Psychology (Functional Area: Brain, Behaviour & Cognitive Science)

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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
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
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
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
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
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
The Association Between Musical Training, Bilingualism, and Executive Function
(2015-08-28) Moradzadeh, Linda; Wiseheart, Melody
Previous research has shown far transfer effects of skill training, such as bilingualism and musical training, on executive function. Despite a growing interest in the subject, some areas of higher cognition have been left under- or un-examined. This dissertation presents two papers that investigated whether exposure to bilingualism or musical training was associated with improvements in four specific domains of executive function, including working memory, inhibitory control, task switching, and dual task performance. Results for working memory and inhibition are presented in Paper 1 and those for task switching and dual task performance are reported in Paper 2. Both papers are based on the same sample of participants, which included 153 university students, who were matched on age and socio-economic status. In Paper 1, results demonstrated a musician advantage on working memory and interference suppression tasks, but not on response inhibition. In comparison, bilinguals did not demonstrate advantages on working memory or inhibitory control abilities compared to monolinguals. Moreover, a combined effect of bilingualism and musical training was not found. Similarly, in Paper 2, results demonstrated cognitive advantages in task switching and dual task performance among musicians compared with non-musicians. However, bilinguals did not demonstrate advantages on either construct relative to monolinguals, and additive effects of bilingualism and musical training were not detected. Taken together, the findings further our understanding of the different domains of cognition that are impacted by musical training, including areas, such as dual task performance, that have not been examined thus far. Moreover, the findings support previous research demonstrating associations between musical training and improvements in executive function, while recognizing that associations between bilingualism and executive function may require further investigation.
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)).
Open Access
Remote Effects of OFA Disruption on the Face Perception Network Revealed by Consecutive TMS-FMRI
(2015-08-28) Solomon-Harris, Lily Marissa; Steeves, Jennifer
The face perception system is comprised of a network of connected regions including the middle fusiform gyrus (“fusiform face area” or FFA), the inferior occipital gyrus (“occipital face area” or OFA), and the posterior part of the superior temporal sulcus. These regions are typically active bilaterally but may show right hemisphere dominance. The functional magnetic resonance imaging (fMRI) response of the right FFA is normally attenuated for face stimuli of the same compared to different identities, called fMR-adaptation. The recovery in fMRI signal, or release from fMR-adaptation, for faces of different identities indicates that the neural population comprising the FFA is involved in coding face identity. Patients with prosopagnosia who are unable to visually recognize faces and who show right OFA damage, nonetheless show face-selective activation in the right FFA (Rossion et al., 2003; Steeves et al., 2006). However, the sensitivity to face identity is abnormal in the right FFA and does not show the typical release from adaptation for different face identities (Steeves et al., 2009). This indicates that in these patients the FFA is not differentiating face identity and suggests that an intact right OFA is integral for face identity coding. We used offline repetitive transcranial magnetic stimulation (TMS) to temporarily disrupt processing in the right OFA in healthy subjects. We then immediately performed fMRI to measure changes in blood oxygenation level dependent (BOLD) signal across the face network using a face fMR-adaptation paradigm. We hypothesized that TMS to the right OFA would induce abnormal face identity coding in the right FFA, reflected by a decreased adaptation response. Indeed, activation for different but not same identity faces in the right FFA decreased after TMS was applied to the right OFA compared to sham TMS and TMS to a control site, the nearby object-selective right lateral occipital area (LO). Our findings indicate that TMS to the OFA selectively disrupts face but not butterfly identity coding in both the OFA and FFA. Congruent with mounting evidence from both patients and healthy subjects, here we causally demonstrate the importance of the often-overlooked OFA for normal face identity coding in the FFA.
Open Access
Age Estimation from Children's Faces
(2015-08-28) Harrington, Alexandra Elizabeth; Wilkinson, Frances E.
In this thesis, we addressed the question of whether or not people could estimate age from children’s faces 7 to 11 years of age. We found that undergraduates were able to make accurate relative age judgments for males and females, even in faces as little as two years apart, and that their performance improved as the age differences between the faces being compared increased. They were also able to make accurate absolute age judgments that increased with increasing face age for both genders. We also looked at estimate bias and while estimates were generally low in bias, the bias was in direction of the mean age of the stimuli. Additionally, we found that there is generally an advantage for male faces presented in frontal view. Finally, we looked at one possible factor influencing age estimates– facial expression. It was unlikely that facial expression was a primary cue informing age estimates.
