.
Open Access
Perceived Depth Modulates Perceptual Resolution
(2021-11-15) Ahsan, Tasfia; Freud, Erez
The goal of this thesis was to investigate whether changes to perceived depth affects the resolution of object perception. In a series of four experiments, I used psychophysical methods to examine how perceived depth, defined by 2D pictorial cues in the Ponzo Illusion, modulated perceptual resolution even when it was independent to the task at hand. For Experiments 1-2, participants completed size and orientation discrimination tasks with a pair of lines, where the stimuli were placed either on the "close" or "far" portion of the Ponzo Illusion, as well as a non-Illusory "flat" portion. Across both experiments, more precise and faster discrimination abilities were found for lines perceived as closer to the observer. To rule out a potential confound of surface size, a follow up control experiment was conducted on the orientation task (Experiment 2b) using two size-matched non-illusory version of the Ponzo illusion. The results continued to show a persistent enhancement of close objects even when surface size was controlled for. Lastly, in agreement with previous findings, results of Experiment 3 showed that this close benefit extends even to high level perceptual processing such as a face identification task. Together these findings support the idea that the human visual system may have dedicated processes for closer things.
Open Access
Movement-Based Cues Aid the Formation and Retrieval of Multiple Motor Memories
(2021-11-15) Ayala, Maria Nadine; Henriques, Denise
The ability to switch between different visuomotor mapping accurately and efficiently is an invaluable feature to a flexible and adaptive human motor system. This can be examined in dual adaptation paradigms where the motor system is challenged to perform under randomly switching, opposing perturbations. Typically, dual adaptation doesnt proceed unless each mapping is trained in association with a predictive contextual cue. To investigate this, in Experiment 1 I explored whether dual adaptation occurs if cued by distinct movement types (ballistic or pursuit/tracking reaches), and how adaptation to a perturbation while tracking an object generalize to ballistic reaches. Next, motivated by Experiment 1 findings that support the idea that "intrinsic" or motor-based cues (i.e., pertaining to a distinct goal) is key to dual adaptation along with recent work that shows the critical role of motor planning in dual adaptation, in Experiment 2 I looked at whether movement skew as elicited by distinct visual obstacles can facilitate dual adaptation. Next, in Experiment 3 I look at whether intrinsic cues need to be actively produced to elicit dual adaptation. Additionally, to better understand the underlying components of dual learning, I implement a Process Dissociation Procedure borrowed from cognitive sciences literature to understand the underlying explicit and implicit processes contributing to dual adaptation. In Experiment 4 I give participants an explicit strategy to drive learning where it otherwise would not occur due to an insufficient extrinsic visual cue. Finally, to understand dual adaptation in the most ecologically valid manner, in Experiment 5 I implemented the conventional virtual reality paradigm in Head-mounted VR, while also answering how the brain attributes error in this novel setup. Together, these findings provide further insight as to how the motor system plans movements and learns to adapt to an ever-changing environment, and the underlying mechanisms that drive it.
Open Access
Do Great Apes Choose to Choose?: An Investigation of Preference for Computer-Provided Choice in Orangutans (Pongo abelii)
(2021-03-08) Ritvo, Sarah Elizabeth; MacDonald, Suzanne
This dissertation examined orangutans preference for computer touchscreen-provided choice and their capacity to recognize the content of 2-D pictures. Investigation of these factors is important for advancing our understanding of orangutan cognition and the development of Animal-Computer Interaction systems that provide captive great apes environmental enrichment through provision of choice. Using a concurrent chain procedure presented on a touchscreen computer, the first experiment examined three orangutans intrinsic valuation of choice by assessing preference for free- or forced- choice when neither choice options nor outcomes vary. Initial results indicated a preference for free-choice across all participants. However, in two control conditions, preferences varied, suggesting a weaker tendency to exercise choice than species previously tested. Motivated by subjects difficulty learning associations between application icons and food rewards, a series of three experiments investigated five orangutans capacity to spontaneously recognize the content of novel pictorial stimuli by assessing if they demonstrated the same hierarchical preferences for food and pictures of food. Results indicated that orangutans only recognized picture content in certain formats and that they were more proficient in print than in digital mediums. Having confirmed that orangutans could recognize digital food images in a single format, this format was employed in the final pair of experiments to examine whether increasing the fidelity of the experimental choice paradigm elicited stronger free-choice preferences. This research question was investigated in a stepwise manner: Experiment 1 provided varied choices options that led to a single outcome and Experiment 2 varied both the choice options and outcomes. Results indicated a preference for free-choice in orangutans, but one that can be overwhelmed by competing factors and depend on the advantage afforded by it. Moreover, findings indicated that for orangutans, the strength and quality of preference for free-choice can be affected by the fidelity of the choice paradigm and vary between individuals. In light of these results, I suggest that preference for choice may be more accurately conceptualized along a spectrum rather than a dichotomy of preference for choice or lack thereof.
