Deborah Giaschi

University of British Columbia - Vancouver, Vancouver, British Columbia, Canada

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Publications (53)167.11 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: There is growing evidence for deficits in motion perception in amblyopia, but these are rarely assessed clinically. In this prospective study we examined the effect of occlusion therapy on motion-defined form perception and multiple-object tracking. Participants included children (3-10 years old) with unilateral anisometropic and/or strabismic amblyopia who were currently undergoing occlusion therapy and age-matched control children with normal vision. At the start of the study, deficits in motion-defined form perception were present in at least one eye in 69% of the children with amblyopia. These deficits were still present at the end of the study in 55% of the amblyopia group. For multiple-object tracking, deficits were present initially in 64% and finally in 55% of the children with amblyopia, even after completion of occlusion therapy. Many of these deficits persisted in spite of an improvement in amblyopic eye visual acuity in response to occlusion therapy. The prevalence of motion perception deficits in amblyopia as well as their resistance to occlusion therapy, support the need for new approaches to amblyopia treatment. Copyright © 2015. Published by Elsevier Ltd.
    Vision research 06/2015; DOI:10.1016/j.visres.2015.05.015 · 2.38 Impact Factor
  • Sae Kaneko · Deborah Giaschi · Stuart Anstis
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    ABSTRACT: Independent channels respond to both the spatial and temporal characteristics of visual stimuli. Gratings <3cycles per degree (cpd) are sensed by transient channels that prefer intermittent stimulation, while gratings >3cpd are sensed by sustained channels that prefer steady stimulation. From this we predict that adaptation to a spatially uniform flickering field will selectively adapt the transient channels and raise the apparent spatial frequency of coarse sinusoidal gratings. Observers adapted to a spatially uniform field whose upper or lower half was steady and whose other half was flickering. They then adjusted the spatial frequency of a stationary test (matching) grating on the previously unmodulated half field until it matched the apparent spatial frequency of a grating falling on the previously flickering half field. The adapting field flickered at 8Hz and the spatial frequency of the gratings was varied in octave steps from 0.25 to 16cpd. As predicted, adapting to flicker raised the apparent spatial frequency of the test gratings. The aftereffect reached a peak of 11% between 0.5 and 1cpd and disappeared above 4cpd. We also observed that superimposed 10Hz luminance flicker raised the apparent spatial frequency of 0.5cpd test gratings. The effect was not seen with slower flicker or finer test gratings. Altogether, our study suggests that apparent spatial frequency is determined by the balance between transient and sustained channels and that an imbalance between the channels caused by flicker can alter spatial frequency perception. Copyright © 2015. Published by Elsevier Ltd.
    Vision Research 02/2015; 108. DOI:10.1016/j.visres.2015.01.005 · 2.38 Impact Factor
  • Kimberly Meier · Deborah Giaschi
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    ABSTRACT: The typical development of motion perception is commonly assessed with tests of global motion integration using random dot kinematograms. 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. To address these discrepancies, the current study measured the effect of frame duration (Δt) and signal dot spatial offset (Δx) on motion coherence thresholds in adults and children. Two Δt values were used in combination with seven Δx values, for a range of speeds (0.3-38 deg/s). Developmental comparisons showed that for the longer Δt, children performed as well as adults for larger Δx, and were immature for smaller Δx. 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 Δx and Δt 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.
