Center for Vision Research

Toronto, Canada

Center for Vision Research

Toronto, Canada
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Philip K.,Brien Holden Vision Institute | Philip K.,University of New South Wales | Philip K.,The Vision Cooperative Research Center | Martinez A.,University of New South Wales | And 14 more authors.
Vision Research | Year: 2012

Total ocular higher order aberrations and corneal topography of myopic, emmetropic and hyperopic eyes of 675 adolescents (16.9 ± 0.7 years) were measured after cycloplegia using COAS aberrometer and Medmont videokeratoscope. Corneal higher order aberrations were computed from the corneal topography maps and lenticular (internal) higher order aberrations derived by subtraction of corneal aberrations from total ocular aberrations. Aberrations were measured for a pupil diameter of 5 mm. Multivariate analysis of variance followed by multiple regression analysis found significant difference in the fourth order aberrations (SA RMS, primary spherical aberration coefficient) between the refractive error groups. Hyperopic eyes (+0.083 ± 0.05 μm) had more positive total ocular primary spherical aberration compared to emmetropic (+0.036 ± 0.04 μm) and myopic eyes (low myopia = +0.038 ± 0.05 μm, moderate myopia = +0.026 ± 0.06 μm) (p< 0.05). No difference was observed for the anterior corneal spherical aberration. Significantly less negative lenticular spherical aberration was observed for the hyperopic eyes (-0.038 ± 0.05 μm) than myopic (low myopia = -0.088 ± 0.04 μm, moderate myopia = -0.095 ± 0.05. μm) and emmetropic eyes (-0.081 ± 0.04 μm) (p<0.05). These findings suggest the existence of differences in the characteristics of the crystalline lens (asphericity, curvature and gradient refractive index) of hyperopic eyes versus other eyes. © 2011.


Jones S.A.H.,Center for Vision Research | Jones S.A.H.,York University | Cressman E.K.,University of Ottawa | Henriques D.Y.P.,Center for Vision Research | Henriques D.Y.P.,York University
Experimental Brain Research | Year: 2010

The present study examined the accuracy of proprioceptive localization of the hand using two paradigms. In our proprioceptive estimation paradigm, participants judged the position of a target hand relative to visual references, or their body's midline. Placement of the target hand was active (participants pushed a robot manipulandum along a constrained path) or passive (the robot manipulandum positioned participants' target hand). In our proprioceptive-guided reaching paradigm, participants reached to the unseen location of a hand; both the left and right hands served as the target hand and the reaching hand. In both paradigms, subjects were relatively good at estimating the location of each hand (i.e. relative to a reference marker or using a reach), with directional errors falling within 2 cm of the actual target location, and little variation across the workspace. In our proprioceptive estimation paradigm, biases when the target hand was passively placed were no larger than those made when the target hand was actively placed. Participants perceived their left hand to be more to the left than it actually was, and their right hand to be more rightward than it actually was, but with a similar error magnitude across target hands. In our reaching paradigm, participants' estimates of left hand location were deviated more leftwards than their estimates of right hand location, but showed a small but similar pattern of locationdependent reach errors across the two hands. Precision of estimates did not diVer between the two hands or vary with target location for either paradigm. © 2010 Springer-Verlag.


Philip K.,University of New South Wales | Sankaridurg P.,Brien Holden Vision Institute | Sankaridurg P.,The Vision Co operative Research Center | Sankaridurg P.,University of New South Wales | And 8 more authors.
Vision Research | Year: 2014

