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Modulation of sensory processing during simultaneous bimodal stimulation: Effects of sensorimotor integrationMeehan, Sean K. January 2008 (has links)
Illusions such as the McGurk (McGurk and MacDonald, 1976) and ventriloquist (Radeau and Bertelson, 1974) effects or visual capture sensorimotor deficits (Holmes et al., 2004) demonstrate that our perception of and interaction with our environment is shaped by our ability to extract and integrate relevant sensory inputs across multiple modalities. Physiologically extraction occurs through a mechanism that facilitates relevant sensory representations and/or suppresses irrelevant ones within secondary sensory cortices, areas traditionally viewed as “modality-specific” cortex. This mechanism is commonly called “attention”. The purpose of the current thesis is to investigate the influence of motor requirements upon attentional modulation of sensory processing. It was hypothesized that different task demands associated with sensory processing for continuous movement rather than perception would result in earlier loci and/or different mechanisms of attentional modulation. Two studies used functional magnetic resonance imaging (fMRI) to investigate intermodal influences between a vibrotactile and visuospatial stimulus during a continuous sensorimotor task. These studies revealed that attention to vibrotactile stimulation guiding a continuous movement resulted in decreased activation in primary somatosensory cortex (S1) relative to when the same stimulus was an irrelevant distracter. This was regardless of the spatial or temporal properties of the two modalities. In a third study, somatosensory evoked potentials (SEPs) demonstrated that somatosensory processing is influenced as early as arrival to S1 from thalamic-cortical projections, however, SEPs did not demonstrate decreased activation during vibrotactile tracking. A fourth study using transcranial magnetic stimulation (TMS) confirmed differential excitability of S1 dependent upon whether the same sensory stimulus was used for perception or to guide a continuous sensorimotor transformation. Finally, a fifth study using behavioral measures demonstrated that the intramodal signal to noise ratio is an important factor in determining intermodal influence. This thesis provides insight into the influence of motor requirements upon sensory processing and demonstrates its importance in understanding how information is extracted from our environment. Understanding this has important implications for the interpretation/development of future work investigating intermodal influences upon sensory-processing.
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The Influence of Study Context on Recollection: Cognitive, Neural, and Age-Related ProcessesSkinner, Erin I. January 2009 (has links)
This thesis examines how the context in which an item is studied affects the phenomenological experience of the rememberer. Previous research has extensively studied how the match between study and test context affect subsequent memory performance; however, little work has attempted to examine how visual context information provided at study affects later recollection when that context information is not re-presented at retrieval. In particular, the quality of the memory retrieved may be enhanced when highly meaningful visual context information is provided at study. In each of seven experiments in the current thesis, participants studied words presented with context information high or low in meaningful content, and on a later recognition memory test made a Remember, Know, or New response to the words presented alone. Experiment 1 showed that participants had better overall memory, specifically recollection, for words studied with pictures of intact as opposed to scrambled faces. In Experiment 2, these results were replicated and recollection was shown to be higher for words studied with versus without pictures of faces. Experiment 3 showed that participants had higher memory performance, and recollection in particular, for words studied with upright compared to inverted faces. In Experiment 4, participants showed equivalent memory for words studied with novel or familiar faces. These results suggest that recollection benefits when visual context information high in meaningful content accompanies study words, and that this benefit is not related to the novelty of the context.
To further test the claim that participants engage in elaborative processes at study to bind item and context information, improving subsequent recollection, the subsequent set of experiments examined how normal, healthy aging affects participants’ ability to use context information provided at study to benefit subsequent recollection. Older adults have been shown to experience deficits both in memory for context and in recollection, suggesting that they might fail to use context effectively to increase recollection, in contrast to younger adults. Experiment 5 found that younger, but not older, adults showed higher recollection for words studied with faces as compared to rectangles. To determine the type of cognitive processing required to obtain recollection benefits, and to examine whether instruction could alleviate age-related deficits, in Experiment 6, the type of processing engaged during the encoding of context-word pairs was manipulated. Younger and older adults studied words presented with a picture of a face under a surface feature or binding feature instruction condition. Both age groups showed higher recollection in the binding than surface instruction condition. Results suggest that older adults do not spontaneously engage in the processes required to boost recollection when visual context information is provided at study, although instructional manipulation during encoding lessens this deficit. This is in line with the Associative Deficit Hypothesis (Naveh-Benjamin, 2000), suggesting that older adults’ recollection deficit involves a specific difficulty in binding item and context information.
