24 research outputs found
Unbewusste Modulatoren der somatosensorischen Wahrnehmung
It is intriguing that perception of the same stimulus can vary profoundly from trial to trial. For example, it has been shown in many studies that weak, so-called “near-threshold stimuli” are sometimes consciously perceived and sometimes not. In my thesis, I have been investigating factors which underlie this profound perceptual variability in the somatosensory domain. Together with my colleagues, I performed three studies in which we tested three different types of presumed non-conscious modulators of somatosensory perception.
In the first – behavioral - study, we investigated how the presence of subliminal noise during a peripheral somatosensory stimulation influences perception. Counter-intuitively, we found that peripheral noise can even improve perception of weak somatosensory stimuli. In our interpretation, this occurs most likely due to “stochastic resonance” effects (Study I: Iliopoulos et al. 2014).
In the second – behavioral and EEG - study, we tested the effect of different forms of pulsed subliminal stimulation (single pulses versus pulse trains) on brain rhythms and somatosensory perception. Following-up on previous results of our group, we tested the hypothesis that subliminal pulsed stimulation impairs perception of subsequent stimuli via centrally enhanced Mu rhythm. Interestingly, the main result of this study was that trains of subliminal stimuli indeed inhibited subsequent somatosensory detection, however, - in contrast to our previous findings for single pulses – trains were associated with decreased Mu rhythm. We conclude that central rhythms most likely play a role in mediating the perceptual modulation of peripheral subliminal stimuli, however, the relationship is more complex than previously assumed (Study II: Iliopoulos et al. 2020).
In the third study, we examined the influence of interoceptive signaling, especially from the heart, on somatosensory perception. The hypothesis was that the cardiac phase (systole versus diastole) and the so-called heart-evoked potential (HEP) would modulate somatosensory perception. Indeed, our study showed that somatosensory perception was better during diastole than during systole and detection performance declined as the amplitude of the HEP increased. Our interpretation of the former effect assumes that all events which occur simultaneously with the “pulse” are assumed by the brain to be pulse-synchronous peripheral noise and therefore suppressed. Our interpretation of the latter effect (HEP) assumes that HEP is a marker of the relative balance between interoception and exteroception (Study III: Al et al. 2020).
In conclusion, in the studies which form the basis for my thesis, we have shown that somatosensory perception is modulated by peripheral effects (modes of peripheral stimulation, peripheral noise), central effects (Mu rhythm) and interoceptive signals from the heart. The precise interplay between these modulators is an exciting research topic for future studies.Interessanterweise kann die Wahrnehmung desselben Reizes von Augenblick zu Augenblick so stark variieren, dass dieser manchmal bewusst wahrgenommen wird und manchmal nicht. In meiner Dissertation habe ich Faktoren untersucht, die dieser Wahrnehmungsvariabilität im somatosensorischen (SS) System zugrunde liegen. Mit meinen Kollegen habe ich drei Studien durchgeführt, in denen wir verschiedene mutmaßlich unbewusste Modulatoren der SS-Wahrnehmung untersuchten.
In der ersten Studie untersuchten wir, wie die Wahrnehmung peripherer SS-Reize durch unterschwelliges Rauschen beeinflusst wird. Wir konnten zeigen, dass peripheres Rauschen die Wahrnehmung schwacher Reize verbessert. Dies ist ein Hinweis auf das Vorliegen von "stochastischen Resonanzeffekten" (Studie I: Iliopoulos et al. 2014).
In der zweiten Studie, die neben behavioralen Messungen auch elektroencephalographische (EEG) Messungen umfasste, testeten wir die Auswirkung verschiedener Formen gepulster unterschwelliger elektrischer Fingerstimulationen (Einzelpulse gegen Pulsserien) auf die Wahrnehmung und auf Hirn-rhythmen. Ausgehend von früheren Ergebnissen unserer Arbeitsgruppe überprüften wir, ob repetitive subliminale Stimulationen die Wahrnehmung nachfolgender Reize über einen zentral verstärkten Mu-Rhythmus beeinträchtigen. Das Ergebnis dieser Studie war, dass Serien unterschwelliger Reize tatsächlich die nachfolgende SS-Wahrnehmung hemmten, jedoch - im Gegensatz zu früheren Ergebnissen für Einzelimpulse – die Reizserien mit einem verringerten Mu-Rhythmus verbunden waren. Daraus schließen wir, dass zentrale Rhythmen höchstwahrscheinlich eine Rolle bei der Wahrnehmungsmodulation durch periphere unterschwellige Reize spielen, dass aber der Zusammenhang zwischen beiden komplexer ist als bisher vermutet (Studie II: Iliopoulos et al. 2020).