Refractive error, higher order aberrations (HOA), axial length (AL), anterior chamber depth (ACD) and average corneal radius of curvature were measured after cycloplegia from 166 emmetropic participants at the Sydney Myopia Study (SMS, 2004-2005, age 12.63±0.48years). Measurements were repeated approximately 5years later at the Sydney Adolescent Vascular and Eye Study (SAVES, 2009-2010, age 17.08±0.67years). The baseline spherical equivalent (M) did not differ significantly between the participants lost to follow-up (65%) and the participants enrolled in SAVES study (p=0.932). Refractive error and HOA were measured using a Shack-Hartmann aberrometer for a pupil diameter of 5mm and AL, ACD and average corneal curvature measured using IOL Master at both visits. Retinal image quality in terms of Visual Strehl ratio (VSOTF) for a 5mm pupil diameter was determined using on-axis lower and HOA. General linear model was used to determine the association of HOA and retinal image quality with change in refraction. Of the 166 emmetropes, 41 (25%) had myopic change (change in M>-0.50D) and 125 (75%) had no change in refraction (change in M between +0.49D and -0.49 D). Change in C[4,0] (p<0.001, R2=0.236), fourth order RMS (p=0.003, R2=0.097) and coma RMS (p=0.004, R2=0.056) from baseline were significantly correlated with change in refraction. More positive change in C[4,0] was associated with lesser myopic change in refraction. The eyes with myopic change in refraction decreased in positive C[4,0] (at baseline=+0.049±0.05μm, at follow-up=+0.024±0.05μm, p<0.05). In comparison, eyes with no change increased in positive C[4,0] (at baseline=+0.033±0.04μm, at follow-up=+0.047±0.04μm, p<0.05). Thus in conclusion, no significant association was observed between HOA and retinal image quality at baseline and development and progression of myopia among emmetropic eyes. The change in spherical aberration (C[4,0]) with myopic change is possibly associated with changes occurring in crystalline lens during ocular growth. © 2014 Elsevier Ltd.


PubMed | York University and Center for Vision Research
Type: | Journal: Hippocampus | Year: 2016

Memory for scenes is supported by the hippocampus, among other interconnected structures, but the neural mechanisms related to this process are not well understood. To assess the role of the hippocampus in memory-guided scene search, we recorded local field potentials and multi-unit activity from the hippocampus of macaques as they performed goal-directed search tasks using natural scenes. We additionally measured pupil size during scene presentation, which in humans is modulated by recognition memory. We found that both pupil dilation and search efficiency accompanied scene repetition, thereby indicating memory for scenes. Neural correlates included a brief increase in hippocampal multi-unit activity and a sustained synchronization of unit activity to gamma band oscillations (50-70 Hz). The repetition effects on hippocampal gamma synchronization occurred when pupils were most dilated, suggesting an interaction between aroused, attentive processing and hippocampal correlates of recognition memory. These results suggest that the hippocampus may support memory-guided visual search through enhanced local gamma synchrony. This article is protected by copyright. All rights reserved.


Monteon J.A.,Center for Vision Research | Constantin A.G.,Center for Vision Research | Wang H.,Center for Vision Research | Martinez-Trujillo J.,McGill University | And 2 more authors.
Journal of Neurophysiology | Year: 2010

The frontal eye field (FEF) is a region of the primate prefrontal cortex that is central to eye-movement generation and target selection. It has been shown that neurons in this area encode commands for saccadic eye movements. Furthermore, it has been suggested that the FEF may be involved in the generation of gaze commands for the eye and the head. To test this suggestion, we systematically stimulated (with pulses of 300 Hz frequency, 200 ms duration, 30-100 μA intensity) the FEF of two macaques, with the head unrestrained, while recording three-dimensional (3D) eye and head rotations. In a total of 95 sites, the stimulation consistently elicited gaze-orienting movements ranging in amplitude from 2 to 172°, directed contralateral to the stimulation site, and with variable vertical components. These movements were typically a combination of eye-in-head saccades and head-in-space movements. We then performed a comparison between the stimulation-evoked movements and gaze shifts voluntarily made by the animal. The kinematics of the stimulation-evoked movements (i.e., their spatiotemporal properties, their velocity-amplitude relationships, and the relative contributions of the eye and the head as a function of movement amplitude) were very similar to those of natural gaze shifts. Moreover, they obeyed the same 3D constraints as the natural gaze shifts (i.e., modified Listing's law for eye-in-head movements). As in natural gaze shifts, saccade and vestibuloocular reflex torsion during stimulation-evoked movements were coordinated so that at the end of the head movement the eye-in-head ended up in Listing's plane. In summary, movements evoked by stimulation of the FEF closely resembled those of naturally occurring eye- head gaze shifts. Thus we conclude that the FEF explicitly encodes gaze commands and that the kinematic aspects of eye- head coordination are likely specified by downstream mechanisms. Copyright © 2010 The American Physiological Society.