Open Access
The Effect of Professional Ballet Training on Brain Structure: A Tale of Two Fractional Anisotropy Metrics
(2015-08-28) Leger, Charles Stevens; DeSouza, Joseph
This research investigated structural brain changes associated with long-term professional ballet dance training. The primary measure used was fractional anisotropy (FA), a diffusion tensor (DTI) derived index of water molecule diffusion, which putatively quantifies main neural tract efficiency. Dancers had higher FA (p = .062, FWE corrected), which ostensibly reflects greater axonal ability to communicate. Dancers also had differing FA lateralization (p = .038, FWE corrected). Large percentages (30% to 55%) of variability in these metrics were shared by years of dance training, implicating a substantive impact of dance training on brain structure. Other DTI-derived indices where used to help characterize FA (i.e. axial diffusion, radial diffusion, and mean diffusion), and the results implicate enhanced conduction from altered tract properties, perhaps increased myelination. In addition, dancers had greater global grey matter and white matter volume, large percentages in the variability of which were also shared by years of training.
Open Access
The Neural Correlates of Vection: An fMRI Study
(2015-08-28) Kirollos, Ramy; Allison, Robert
Vection is an illusion of visually-induced self-motion in a stationary observer. I used different types of vection stimuli in a functional magnetic resonance imaging (fMRI) study to determine the interaction between cortical visual regions and cortical vestibular regions during vection. My findings suggest that the cingulate sulcus visual area is heavily involved in self-motion processing. The parieto-insular vestibular cortex, showed a significant change in blood oxygenation level dependent signal activity during vection but to a lesser extent than CSv. Behavioural data correlated with the neuroimaging data (in CSv and PIVC) as both show a significant difference when comparing the radial oscillating condition to the radial smooth condition in CSv and PIVC - suggesting a neural correlate of the jitter effect. My results suggest that the brain region of primary importance in the self-motion debate is CSv - a region that has received little attention in the vection literature to date.
Open Access
Context-Dependent Dual Adaptation to Opposing Visuomotor Rotations
(2015-12-16) Ayala, Maria Nadine; Henriques, Densie
When reaching towards objects, the human central nervous system (CNS) can actively compensate for two different perturbations simultaneously (dual adaptation), though this does not simply occur upon presentation. Dual adaptation is made more difficult when the desired trajectories and targets are identical and hence do not cue the impending perturbation. In cases like this, the CNS requires contextual cues in order to predict the dynamics of the environment. Not all cues are effective at facilitating dual adaptation. In two experiments we investigated the efficacy of hand and body posture contextual cues that are intrinsic to the CNS. For the hand posture experiment, we also look at the role of extended training. We found that how people held the tool or oriented their body while reaching is sufficient for concurrently adapting separate visuomotor mappings such that over time, reach errors significantly decrease. Extended practice did not lead to further benefits though.
Open Access
The Effects of Musical Expertise on Sensory Processing
(2016-09-20) Olshansky, Michael Peter; DeSouza, Joseph
The goal of this thesis was to assess sensorimotor musical experience and its impact on the way that individuals perceive and interact with real-world musical stimuli. Experiment #1 investigated multisensory integration in 14 musicians and 10 non-musicians using a two alternative forced-choice (2AFC) discrimination task, and was designed to examine whether musical expertise augmented multisensory enhancement. Musical experience did not alter the outcomes of multisensory integration, but there may be asymmetries between musicians and non-musicians in their use of auditory cues. Experiment #2 was a neuroimaging case study investigating the influence of musical familiarity on the kinesthetic motor imagery of dance accompanied by music in expert dancers. Familiarity resulted in increased hemodynamic responses in the supplementary motor area (SMA) and decreased responses in Heschls gyrus (HG). These findings provide new evidence regarding the influence of musical expertise on sensory processing using real-world complex stimuli. This thesis suggests that expert practice shapes the way experts perceive and interact with their environments, and emphasizes the need for, and challenges of using naturalistic stimuli.