In der dritten Studie untersuchten wir den Einfluss interozeptiver Signale aus dem Herzen auf die SS-Wahrnehmung. Die Hypothese war, dass die Herzphase und das so genannte Herz-evozierte Potenzial (HEP) die SS-Wahrnehmung modulieren. Wir zeigten, dass die SS-Wahrnehmung während der Diastole besser war als während der Systole und dass die Wahrnehmung in umgekehrtem Verhältnis zur Amplitude des vorausgehenden HEP stand. Für den ersten Effekt legen unsere Daten nahe, dass alle Ereignisse, die zusammen mit der Pulswelle auftreten, vom Gehirn als puls-synchrones peripheres Rauschen angenommen und daher unterdrückt werden. Der zweite Befund wird in Übereinstimmung mit der Literatur am besten dadurch erklärt, dass das HEP ein Marker für das relative Gleichgewicht zwischen Interozeption und Exterozeption darstellt (Studie III: Al et al. 2020).
Zusammenfassend zeigen die Ergebnisse dieser Arbeit, wie die SS-Wahrnehmung durch periphere Effekte (Art der Stimulation, Rauschen), zentrale Effekte (Mu-Rhythmus) und interozeptive Signale des Herzens moduliert wird. Das genaue Zusammenspiel zwischen diesen Modulatoren ist ein spannendes Forschungsthema fĂĽr zukĂĽnftige Studien
Magnetoencephalography for the investigation and diagnosis of Mild Traumatic Brain Injury
Mild Traumatic Brain Injury (mTBI), (or concussion), is the most common type of brain injury. Despite this, it often goes undiagnosed and can cause long term disability—most likely caused by the disruption of axonal connections in the brain. Objective methods for diagnosis and prognosis are needed but clinically available neuroimaging modalities rarely show structural abnormalities, even when patients suffer persisting functional deficits. In the past three decades, new powerful techniques to image brain structure and function have shown promise in detecting mTBI related changes. Magnetoencephalography (MEG), which measures electrical brain activity by detecting magnetic fields outside the head generated by neural currents, is particularly sensitive and has therefore gained interest from researchers. Numerous studies are proposing abnormal low-frequency neural oscillations and functional connectivity—the statistical interdependency of signals from separate brain regions—as potential biomarkers for mTBI. However, typically small sample sizes, the lack of replication between groups, the heterogeneity of the cohorts studied, and the lack of longitudinal studies impedes the adoption of MEG as a clinical tool in mTBI management. In particular, little is known about the acute phase of mTBI.
In this thesis, some of these gaps will be addressed by analysing MEG data from individuals with mTBI, using novel as well as conventional methods. The potential future of MEG in mTBI research will also be addressed by testing the capabilities of a wearable MEG system based on optically pumped magnetometers (OPMs).
The thesis contains three main experimental studies. In study 1, we investigated the signal dynamics underlying MEG abnormalities, found in a cohort of subjects scanned within three months of an mTBI, using a Hidden Markov Model (HMM), as growing evidence suggests that neural dynamics are (in part) driven by transient bursting events. Applying the HMM to resting-state data, we show that previously reported findings of diminished intrinsic beta amplitude and connectivity in individuals with mTBI (compared to healthy controls) can be explained by a reduction in the beta-band content of pan-spectral bursts and a loss in the temporal coincidence of bursts respectively. Using machine learning, we find the functional connections driving group differences and achieve classification accuracies of 98%. In a motor task, mTBI resulted in reduced burst amplitude, altered modulation of burst probability during movement and decreased connectivity in the motor network.
