Relevant Thesis-Based Degree Programs
Affiliations to Research Centres, Institutes & Clusters
Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Descriptions of atypical visual processing have been associated with Autism Spectrum Disorder (ASD). Pinpointing the source of altered perception has been challenging. It is possible that the divergence occurs early in visual processing. There have been reports of higher prevalence of refractive errors for children with ASD, but few studies assessing refractive error status of adults on the spectrum. We contribute to this gap by providing complete optometric eye exams to assess refractive status in a group of adults with ASD and Controls. We find no significant differences between our ASD and Control groups for presence or severity of refractive errors, but higher rates of myopia for both groups compared to prevalence in the general population. Results from behavioural studies suggest altered visual functioning may occur further downstream, possibly in the earliest cortical visual areas. The Enhanced Perceptual Functioning (EPF) model proposes that behavioural results can be explained as a consequence of superior perception for “simple visual material”. This model suggests that low-level properties of images may be processed differently in ASD. We examine this assertion for aspects of orientation processing, which is associated with low-level perception. In three behavioural psychophysical tasks, we examine the status of orientation discrimination, veridical perception, and orientation detection in adults with and without ASD. We find no significant differences between our ASD and Control groups for any aspect of orientation perception tested. As social difficulties are a criterion for diagnosis of ASD, various aspects of face processing have been studied in this population, with mixed results. The social motivation hypothesis and amygdala dysfunction hypothesis both suggest face processing abilities may be associated with social competency difficulties in ASD. We examine two different aspects of face processing: identification and recognition of expression, and compare performance to measures of ASD symptom severity and social competence. We find impaired identity and expression perception across all tasks for our ASD group, but only expression processing was associated with social competence. These results have implications for our understanding of visual perception differences in ASD and offer recommendations for future research directions and intervention tools.
Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
It has recently been shown that Alzheimer’s Disease (AD) can be detected using machine learning methods and based on retinal fundus images, which are readily available in contrast to conventional diagnosis methods, which are highly invasive and expensive. This study aims to design and validate a methodology for explainable diagnosis of AD based on fundus images using deep learning. Because of the rarity of positive AD labels in the available fundus datasets, patient’s sex was alternatively used as a case study since this trait is also invisible to the experts while convolutional neural networks (CNNs) can predict it. This thesis proposes a novel three-phased methodology to investigate the features in retinal fundus images that enable the CNNs to classify sex. In the first phase, a CNN model is trained and tested on the sex classification task using ODIR and DOVS datasets with 3,146 and 1,600 normal images, respectively. In the next phase, deep learning interpretation techniques were used to hypothesize possible sex differences in the retina. In the third and last phase, the hypotheses were tested using an independent dataset called VCH comprising 500 healthy fundus images. The model achieved AUC scores of 0.68 (95% CI: [0.63, 0.72]) and 0.78 (95% CI: [0.73, 0.84]) on ODIR and DOVS test sets respectively. CNN interpretation results demonstrated that the optic disc, retinal vessels, and fovea are the main anatomical parts attended by the model to predict sex. Feature visualization results followed by statistical tests showed that males have more prominent retinal vasculature by showing more nodes (p=.014), more branches (p=.016), and a greater total length of branches (p=.020) in the retinal vessel network as well as a higher superior temporal vessel coverage (p=.027). Also, the peripapillary area was darker in males compared to females (p=.008). The results confirm the capability of the proposed methodology in identifying the retinal features that are relevant to the task on which the CNN model is trained. The same approach can be extended to other clinically important areas, such as AD diagnosis, considering the ability of CNNs to detect this label.