The final experiment used functional Magnetic Resonance Imaging (fMRI) to examine the neural correlates of recollection, specifically testing the hypothesis that sensory-specific reactivation of context information occurs during item recollection. In Experiment 7, brain activation for Remember responses given to words studied with and without meaningful context information was compared. Behaviourally, 8 of the 14 participants showed a higher proportion of Remember responses to words studied with faces than scrambled faces, and 6 did not. Whole brain analysis showed that, for only those participants who showed higher memory performance for words studied with faces, activation in the fusiform gyrus and hippocampus was higher, and a region-of-interest analysis showed increased activation in the functionally-defined FFA (identified in a localizer task), for Remember responses given to words studied with faces compared to scrambled faces. A regression analysis additionally showed that activation in the fusiform gyrus increased as the relative recollection benefit for words studied with meaningful (face) compared to non-meaningful (scrambled face) context information increased across participants. Results suggest that encoding context can influence the pattern of recollection responses on a recognition task and that sensory-specific reactivation is related to behavioural performance. The findings of these experiments suggest that participants can use context information high in meaningful content at study to improve subsequent recollection and I suggest that this involves the use of elaborative processes at encoding that integrates item and meaningful contexts. Such recollection benefits can also be observed in older adults when they are provided experimental instructions to bind item and context at encoding. In addition, the brain regions used to process context information are reactivated at retrieval and, importantly, that this neural pattern determines whether a boost in recollection, from the encoding manipulation, is observed. Participants can thus use context information provided at study to boost subsequent recollection, and I suggest that this involves cognitive processes that bind item and context information at encoding and the reactivation of sensory-specific brain regions at retrieval.
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Investigating Spatial Working Memory and Saccadic Remapping Processes in Healthy Young and Elderly ParticipantsGoldberg, Lana January 2009 (has links)
Additional cognitive deficits, including impairments in spatial working memory and/or saccadic remapping processes, have recently been implicated in unilateral neglect – a neurological condition classically characterized as a disorder of attention. The interactions between saccadic remapping and three memory processes (position memory, object memory and object-location binding) were investigated in healthy young (n=27) and elderly (n=20) participants to establish a baseline of comparison for future use with neglect patients and to study the effects of aging on these processes. In a computerized task, participants were instructed to first detect a target, and then hold in memory either its position, identity or both over a delay period. Subsequently, participants were tested on their memory for that particular task. The saccadic remapping component was introduced at the onset of the delay period with the fixation cross shifting either to the left, or right, requiring participants to remap the visual array into either right or left space, or remaining in the centre of the screen (i.e., no remapping condition). In the position memory and object-location binding task, a consistent cost to memory performance was found when remapping right only for the young participants. Overall the elderly did not perform any of the tasks involving a position memory component as well as the young participants and showed spatial asymmetries in the target detection task. The lack of an effect of remapping in the elderly group may be due to a general decrement in performance. These results are discussed in terms of hemispheric asymmetries and cognitive theories of aging.