In study 2, we further test our HMM-based method in a cohort of subjects with mTBI and non-head trauma—scanned within two weeks of injury—to ensure specificity of any observed effects to mTBI and replicate our previous finding of reduced connectivity and high classification accuracy, although not the reduction in burst amplitude. Burst statistics were stable over both studies—despite data being acquired at different sites, using different scanners. In the same cohort, we applied a more conventional analysis of delta-band power. Although excess low-frequency power appears to be a promising candidate marker for persistently symptomatic mTBI, insufficient data exist to confirm this pattern in acute mTBI. We found abnormally high delta power to be a sensitive measure for discriminating mTBI subjects from healthy controls, however, similarly elevated delta amplitude was found in the cohort with non-head trauma, suggesting that excess delta may not be specific to mTBI, at least in the acute stage of injury.
Our work highlights the need for longitudinal assessment of mTBI. In addition, there appears to be a need to investigate naturalistic paradigms which can be tailored to induce activity in symptom-relevant brain networks and consequently are likely to be more sensitive biomarkers than the resting state scans used to date. Wearable OPM-MEG makes naturalistic scanning possible and may offer a cheaper and more accessible alternative to cryogenic MEG, however, before deploying OPMs clinically, or in pitch-side assessment for athletes, for example, the reliability of OPM-derived measures needs to be verified. In the third and final study, we performed a repeatability study using a novel motor task, estimating a series of common MEG measures and quantifying the reliability of both activity and connectivity derived from OPM-MEG data. These initial findings—presently limited to a small sample of healthy controls—demonstrate the utility of OPM-MEG and pave the way for this technology to be deployed on patients with mTBI
Attention and Working Memory Deficits in OCD Checking Behaviour
The evidence for memory impairments in obsessive-compulsive disorder (OCD) is mixed (Hermans et al., 2008). For example, findings are inconsistent, whether OCD have poorer memory capacity compared to neuro-typical controls, or whether verbal memory is less affected than visuospatial memory (Muller and Roberts, 2005b). Some evidence (Greisberg and McKay, 2003) pointed to a more subtle interaction with executive dysfunction leading to impaired memory performance. In a review of 58 experiments Harkin and Kessler (2011) argued that rather than classifying memory deficits in OCD by modality, for example verbal vs visuospatial, it is more instructive to classify the experiments by their task demand in terms of Executive function (E), Binding complexity (B) and memory Load (L). Using the EBL classification system in combination with the Baddeley model of working memory (Baddeley 2000) with an episodic buffer, performance in working memory tasks could be better explained in terms of task demands of executive function. For example, working memory (WM) performance of subclinical OCD checkers can be impaired if presented with irrelevant but misleading information during the retention period. The aim of this thesis was firstly, using magnetoencephalography (MEG) and a paradigm designed to provoke executive dysfunction in OCD participants, to measure the neural correlates of deficient working memory processing. Secondly, to use MEG to investigate the neural correlates of attentional bias and executive dysfunction in OCD checking behaviour when engaged in an endogenous attention (Stroop) task. Lastly, using transcranial magnetic stimulation (TMS) to target task relevant brain areas in attempt to affect beneficially the task performance of OCD checker participants engaged in an exogenous attention (Inhibition of Return) task, an endogenous attention (Stroop) task and in the working memory task. Using ecologically valid stimuli that resonate with the checkers’ OCD related concerns, the neuroimaging data revealed different patterns of activity, comparing subclinical OCD checkers with neuro-typical controls. These patterns are consistent with the stimuli provoking deficient executive function in the subclinical checkers. The brain activity recorded was consistent with repeated memory checking and poor suppression of irrelevant stimuli. Efforts to remediate executive dysfunction with TMS were only partially successful. In accord with the EBL classification system, the ecologically valid threat stimuli in combination with the WM and Stroop tasks were successful in exploiting executive dysfunction in subclinical checkers in domains of working memory and endogenous attention. Neural correlates of the impaired processing were measured successfully using MEG
Magnetoencephalography for the investigation and diagnosis of Mild Traumatic Brain Injury
Mild Traumatic Brain Injury (mTBI), (or concussion), is the most common type of brain injury. Despite this, it often goes undiagnosed and can cause long term disability—most likely caused by the disruption of axonal connections in the brain. Objective methods for diagnosis and prognosis are needed but clinically available neuroimaging modalities rarely show structural abnormalities, even when patients suffer persisting functional deficits. In the past three decades, new powerful techniques to image brain structure and function have shown promise in detecting mTBI related changes. Magnetoencephalography (MEG), which measures electrical brain activity by detecting magnetic fields outside the head generated by neural currents, is particularly sensitive and has therefore gained interest from researchers. Numerous studies are proposing abnormal low-frequency neural oscillations and functional connectivity—the statistical interdependency of signals from separate brain regions—as potential biomarkers for mTBI. However, typically small sample sizes, the lack of replication between groups, the heterogeneity of the cohorts studied, and the lack of longitudinal studies impedes the adoption of MEG as a clinical tool in mTBI management. In particular, little is known about the acute phase of mTBI.
