Centre for Vision Research

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Open Access
Speaker and Poster Abstracts, CVR Conference 2013
(2013-06-26) Harris, Laurence
We are very pleased to welcome you to the 2013 CVR conference at York University at which we will celebrate the research careers of two esteemed CVR members, Drs. Hugh Wilson and Marty Steinbach. We have a stellar line up of speakers along with many interesting poster presentations.
Open Access
Anterior Cingulate Cortex Cells Identify Errors of Attentional Control Prior to Prefrontal Disengagement
(2014-07-09) Shen, Chen; Womelsdorf, Thilo
The anterior cingulate cortex (ACC) is implicated in the detection of errors and the allocation of correctional adjustments. However, error detection alone is not sufficient to resolve and prevent future mistakes since errors can occur in various ways, subsequently requiring different adjustments. I therefore investigated whether the ACC tracks specific processing states that give rise to errors in order to identify which specific processing aspects need readjustment. To do this, my lab recorded from cells in the prefrontal cortex (PFC) of macaques while they were performing a selective-attention task that elicited three types of error. My study provides support for the functional role of the ACC in performance monitoring and specifying correctional adjustments through the tracking of specific sources of erroneous task outcomes.
Open Access
Visual System Development in People with One Eye: Behaviour and Structural Neural Correlates
(2015-01-26) Kelly, Krista Rose; Steeves, Jennifer
Postnatal monocular deprivation from the surgical removal (enucleation) of one eye in humans results in intact spatial form vision, although its consequences on motion perception development are less clear. Changes in brain structure following early monocular enucleation have either been assessed in species whose visual system is quite different from humans, or in enucleated monkeys and humans following short-term survival. In this dissertation, I sought to determine the long-term effects of enucleation on visual system development by examining behavioural visual abilities and visual system morphology in adults who have had one eye enucleated early in life due to retinoblastoma. In Chapter II, I conducted a series of speed and luminance contrast discrimination tasks not yet implemented in this group. Early monocular enucleation results in impaired speed discrimination but intact contrast perception compared to binocular and monocular viewing controls. These findings suggest differential effects of enucleation on the development of spatial form vision and motion perception. In Chapters III and IV, I obtained high-resolution structural magnetic resonance images to assess the morphological development of subcortical (Chapter III) and cortical (Chapter IV) structures in the visual pathway. Early monocular enucleation resulted in decreased optic chiasm width and volume, optic tract diameters, and lateral geniculate nuclei (LGN) volumes compared with binocularly intact controls. Surprisingly, however, optic tract diameter and LGN volume decreases were less severe contralateral to the remaining eye. Early monocular enucleation also resulted in increased grey matter surface area of visual and non-visual cortices compared with binocularly intact controls. Consistent with the LGN asymmetry, increased surface area of the primary visual cortex was restricted to the hemisphere contralateral to the remaining eye. Surprisingly, however, these increases were found for those with right- but not left-eye enucleation, suggesting different developmental time periods for each hemisphere. Possible mechanisms of altered development following early monocular enucleation include: 1) recruitment of deafferented cells by the remaining eye, 2) retention of deafferented cells due to feedback from visual cortex, and 3) a disruption in synaptic pruning. These data highlight the importance of receiving normal levels of binocular visual input during infancy for typical visual development.
