Deborah Giaschi

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Research Interests

motion perception
binocular vision
visual development

Relevant Thesis-Based Degree Programs


Research Methodology


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.

The perception of global motion in typical and atypical visual development (2018)

Sensitivity to motion information emerges early in life, but full maturation of motion perception can take many years. Reports on the age at which typically-developing children reach adult-like global motion perception have ranged from 3-14 years. There are also conflicting reports on whether people with amblyopia (a visual disorder that occurs when a young child experiences abnormal visual input to one eye for a prolonged period) show deficits on these tasks. This dissertation examines the spatio-temporal factors underlying immaturities and deficits in motion perception. I tested the hypothesis that perception of motion stimuli created with small spatial displacements would mature later than those created with large displacements; and as a consequence, children with amblyopia would show selective deficits for these small spatial displacements. First, I investigated typical maturation of motion perception across a range of stimulus parameters in people aged 7-30 years (Chapter 3). The youngest children performed similar to adults for large displacements, but mature performance was not reached until middle teenage years for small displacements. Second, I investigated performance for the same stimulus parameters in children with amblyopia (Chapter 4). Deficits were only present for parameters where healthy control children showed late maturation. Finally, I examined two factors that might account for the immaturities and deficits I found: spatial integration and eye stability. I determined that increasing the stimulus area had the same impact on coherence thresholds in 4-6 year-olds and adults (Chapter 5), suggesting children’s immature performance for small displacements was not restricted by spatial integration limitations at stages prior to motion processing. I also determined that eye stability had no relationship with performance in healthy adults (Chapter 6), indicating that poor fixational stability alone could not account for poor performance on a global motion task. This work contributes to a better understanding of how the developing brain is impacted by amblyopia, in turn providing insight into sensitive periods for typical visual development.

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Academic and neuroimaging outcomes of school-based reading interventions (2017)

Early intervention is important for decreasing the prevalence of reading disabilities. However, despite receiving treatment, some children continue to struggle with reading and therefore they require ongoing supports. Intensive and individualized programs may be beneficial for the lowest-performing readers, however, empirical review of intensive and individualized programs has not been widely conducted. Furthermore, there is a neurobiological basis to reading impairments. Children with poor reading skills have differences in brain function and structure when compared to typically-developing readers, and there may be changes in the brain after intervention. However, the combination of multiple reading tasks in functional brain imaging along with measures of grey and white matter structure has not been conducted previously. Therefore, the purpose of my dissertation was to evaluate the academic and neurobiological outcomes of an intensive reading program as well as to determine the predictors of reading success. In Chapter 2, poor readers receiving intensive instruction were compared to other poor readers receiving small group supports as well as to good readers not receiving additional supports. Performance on academic and cognitive measures were evaluated before and after 3 months of instruction and one year later. In Chapters 3 and 4, poor readers and good readers completed functional imaging tasks (Chapter 3) and scans of grey and white matter (Chapter 4) before and after 3 months of instruction. The results showed that students in the intensive program had improved word recognition and decoding fluency immediately after intervention and one year later. Changes after intervention were also shown in functional brain activity during a rhyming task, but not during a spelling task or in grey and white matter structures. However, baseline reading and spelling skills, brain activity in the left hemisphere, and white matter organization in the right hemisphere were associated with gains in reading skills over time. Although improvements in reading were shown, a significant gap between poor and good readers persisted in the third and fourth grades. Overall, this dissertation illustrates the importance of an intensive reading program and the need for continuing supports, and that both academic and neuroimaging measures are associated with reading outcome.

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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.

Resolving inconsistencies in the maturation of human global motion perception (2013)