In this thesis, some of these gaps will be addressed by analysing MEG data from individuals with mTBI, using novel as well as conventional methods. The potential future of MEG in mTBI research will also be addressed by testing the capabilities of a wearable MEG system based on optically pumped magnetometers (OPMs).
The thesis contains three main experimental studies. In study 1, we investigated the signal dynamics underlying MEG abnormalities, found in a cohort of subjects scanned within three months of an mTBI, using a Hidden Markov Model (HMM), as growing evidence suggests that neural dynamics are (in part) driven by transient bursting events. Applying the HMM to resting-state data, we show that previously reported findings of diminished intrinsic beta amplitude and connectivity in individuals with mTBI (compared to healthy controls) can be explained by a reduction in the beta-band content of pan-spectral bursts and a loss in the temporal coincidence of bursts respectively. Using machine learning, we find the functional connections driving group differences and achieve classification accuracies of 98%. In a motor task, mTBI resulted in reduced burst amplitude, altered modulation of burst probability during movement and decreased connectivity in the motor network.
In study 2, we further test our HMM-based method in a cohort of subjects with mTBI and non-head trauma—scanned within two weeks of injury—to ensure specificity of any observed effects to mTBI and replicate our previous finding of reduced connectivity and high classification accuracy, although not the reduction in burst amplitude. Burst statistics were stable over both studies—despite data being acquired at different sites, using different scanners. In the same cohort, we applied a more conventional analysis of delta-band power. Although excess low-frequency power appears to be a promising candidate marker for persistently symptomatic mTBI, insufficient data exist to confirm this pattern in acute mTBI. We found abnormally high delta power to be a sensitive measure for discriminating mTBI subjects from healthy controls, however, similarly elevated delta amplitude was found in the cohort with non-head trauma, suggesting that excess delta may not be specific to mTBI, at least in the acute stage of injury.
Our work highlights the need for longitudinal assessment of mTBI. In addition, there appears to be a need to investigate naturalistic paradigms which can be tailored to induce activity in symptom-relevant brain networks and consequently are likely to be more sensitive biomarkers than the resting state scans used to date. Wearable OPM-MEG makes naturalistic scanning possible and may offer a cheaper and more accessible alternative to cryogenic MEG, however, before deploying OPMs clinically, or in pitch-side assessment for athletes, for example, the reliability of OPM-derived measures needs to be verified. In the third and final study, we performed a repeatability study using a novel motor task, estimating a series of common MEG measures and quantifying the reliability of both activity and connectivity derived from OPM-MEG data. These initial findings—presently limited to a small sample of healthy controls—demonstrate the utility of OPM-MEG and pave the way for this technology to be deployed on patients with mTBI
A ciência da leitura e a produção acadêmica: caminhos trilhados
Linguistics focuses on the different phenomena of language. In macrolinguistics areas, there
is Psycholinguistics. This subfield researches (de)coding processes of messages with verbal
codes. Thus, one of its influential fields of activity is reading. Reading is one of the most
complex information processing tasks. It begins with the graphemes decoding and it finishes
with the text comprehension. Regarding the assessment of reading, there are several exams
and large-scale tests, such as Pisa, Saeb (Aneb and Anresc/Prova Brasil), ENEM. Alarming
statistics come with the indicators from these evaluative instruments. There are, among
Brazilians, low levels of reading comprehension and marked functional illiteracy rate.