Open Access
The Role of the Dorsal Premotor and Superior Parietal Cortices in Decoupled Visuomotor Transformations
(2015-01-26) Sayegh, Patricia; Sergio, Lauren
In order to successfully interact with objects located within our environment, the brain must be capable of combining visual information with the appropriate felt limb position (i.e. proprioception) in order compute an appropriate coordinated muscle plan for accurate motor control. Eye-hand coordination is essential to our independence as a species and relies heavily on the reciprocally-connected regions of the parieto-frontal reach network. The dorsal premotor cortex (PMd) and the superior parietal lobule (SPL) remain prime candidates within this network for controlling the transformations required during visually-guided reaching movements. Our brains are primed to reach directly towards a viewed object, a situation that has been termed a “standard” or coupled reach. Such direct eye-hand coordination is common across species and is crucial for basic survival. Humans, however, have developed the capacity for tool-use and thus have learned to interact indirectly with an object. In such “non-standard” or decoupled situations, the directions of gaze and arm movement have been spatially decoupled and rely on both the implementation of a cognitive rule and on online feedback of the decoupled limb. The studies included within this dissertation were designed to further characterize the role of PMd and SPL during situations in which when a reach requires a spatial transformation between the actions of the eyes and the hand. More specifically, we were interested in examining whether regions within PMd (PMdr, PMdc) and SPL (PEc, MIP) responded differently during coupled versus decoupled visuomotor transformations. To address the relative contribution of these various cortical regions during decoupled reaching movements, we trained two female rhesus macaques on both coupled and decoupled visually-guided reaching tasks. We recorded the neural activity (single units and local field potentials) within each region while the animals performed each condition. We found that two separate networks emerged each contributing in a distinct ways to the performance of coupled versus decoupled eye-hand reaches. While PMdr and PEc showed enhanced activity during decoupled reach conditions, PMdc and MIP were more enhanced during coupled reaches. Taken together, these data presented here provide further evidence for the existence of alternate task-dependent neural pathways for visuomotor integration.
Open Access
Measuring Memory in an Alzheimer's Treatment Trial Using a Visual Search Task
(2015-01-26) Dragan, Michelle; Hoffman, Kari
Alzheimer’s Disease (AD) is characterized by episodic memory deficits attributed to damage to the hippocampal formation. AD therapies specifically targeting hippocampal function may be best evaluated through the use of selective hippocampal tasks. I used a nonverbal hippocampal-dependent target-in-scene detection task to determine if task performance shows age-related decline and/or AD-related impairments. Participants located objects (‘targets’) that appeared/disappeared in flickering natural scenes, yielding faster search times for remembered targets than for forgotten ones. AD patients took longer and required more fixations to detect targets, indicating impaired memory. Furthermore, the AD and aged populations exhibited slower pupillary responses. As part of a clinical trial, I next asked whether deep-brain stimulation of the extended hippocampal circuit would modify memory performance in patients with early AD. The double-blind treatment trial is still underway, thus treatment efficacy is yet to be evaluated, however, trial participants showed a measurable, progressive memory impairment in this task.
Open Access
ACT-R Based Models For Learning Interactive Layouts
(2015-01-26) Das, Arindam; Stuerzlinger, Wolfgang
This dissertation presents research on learning of interactive layouts. I develop two models based on a theory of cognition known as ACT-R (Adaptive Control of Thought–Rational). I validate them against experimental data collected by other researchers. The first model is a simulation model that emulates the transition from novice to expert level in text entry. The model transcribes the presented English letters on a traditional phone keypad. It predicts the non-movement time to copy a pre-cued letter. It explains the visual exploration strategy that a user may employ in the novice to expert continuum. The second model is a closed-form model that accounts for the combined effect of practice, decay, proactive interference and mental effort on task completion time while practicing target acquisition on an interactive layout. The model can quantitatively compare a set of layouts in terms of the mental effort expended to learn them. My first model provides insight into how much practice is needed by a learner to progress from novice to expert level for an interactive layout. My second model provides insight into how effortful is it to learn a layout relative to other layouts.
Open Access
Sex- and Experience-Related Differences in Bimanual Coordination Development
(2015-01-26) Albines, David; Sergio, Lauren
Sex- and experience-related differences in bimanual coordination have been found previously but are often reported separately. Here, we characterize visuomotor skill performance in relation to age, sex, and athletic experience in order to indirectly gain insight into the neural processes that underlie this advanced level of eye-hand coordination. We use a novel precision bimanual task composed of a modified washer-peg board. We recruited three age and two experience groups (9-10, 11-12 and 13-15, elite versus house league). We also developed a Whole-hand bimanual task in order to account for any manual dexterity discrepancies. The results show that the effect of skill and sex are not seen until later years developmentally, at that point there is a strong effect of sex on bimanual coordination. Future research that aims to look at the development of motor skills and control should also look at sex and experience effects.