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RELPH: A Computational Model for Human Decision MakingMohammadi Sepahvand, Nazanin January 2013 (has links)
The updating process, which consists of building mental models and adapting them to the changes occurring in the environment, is impaired in neglect patients. A simple rock-paper-scissors experiment was conducted in our lab to examine updating impairments in neglect patients. The results of this experiment demonstrate a significant difference between the performance of healthy and brain damaged participants. While healthy controls did not show any difficulty learning the computer’s strategy, right brain damaged patients failed to learn the computer’s strategy. A computational modeling approach is employed to help us better understand the reason behind this difference and thus learn more about the updating process in healthy people and its impairment in right brain damaged patients. Broadly, we hope to learn more about the nature of the updating process, in general. Also the hope is that knowing what must be changed in the model to “brain-damage” it can shed light on the updating deficit in right brain damaged patients. To do so I adapted a pattern detection method named “ELPH” to a reinforcement-learning human decision making model called “RELPH”. This model is capable of capturing the behavior of both healthy and right brain damaged participants in our task according to our defined measures. Indeed, this thesis is an effort to discuss the possible differences among these groups employing this computational model.
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Visual Inputs and Motor Outputs as Indivduals Walk Through Dynamically Changing EnvironmentsCinelli, Michael 24 August 2006 (has links)
Walking around in dynamically changing environments require the integration of three of our sensory systems: visual, vestibular, and kinesethic. Vision is the only modality of these three sensory systems that provides information at a distance for proactively controlling locomotion (Gibson, 1958). The visual system provides information about self-motion, about body position and body segments relative to one another and the environment, and environmental information at a distance (Patla, 1998). Gibson (1979) developed the idea that everyday behaviour is controlled by perception-action coupling between an action and some specific information picked up from the optic flow that is generated by that action. Such that visual perception guides the action
required to navigate safely through an environment and the action in turn alters perception. The objective of my thesis was to determine how well perception and action are coupled when approaching and walking through moving doors with dynamically changing apertures. My first two studies were grouped together and here I found that as the level of threat increased, the parameters of control changed and not the controlling mechanism. The two dominant action control parameters observed were a change in approach velocity and a change in posture (i.e. shoulder rotation). These findings add to previous work done in this area using a similar set-up in virtual reality,
where after much practice participants increased success rate by decreasing velocity prior to crossing the doors. In my third study I found that visual fixation patterns and action parameters were similar when the location of the
aperture was predictable and when it was not. Previous work from other researchers has shown that vision and a subsequent action are tightly coupled with a latency of about 1second. I have found that vision only tightly
couples action when a specific action is required and the threat of a collision increases. My findings also point in the same direction as previous work that has shown that individuals look where they are going. My last study
was designed to determine if we go where we are looking. Here I found that action does follow vision but is only loosely correlated. The most important and common finding from all the studies is that at 2 seconds prior to crossing the moving doors (any type of movement) vision seems to have the most profound effect on action. At this time variability in action is significantly lower than at prior times. I believe that my findings will help to understand how individuals use vision to modify actions in order to avoid colliding with other people or other moving objects within the environment. And this knowledge will help elderly individuals to be better able to cope with walking
in cluttered environments and avoid contacting other objects.
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Subtle Effects of Sleepiness on Electrocortical Indices of Attentional Resources and Performance MonitoringMurphy, Timothy Ian 02 February 2007 (has links)
In this dissertation, the effect of mild sleep deprivation on attentional allocation and performance monitoring was investigated using a variety of event-related potential (ERP) paradigms with ecologically realistic periods of sleep deprivation. Seventeen female young adults completed several tasks under alert and sleepy conditions, after 3 and 20 hours of wakefulness, respectively. Objective behavioural measures of response times and error rates indicated virtually no decrements that could be attributed exclusively to sleepiness; however, there were consistent alterations in the ERPs indicative of subtly reduced attentional resources and performance monitoring.
