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Exploring the Impact of Target Eccentricity and Task Difficulty on Covert Visual Spatial Attention and Its Implications for Brain Computer Interfacing  [PDF]
Linsey Roijendijk, Jason Farquhar, Marcel van Gerven, Ole Jensen, Stan Gielen
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0080489
Abstract: Objective Covert visual spatial attention is a relatively new task used in brain computer interfaces (BCIs) and little is known about the characteristics which may affect performance in BCI tasks. We investigated whether eccentricity and task difficulty affect alpha lateralization and BCI performance. Approach We conducted a magnetoencephalography study with 14 participants who performed a covert orientation discrimination task at an easy or difficult stimulus contrast at either a near (3.5°) or far (7°) eccentricity. Task difficulty was manipulated block wise and subjects were aware of the difficulty level of each block. Main Results Grand average analyses revealed a significantly larger hemispheric lateralization of posterior alpha power in the difficult condition than in the easy condition, while surprisingly no difference was found for eccentricity. The difference between task difficulty levels was significant in the interval between 1.85 s and 2.25 s after cue onset and originated from a stronger decrease in the contralateral hemisphere. No significant effect of eccentricity was found. Additionally, single-trial classification analysis revealed a higher classification rate in the difficult (65.9%) than in the easy task condition (61.1%). No effect of eccentricity was found in classification rate. Significance Our results indicate that manipulating the difficulty of a task gives rise to variations in alpha lateralization and that using a more difficult task improves covert visual spatial attention BCI performance. The variations in the alpha lateralization could be caused by different factors such as an increased mental effort or a higher visual attentional demand. Further research is necessary to discriminate between them. We did not discover any effect of eccentricity in contrast to results of previous research.
A Role of Eye Vergence in Covert Attention  [PDF]
Maria Solé Puig, Laura Pérez Zapata, J. Antonio Aznar-Casanova, Hans Supèr
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0052955
Abstract: Covert spatial attention produces biases in perceptual and neural responses in the absence of overt orienting movements. The neural mechanism that gives rise to these effects is poorly understood. Here we report the relation between fixational eye movements, namely eye vergence, and covert attention. Visual stimuli modulate the angle of eye vergence as a function of their ability to capture attention. This illustrates the relation between eye vergence and bottom-up attention. In visual and auditory cue/no-cue paradigms, the angle of vergence is greater in the cue condition than in the no-cue condition. This shows a top-down attention component. In conclusion, observations reveal a close link between covert attention and modulation in eye vergence during eye fixation. Our study suggests a basis for the use of eye vergence as a tool for measuring attention and may provide new insights into attention and perceptual disorders.
Counterproductive Effect of Saccadic Suppression during Attention Shifts  [PDF]
Alexandre Zénon, Brian D. Corneil, Andrea Alamia, Nabil Filali-Sadouk, Etienne Olivier
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086633
Abstract: During saccadic eye movements, the processing of visual information is transiently interrupted by a mechanism known as “saccadic suppression” [1] that is thought to ensure perceptual stability [2]. If, as proposed in the premotor theory of attention [3], covert shifts of attention rely on sub-threshold recruitment of oculomotor circuits, then saccadic suppression should also occur during covert shifts. In order to test this prediction, we designed two experiments in which participants had to orient towards a cued letter, with or without saccades. We analyzed the time course of letter identification score in an “attention” task performed without saccades, using the saccadic latencies measured in the “saccade” task as a marker of covert saccadic preparation. Visual conditions were identical in all tasks. In the “attention” task, we found a drop in perceptual performance around the predicted onset time of saccades that were never performed. Importantly, this decrease in letter identification score cannot be explained by any known mechanism aligned on cue onset such as inhibition of return, masking, or microsaccades. These results show that attentional allocation triggers the same suppression mechanisms as during saccades, which is relevant during eye movements but detrimental in the context of covert orienting.