Open Access
In-Air Un-Instrumented Pointing Performance
(2015-01-26) Brown, Michelle Andree; Stuerzlinger, Wolfgang
I present an analysis of in-air un-instrumented pointing and selection. I look at the performance of these systems and how this performance can be improved, with the eventual goal that their throughput reaches that of the mouse. Many potential limiting factors were explored, such as latency, selection reliability, and elbow stabilization. I found that the un-instrumented in-air pointing as currently implemented performed significantly worse, at less than 75% of mouse throughput. Yet, my research shows that this value can potentially reach mouse-like levels with lower system latencies, user training, and potentially improved finger tracking. Even without these improvements, the large range of applications for un-instrumented 3D hand tracking makes this technology still an attractive option for user interfaces.
Open Access
Do the Subjective Visual Vertical and the Subjective Haptic Vertical Probe a Common Estimate of Gravitational Upright?
(2015-01-26) Fraser, Lindsey Ellen; Harris, Laurence
In the subjective visual vertical (SVV) and the subjective haptic vertical (SHV) task, participants must judge the alignment of a probe rod with perceived gravitational vertical by sight or by touch. Previous research suggests that as the body is roll-tilted, SVV and SHV show a systematic, distinct pattern of errors, although reports vary. The purpose of this research was to identify whether SVV and SHV probe the same underlying representation of gravity. In Experiment 1, I confirmed that SVV and SHV errors are divergent by comparing the two measures in the same participants. In Experiment 2, I varied the tilt of the head and body separately and applied galvanic vestibular stimulation to introduce vestibular noise. I found these manipulations had differential effects on SVV and SHV. Experiment 3 showed that when neck afferents were stimulated, SVV and SHV integrate optimally, pointing to two distinct underlying estimates of gravity vertical.
Open Access
The Connection between Body Representation and Tactile Sensation Thresholds
(2015-01-26) Olwen D'amour, Sarah Anne; Harris, Laurence
In order to accurately interpret tactile information, the brain needs to have an accurate representation of the body to which to refer the sensations. Despite this, body representation has only recently been incorporated into the study of tactile perception. The effect of body representation on tactile thresholds was explored in two different ways. First, tendon vibration illusions were used to investigate whether distortions of body representation affect tactile sensations. Tactile acuity and sensitivity were increased when perceived size of the arm and waist were altered. Secondly, masking was used to investigate whether stimulation to one part of the body representation alters thresholds at other sites. Contralateral masking on the arms was found, along with spatial tuning of this effect. Masking through the body was also demonstrated by measuring the effect of a masking stimulus on the back on the tactile sensitivity of the corresponding point on the front.
Open Access
Reach Adaptation and Proprioceptive Recalibration Following Terminal Visual Feedback of the Hand
(2015-01-26) Barkley, Victoria Aurelia; Henriques, Densie
Reaches are adapted and proprioceptive sense of hand position is partially recalibrated after training with continuous, misaligned visual feedback. When visual feedback is provided only at the end of the movement, it is unclear if similar changes arise. To test this, participants reached to targets, first with aligned-cursor, then three times with rotated-cursor. After each block, we measured no-cursor reaches and perceived felt hand positions relative to a reference marker. We found that reach aftereffects were slightly smaller than that following training with continuous visual feedback. Additionally, terminal feedback participants incrementally recalibrated their sense of felt hand position over the rotated training blocks. Final proprioceptive recalibration levels were comparable to those in our continuous feedback study. Thus, compared to continuous feedback findings, terminal feedback produced significant, yet smaller, reach aftereffects but similar changes in hand proprioception. Taken together, terminal feedback is sufficient to drive motor adaptation and proprioceptive recalibration.