The typical development of motion perception is commonly assessed with tests of global motion integration using random dot kinematograms (RDKs). There are discrepancies, however, with respect to when typically-developing children reach adult-like performance on this task, ranging from as early as 3 years to as late as 12 years. While much research characterizes performance in terms of dot speed, there is evidence that different spatial and temporal components can impact performance on this task in adults and in children. Other studies suggest that the distance that dots are displaced each animation frame (∆x), rather than frame duration (∆t) or dot speed (∆x/∆t) per se, determines performance in developing macaques. No studies have directly investigated whether psychophysical performance follows this pattern in children. The current studies measured motion coherence thresholds in adults and children in two experiments. Experiment 1 examined differences in adult performance in two studies with similar RDK parameters except for the ∆x and ∆t used to make up similar speeds. This experiment tested four ∆x/∆t pairs yielding a speed of 1 deg/s, and held the number of presented frames constant, or the duration of the stimulus constant. These factors had no effect on the thresholds of adults. Experiment 2 was designed to replicate the results of macaque studies in human children, and compare their thresholds to adults. Two ∆t values were used in combination with seven ∆x values, for a range of speeds (0.3-38 deg/s). Adult thresholds followed a u-shape as a function of ∆x, with lower coherence thresholds for larger ∆t when ∆x was small. Child thresholds followed a rough u-shape as a function of ∆x, regardless of ∆t. Developmental comparisons showed children performed as well as adults for larger ∆x, and were immature for smaller ∆x. When parameters were expressed as speed, there was a range of intermediate speeds (4-12 deg/s) for which maturity was dependent on the values of ∆x and ∆t tested. These results resolve previous discrepancies by showing that motion sensitivity to a given speed may be mature, or not, depending on the underlying spatial and temporal properties of the motion stimulus.

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A functional MRI investigation into the neural correlates of the multiple-object-tracking deficit in amblyopia (2010)

Amblyopia is a visual developmental disorder defined by reduced visual acuity in one (amblyopic) eye, while the other (fellow) eye has normal visual acuity and is otherwise healthy. Deficits in motion perception – such as multiple object tracking - affect both the amblyopic eye and the fellow eye. This thesis examined the neural correlates of the multiple-object tracking deficit to further understand the cortical deficit in amblyopia. Functional data were collected as participants with and without a history of amblyopia performed the multiple-object tracking task monocularly inside a 3T MRI scanner. Participants were asked to use their attention to track 0, 1, 2 or 4 of 9 moving balls (6 deg/s) for 12 seconds. MR signal change relative to fixation, as a function of target numerosity (track 0, track 1, track 2, track 4), group (control, amblyopia), and eye were examined in six regions of interest: putative V1, MT, superior parietal lobule, frontal eye fields, anterior intraparietal sulcus, and posterior intraparietal sulcus. For all four tracking conditions, area MT was found to be less active in participants with amblyopia with both fellow and amblyopic eye viewing. When tracking 4 balls, the anterior intraparietal sulcus was found to be less active in participants with amblyopia, only with amblyopic eye viewing. This finding suggests the functional differences in this region may be subtle. Future investigations targeting the network involved in sustained attention can determine the extent to which posterior parietal function may be impaired in amblyopia. Overall, this thesis provided neuroimaging evidence that the MT region is affected in human amblyopia, and that both eyes are affected by underlying cortical changes in dorsal extra-striate areas.

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Overlapping cortical regions for reading and temporal processing in developmental dyslexia (2010)

Children with developmental dyslexia have difficulty learning to read. These children may also have deficits in temporal processing, which is the perception and integration of rapidly presented stimuli. Behavioural research indicates a link between reading and temporal processing ability; however, the cortical relationship between these two skills has not been established. This thesis examined whether tasks of reading and temporal processing activate similar cortical regions in children with average reading ability and in children with dyslexia. Using functional magnetic resonance imaging (fMRI), activity for two reading tasks (phonological and orthographic) and two temporal processing tasks (dichotic pitch and global motion perception) was assessed. Three regions of interest were established in each participant: the lateral occipital cortex (LOC) and areas engaged by dichotic pitch and global motion tasks. Results demonstrated that both groups had increased activity in bilateral LOC during reading. In average readers, left LOC was more active than right regions during the phonological task, while dyslexic readers showed equivalent activity between left and right LOC for both reading tasks. The dichotic pitch regions did not show any evidence of activation during reading in either group. However, children with dyslexia exhibited significant activity in right global motion regions during the phonological task, but only on the difficult word condition. Average readers did not illustrate activation in global motion areas during reading. The current results suggest that LOC is involved with the reading process and children with dyslexia may have a deficit in left LOC. It was hypothesized that dyslexic readers may have increased attentional processing and recruitment from additional cortical regions during difficult tasks, which may explain the similar activity between global motion and phonological reading. Since there were no similar regions between dichotic pitch and reading, this suggests that these may not be directly related through cortical activity. The current results provide novel evidence that reading and visual temporal processing may involve some of the same cortical areas, at least in children with dyslexia. Future research will investigate links between reading and temporal processing in younger children and will examine differences in white matter connectivity.

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BC Children's Hospital

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