Therefore, this study aimed to research what scientific communication has shared in terms of
knowledge about reading. Specifically, the objectives were synthesize, considering the
psycholinguistic approach of reading research, studies and research with the most recurrent
theme in the reading field evidenced from the electronic communication, in order to
investigate the dimensions and limitations of knowledge about this subject. For this, through
WebQualis system, Qualis A1 and A2 scientific journals with electronic format and with
focuses/scopes related to reading from the areas of (1) Language Arts/Linguistics, (2)
Psychology and (3) Education were selected. With the selected journals and through Capes
Journals Portal, all their volumes and issues from 2011 to 2015 were analyzed. With this,
scientific articles related to reading were mapped. With the mapped articles abstracts, the
recurrent themes in reading in the scientific production were observed. Finally, with the full
articles that had the recurrent theme, the researches results were integrated, synthesizing and
pondering about them. With a critical-reflexive assessment of the data, relevant information
was found. First, on one hand, it was noted that the reading has achieved a stable and upward
space through the electronic communication. On the other one, it was checked that the
contributions of Psychology have a great influence in reading and comprehension research.
Second, it was shown that the most frequent theme in electronic productions is
comprehension. Finally, with the synthesis, it was found that, increasingly, comprehension
topics related to reading neurobiological aspects were empirical and directly investigated. In
addition, there are several studies that propose reading teaching methods as well as strategies
for improving the comprehension, including the use of TICs. Moreover, it was found that
many research results are limited. This is because the comprehension involves several
components – cognitive processes and skills. Researches often focus attention on one or the
other component of it only, and each research fixes a specific methodology design and that
vary considerabably. Regarding the assessment of reading, many of the methodological
apparatus tasks evaluate only the product of comprehension and not its process. In other
words, built mental representations are evaluated and not how the encoding of this text
occurred. Therefore, in short, both the researches advancement in the comprehension field and
several limitations were observed.A LinguĂstica atĂ©m-se aos mais diferentes fenĂ´menos da lĂngua(gem). Nos domĂnios
macrolinguĂsticos, há a PsicolinguĂstica. Essa subárea tem como foco de investigação os
processos de (de)codificação de mensagens de códigos verbais. Assim, um de seus influentes
campos de atuação é o de leitura. A leitura é uma das tarefas de processamento de
informações mais complexas. Ela tem como princĂpio a decodificação grafĂŞmica e como fim a
compreensão textual. Em relação à avaliação da leitura, existem diversos testes e provas em
larga escala, como o Pisa, o Saeb (Aneb e Anresc/Prova Brasil), o ENEM. Com os
indicadores desses instrumentos avaliativos, vĂŞm estatĂsticas alarmantes. Há, entre os
brasileiros, baixos nĂveis de compreensĂŁo leitora e acentuado Ăndice de analfabetismo
funcional. Por conseguinte, este trabalho pretendeu investigar o que a comunicação cientĂfica
tem compartilhado em termos de conhecimento sobre leitura. Especificamente, objetivou-se
sintetizar, considerando a abordagem psicolinguĂstica de investigação da leitura, estudos e
pesquisas cuja temática evidenciada da comunicação eletrônica fosse a mais recorrente no
campo da leitura, a fim de investigar dimensões e limitações do conhecimento a respeito dessa