Open Access
The Accuracy and Stability of Body Representation
(2021-03-08) D'amour, Sarah Anne Olwen; Harris, Laurence
How we perceive our bodies and how the body is represented in the brain is not yet fully understood. We need accurate information about our bodies in order to interpret and react to sensory information that is constantly being received and that is coded relative to our body. My dissertation aims to understand how the body is perceived and represented in the brain by exploring the accuracy and stability of body representation. I developed a novel two-alternative forced choice adaptive staircase psychophysical method to determine how accurate people are in judging real and distorted life-size images of their body. Participants were sequentially shown two life-size images of their body (one interval containing the undistorted image and one interval containing the distorted image) and had to report which image most closely matched their own perception of their body size. Width and length dimensions were distorted separately. The image was also presented in different orientations (such as upright, right, left, and upside down) in order to assess how accuracy perception changes when the image is presented in familiar and unfamiliar views. Four separate experiments were conducted to test perceived size for: 1) the face, 2) the arm, 3) the hand, and 4) the full body. The goal of these studies was to measure accuracy in different orientations, for both the width and length dimensions, to obtain baseline values of how distorted the brains representation of various body parts are. I demonstrated that there are distortions in perceived size and that factors such as body part, orientation, sex, and body satisfaction impacted accuracy. To explore the nature and extent of the brains plasticity and flexibility, I investigated how manipulating body representation affects body perception and whether accuracy values can be changed. Manipulating body representation using both visual and vestibular methods resulted in changes to perceived body size accuracy. These results provide insights into how the brain represents the body, revealing that body size perception is flexible and plastic.
Open Access
The Effect of Perceived Self-Orientation on the Perception of Visually Induced Self-Motion
(2021-03-08) McManus, Meaghan Elizabeth; Harris, Laurence
In certain environments the direction of up indicated by vision and gravity can be in conflict where these directions do not agree. Some people resolve this conflict by relying on their visual cues. In this case, when a participant and the room in which they are sitting are both tilted together, they would feel as if they were standing upright and would experience what is called a Visual Reorientation Illusion (VRI). A VRI on Earth might result from either (1) ignoring the gravity up in favour of the visual up, resulting in a higher visual weighting, or (2) misinterpreting the ambiguous vestibular acceleration cue not as a tilt but as a translation. In Chapter 2, I present evidence that during a VRI individuals require less visual motion to perceive that they have traveled through a specified distance: the move-to-target task. This might result from an enhancement of the visual cue due to a higher visual weighting while down-weighting the conflicting gravity cue, here referred to as my reweighting hypothesis. In Chapter 3, I find that people with VRIs actually have a lower visual weight and higher gravity weight when determining their perceived upright. This suggests that either the reweighting theory is incorrect or that the participants with a higher gravity weight might be more likely to detect, and then reweight, the conflicting visual and vestibular cues. In Chapter 4, I find that when the gravity cue is removed by moving into a 0g environment, initially there is no difference in performance on the move-to-target task compared to on Earth, but after adapting to microgravity and also upon return to 1g, participants need more visual motion to feel they have passed through a specified distance. Chapter 4 provides further evidence that my reweighting theory is incorrect. My research demonstrates that even within the same environment and while viewing the same stimuli, different people can have different interpretations of the environment which are related to changes in behaviour. Specifically, a persons perceived orientation can affect their self-motion perception. The findings are discussed in terms of sensory cue conflict and reweighting, as well as differences between how we perceive visual motion versus how we use it.
Open Access
The Impact of Perceptual Organization on the Limits of Binocular Fusion
(2021-03-08) Aksay, Arleen Anouche; Wilcox, Laurie M.
As a consequence of the separation of the two eyes in the head, the images of objects projected onto the two retinas are in different positions, called binocular disparity. The brain uses this positional information to represent the 3D layout or depth in a scene, a process called stereopsis. The two monocular half-images of objects will be integrated and seen as single if the binocular disparity is within Panums fusional area. Objects with disparities beyond this region will be seen as double. There are likely many factors which influence the perception of diplopia, including cognition (i.e., attention or suppression) or low-level object features (i.e., size). This thesis evaluates the proposal that higher-order visual processing, grouping through uniform connectedness, diminishes the perception of diplopia. To this end, in a series of experiments I presented isolated single elements, pairs of isolated and connected elements, and elements with varying levels of connectedness. Taken together, the results show that connecting elements elevates diplopia thresholds. This result is consistent with both the impact of perceptual organization and the use of larger receptive fields to process the disparity of the object. These two possibilities are discussed along with future experiments designed to distinguish between these accounts.