    Vision research 12/2013; 95. DOI:10.1016/j.visres.2013.12.007 · 2.38 Impact Factor
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    ABSTRACT: Stereoscopic depth perception may be obtained from small retinal disparities that can be fused for single vision (fine stereopsis), but reliable depth information is also obtained from larger disparities that produce double vision (coarse stereopsis). Here we assess the possibility that the early development of coarse stereopsis makes it resilient to the factors that cause amblyopia by comparing performance in children with a history of strabismic, anisometropic, or aniso-strabismic amblyopia and age-matched controls (5-12 years). The task was to indicate whether a cartoon character was nearer or farther away than a zero-disparity reference frame. Test disparities were grouped into fine and coarse ranges based on preliminary assessment of diplopia thresholds. In the fine range, accuracy increased with disparity for both groups, but children in the amblyopia group performed significantly worse than children in the control group, particularly when their amblyopia was associated with strabismus. In the coarse range, accuracy was constant across all disparities for both groups although performance appeared to be poorer in the aniso-strabismic group. These results suggest that, under some conditions, stereopsis for large disparities may be spared when stereopsis for small disparities is disrupted by early visual deprivation. This undetected residual binocular function has important clinical implications given recent efforts to improve amblyopia treatment outcomes by employing binocular treatment protocols.
    Journal of Vision 08/2013; 13(10). DOI:10.1167/13.10.17 · 2.73 Impact Factor
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    ABSTRACT: Stereoscopic depth perception may be obtained from small retinal disparities that can be fused for single vision (fine stereopsis), but reliable depth information is also obtained from larger disparities that produce double vision (coarse stereopsis). While there is some evidence that stereoacuity improves with age, little is known about the development and maturation of coarse stereopsis. Here we address this gap by assessing the maturation of stereoscopic depth perception in children (4 to 14 years) and adults over a large range of disparities from fused (fine) to diplopic (coarse). The observer's task was to indicate whether a stereoscopic cartoon character was nearer or farther away than a zero-disparity reference frame. The test disparities were grouped into fine (0.02, 0.08, 0.17, 0.33, 0.68, 1.0 deg) and coarse (2.0, 2.5, 3.0, 3.5 deg) ranges based on an initial determination of the diplopia threshold for each observer. Next, percent correct depth direction was determined as a function of disparity. In the coarse range, accuracy decreased slightly with disparity and there were no differences as a function of age. In the fine range, accuracy was constant across all disparities in adults and increased with disparity in children of all ages. Performance was immature in all children at the finest disparity tested. We conclude that stereopsis in the coarse range is mature at 4 years of age, but stereopsis in the fine range, at least for small disparities, continues to mature into the school-age years.
    Vision research 07/2013; 89. DOI:10.1016/j.visres.2013.07.011 · 2.38 Impact Factor
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    ABSTRACT: The current study examined auditory processing deficits in dyslexia using a dichotic pitch stimulus and functional MRI. Cortical activation by the dichotic pitch task occurred in bilateral Heschl's gyri, right planum temporale, and right superior temporal sulcus. Adolescents with dyslexia, relative to age-matched controls, illustrated greater activity in left Heschl's gyrus for random noise, less activity in right Heschl's gyrus for all auditory conditions, and less activity in right superior temporal sulcus for a dichotic melody. Subsequent analyses showed that these group differences were attributable to dyslexic readers who performed poorly on the psychophysical task. Furthermore, behavioral performance on phonological reading was correlated to activity from dichotic conditions in right Heschl's gyrus and right superior temporal sulcus. It is postulated that these differences between reader groups is primarily due to a noise exclusion deficit shown previously in dyslexia.
    Brain and Language 10/2012; 123(2):104-12. DOI:10.1016/j.bandl.2012.09.002 · 3.31 Impact Factor
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    ABSTRACT: Background / Purpose: Stereoscopic depth percepts result from small retinal disparities within Panum’s fusional area (fine stereopsis) as well as from larger disparities that cannot be fused (coarse stereopsis). Recently we showed that coarse stereopsis is mature by age 4 when fine stereopsis is still developing (see “Narasimhan et al 2012” ;http://f1000.com/posters). We hypothesize that the early development of coarse stereopsis makes it less susceptible to amblyogenic factors. 17 children with strabismic or anisometropic amblyopia and 17 age-matched control children (5-12 years) were tested on computerized tests of fine (disparity levels of 0.02, 0.1, 0.17, 0.33, 0.68, 1.0 deg) and coarse (disparity levels of 2, 2.5, 3, 3.5 deg) stereopsis. Main conclusion: Participants were asked to indicate whether a Pokemon character was nearer or farther than a zero-disparity reference frame. Children with amblyopia performed significantly worse than control children at all fine disparities, but there was no significant difference in performance between the two groups at all coarse disparities. The early development of coarse stereopsis may provide its resilience to amblyogenic factors.