temática. Para isso, selecionaram-se, por meio do sistema WebQualis, periĂłdicos cientĂficos
Qualis A1 e A2 em formato eletrônico e com focos/escopos relacionados à leitura, das áreas
de (1) Letras/LinguĂstica, (2) Psicologia e (3) Educação. Com os periĂłdicos selecionados e
por meio do Portal de PeriĂłdicos Capes, analisaram-se todos os seus volumes e nĂşmeros de
2011 a 2015, a fim de mapear artigos cientĂficos com assunto em leitura. Com os resumos dos
artigos mapeados, evidenciaram-se temáticas mais recorrentes na produção cientĂfica em
leitura. Por fim, dos artigos completos cuja temática era a mais recorrente, integraram-se
resultados das pesquisas, fazendo-se uma análise, com fins de sĂntese e reflexĂŁo. Da
apreciação crĂtico-reflexiva dos dados, constataram-se relevantes informações. Em primeiro
lugar, de um lado, observou-se que a leitura tem conquistado um estável e ascendente espaço
em meio à comunicação eletrônica. De outro, demonstrou-se que contribuições da Psicologia
tĂŞm forte influĂŞncia na pesquisa de leitura e compreensĂŁo. Em segundo, evidenciou-se que a
compreensĂŁo Ă© a temática mais frequente nas produções eletrĂ´nicas. Por fim, com a sĂntese,
constatou-se que, cada vez mais, se investiga empĂrica e diretamente facetas da compreensĂŁo
em relação às bases neurobiológicas da leitura. Igualmente, há diversas pesquisas que
propõem metodologias de ensino da leitura, bem como estratégias para a melhoria da
compreensão, incluindo a utilização das TICs. Além disso, concluiu-se que muitos resultados
de pesquisas são limitados. Isso porque a compreensão envolve diversos componentes –
processos cognitivos e habilidades. E as pesquisas, muitas vezes, apenas focam a atenção em
um ou em outro componente, alĂ©m de definirem especĂficos e variados designs de
metodologia. Em relação à avaliação da leitura, muitas das tarefas do aparato metodológico
das pesquisas apenas avaliam o produto da compreensĂŁo e nĂŁo o seu processo. Ou seja,
avaliam-se representações mentais construĂdas e nĂŁo como ocorreu a codificação desse texto
na mente do leitor. Por conseguinte, em suma, tanto o avanço de pesquisas no campo de
compreensão quanto, também, diversas limitações ficaram evidentes
Magnetoencephalography
This is a practical book on MEG that covers a wide range of topics. The book begins with a series of reviews on the use of MEG for clinical applications, the study of cognitive functions in various diseases, and one chapter focusing specifically on studies of memory with MEG. There are sections with chapters that describe source localization issues, the use of beamformers and dipole source methods, as well as phase-based analyses, and a step-by-step guide to using dipoles for epilepsy spike analyses. The book ends with a section describing new innovations in MEG systems, namely an on-line real-time MEG data acquisition system, novel applications for MEG research, and a proposal for a helium re-circulation system. With such breadth of topics, there will be a chapter that is of interest to every MEG researcher or clinician
Electrophysiological and behavioural consequences of cross-modal phase resetting
No abstract available
Improving Electro-Magnetic Interference of Embedded Systems Through Jittered-Delay Desynchronization
ICs are required to satisfy always increasing performance needs for modern electronic applications. This results in higher operating frequencies for digital circuits, thus increasing the generated Electro-Magnetic Interference (EMI).
International standards and industrial regulations, in domains such as automotive applications, enforce strict rules about the EMI behavior of electronic systems. Thus, EMI is becoming a major concern for designers, with direct implications on the commercial viability of a product.