Le A.,University of Toronto | Vesia M.,University of Toronto | Yan X.,Center for Vision Research | Niemeier M.,University of Toronto | And 2 more authors.
Cerebral cortex (New York, N.Y. : 1991) | Year: 2014

Grasping with 2 limbs in opposition to one another is older than the hand, yet the neural mechanisms for bimanual grasps remain unclear. Similar to unimanual grasping, bimanual grasping may require regions in the parietal cortex that use visual object-feature information to find matching stable grasp points on the object. The localization of matching points is computationally expensive, so it might make sense for the signals to converge in a single cortical area. To examine this, we use transcranial magnetic stimulation (TMS) to probe the contribution of cortical areas known to be associated with unimanual grasping, while participants performed bimanual grasps. We applied TMS to the anterior and caudal portion of the intra-parietal sulcus (aIPS and cIPS) in each hemisphere during a size-perturbation task using the index fingers of both hands to grasp an object whose orientation might or might not change. We found significant interaction effects between TMS and perturbation of the grasp-relevant object dimension that increased grip aperture only for the right aIPS. These results indicate that the aIPS is involved not only in unimanual, but also bimanual grasping, and the right aIPS is critically involved in bimanual grasps. This suggests that information from both hemispheres converges in the right hemisphere to achieve bimanual grasps. © The Author 2013. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.


Andreopoulos A.,Center for Vision Research | Tsotsos J.K.,Center for Vision Research
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2012

Most current algorithm evaluation protocols use large image databases, but give little consideration to imaging characteristics used to create the data sets. This paper evaluates the effects of camera shutter speed and voltage gain under simultaneous changes in illumination and demonstrates significant differences in the sensitivities of popular vision algorithms under variable illumination, shutter speed, and gain. These results show that offline data sets used to evaluate vision algorithms typically suffer from a significant sensor specific bias which can make many of the experimental methodologies used to evaluate vision algorithms unable to provide results that generalize in less controlled environments. We show that for typical indoor scenes, the different saturation levels of the color filters are easily reached, leading to the occurrence of localized saturation which is not exclusively based on the scene radiance but on the spectral density of individual colors present in the scene. Even under constant illumination, foreshortening effects due to surface orientation can affect feature detection and saliency. Finally, we demonstrate that active and purposive control of the shutter speed and gain can lead to significantly more reliable feature detection under varying illumination and nonconstant viewpoints. © 2012 IEEE.


Freeman N.E.,Center for Vision Research | Templeton J.P.,Center for Vision Research | Orr W.E.,Center for Vision Research | Lu L.,Center for Vision Research | And 2 more authors.
Molecular Vision | Year: 2011