Open Access
Speaker and Poster Abstracts, CVR Conference 2015
(Centre for Vision Research, York University, 2015-06-23) Elder, James
A principal challenge for both human and machine vision systems is to integrate and organize the diversity of cues received from the environment into the coherent global representations required to make good decisions and take effective actions. This conference brings together an interdisciplinary roster of leading researchers in both biological and computer vision to report and discuss the latest research on this process of perceptual organization.
Open Access
Revealing Connections in Object and Scene Processing Using Consecutive TMS and fMR-Adaptation
(2015-08-28) Rafique, Sara; Steeves, Jennifer
When processing the visual world, our brain must perform many computations that may occur across several regions. It is important to understand communications between regions in order to understand perceptual processes underlying processing of our environment. We sought to determine the connectivity of object and scene processing regions of the cortex, which are not fully established. In order to determine these connections repetitive transcranial magnetic stimulation (rTMS) and functional magnetic resonance-adaptation (fMR-A) were paired together. rTMS was applied to object-selective lateral occipital (LO) and scene-selective transverse occipital sulcus (TOS). Immediately after stimulation, participants underwent fMR-A, and pre- and post-TMS responses were compared. TMS disrupted remote regions revealing connections from LO and TOS to remote object and scene-selective regions in the occipital cortex. In addition, we report important neural correlates regarding the transference of object related information between modalities, from LO to outside the ventral network to parietal and frontal areas.
Open Access
Cognitive-Motor Integration In Normal Aging And Preclinical Alzheimer's Disease: Neural Correlates And Early Detection
(2015-08-28) Hawkins, Kara-Lynn Marie; Sergio, Lauren
The objectives of the studies included in this dissertation were to characterize how the ability to integrate cognition into action is disrupted by both normal and pathological aging, to evaluate the effectiveness of kinematic measures in discriminating between individuals who are and are not at increased Alzheimer’s disease (AD) risk, and to examine the structural and functional neural correlates of cognitive-motor impairment in individuals at increased AD risk. The underlying hypothesis, based on previous research, is that measuring visuomotor integration under conditions that place demands on visual-spatial and cognitive-motor processing may provide an effective behavioural means for the early detection of brain alterations associated with AD risk. To this end, the first study involved testing participants both with and without AD risk factors on visuomotor tasks using a dual-touchscreen tablet. Comparisons between high AD risk participants and both young and old healthy control groups revealed significant performance disruptions in at-risk participants in the most cognitively demanding task. Furthermore, a stepwise discriminant analysis was able to distinguish between high and low AD risk participants with a classification accuracy of 86.4%. Based on the prediction that the impairments observed in high AD risk participants reflect disruption to the intricate reciprocal communication between hippocampal, parietal, and frontal brain regions required to successfully prepare and update complex reaching movements, the second and third studies were designed to examine the underlying structural and functional connectivity associated with cognitive-motor performance. Young adult and both low AD risk and high AD risk older adult participants underwent anatomical, diffusion-weighted, and resting-state functional connectivity scans. These data revealed significant age-related declines in white matter integrity that were more pronounced in the high AD risk group. Decreased functional connectivity in the default mode network (DMN) was also found in high AD risk participants. Furthermore, measures of white matter integrity and resting-state functional connectivity with DMN seed-regions were significantly correlated with task performance. These data support our hypothesis that disease-related disruptions in visuomotor control are associated with identifiable brain alterations, and thus behavioural assessments incorporating both cognition and action together may be useful in identifying individuals at increased AD risk.