The first study (Chapter 2) examined the effect of distraction on the P300, an ERP component related to attention and stimulus processing. Participants performed an auditory oddball task with and without a secondary visual working memory task. Response times (RTs) and P300 amplitudes were affected by the addition of the secondary working memory task. However, an interaction showed that the P300 latency was significantly increased by the secondary task only in the sleepy condition, indicating that processing speed is impaired by a secondary task only when the participant is sleepy. The next study (Chapter 3) used a Go/NoGo contingent negative variation (CNV) task. The CNV is reflective of sustained attention, and is known to be associated with frontal lobe functioning. This task was performed twice, with and without a financial incentive for fast responses, to assess the effect of motivation. The P300 amplitude to the first stimulus and CNV prior to the second were clearly larger to Go stimuli for both levels of alertness when the participant was motivated by the financial incentive. However, with no incentive in the sleepy condition, there was reduced differentiation of the two types of stimuli, indicating a reduced ability to discriminate between important and less important information.
In chapters 4 and 5, performance monitoring was examined using two tasks, the Eriksen Flanker task and the Anti-Saccade task, producing an ERP related to errors with two basic components: the error-negativity (Ne/ERN) and error-positivity (Pe), thought to be related to error recognition and error evaluation, respectively. In both data sets, the amplitude of the Ne/ERN was not significantly reduced by sleep deprivation, but the amplitude of the Pe was. In addition, smaller anti-saccade errors produced reduced Ne/ERN amplitudes compared to larger anti-saccade errors. Another marker of performance monitoring is post-error slowing, which was present in the flanker task only during the alert condition. These results indicate that error detection or recognition (Ne/ERN) appears to be relatively preserved during sleep deprivation, but further error evaluation (Pe) and compensation (post-error slowing) are impaired.
Taken together, the findings demonstrate that even mild sleep deprivation has a subtle but reliable effect on electrocortical activity associated with attention and performance monitoring despite an absence of behavioural changes, indicating deleterious effects before behavioural changes are observed. Therefore, relying on behavioural tests to determine at what point an individual becomes unsafe to operate machinery or perform various tasks may be misleading.
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Grapheme-Colour Synaesthesia Influences Overt Visual AttentionCarriere, Jonathan Scott Andrew January 2007 (has links)
Synaesthesia is a fascinating condition in which ordinary stimuli elicit extraordinary sensory experiences. For example, specific tastes may elicit unusual tactile sensations and standard black letters may elicit highly specific colour experiences. These unusual experiences have been shown to have substantial impact on cognition, emotion, perception, and covert attention. Two experiments are presented which show that synaesthesia also influences overt visual attention. In these experiments two grapheme-colour synaesthetes viewed coloured letters while their eye movements were tracked. Letters were presented in colours that were either congruent or incongruent with the synaesthetes' colours. Eye tracking analysis showed that synaesthetes exhibited a colour congruity bias – a propensity to fixate congruently coloured letters more often and for longer durations than incongruently coloured letters – in a naturalistic free viewing task. In a more structured visual search task, this congruity bias caused synaesthetes to rapidly fixate and identify congruently coloured target letters, but led to problems in identifying incongruently coloured target letters. The results are discussed in terms of their implications for perception in synaesthesia.