Open Access
Effects of Gaze Position on Touch Localization
(2016-09-20) Pritchett, Lisa Marie; Harris, Laurence
Previous research has shown that the direction of gaze relative to the body affects the perceived location of touch, and has argued that these effects indicate that a gaze-centered reference frame is used for touch localization. In this dissertation I examine a discrepancy in the existing literature: why do different studies report opposite directions of effects when eye and head positions are manipulated separately? I resolve this discrepancy by showing that it is not due to whether eye or head position is manipulated (chapter 2) but is in fact due to the nature of the task (chapter 3). I also find that the effect occurs on the back of the body (chapter 4), a body part that is not normally in view and thus would be less likely to use gaze as a reference point. I test theories for why these effects occur (chapter 5), and find that results are compatible with the perceived location of a touch being attracted towards the location of gaze, at least for perceptual measures. When location was reported by pointing, an action-based measure, I find no effect of gaze direction on touch localization, suggesting that a gaze-independent reference frame is used for action. These behavioral results are complementary to recent neurophysiological and neuroimaging findings indicating that spatial locations are coded in a range of different reference frames, and indicate that gaze-related reference frames are behaviorally relevant in tactile localization.
Open Access
The Impact of Stereoscopic 3-D on Visual Short-Term Memory
(2016-09-20) Zohar, Sarah Rose; Wilcox, Laurie M.
Visual short-term memory has been studied extensively, however nearly all research on this topic has assessed two-dimensional object properties. This is unexpected, given that most individuals perceive the visual environment in three-dimensions. In the experiments reported here, I investigate the stimuli necessary to assess visual short-term memory while eliminating potential confounds: the use of verbal memory to encode visual information, and the unintentional use of mental resources directed at irrelevant aspects of the memory task. I assess the impact of the amount of disparity, and the distribution of elements in depth, on visual short-term memory. Individuals retain simple visual stimuli equivalently when information is displayed in 2-D or 3-D, regardless of how objects are distributed in 3-D. Conversely, ease of encoding does influence visual short-term memory. Tasks that facilitate encoding result in better visual short-term memory performance. The experiments reported show that stereoscopic 3-D does not improve visual short-term memory.
Open Access
Effects of Lateral Motion on Stereoacuity Thresholds for Physically Moving Targets
(2016-09-20) Cutone, Matthew Daniel; Wilcox, Laurie M. Wilcox
The goal of this thesis was to determine the impact of lateral retinal motion on stereoacuity under natural viewing conditions. I found that stereoacuity thresholds remained stable when target velocities varied between 0 and 16 /s. These results do not agree with previous literature (Ramamurthy, Bedell & Patel, 2005) which found that stereoacuity degraded at higher velocities (greater than 3 deg/s). I suggest that depth is acquired very rapidly at target onset when targets are relatively broadband and have not been distorted by motion smear. Subsequent experiments ruled out the potential effects of monocular cues, retinal smear size and inter-stimulus delay enhancing perceived depth. I conclude that artefacts introduced by the graphical displays used by Ramamurthy et al. (2005) were responsible for the observed elevation of thresholds at higher velocities.
Open Access
The Impact of 2-D and 3-D Grouping Cues on Depth From Binocular Disparity
(2016-09-20) Deas, Lesley Margaret; Wilcox, Laurie M.
Stereopsis is a powerful source of information about the relative depth of objects in the world. In isolation, humans can see depth from binocular disparity without any other depth cues. However, many different stimulus properties can dramatically influence the depth we perceive. For example, there is an abundance of research showing that the configuration of a stimulus can impact the percept of depth, in some cases diminishing the amount of depth experience. Much of the previous research has focused on discrimination thresholds; in one example, stereoacuity for a pair of vertical lines was shown to be markedly reduced when these lines were connected to form a rectangle apparently slanted in depth (eg: McKee, 1983). The contribution of Gestalt figural grouping to this phenomenon has not been studied. This dissertation addresses the role that perceptual grouping plays in the recovery of suprathreshold depth from disparity. First, I measured the impact of perceptual closure on depth magnitude. Observers estimated the separation in depth of a pair of vertical lines as the amount of perceptual closure was varied. In a series of experiments, I characterized the 2-D and 3-D properties that contribute to 3-D closure and the estimates of apparent depth. Estimates of perceived depth were highly correlated to the strength of subjective closure. Furthermore, I highlighted the perceptual consequences (both costs and benefits) of a new disparity-based grouping cue that interacts with perceived closure, which I call good stereoscopic continuation. This cue was shown to promote detection in a visual search task but reduces depth percepts compared to isolated features. Taken together, the results reported here show that specific 2-D and 3-D grouping constraints are required to promote recovery of a 3-D object. As a consequence, quantitative depth is reduced, but the object is rapidly detected in a visual search task. I propose that these phenomena are the result of object-based disparity smoothing operations that enhance object cohesion.