Open Access
What's Up with High- and Low-Pitched Sounds? Reference Frames used in the Crossmodal Correspondence Between Auditory Pitch and Visuospatical Height
(2015-08-28) Carnevale, Michael James; Harris, Laurence
Low- and high-pitched sounds are perceptually associated with low and high visuospatial elevations, respectively. The spatial properties of this association are not well understood so two experiments were performed to investigate the following questions. Can low and high tones be used as spatial cues to upright for self-orientation? And what spatial frame(s) of reference is used to perceptually bind these crossmodal features? In experiment 1, participants’ Perceptual Upright (PU) was measured with and without presented auditory orientation cues but there was no effect of sound. In experiment 2, the biasing effects of ascending and descending tones on ambiguous visual motion was measured when presented along both the gravitational and body reference frames, while participants sat either upright or laid on their side. There were effects of sound along both reference frames. A model predicting the axis of optimal association tentatively explains the findings of experiments 1 and 2.
Open Access
Exploring Topological Environments
(2015-08-28) Wang, Hui Victor; Jenkin, Michael
Simultaneous localization and mapping (SLAM) addresses the task of incrementally building a map of the environment with a robot while simultaneously localizing the robot relative to that map. SLAM is generally regarded as one of the most important problems in the pursuit of building truly autonomous mobile robots. This thesis considers the SLAM problem within a topological framework, in which the world and its representation are modelled as a graph. A topological framework provides a useful model within which to explore fundamental limits to exploration and mapping. Given a topological world, it is not, in general, possible to map the world deterministically without resorting to some type of marking aids. Early work demonstrated that a single movable marker was sufficient but is this necessary? This thesis shows that deterministic mapping is possible if both explicit place and back-link information exist in one vertex. Such 'directional lighthouse' information can be established in a number of ways including through the addition of a simple directional immovable marker to the environment. This thesis also explores non-deterministic approaches that map the world with less marking information. The algorithms are evaluated through performance analysis and experimental validation. Furthermore, the basic sensing and locomotion assumptions that underlie these algorithms are evaluated using a differential drive robot and an autonomous visual sensor.
Open Access
Planning Practical Paths in High-Dimensional Space
(2015-08-28) Yang, Jing; Jenkin, Michael R.
Unlike traditional manipulator robots which tend to have small numbers of degree of freedom (DOF), tentacle robots utilize redundant DOFs in order to enhance their ability to deal with complex environments and tasks. However, it also makes the planning and control of such devices extremely difficult. One of the fundamental tasks robots have to perform is planning their motions while avoiding collisions with obstacles in the environment, which is known to be PSPACE-complete in the robot's DOF. As a consequence heuristic sampling-based approaches have been developed to solve high-dimensional real-world path planning problems. A shortcoming of the current sampling-based algorithms is that they can obtain highly non-optimal solutions since they rely upon randomization to explore the search space. Although these planners may find a valid solution, the solutions found are often not practical in that they do not take into account soft application-specific constraints. This thesis integrates soft constraints in addition to the basic geometric or hard constraints in the general path planning process for high DOF robots. The practicality of paths are formulated based on the notion of soft constraints found in the Planning Domain Definition Language 3 (PDDL3). A range of optimization strategies are developed targeted towards user-preferred qualities by integrating soft constraints in the pre-processing (i.e. sampling), planning and post-processing phases of the sampling-based path planners. An auction-based resource allocation approach coordinates competing optimization strategies. This approach uses an adaptive bidding strategy for each optimizer and in each round the optimizer with the best predicted performance is selected. This general coordination system allows for flexibility in both the number and types of the optimizers to be used. Experimental validation with real and simulated tentacle robots demonstrate the effectiveness of the approach.
Open Access
Attention and Sensor Planning in Autonomous Robotic Visual Search
(2015-08-28) Rasouli, Amir; Tsotsos, John K.
This thesis is concerned with the incorporation of saliency in visual search and the development of sensor planning strategies for visual search. The saliency model is a mixture of two schemes that extracts visual clues regarding the structure of the environment and object specific features. The sensor planning methods, namely Greedy Search with Constraint (GSC), Extended Greedy Search (EGS) and Dynamic Look Ahead Search (DLAS) are approximations to the optimal solution for the problem of object search, as extensions to the work of Yiming Ye. Experiments were conducted to evaluate the proposed methods. They show that by using saliency in search a performance improvement up to 75% is attainable in terms of number of actions taken to complete the search. As for the planning strategies, the GSC algorithm achieved the highest detection rate and the best efficiency in terms of cost it incurs to explore every percentage of an environment.