Open Access
Dynamic Neural Correlates of Mental Attention Capacity
(2021-03-08) Zarie, Amir Abbas; Stevens, Dale
Mental attention capacity (M-capacity) the maximum amount of information one can process simultaneously is a predictor of academic and professional success. However, its neural underpinnings are not well understood. Here, a novel implementation of dynamic functional connectivity (dFC) analysis of resting-state functional MRI data with parcellation of individual brains into a common set of functional areas (Group Prior Individual Parcellation, GPIP) was used to determine whether dFC is 1) related to individual differences in M-capacity and 2) modulated by prior performance of a demanding M-capacity task. Additionally, the novel dFC approach using GPIP was validated against a well-established dFC method (Group ICA of fMRI Toolbox, GIFT). While one measure of dFC accounted for individual differences in Mcapacity, dFC was not modulated by prior task performance. The novel dFC analysis using GPIP produced similar results to GIFT dFC, demonstrating the validity and potential advantages of this novel approach to dFC analysis
Open Access
Predictive Modeling of Early Stage Parkinsons Disease
(2020-11-13) Leger, Charles Stevens; DeSouza, Joseph FX
Background: Early stage (preclinical) detection of Parkinsons disease (PD) remains challenged yet is crucial to both differentiate it from other disorders and facilitate timely administration of neuroprotective treatment as it becomes available. Objective: In a cross-validation paradigm, dual binary classifications analyses were conducted: early PD versus controls and early PD versus SWEDD (scan without evidence of dopaminergic deficit). It was hypothesized that five distinct model types using combined non-motor and biomarker features would distinguish early PD from controls with > 80% cross-validated AUC, but that the diverse nature of SWEDD would reduce early PD versus SWEDD CV classification AUC and alter model-based rank of predictor importance among model types. Methods: Baseline data was acquired from the Parkinsons Progressive Markers Initiative (PPMI). Logistic regression, general additive (GAM), decision tree, random forest and XGBoost models were fitted using non-motor clinical and biomarker features. Randomized train and test data partitions were used. Model classification CV performance was compared using the area under the curve (AUC), accuracy, sensitivity, specificity and the Kappa statistic. Results: All five models achieved >.80 AUC CV accuracy to distinguish early PD from controls using non-motor clinical and biomarker features. The GAM (CV AUC .928, sensitivity .898, specificity .897) and XGBoost (CV AUC .923, sensitivity .875, specificity .897) models were the top classifiers. Performance across all models was consistently lower in the early PD/SWEDD analyses. The two highest performing models were XGBoost (CV AUC .863, sensitivity .905, specificity .748) and random forest (CV AUC .822, sensitivity .809, specificity .721); XGBoost detection of non-PD SWEDD matched 1-2yr curated diagnoses in 81.25% (13/16) cases. In both early PD/control and early PD/SWEDD analyses, and across all models, olfactory function was the single most important feature to classification; rapid eye movement behaviour disorder and cognition were the next most commonly high ranked features. Alpha-synuclein was a feature of import to early PD/control but not to early PD/SWEDD classification and daytime sleepiness was antithetically important to the latter but not former. Interpretation: Non-motor clinical and biomarker variables enable high CV discrimination of early PD versus controls but are less effective discriminating early PD from SWEDD.
Open Access
It Wasn't Me: External Error Attribution Dampens Efferent-Based Predictions but not Proprioceptive Changes in Hand Localization
(2020-11-13) Gastrock, Raphael Quijano; Henriques, Denise
Knowing ones limb location is crucial in order to produce efficient movements. When a movement error is experienced, people account for whether the source of the error is external or internal in nature. When the error is clearly not caused by oneself, it is intuitive to correct for these errors without updating internal models for movement or estimating the position of the effector. That is, there should be reduced or no reliance on implicit learning. However, merely inducing explicit adaptation does not affect measures of implicit learning. Here, we use different visual manipulations that make the external nature of the error clear, and test how these manipulations affect both motor behaviour and hand location estimates. We manipulate the extent of external error attribution in four ways, while participants learn to perform a 30-degree visuomotor rotation task: a Non-instructed control group that receives neither instructions nor different visual stimuli, an Instructed group that receives a counter strategy for dealing with the rotation, a Cursor Jump group that sees the cursor misalignment mid-reach on every training trial, and a Hand View group that sees both the misaligned cursor and their actual hand on every trial. Although an initial advantage in learning is seen for the Instructed group, performance across all groups are not different by the end of training, suggesting that any effects observed for changes in motor behaviour and hand localization are due to the manipulations. During reaches without visual feedback about the cursor location, participants are instructed to perform reaching movements, while either including or excluding any strategy they may have developed during adaptation training to counter for the visuomotor rotation. All groups show awareness of the nature of the perturbation except for the Non-instructed group. Implicit changes in motor behaviour, measured with reach aftereffects, persist for all groups but are greatly reduced for the Hand View group. For hand localization, participants either generate their own movement (allowing for hand localization with both afferent-based proprioceptive information and efferent-based predictions of sensory consequences) or a robot moves their hand (allowing for only proprioceptive information). We find that afferent-based changes in hand localization persists across all groups, but efferent-based changes are reduced for only the Hand View group. These results show that the brain incorporates source attribution for estimating the position of the effector during motor learning, and that proprioceptive recalibration during hand localization is an implicit process impervious to external error attribution.