Measurement of saccadic eye movements by electrooculography for simultaneous EEG recording

Eye movements are an important index of the neural functions of visual information processing, decision making, visuomotor coordination, sports performance, and so forth. However, the available optical tracking methods are impractical in many situations, such as the wearing of eyeglasses or the presence of ophthalmic disorders, and this can be overcome by accurate recording of eye movements by electrooculography (EOG). In this study we recorded eye movements by EOG simultaneously with high-density electroencephalogram (EEG) recording using a 128-channel EGI electrode net at a 500-Hz sampling rate, including appropriate facial electrodes. The participants made eye movements over a calibration target consisting of a 5×5 grid of stimulus targets. The results showed that the EOG methodology allowed accurate analysis of the amplitude and direction of the fixation locations and saccadic dynamics with a temporal resolution of 500 Hz, under both cued and uncued analysis regimes. Blink responses could be identified separately and were shown to have a more complex source derivation than has previously been recognized. The results also showed that the EOG signals recorded through the EEG net can achieve results as accurate as typical optical eye-tracking devices, and also allow for simultaneous assessment of neural activity during all types of eye movements. Moreover, the EOG method effectively avoids the technical difficulties related to eye-tracker positioning and the synchronization between EEG and eye movements. We showed that simultaneous EOG/EEG recording is a convenient means of measuring eye movements, with an accuracy comparable to that of many specialized eye-tracking systems

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Do Horizontal Saccadic Eye Movements Increase Interhemispheric Coherence? Investigation of a Hypothesized Neural Mechanism Underlying EMDR

Series of horizontal saccadic eye movements (EMs) are known to improve episodic memory retrieval in healthy adults and to facilitate the processing of traumatic memories in eye movement desensitization and reprocessing (EMDR) therapy. Several authors have proposed that EMs achieve these effects by increasing the functional connectivity of the two brain hemispheres, but direct evidence for this proposal is lacking. The aim of this study was to investigate whether memory enhancement following bilateral EMs is associated with increased interhemispheric coherence in the electroencephalogram (EEG). Fourteen healthy young adults were asked to freely recall lists of studied neutral and emotional words after a series of bilateral EMs and a control procedure. Baseline EEG activity was recorded before and after the EM and control procedures. Phase and amplitude coherence between bilaterally homologous brain areas were calculated for six frequency bands and electrode pairs across the entire scalp. Behavioral analyses showed that participants recalled more emotional (but not neutral) words following the EM procedure than following the control procedure. However, the EEG analyses indicated no evidence that the EMs altered participants’ interhemispheric coherence or that improvements in recall were correlated with such changes in coherence. These findings cast doubt on the interhemispheric interaction hypothesis, and therefore may have important implications for future research on the neurobiological mechanism underlying EMDR

Visual short‐term memory‐related EEG components in a virtual reality setup

Virtual reality (VR) offers a powerful tool for investigating cognitive processes, as it allows researchers to gauge behaviors and mental states in complex, yet highly controlled, scenarios. The use of VR head-mounted displays in combination with physiological measures such as EEG presents new challenges and raises the question whether established findings also generalize to a VR setup. Here, we used a VR headset to assess the spatial constraints underlying two well-established EEG correlates of visual short-term memory: the amplitude of the contralateral delay activity (CDA) and the lateralization of induced alpha power during memory retention. We tested observers' visual memory in a change detection task with bilateral stimulus arrays of either two or four items while varying the horizontal eccentricity of the memory arrays (4, 9, or 14 degrees of visual angle). The CDA amplitude differed between high and low memory load at the two smaller eccentricities, but not at the largest eccentricity. Neither memory load nor eccentricity significantly influenced the observed alpha lateralization. We further fitted time-resolved spatial filters to decode memory load from the event-related potential as well as from its time-frequency decomposition. Classification performance during the retention interval was above-chance level for both approaches and did not vary significantly across eccentricities. We conclude that commercial VR hardware can be utilized to study the CDA and lateralized alpha power, and we provide caveats for future studies targeting these EEG markers of visual memory in a VR setup.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Cooperation between the Max Planck Society and the Fraunhofer GesellschaftDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Investigating the relationship between microsaccades and oscillations in the human visual cortex

Neural oscillations play important roles in vision and attention. Most studies of oscillations use visual fixation to control the visual input. Small eye movements, called microsaccades, occur involuntarily ~ 1-2 times per second during fixation and they are also thought to play important roles in vision and attention. The aim of the work described in this thesis was to explore the relationship between microsaccades and oscillations in the human visual cortex. In Chapter 2, I describe how remote video eye tracking can be used to detect and characterize microsaccades during MEG recordings. Tracking based on the pupil position only, without corneal reflection, and with the participant’s head immobilized in the MEG dewar, resulted in high precision gaze tracking and enabled the following investigations. In Chapter 3, I investigated the relationship between induced visual gamma oscillations and microsaccades in a simple visual stimulation paradigm. I did not find evidence for the relationship. This finding supports the view that sustained gamma oscillations reflect local processing in cortical columns. In addition, early transient gamma response had a reduced amplitude on trials with microsaccades, however the exact nature of this effect will have to be determined in future studies. In Chapter 4, I investigated the relationship between alpha oscillations and microsaccades in covert spatial attention. I did not find evidence for a relationship between hemispheric lateralization of the alpha amplitude and the directional bias of microsaccades. I propose that microsaccades and alpha oscillations represent two independent attentional mechanisms - the former related to early attention shifting and the latter to maintaining sustained attention. In Chapter 5, I recorded, for the first time, microsaccade-related spectral responses. Immediately after their onset, microsaccades increased amplitude in theta and beta bands and this effect was modulated by stimulus type. Moreover, microsaccades reduced alpha amplitude ~ 0.3 s after their onset and this effect was independent of stimulus type. These results have important implications for the interpretation of the classical oscillatory effects in the visual cortex as well as for the role of microsaccades in vision and attention

In pursuit of visual attention: SSVEP frequency-tagging moving targets.