Covert Shift of Attention Modulates the Ongoing Neural Activity in a Reaching Area of the Macaque Dorsomedial Visual Stream  [PDF]
Claudio Galletti,Rossella Breveglieri,Markus Lappe,Annalisa Bosco,Marco Ciavarro,Patrizia Fattori
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0015078
Abstract: Attention is used to enhance neural processing of selected parts of a visual scene. It increases neural responses to stimuli near target locations and is usually coupled to eye movements. Covert attention shifts, however, decouple the attentional focus from gaze, allowing to direct the attention to a peripheral location without moving the eyes. We tested whether covert attention shifts modulate ongoing neuronal activity in cortical area V6A, an area that provides a bridge between visual signals and arm-motor control.
Covert orienting visual attention in full remitted single manic patients  [cached]
Majid Barekatain,Mohammad Haghighi,Leila Jahangard,Farzad Ranjkesh
Journal of Research in Medical Sciences , 2008,
Abstract: BACKGROUND: Attentional disturbances in Bipolar I Disorder (BID) have been increasingly reported but the majority of studies have not identified a model emphasizing component operations involved in attentional processes. In this study we sought to assess elementary attentional operations using the Posner paradigm for covert orienting of visuospatial attention, with and without cues, to dissect levels of attentional impairment. METHODS: The study was carried out with 11 fully remitted BID single manic episode patients and 11 age-matched normal control subjects. The Hamilton Depression Rating Scale (HDRS), Young Mania Rating Scale (YMRS) and Covert Orienting of Visuospatial Attention Task (COVAT) were administered. Reaction Times (RT) on the Posner task were examined with a multivariate approach by an Analysis of Variance (ANOVA) for repeated measures with Group as the between-subject factor and Stimulus Onset Asynchrony (SOA), Cue, and Visual Field as the within subject factors. RESULTS: The main effects involved Group, Cue, and SOA as well as interactions of Cue by SOA and SOA by Group. There was neither detectable effect of visual field, nor interactions involving visual field. The Group by Cue did not show a main effect. There was no abnormality in the covert orienting in patients (i.e., Group by Cue by SOA by FIELD). RTs in the valid cues were significantly faster than the RTs in the invalid cues in the both groups. Only SOA had a main effect on the reaction time differences between invalid and valid cues. CONCLUSIONS: The main finding is that BID patients are generally slower compared to controls; however, the slowing is most pronounced at short SOA, suggesting that they are slower to initiate information processing following the cue. Interestingly, BID patients still show a cueing effects (valid RTs < invalid RTs) at short SOAs, suggesting that the RT deficit does not have any relationship with orienting attention, but rather is a deficit in general arousal. KEY WORDS: Attention, covert orienting, full remission, mania.
The Pupillary Light Response Reveals the Focus of Covert Visual Attention  [PDF]
Sebastiaan Math?t, Lotje van der Linden, Jonathan Grainger, Fran?oise Vitu
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0078168
Abstract: The pupillary light response is often assumed to be a reflex that is not susceptible to cognitive influences. In line with recent converging evidence, we show that this reflexive view is incomplete, and that the pupillary light response is modulated by covert visual attention: Covertly attending to a bright area causes a pupillary constriction, relative to attending to a dark area under identical visual input. This attention-related modulation of the pupillary light response predicts cuing effects in behavior, and can be used as an index of how strongly participants attend to a particular location. Therefore, we suggest that pupil size may offer a new way to continuously track the focus of covert visual attention, without requiring a manual response from the participant. The theoretical implication of this finding is that the pupillary light response is neither fully reflexive, nor under complete voluntary control, but is instead best characterized as a stereotyped response to a voluntarily selected target. In this sense, the pupillary light response is similar to saccadic and smooth pursuit eye movements. Together, eye movements and the pupillary light response maximize visual acuity, stabilize visual input, and selectively filter visual information as it enters the eye.