Purpose: The present study examines the structure and covariance of endogenous variation in gene expression across the recently expanded family of C57BL/6J (B) X DBA/2J (D) Recombinant Inbred (BXD RI) strains of mice. This work is accompanied by a highly interactive database that can be used to generate and test specific hypotheses. For example, we define the genetic network regulating growth associated protein 43 (Gap43) and phosphatase tensin homolog (Pten). Methods: The Hamilton Eye Institute (HEI) Retina Database within GeneNetwork features the data analysis of 346 Illumina Sentrix BeadChip Arrays (mouse whole genome-6 version 2). Eighty strains of mice are presented, including 75 BXD RI strains, the parental strains (C57BL/6J and DBA/2J), the reciprocal crosses, and the BALB/cByJ mice. Independent biologic samples for at least two animals from each gender were obtained with a narrow age range (48 to 118 days). Total RNA was prepared followed by the production of biotinylated cRNAs, which were pipetted into the Mouse WG-6V2 arrays. The data was globally normalized with rank invariant and stabilization (2z+8). Results: The HEI Retina Database is located on the GeneNetwork website. The database was used to extract unique transcriptome signatures for specific cell types in the retina (retinal pigment epithelial, amacrine, and retinal ganglion cells). Two genes associated with axonal outgrowth (Gap43 and Pten) were used to display the power of this new retina database. Bioinformatic tools located within GeneNetwork in conjunction with the HEI Retina Database were used to identify the unique signature Quantitative Trait Loci (QTLs) for Gap43 and Pten on chromosomes 1, 2, 12, 15, 16, and 19. Gap43 and Pten possess networks that are similar to ganglion cell networks that may be associated with axonal growth in the mouse retina. This network involves high correlations of transcription factors (SRY sex determining region Y-box 2 [Sox2], paired box gene 6 [Pax6], and neurogenic differentiation 1 [Neurod1]), and genes involved in DNA binding (proliferating cell nuclear antigen [Pcna] and zinc finger, BED-type containing 4 [Zbed4]), as well as an inhibitor of DNA binding (inhibitor of DNA binding 2, dominant negative helix-loop-helix protein [Id2]). Furthermore, we identified the potential upstream modifiers on chromosome 2 (teashirt zinc finger homeobox 2 [Tshz2], RNA export 1 homolog [Rae1] and basic helix-loop-helix domain contatining, class B4 [Bhlhb4]) on chromosome 15 (RAB, member of RAS oncogene family-like 2a [Rabl2a], phosphomannomutase 1 [Pmm1], copine VIII [Cpne8], and fibulin 1 [Fbln1]). Conclusions: The endogenous variation in mRNA levels among BXD RI strains can be used to explore and test expression networks underlying variation in retina structure, function, and disease susceptibility. The Gap43 and Pten network highlights the covariance of gene expression and forms a molecular network associated with axonal outgrowth in the adult retina. © 2011 Molecular Vision.


PubMed | Center for Vision Research
Type: Journal Article | Journal: Experimental brain research | Year: 2010

The present study examined the accuracy of proprioceptive localization of the hand using two paradigms. In our proprioceptive estimation paradigm, participants judged the position of a target hand relative to visual references, or their bodys midline. Placement of the target hand was active (participants pushed a robot manipulandum along a constrained path) or passive (the robot manipulandum positioned participants target hand). In our proprioceptive-guided reaching paradigm, participants reached to the unseen location of a hand; both the left and right hands served as the target hand and the reaching hand. In both paradigms, subjects were relatively good at estimating the location of each hand (i.e. relative to a reference marker or using a reach), with directional errors falling within 2 cm of the actual target location, and little variation across the workspace. In our proprioceptive estimation paradigm, biases when the target hand was passively placed were no larger than those made when the target hand was actively placed. Participants perceived their left hand to be more to the left than it actually was, and their right hand to be more rightward than it actually was, but with a similar error magnitude across target hands. In our reaching paradigm, participants estimates of left hand location were deviated more leftwards than their estimates of right hand location, but showed a small but similar pattern of location-dependent reach errors across the two hands. Precision of estimates did not differ between the two hands or vary with target location for either paradigm.


PubMed | Center for Vision Research
Type: Journal Article | Journal: Journal of optometry | Year: 2016

We investigated the dynamics of accommodative and pupillary responses to random-dot stereograms presented in crossed and uncrossed disparity in six visually normal young adult subjects (mean age=25.83.1 years). Accommodation and pupil measures were monitored monocularly with a custom built photorefraction system while subjects fixated at the center of a random-dot stereogram. On each trial, the stereogram initially depicted a flat plane and then changed to depict a sinusoidal corrugation in depth while fixation remained constant. Increase in disparity specified depth resulted in pupil constriction during both crossed and uncrossed disparity presentations. The change in pupil size between crossed and uncrossed disparity conditions was not significantly different (p>0.05). The change in pupil size was also accompanied by a small concomitant increase in accommodation. In addition, the dynamic properties of pupil responses varied as a function of their initial (starting) diameter. The finding that accommodation and pupil responses increased with disparity regardless of the sign of retinal disparity suggests that these responses were driven by apparent depth rather than shifts in mean simulated distance of the stimulus. Presumably the need for the increased depth of focus when viewing stimuli extended in depth results in pupil constriction which also results in a concomitant change in accommodation. Starting position effects in pupil response confirm the non-linearity in the operating range of the pupil.

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