Open Access
Automatic Extraction of Closed Contours Bounding Salient Objects: New Algorithms and Evaluation Methods
(2015-08-28) Movahedi, Vida; Elder, James
The problem under consideration in this dissertation is achieving salient object segmentation of natural images by means of probabilistic contour grouping. The goal is to extract the simple closed contour bounding the salient object in a given image. The method proposed here falls in the Contour Grouping category, searching for the optimal grouping of boundary entities to form an object contour. Our first contribution is to provide both a ground truth dataset and a performance measure for empirical evaluation of salient object segmentation methods. Our Salient Object Dataset (SOD) provides ground truth boundaries of salient objects perceived by humans in natural images. We also psychophysically evaluated 5 distinct performance measures that have been used in the literature and showed that a measure based upon minimal contour mappings is most sensitive to shape irregularities and most consistent with human judgements. In fact, the Contour Mapping measure is as predictive of human judgements as human subjects are of each other. Contour grouping methods often rely on Gestalt cues locally defined on pairs of oriented features. Accurate integration of these local cues with global cues is a challenge. A second major contribution of this dissertation is a novel, effective method for combining local and global cues. A third major contribution in this dissertation is a novel method based on Principal Component Analysis for promoting diversity among contour hypotheses, leading to substantial improvements in grouping performance. To further improve the performance, a multiscale implementation of this method has been studied. A fourth contribution in this dissertation is studying the effect of the multiscale prior on the performance and analysing the method for combining the results obtained in different resolutions. Our final contribution is comparing the performance of univariate distribution models for local cues used by our method with the use of a multivariate mixture model for their joint distribution. We obtain slight improvement by the mixture models. The proposed method has been evaluated and compared with four other state-of-the-art grouping methods, showing considerably better performance on the SOD ground truth dataset.
Open Access
First and Second Order Stereoscopic Processing of Fused and Diplopic Targets
(2015-08-28) Stransky, Debi; Wilcox, Laurie M.
Depth from stereopsis is due to the positional difference between the two eyes, which results in each eye receiving a different view of the world. Although progress has been made in understanding how the visual system processes stereoscopic stimuli, a number of questions remain. The goal of this work was to assess the relationship between the perceptual, the temporal and the 1st- /2nd- order dichotomies of stereopsis and in doing so, determine an appropriate method for measuring depth from large disparities. To this end, stereosensitivity and perceived depth were assessed using 1st- and 2nd- order stimuli over a range of test disparities and conditions. The main contributions of this research are as follows: 1) The sustained/transient dichotomy proposed by Edwards, Pope and Schor (2000) is best considered in terms of the spatial dichotomy proposed by Hess and Wilcox (1994). At large disparities it is not possible to categorize performance based on exposure duration alone; 2) There is not a simple correspondence between Ogle's (1952) patent / qualitative perceptual categories and the 1st- /2nd- order dichotomy proposed by Hess and Wilcox (1994); 3) Quantitative depth is provided by both 1st- and 2nd- order mechanisms in the fused range, but only the 2nd- order signal is used when stimuli are diplopic; 3) The quantitative depth provided by a 2nd- order stimulus scales with envelope size; and 4) The monoptic depth phenomenon may be related to depth from diplopic stimuli, but for conditions tested here when both monoptic depth and 2nd- order stereopsis are available, the latter is used to encode depth percepts. The results reported here expand on earlier work on 1st- and 2nd- order stereopsis and address the issues in the methodologies used to study depth from large disparities. These results are consistent with the widely accepted filter-rectify-filter model of 2nd- order processing, and 1st- and 2nd- order stimuli are likely encoded by disparity-sensitive neurons via a two-stream model (see Wilson, Ferrera, and Yo (1992); Zhou and Baker (1993)).