    Vision Sciences Society Annual Meeting 2012; 07/2012
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    ABSTRACT: Background / Purpose: Stereoscopic depth perception may be obtained from small retinal disparities that can be fused for single vision (fine stereopsis), but reliable depth information is also obtained from larger disparities that produce double vision (coarse stereopsis). While there is some evidence that stereoacuity improves with age, little is known about the development and maturation of coarse stereopsis. We tested 114 children (4-13 years) and 18 adults (18-40 years) on a computerized stereopsis test where the participant’s task was to specify whether a Pokemon character was nearer or farther away than a reference frame at zero disparity. Main conclusion: In the fine range (disparity levels of 0.02, 0.1, 0.17, 0.33, 0.68, 1.0 deg), accuracy was lower in children under the age of 12 at the finest disparity only. There was no effect of age in the coarse range (disparity levels of 2, 2.5, 3, 3.5 deg). Our results suggest that coarse stereopsis matures before age 4, while fine stereopsis continues to develop into the school-age years.
    Vision Sciences Society Annual Meeting 2012; 07/2012
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    Sathyasri Narasimhan · Emily R Harrison · Deborah E Giaschi
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    ABSTRACT: In this study we explored the possibility of using a dichoptic global motion technique to measure interocular suppression in children with amblyopia. We compared children (5-16 years old) with unilateral anisometropic and/or strabismic amblyopia to age-matched control children. Under dichoptic viewing conditions, contrast interference thresholds were determined with a global motion direction-discrimination task. Using virtual reality goggles, high contrast signal dots were presented to the amblyopic eye, while low contrast noise dots were presented to the non-amblyopic fellow eye. The contrast of the noise dots was increased until discrimination of the motion direction of the signal dots reached chance performance. Contrast interference thresholds were significantly lower in the strabismic group than in the anisometropic and control group. Our results suggest that interocular suppression is stronger in strabismic than in anisometropic amblyopia.
    Vision research 06/2012; 66(11):1-10. DOI:10.1016/j.visres.2012.06.007 · 2.38 Impact Factor
  • Sathyasri Narasimhan · Deborah Giaschi
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    ABSTRACT: The purpose of this study was to investigate the effect of dot speed and dot density on the development of global motion perception by comparing the performance of adults and children (5-6years old) on a direction-discrimination task. Motion coherence thresholds were measured at two dot speeds (1 and 4deg/s) and three dot densities (1, 15, 30dots/deg(2)). Adult coherence thresholds were constant at approximately 9%, regardless of speed or density. Child coherence thresholds were significantly higher across conditions, and were most immature at the slow speed and at the sparse density. Thus, the development of global motion perception depends heavily on stimulus parameters. This finding can account for some of the discrepancy in the current developmental literature. Our results, however, caution against making general claims about motion deficits in clinical populations based on only a single measurement at a specific combination of speed and density.
    Vision research 04/2012; 62(15):102-7. DOI:10.1016/j.visres.2012.02.016 · 2.38 Impact Factor
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    John Secen · Jody Culham · Cindy Ho · Deborah Giaschi
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    ABSTRACT: Deficits in multiple-object tracking have previously been reported in both the amblyopic and the clinically unaffected fellow eye of patients with amblyopia. We examined the neural correlates of this deficit using functional MRI. Attentive tracking of 1, 2 or 4 moving targets was compared to passive viewing and to baseline fixation in an amblyopic group and an age-matched control group in six regions of interest: V1, middle temporal complex (MT+), superior parietal lobule (SPL), frontal eye fields (FEF), anterior intraparietal sulcus (IPS), and posterior IPS. Activation in all regions of interest, except V1, increased with attentional load in both groups. MT+ was less active in both eyes of the amblyopic group relative to controls for passive viewing and each of the tracking conditions. Anterior IPS and FEF were less active with amblyopic eye viewing when tracking four targets. These results implicate both the low-level passive and high-level active motion systems in the multiple-object tracking deficit in amblyopia.