Open Access
The Effects of Gravity on Self-Motion Perception
(2016-11-25) Guterman, Pearl Shaina; Allison, Robert
Gravity is the most pervasive force that we encounter. For instance, we observe a variety of objects being accelerated toward the Earth by gravity, but we also experience these forces when we are simply stationaryas gravity is a constant accelerationor when we are ourselves in motion, such as when we are locomoting on foot, driving a vehicle, jumping or skiing. It follows that our ability to successfully navigate our environment must somehow take into account the effects of gravity on our body's motion-detecting sensesa dynamic relationship which changes with self-motion and self-orientation. The goal of this dissertation was to investigate how body orientation relative to gravity influences visual-vestibular interactions in visually-induced perception of self-motion (i.e., vection). Specifically, I examined this relationship by placing observers in varied postures and presenting visual displays simulating forward/backward self-motion with vertical/horizontal viewpoint oscillation, that mimics components produced by head-movements in real self-motion. I found that tilting observers reduced vection and the two viewpoint oscillations similarly enhanced vection, suggesting that current postural and oscillation-based vection findings are best explained by ecology. I also examined the influence of scene structure and alignment of the body and visual motion relative to gravity on vection. Observers in different postures viewed simulated translational self-motion displays consisting of either a single rigid structure or dots. The experimental data showed that vection depended on both posture and the perceived interpretation of the visual scene, indicating that self-motion perception is modulated by high-order cognitive processes. I also found that observers reported illusory tilt of the stimulus when they were not upright. I investigated these observer reports of a posture-dependent perceived stimulus tilt by presenting upright and tilted observers with static and motion stimuli that were tilted from the graviational vertical. Postural-dependent tilt effects were found for both these stimuli and were greater for motion experienced as self-motion than external motion. Taken together, the results of this dissertation demonstrate that our perception of self-motion is influenced by gravity, and by prior experiences and internal mental representations of our visual world.
Open Access
Quantifying Self Perception: Multisensory Temporal Asynchrony Discrimination As A Measure of Body Ownership
(2016-11-25) Hoover, Adria Erin Nicole; Harris, Laurence
There are diffuse and distinct cortical networks involved in the various aspects of body representation that organize information from multiple sensory inputs and resolve conflicts when faced with incongruent situations. This coherence is typically maintained as we maneuver around the world, as our bodies change over the years, and as we gain experience. An important aspect of a congruent representation of the body in the brain is the visual perspective in which we are able to directly view our own body. There is a clear separation of the cortical networks involved in seeing our own body and that of another person. For the projects presented in my dissertation, I used an experimental design in which participants were required to make a multisensory temporal asynchrony discrimination after self-generated movements. I measured sensitivity for visual delay detection between the movement (proprioceptive, efferent and afferent information) and the visual image of that movement under differing visual, proprioceptive, and vestibular conditions. The self-advantage is a signature of body ownership and is characterized by a significantly lower threshold for delay detection for views of the body that are considered self compared to those that are regarded as other. Overall, the results from the collection of studies suggest that the tolerance for temporally matching visual, proprioceptive and efferent copy information that informs about the perceived position of body parts depends on: whether one is viewing ones own body or someone elses; the perspective in which the body is viewed; the dominant hand; and the reliability of vestibular cues which help us situate our body in space. Further, the self-advantage provides a robust measure of body ownership. The experiments provide a window on and support for the malleable nature of the representation of the body in the brain.