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ATTENTION AND THE PARIETAL CORTEX: INVESTIGATIONS OF SPATIAL NEGLECT, OPTIC ATAXIA, AND THE INFLUENCE OF PRISM ADAPTATION ON ATTENTIONStriemer, Christopher 21 April 2008 (has links)
Some authors have argued that the primary function of the posterior parietal cortex is to control visual attention and awareness, whereas others have argued that the posterior parietal cortex is specialized for controlling actions. The purpose of the present thesis was to examine the influence of prism adaptation – a visuomotor adaptation technique – on visual attention deficits in patients with lesions of parietal cortex. Lesions to dorsal regions of the posterior parietal cortex lead to optic ataxia – a disorder in which visually guided reaching is disrupted. In contrast lesions to ventral (i.e. inferior) regions of the posterior parietal cortex of the right hemisphere lead to spatial neglect – a disorder in which patients are unaware of people or objects in contralesional (left) space. Chapter 1 presents an overview of the organization of the posterior parietal cortex, as well as an introduction to the disorders of spatial neglect and optic ataxia and the use of prism adaptation as a treatment for spatial neglect. Chapter 2 examined the influence of prism adaptation on attentional deficits in patients with right brain damage. Results demonstrated that prism adaptation reduced both the disengage deficit and the rightward attentional bias, two of the classic attentional deficits in neglect. Chapter 3 investigated the role of the dorsal posterior parietal cortex in controlling both reflexive and voluntary attention in two patients with optic ataxia. Lesions to the dorsal posterior parietal cortex led to both a disengage deficit and a rightward attentional bias, similar to patients with neglect, even though neither of the patients had any clinical symptoms of neglect. Contrary to previous work these results indicated that dorsal portions of the posterior parietal cortex – a region not commonly damaged in neglect – are important for controlling the orienting and reorienting of both reflexive and voluntary attention. Furthermore, these results indicated that optic ataxia is not purely a visuomotor disorder that is independent of any perceptual or attentional deficits as was previously assumed. Based on the results of Chapters 2 and 3 it was hypothesized that the beneficial effects of prism adaptation on attention may operate via the superior parietal lobe, a region which is typically undamaged in neglect, and is known to be important for controlling attention and action. Chapter 4 provided support for this hypothesis by demonstrating that a patient with lesions to the superior parietal lobe, who had the same attentional deficits as the right brain damaged patients tested in Chapter 2, failed to demonstrate any beneficial effects of prism adaptation on his attentional performance. Specifically, prism adaptation had no influence on his disengage deficit or his rightward attentional bias. Therefore, these data provide direct evidence that the beneficial effects of prisms on attention rely, at least in part, on the superior parietal lobe. Finally, Chapter 5 concludes with a summary of the research findings from the present thesis, and puts forward a new theory to conceptualize the mechanisms underlying the beneficial effects of prisms in patients with neglect.
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Modulation of sensory processing during simultaneous bimodal stimulation: Effects of sensorimotor integrationMeehan, Sean K. January 2008 (has links)
Illusions such as the McGurk (McGurk and MacDonald, 1976) and ventriloquist (Radeau and Bertelson, 1974) effects or visual capture sensorimotor deficits (Holmes et al., 2004) demonstrate that our perception of and interaction with our environment is shaped by our ability to extract and integrate relevant sensory inputs across multiple modalities. Physiologically extraction occurs through a mechanism that facilitates relevant sensory representations and/or suppresses irrelevant ones within secondary sensory cortices, areas traditionally viewed as “modality-specific” cortex. This mechanism is commonly called “attention”. The purpose of the current thesis is to investigate the influence of motor requirements upon attentional modulation of sensory processing. It was hypothesized that different task demands associated with sensory processing for continuous movement rather than perception would result in earlier loci and/or different mechanisms of attentional modulation. Two studies used functional magnetic resonance imaging (fMRI) to investigate intermodal influences between a vibrotactile and visuospatial stimulus during a continuous sensorimotor task. These studies revealed that attention to vibrotactile stimulation guiding a continuous movement resulted in decreased activation in primary somatosensory cortex (S1) relative to when the same stimulus was an irrelevant distracter. This was regardless of the spatial or temporal properties of the two modalities. In a third study, somatosensory evoked potentials (SEPs) demonstrated that somatosensory processing is influenced as early as arrival to S1 from thalamic-cortical projections, however, SEPs did not demonstrate decreased activation during vibrotactile tracking. A fourth study using transcranial magnetic stimulation (TMS) confirmed differential excitability of S1 dependent upon whether the same sensory stimulus was used for perception or to guide a continuous sensorimotor transformation. Finally, a fifth study using behavioral measures demonstrated that the intramodal signal to noise ratio is an important factor in determining intermodal influence. This thesis provides insight into the influence of motor requirements upon sensory processing and demonstrates its importance in understanding how information is extracted from our environment. Understanding this has important implications for the interpretation/development of future work investigating intermodal influences upon sensory-processing.