In this paper, we apply the desynchronization methodology, down to the physical layout level, to an industrial microprocessor used in automotive applications. The results show that we can both use the advantages from desynchronization, i.e., average case performance and better variability tolerance, and achieve significant EMI reductions, without excessive costs in area
or power consumption. While our paper confirms earlier claims that indeed asynchronous circuits reduce EMI, it also shows clearly that by far the largest EMI gain can be obtained by adding
dynamically varying delays (which in turn cause local clock jittering) on top of desynchronization
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Investigating the function of alpha frequency oscillatory activity
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonA fundamental challenge in modern neuroscience is to understand the role of synchronous oscillatory activity of groups of neurons in information processing. This thesis addressed the problem of how alpha frequency oscillatory activity might help control the flow of information from both the external world and from higher cognitive areas (responsible for inhibitory control, top-down and bottom-up information flow). A series of experiments investigated how alpha neuronal dynamics might aid/control cognition. In order to study the functional significance of alpha frequency oscillatory activity, the effects on performance in cognitive tasks of alpha activity directly elicited using photic stimulation were examined. Initially, we were interested in the role of alpha oscillations in information transfer across cortical areas, which was probed using a numerical Stroop task with every trial preceded by a flicker prime. The incongruent trials of the Stroop task introduce a conflict between competing responses which results in people being slower in responses to the task compared with congruent trials. That slower response has been related to increased communication between conflict processing fronto-parietal and early somatosensory regions. If alpha oscillations improve communication efficiency across the cortex it was predicted that inducing stronger alpha oscillations would affect the performance, (i.e. the Stroop cost would diminish). That hypothesis was tested in a series of three experiments. None of the manipulations (different frequencies, amplitudes induced and alpha phases where the Stroop task was initiated) showed that alpha oscillatory activity reduces the Stroop effect. However, the last task showed that people were faster when the task was preceded by an alpha frequency flicker prime, especially around 10Hz. The fourth experiment built on the well-established phenomena that when alpha activity is elicited in a particular hemisphere it attenuates processing of sensory information in that hemisphere, while the opposite hemisphere, is characterised by increased efficiency of information processing/flow. The study tested whether that could occur within a hemisphere by localised entrainment of part of the visual field. This hypothesis was tested by examining whether it could resolve differences in results previously published by Mathewson et al., (2012) and Spaak et al., (2014). In this study, a target circle was presented at time points after the offset of an alpha flicker prime, such that it was either in or out of phase with the prime. The target was displayed briefly, and then a masking ring appeared around the target location. There were two experimental conditions. First priming occurred at the central target location, and this was expected to inhibit perception at that location, (i.e. the target would be best detected at out of alpha phase time points). In contrast, in the second condition, the target surround area (e.g. the mask location) was stimulated, and this was expected to inhibit perception at that location, (i.e. the mask would be most effective in phase time points and so the target more easily detected). However, in both instances, target detection was best at in-phase time points and attenuated at out of phase time points, in line with Mathewson et al., (2012) results. This gives us some insight into the role of the alpha phase in allowing the external stimuli to be perceived/detected. The fifth experiment tested whether the level of spatial uncertainty of briefly presented target determines the alpha phase position for its best detection. This task used a similar masked circle paradigm as the fourth experiment, but the target could appear at one of two locations either side of fixation, which were both preceded by a flicker prime (either alpha frequency or randomly jittered) and followed by masking rings. The hypothesis was that the optimal alpha phase for target detection depends on whether people are pre-guided (by an arrow cue) to the target location or uncued (a higher level of spatial uncertainty). This hypothesis was again tested by examining whether it could resolve differences in results previously published by Mathewson et al., (2012) and Spaak et al., (2014). This experiment showed that the level of spatial uncertainty of briefly presented target determines the optimal alpha phase for its detection. Targets whose location was not pre-guided were the most likely to be detected when presented at time points out of phase with the entrained alpha prime; targets whose location was pre-guided by a brief arrow were the most likely to be detected when presented at time points in phase with the entrained alpha prime. The sixth experiment used EEG to investigate the neural dynamics underlying the behaviourally tested phenomenon in the previous experiment. Results showed that for targets with a high level of spatial uncertainty, the average alpha power peak was detected earlier in anterior electrodes compared with posterior electrodes, which is consistent with a greater reliance on alpha top-down dynamics. In contrast, for targets at a spatially cued location, the average alpha power peak was detected earlier at posterior electrodes, which suggests a greater reliance on bottom-up alpha neuronal dynamics. In summary, this thesis confirmed that mid-alpha phase determines the probability of detection of a briefly presented target. Also, it showed that optimal alpha phase for detecting briefly presented target would differ depending on the level of spatial uncertainty of that target. Targets at non-predictable locations are more likely to be detected at a trough in the phase of alpha activity whilst those at cued locations are most likely to be detected in-phase. Hence, perception depends not only on the internal neuronal alpha dynamics but also on the type of the visual percept. This difference may highlight the role of two different neuronal alpha sources which dominate in the different scenarios. When the target location is uncertain, top-down alpha dynamics dominate. However, when the target location is pre-guided, bottom-up alpha dynamics dominate