    Vision research 12/2011; 51(23-24):2517-27. DOI:10.1016/j.visres.2011.10.011 · 2.38 Impact Factor
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    Jake Hayward · Grace Truong · Marita Partanen · Deborah Giaschi
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    ABSTRACT: We determined the effect of dot speed on the typical and atypical development of motion-defined form perception. Monocular motion coherence thresholds for orientation discrimination of motion-defined rectangles were determined at slow (0.1 deg/s), medium (0.9 deg/s) and fast (5.0 deg/s) dot speeds. First we examined typical development from age 4 to 31 years. We found that performance was most immature at the slow speed and in the youngest group of children (4-6 years). Next we measured motion-defined form perception in the amblyopic and fellow eyes of patients with amblyopia. Deficits were found in both eyes and were most pronounced at the slow speed. These results demonstrate the importance of dot speed to the development of motion-defined form perception. Implications regarding sensitive periods and the neural correlates of motion-defined form perception are discussed.
    Vision research 09/2011; 51(20):2216-23. DOI:10.1016/j.visres.2011.08.023 · 2.38 Impact Factor
  • P. S. Paul · D. Giaschi · P. Cavanagh · R. Cline
    Journal of Vision 12/2010; 1(3):80-80. DOI:10.1167/1.3.80 · 2.73 Impact Factor
  • A. Solski · D. Giaschi · L. Wilcox
    Journal of Vision 08/2010; 10(7):367-367. DOI:10.1167/10.7.367 · 2.73 Impact Factor
  • M. Scheel · L. J. Lanyon · D. Giaschi · J. J. Barton
    Journal of Vision 08/2010; 9(8):772-772. DOI:10.1167/9.8.772 · 2.73 Impact Factor
  • D. Giaschi · A. Zwicker · S. A. Young · B. Lee · B. Bjornson
    Journal of Vision 06/2010; 7(9):751-751. DOI:10.1167/7.9.751 · 2.73 Impact Factor
  • D. Giaschi · K. MacKenzie · C. Boden · A. Solski · L. Wilcox
    Journal of Vision 05/2010; 8(6):99-99. DOI:10.1167/8.6.99 · 2.73 Impact Factor
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    ABSTRACT: Motion perception may be preserved after damage to striate cortex (primary visual cortex, area V1). Awareness and normal discrimination of fast-moving stimuli have been observed even in the complete absence of V1. These facts suggest that motion-sensitive cortex (the V5/MT complex or V5/MT+) may be activated by direct thalamic or collicular inputs that bypass V1. Such projections have been identified previously in monkeys but have not been shown in humans using neuroimaging techniques. We used diffusion tensor imaging (DTI) tractography to visualize white matter fiber tracts connecting with V5/MT+ in 10 healthy volunteers. V5/MT+ was localized for each subject using functional MRI (fMRI). Functional activity maps were overlaid on high-resolution anatomical images and registered with the diffusion-weighted images to define V5/MT+ as the region of interest (ROI) for DTI tractography analysis. Fibers connecting to V1 were excluded from the analysis. Using conservative tractography parameters, we found connections between the V5/MT+ region and the posterior thalamus and/or superior colliculus in 4 of 10 subjects. Connections between the V5/MT+ region and the posterior thalamus and/or superior colliculus may explain visual motion awareness in the absence of a functioning V1.