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The Influence of Study Context on Recollection: Cognitive, Neural, and Age-Related ProcessesSkinner, Erin I. January 2009 (has links)
This thesis examines how the context in which an item is studied affects the phenomenological experience of the rememberer. Previous research has extensively studied how the match between study and test context affect subsequent memory performance; however, little work has attempted to examine how visual context information provided at study affects later recollection when that context information is not re-presented at retrieval. In particular, the quality of the memory retrieved may be enhanced when highly meaningful visual context information is provided at study. In each of seven experiments in the current thesis, participants studied words presented with context information high or low in meaningful content, and on a later recognition memory test made a Remember, Know, or New response to the words presented alone. Experiment 1 showed that participants had better overall memory, specifically recollection, for words studied with pictures of intact as opposed to scrambled faces. In Experiment 2, these results were replicated and recollection was shown to be higher for words studied with versus without pictures of faces. Experiment 3 showed that participants had higher memory performance, and recollection in particular, for words studied with upright compared to inverted faces. In Experiment 4, participants showed equivalent memory for words studied with novel or familiar faces. These results suggest that recollection benefits when visual context information high in meaningful content accompanies study words, and that this benefit is not related to the novelty of the context.
To further test the claim that participants engage in elaborative processes at study to bind item and context information, improving subsequent recollection, the subsequent set of experiments examined how normal, healthy aging affects participants’ ability to use context information provided at study to benefit subsequent recollection. Older adults have been shown to experience deficits both in memory for context and in recollection, suggesting that they might fail to use context effectively to increase recollection, in contrast to younger adults. Experiment 5 found that younger, but not older, adults showed higher recollection for words studied with faces as compared to rectangles. To determine the type of cognitive processing required to obtain recollection benefits, and to examine whether instruction could alleviate age-related deficits, in Experiment 6, the type of processing engaged during the encoding of context-word pairs was manipulated. Younger and older adults studied words presented with a picture of a face under a surface feature or binding feature instruction condition. Both age groups showed higher recollection in the binding than surface instruction condition. Results suggest that older adults do not spontaneously engage in the processes required to boost recollection when visual context information is provided at study, although instructional manipulation during encoding lessens this deficit. This is in line with the Associative Deficit Hypothesis (Naveh-Benjamin, 2000), suggesting that older adults’ recollection deficit involves a specific difficulty in binding item and context information.
The final experiment used functional Magnetic Resonance Imaging (fMRI) to examine the neural correlates of recollection, specifically testing the hypothesis that sensory-specific reactivation of context information occurs during item recollection. In Experiment 7, brain activation for Remember responses given to words studied with and without meaningful context information was compared. Behaviourally, 8 of the 14 participants showed a higher proportion of Remember responses to words studied with faces than scrambled faces, and 6 did not. Whole brain analysis showed that, for only those participants who showed higher memory performance for words studied with faces, activation in the fusiform gyrus and hippocampus was higher, and a region-of-interest analysis showed increased activation in the functionally-defined FFA (identified in a localizer task), for Remember responses given to words studied with faces compared to scrambled faces. A regression analysis additionally showed that activation in the fusiform gyrus increased as the relative recollection benefit for words studied with meaningful (face) compared to non-meaningful (scrambled face) context information increased across participants. Results suggest that encoding context can influence the pattern of recollection responses on a recognition task and that sensory-specific reactivation is related to behavioural performance. The findings of these experiments suggest that participants can use context information high in meaningful content at study to improve subsequent recollection and I suggest that this involves the use of elaborative processes at encoding that integrates item and meaningful contexts. Such recollection benefits can also be observed in older adults when they are provided experimental instructions to bind item and context at encoding. In addition, the brain regions used to process context information are reactivated at retrieval and, importantly, that this neural pattern determines whether a boost in recollection, from the encoding manipulation, is observed. Participants can thus use context information provided at study to boost subsequent recollection, and I suggest that this involves cognitive processes that bind item and context information at encoding and the reactivation of sensory-specific brain regions at retrieval.
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