Improving the Efficacy of ERP-Based BCIs Using Different Modalities of Covert Visuospatial Attention and a Genetic Algorithm-Based Classifier  [PDF]
Mauro Marchetti, Francesco Onorati, Matteo Matteucci, Luca Mainardi, Francesco Piccione, Stefano Silvoni, Konstantinos Priftis
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0053946
Abstract: We investigated whether the covert orienting of visuospatial attention can be effectively used in a brain-computer interface guided by event-related potentials. Three visual interfaces were tested: one interface that activated voluntary orienting of visuospatial attention and two interfaces that elicited automatic orienting of visuospatial attention. We used two epoch classification procedures. The online epoch classification was performed via Independent Component Analysis, and then it was followed by fixed features extraction and support vector machines classification. The offline epoch classification was performed by means of a genetic algorithm that permitted us to retrieve the relevant features of the signal, and then to categorise the features with a logistic classifier. The offline classification, but not the online one, allowed us to differentiate between the performances of the interface that required voluntary orienting of visuospatial attention and those that required automatic orienting of visuospatial attention. The offline classification revealed an advantage of the participants in using the “voluntary” interface. This advantage was further supported, for the first time, by neurophysiological data. Moreover, epoch analysis was performed better with the “genetic algorithm classifier” than with the “independent component analysis classifier”. We suggest that the combined use of voluntary orienting of visuospatial attention and of a classifier that permits feature extraction ad personam (i.e., genetic algorithm classifier) can lead to a more efficient control of visual BCIs.
Voluntary modulations of attention in a semantic auditory-visual matching Task: an ERP study
ORTEGA,RODRIGO; LóPEZ,VLADIMIR; ABOITIZ,FRANCISCO;
Biological Research , 2008, DOI: 10.4067/S0716-97602008000400010
Abstract: the present study explores the neural correlates of voluntary modulations of attention in an auditory-visual matching task. visual stimuli (a female or a male face) were preceded in cióse temporal proximity by auditory stimuli consisting of the spanish word for "man" and "woman" ("hombre" or "mujer"). in 80% of the triáis the gender of the two stimuli coincided. participants were asked to mentally count the specific instances in which a female face appeared after hearing the word "man" (10 % of the triáis). our results show attention-related amplitude modulation of the early visual erp components ni and anterior p2, but also amplitude modulations of (i) the n270 potential usually associated with conflict detection, (ii) a p300 wave related to infrequency, and (iii) an n400 potential related to semantic incongruence. the elicitation of these latter components varied according to task manipulations, evidencing the role of voluntary allocation of attention in fine-tuning cognitive processing, which includes basic processes like detection of infrequency or semantic incongruity often considered to be volition-independent.
Voluntary modulations of attention in a semantic auditory-visual matching Task: an ERP study
RODRIGO ORTEGA,VLADIMIR LóPEZ,FRANCISCO ABOITIZ
Biological Research , 2008,
Abstract: The present study explores the neural correlates of voluntary modulations of attention in an auditory-visual matching task. Visual stimuli (a female or a male face) were preceded in cióse temporal proximity by auditory stimuli consisting of the Spanish word for "man" and "woman" ("hombre" or "mujer"). In 80% of the triáis the gender of the two stimuli coincided. Participants were asked to mentally count the specific instances in which a female face appeared after hearing the word "man" (10 % of the triáis). Our results show attention-related amplitude modulation of the early visual ERP components NI and anterior P2, but also amplitude modulations of (i) the N270 potential usually associated with conflict detection, (ii) a P300 wave related to infrequency, and (iii) an N400 potential related to semantic incongruence. The elicitation of these latter components varied according to task manipulations, evidencing the role of voluntary allocation of attention in fine-tuning cognitive processing, which includes basic processes like detection of infrequency or semantic incongruity often considered to be volition-independent.
Covert Flow Graph Approach to Identifying Covert Channels  [cached]
XiangMei Song,ShiGuang Ju
Journal of Networks , 2011, DOI: 10.4304/jnw.6.12.1740-1746
Abstract: In this paper, the approach for identifying covert channels using a graph structure called Covert Flow Graph is introduced. Firstly, the construction of Covert Flow Graph which can offer information flows of the system for covert channel detection is proposed, and the search and judge algorithm used to identify covert channels in Covert Flow Graph is given. Secondly, an example file system analysis using Covert Flow Graph approach is provided, and the analysis result is compared with that of Shared Resource Matrix and Covert Flow Tree method. Finally, the comparison between Covert Flow Graph approach and other two methods is discussed. Different from previous methods, Covert Flow Graph approach provides a deep insight for system’s information flows, and gives an effective algorithm for covert channel identification.
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