Previous research has shown that visual attention does not always exactly follow gaze direction, leading to the concepts of overt and covert attention. However, it is not yet clear how such covert shifts of visual attention to peripheral regions impact the processing of the targets we directly foveate as they move in our visual field. The current study utilised the co-registration of eye-position and EEG recordings while participants tracked moving targets that were embedded with a 30 Hz frequency tag in a Steady State Visually Evoked Potentials (SSVEP) paradigm. When the task required attention to be divided between the moving target (overt attention) and a peripheral region where a second target might appear (covert attention), the SSVEPs elicited by the tracked target at the 30 Hz frequency band were significantly, but transiently, lower than when participants did not have to covertly monitor for a second target. Our findings suggest that neural responses of overt attention are only briefly reduced when attention is divided between covert and overt areas. This neural evidence is in line with theoretical accounts describing attention as a pool of finite resources, such as the perceptual load theory. Altogether, these results have practical implications for many real-world situations where covert shifts of attention may discretely reduce visual processing of objects even when they are directly being tracked with the eyes

Cortical Coupling Reflects Bayesian Belief Updating in the Deployment of Spatial Attention

The deployment of visuospatial attention and the programming of saccades are governed by the inferred likelihood of events. In the present study, we combined computational modeling of psychophysical data with fMRI to characterize the computational and neural mechanisms underlying this flexible attentional control. Sixteen healthy human subjects performed a modified version of Posner's location-cueing paradigm in which the percentage of cue validity varied in time and the targets required saccadic responses. Trialwise estimates of the certainty (precision) of the prediction that the target would appear at the cued location were derived from a hierarchical Bayesian model fitted to individual trialwise saccadic response speeds. Trial-specific model parameters then entered analyses of fMRI data as parametric regressors. Moreover, dynamic causal modeling (DCM) was performed to identify the most likely functional architecture of the attentional reorienting network and its modulation by (Bayes-optimal) precision-dependent attention. While the frontal eye fields (FEFs), intraparietal sulcus, and temporoparietal junction (TPJ) of both hemispheres showed higher activity on invalid relative to valid trials, reorienting responses in right FEF, TPJ, and the putamen were significantly modulated by precision-dependent attention. Our DCM results suggested that the precision of predictability underlies the attentional modulation of the coupling of TPJ with FEF and the putamen. Our results shed new light on the computational architecture and neuronal network dynamics underlying the context-sensitive deployment of visuospatial attention. Copyright \ua9 2015 Vossel et al

Controlling actions and experiencing control: the influence of movement execution and goal achievement on the Sense of Agency

Some recent theoretical models of the Sense of Agency - i.e., the feeling of controlling one's movements and their impact on the external environment (Aarts et al., 2012; Moore & Fletcher, 2012; Tsakiris et al., 2010) - suggest that this experience relies on the integration of various cues (Synofzik, 2008; Moore & Fletcher, 2012). However, only a few studies (Caspar, et al., 2016; David et al., 2016) manipulated in the same paradigm information about the executed movement and information about the achievement of the goal of the action. Hence, the respective roles of these two action cues for the Sense of Agency remains unclear. My Ph.D. thesis presents the results of two studies aimed at filling this gap. During my Ph.D., my colleagues and I devised a novel paradigm where participants performed a simple goal-directed action – pressing a button of a certain color – while they observed a virtual hand performing an action in a virtual scenario from a first-person perspective. The virtual action could be similar or different with respect to the one executed by the participant, and information about movement and about the achievement of the goal of the action could be independently and simultaneously manipulated. While participants performed the task, we collected direct and indirect measures of their Sense of Agency. In addition, we measured participant’s reaction times: indeed, a second aim of these two studies was to understand whether unexpected movement and goal related information also affects participant’s behavior and leads to behavioral adjustments, similarly to the commission of real errors (Danielmeier & Ullsperger, 2011). A detailed description of the paradigm, and the results of two behavioral studies where we employed it are reported in the thesis. In chapter 1, I provide an overview of literature supporting the fact that the Sense of Agency is sensitive both to the control of one's movements and to the achievement of the goal of the action. However, I also show that these two action cues were mostly investigated separately, which prevents a comparison of their relevance for the Sense of Agency. In chapter 2 I present the result of the first study. Our aim was to understand how violated predictions concerning movement execution and the achievement of the goal of the action influence the Sense of Agency. In Chapter 3, I present the results of the second study, where we compared the effects of the manipulation of information relative to movement execution and goal achievement respectively in freely chosen and cued actions. In particular, we wanted to investigate the influence of freedom to act on the Sense of Agency. Finally, in the Appendix I report preliminary results of an experiment where we investigated the neurocognitive processes (by means of Transcranial Magnetic Stimulation) underlying a different but related topic: the capacity of the individuals to exert agency, i.e., to control one’s own ocular movements when one is exposed to potentially distracting social stimuli (i.e., other’s gaze). Overall, the results of the studies described in chapters 2 and 3 suggest that the Sense of Agency is mostly influenced by movement related information, and that under some specific circumstances the feeling of control is also influenced by goal achievement and by freedom to act. Additionally, unexpected information concerning both the executed movement and the achievement of the goal of the action may lead to behavioral adjustments