Tuning changes of perception from a generalist to a specialist system is termed perceptual narrowing (Werker & Tees, 1984). Observers raised in ethnically homogenous environments show difficulties in recognizing other-race faces (Meissner & Brigham, 2001). Termed the other-race effect (ORE), this phenomenon is in part attributed to lack of visual experience with other-race faces (Chiroro & Valentine, 1995). The ORE is a form of perceptual narrowing that allows specialization for commonly encountered faces. To examine the origin of perceptual narrowing in face recognition we postulate three competing hypotheses. Based on the Resource Bottleneck hypothesis, limited neural and visual resources must be focused to achieve refined processing of own-race faces. Alternatively, the Use/Disuse hypothesis suggests that the ORE is merely due to lack of exposure necessary to reach expertise for unfamiliar face classes. Lastly, the Facilitation hypothesis, suggests that exposure to a diverse set of faces can lead to richer face representations, and thus, advantages in face recognition. To evaluate these hypotheses, we compared face abilities of ‘Bi-ethnics’--individuals with sustained high exposure to both East Asian and Caucasian faces, to ‘Mono-ethnics’—Caucasian and East Asian individuals. Face memory was examined using an old/new task for East Asian and Caucasian faces, as well as upright and inverted Cambridge Memory Tests for East Asian (McKone et al., 2012) and Caucasian (Duchaine & Nakayama, 2006) faces, in comparison to cars (Dennett et al., 2011) as a control stimulus. Lastly, an identity discrimination test of East Asian and Caucasian celebrities was used to examine face perception. Mono-ethnics showed ORE in memory tasks, whereas Bi-ethnics showed near-native level performance for both face categories. Mono-ethnics showed a larger face inversion effect for own-race faces and Bi-ethnics showed similar face inversion patterns for own-race in Mono-ethnics for both face categories. All groups performed similarly in the Caucasian face perception task. However, in the East Asian face task, Caucasians showed ORE, with Bi-ethnics showing a small advantage over East Asians. Results across all tasks rule out the Resource Bottleneck hypothesis, and are consistent with the Use/Disuse hypothesis. Perception results suggest the possibility of Facilitation for Bi-ethnic exposure.
Autism Spectrum Disorder (ASD) is a developmental disorder characterized by deficits in social-communication and interaction in addition to restricted and repetitive behaviours and interests (American Psychiatric Association, 2013). Despite these deficits, a few studies have reported superior performance in various detail-oriented visual tasks, such as visual search (O'Riordan, Plaisted, Driver, & Baron-Cohen, 2001) and embedded figures (Shah & Frith, 1983). It has been suggested that these atypicalities can be attributed to enhanced perceptual functioning (EPF) in the ASD population (Mottron, Dawson, Soulières, Hubert, & Burack, 2006). In the present study we examined basic visual processing of spatial frequency (SF) as a potential source for EPF. We employed three experiments to assess three distinct aspects of SF perception: sensitivity, precision, and accuracy. In Experiment 1, using a 2-interval forced choice (2-IFC) detection paradigm, we measured contrast sensitivity at eight SFs. In Experiment 2, we assessed precision as a function of spatial frequency via a 2-IFC discrimination paradigm. In Experiment 3, we examined accuracy of SF perception (i.e., veridical perception) via a method-of-adjustment paradigm. Finally, in Experiment 4 we implemented a visual search paradigm that has previously demonstrated superior performance in people with ASD (Kemner, van Ewijk, van Engeland, & Hooge, 2007; O'Riordan et al., 2001). No evidence for enhanced perceptual functioning was found in any of our three experiments examining sensitivity, precision, or accuracy of SF perception in ASD (N = 20) compared to age-, gender-, non-verbal IQ-matched controls (N = 20). In addition, in the visual search task we found faster reaction times in our control group, the opposite of previous studies that found superior performance in ASD. These findings are consistent with previous research on visual orientation perception (Shafai, Armstrong, Iarocci, & Oruc, 2015) suggesting that enhanced low-level visual processing is not a source of EPF in ASD, as well as meta-analyses suggesting that EPF is not a characteristic of the overall population with ASD (Muth, Hönekopp, & Falter, 2014; Van der Hallen, Evers, Brewaeys, Van den Noortgate, & Wagemans, 2015).
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