    Journal of neuro-ophthalmology: the official journal of the North American Neuro-Ophthalmology Society 07/2009; 29(2):96-103. DOI:10.1097/WNO.0b013e3181a58ef8 · 1.81 Impact Factor
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    Cindy S Ho · Deborah E Giaschi
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    ABSTRACT: Maximum motion displacement (Dmax) is the largest dot displacement in a random-dot kinematogram (RDK) at which direction of motion can be correctly discriminated [Braddick, O. (1974). A short-range process in apparent motion. Vision Research, 14, 519-527]. For first-order RDKs, Dmax gets larger as dot size increases and/or dot density decreases. It has been suggested that this increase in Dmax reflects greater involvement of high-level feature-matching motion mechanisms and less dependence on low-level motion detectors [Sato, T. (1998). Dmax: Relations to low- and high-level motion processes. In T. Watanabe (Ed.), High-level motion processing, computational, neurobiological, and psychophysical perspectives (pp. 115-151). Boston: MIT Press]. Recent psychophysical findings [Ho, C. S., & Giaschi, D. E. (2006). Deficient maximum motion displacement in amblyopia. Vision Research, 46, 4595-4603; Ho, C. S., & Giaschi, D. E. (2007). Stereopsis-dependent deficits in maximum motion displacement. Vision Research, 47, 2778-2785] suggest that this "switch" from low-level to high-level motion processing is also observed in children with anisometropic and strabismic amblyopia as RDK dot size is increased and/or dot density is decreased. However, both high- and low-level Dmax were reduced relative to controls. In this study, we used functional MRI to determine the motion-sensitive areas that may account for the reduced Dmax in amblyopia In the control group, low-level RDKs elicited stronger responses in low-level (posterior occipital) areas and high-level RDKs elicited a greater response in high-level (extra-striate occipital-parietal) areas when activation for high-level RDKs was compared to that for low-level RDKs. Participants with anisometropic amblyopia showed the same pattern of cortical activation although extent of activation differences was less than in controls. For those with strabismic amblyopia, there was almost no difference in the cortical activity for low-level and high-level RDKs, and activation was reduced relative to the other groups. Differences in the extent of cortical activation may be related to amblyogenic subtype.
    Vision research 07/2009; 49(24):2891-901. DOI:10.1016/j.visres.2009.07.012 · 2.38 Impact Factor
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    Cindy S Ho · Deborah E Giaschi
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    ABSTRACT: Maximum motion displacement (Dmax) represents the largest dot displacement in a random-dot kinematogram (RDK) at which direction of motion can be discriminated. Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed but are stimulus dependent. For first-order RDKs, Dmax is larger as dot size increases and/or dot density decreases. Dmax may be limited by the receptive field size of low-level motion detectors when the dots comprising the RDK are small and densely spaced. With RDKs of increased dot size/decreased dot density, however, Dmax exceeds the spatial limits of these detectors and is likely determined by high-level feature-matching mechanisms. Using functional MRI, we obtained greater activation in posterior occipital areas for low-level RDKs and greater activation in extra-striate occipital and parietal areas for high-level RDKs. This is the first reported neuroimaging evidence supporting proposed low-level and high-level models of motion processing for first-order random-dot stimuli.
    Vision research 05/2009; 49(14):1814-24. DOI:10.1016/j.visres.2009.04.018 · 2.38 Impact Factor

Publication Stats

1k Citations
167.11 Total Impact Points

Institutions

  • 1993–2015
    • University of British Columbia - Vancouver
      • • Department of Ophthalmology and Visual Sciences
      • • Department of Psychology
      Vancouver, British Columbia, Canada
  • 2009
    • Children's & Women's Health Centre of British Columbia
      Vancouver, British Columbia, Canada
  • 2005
    • BC Children's Hospital
      Vancouver, British Columbia, Canada
  • 2004
    • Government of British Columbia, Canada
      Vancouver, British Columbia, Canada
  • 1992
    • University of Toronto
      • Division of Neurology
      Toronto, Ontario, Canada
    • York University
      • Department of Psychology
      Toronto, Ontario, Canada