Caterina Cinel

P300-Based BCI Mouse With Genetically-Optimized Analogue Control

In this paper we propose a brain-computer interface (BCI) mouse based on P300 waves in electroencephalogram (EEG) signals. The system is analogue in that at no point a binary decision is made as to whether or not a P300 was actually produced in response to the stimuli. Instead, the 2D motion of the pointer on the screen, using a novel BCI paradigm, is controlled by directly combining the amplitudes of the output produced by a filter in the presence of different stimuli. This filter and the features to be combined within it are optimised by an evolutionary algorithm.

Fractionating the binding process: neuropsychological evidence distinguishing binding of form from binding of surface features

We present neuropsychological evidence demonstrating that the binding of form elements into shapes dissociates from the binding of surface detail to shape. Data are reported from a patient with bilateral parietal lesions, GK, who manifests left-side visual extinction along with many illusory conjunctions when asked to discriminate both surface and form information about stimuli. We show that there are effects of grouping on both extinction and illusory conjunctions when the tasks require report of object shape. In contrast, illusory conjunctions involving surface and form information were unaffected by grouping based on shape. In addition, grouping was stronger when forms were presented within the same hemifield than when they appeared in different hemifields, whilst illusory conjunctions of form and colour occurred equally often within and across hemifields. These results support a two-stage account of visual binding: form elements are first bound together locally into shapes, and this is followed by a second stage of binding in which shapes are integrated with surface details. The second but not the first stage of binding is impaired in this patient.

Cross-modal illusory conjunctions between vision and touch.

Cross-modal illusory conjunctions (ICs) happen when, under conditions of divided attention, felt textures are reported as being seen or vice versa. Experiments provided evidence for these errors, demonstrated that ICs are more frequent if tactile and visual stimuli are in the same hemispace, and showed that ICs still occur under forced-choice conditions but do not occur when attention to the felt texture is increased. Cross-modal ICs were also found in a patient with parietal damage even with relatively long presentations of visual stimuli. The data are consistent with there being cross-modal integration of sensory information, with the modality of origin sometimes being misattributed when attention is constrained. The empirical conclusions from the experiments are supported by formal models.

Towards cooperative brain-computer interfaces for space navigation

We explored the possibility of controlling a spacecraft simulator using an analogue Brain-Computer Interface (BCI) for 2-D pointer control. This is a difficult task, for which no previous attempt has been reported in the literature. Our system relies on an active display which produces event-related potentials (ERPs) in the users brain. These are analysed in real-time to produce control vectors for the user interface. In tests, users of the simulator were told to pass as close as possible to the Sun. Performance was very promising, on average users managing to satisfy the simulation success criterion in 67.5% of the runs. Furthermore, to study the potential of a collaborative approach to spacecraft navigation, we developed BCIs where the system is controlled via the integration of the ERPs of two users. Performance analysis indicates that collaborative BCIs produce trajectories that are statistically significantly superior to those obtained by single users.

Documenting, modelling and exploiting P300 amplitude changes due to variable target delays in Donchin's speller

The P300 is an endogenous event-related potential (ERP) that is naturally elicited by rare and significant external stimuli. P300s are used increasingly frequently in brain-computer interfaces (BCIs) because the users of ERP-based BCIs need no special training. However, P300 waves are hard to detect and, therefore, multiple target stimulus presentations are needed before an interface can make a reliable decision. While significant improvements have been made in the detection of P300s, no particular attention has been paid to the variability in shape and timing of P300 waves in BCIs. In this paper we start filling this gap by documenting, modelling and exploiting a modulation in the amplitude of P300s related to the number of non-targets preceding a target in a Donchin speller. The basic idea in our approach is to use an appropriately weighted average of the responses produced by a classifier during multiple stimulus presentations, instead of the traditional plain average. This makes it possible to weigh more heavily events that are likely to be more informative, thereby increasing the accuracy of classification. The optimal weights are determined through a mathematical model that precisely estimates the accuracy of our speller as well as the expected performance improvement w.r.t. the traditional approach. Tests with two independent datasets show that our approach provides a marked statistically significant improvement in accuracy over the top-performing algorithm presented in the literature to date. The method and the theoretical models we propose are general and can easily be used in other P300-based BCIs with minimal changes.

Reaction-time binning: A simple method for increasing the resolving power of ERP averages

Stimulus-locked, response-locked, and ERP-locked averaging are effective methods for reducing artifacts in ERP analysis. However, they suffer from a magnifying-glass effect: they increase the resolution of specific ERPs at the cost of blurring other ERPs. Here we propose an extremely simple technique-binning trials based on response times and then averaging-which can significantly alleviate the problems of other averaging methods. We have empirically evaluated the technique in an experiment where the task requires detecting a target in the presence of distractors. We have also studied the signal-to-noise ratio and the resolving power of averages with and without binning. Results indicate that the method produces clearer representations of ERPs than either stimulus-locked and response-locked averaging, revealing finer details of ERPs and helping in the evaluation of the amplitude and latency of ERP waves. The method is applicable to within-subject and between-subject averages.

On the relations between implicit and explicit spatial binding: evidence from Balint's syndrome.

We report two experiments examining whether factors that affect binding in explicit report tasks also affect implicit binding in a patient with Balint’s syndrome, G.K. Replicating prior studies, we showed that there could be implicit binding of visual features in a patient with Balint’s syndrome who was at chance at explicitly discriminating the relations between the features. Nevertheless, when color—form relationships were coded, we showed that G.K.’s implicit binding, as well as his explicit report of binding relationships, was affected by the spatial distance between the stimuli. Similarly, we demonstrated effects of grouping on both implicit and explicit binding of the spatial relations between shapes. We interpret the qualitative similarities between implicit and explicit binding as indicating that they reflect a single process in which binding relations, initially established preattentively, are later consolidated by attention. This later process, of attentional consolidation, is disrupted in Balint’s syndrome.

Exposure to mobile phone electromagnetic fields and subjective symptoms: a double-blind study.

Objectives: The objective of this study was to examine whether acute exposure to radio frequency electromagnetic fields (REFs) emitted by mobile phone may affect subjective symptoms. Methods: Three large groups of volunteers (total 496) were exposed to REFs emitted by mobile phones in one session and sham signals in a different session. REF and sham exposure sessions were counterbalanced and double blinded. Participants were exposed to either Global System for Mobile Communication (GSM) or unmodulated signals, and the mobile phone was positioned either on the left or on the right side of the head. Before and after REF and sham exposure participants completed a questionnaire to rate five symptoms. Any changes in the severity of the symptoms after REF exposure were compared with changes after sham exposure. Results: For one group of participants (N = 160), it was found that dizziness was affected by GSM exposure, but this was not consistently found with the other two groups of participants. No other significant effects were found. Conclusions: We did not find consistent evidence suggesting that exposure to mobile phone REFs affect subjective symptoms. Even though we acknowledge that more research is needed, we believe that our results give an important contribution to the research on mobile phone use and subjective symptoms. REF = radio frequency electromagnetic field; GSM = Global System for Mobile Communication; CW = continuous wave; SAR = specific energy absorption rate; SD = standard deviation.

Collaborative brain-computer interface for aiding decision-making.

We look at the possibility of integrating the percepts from multiple non-communicating observers as a means of achieving better joint perception and better group decisions. Our approach involves the combination of a brain-computer interface with human behavioural responses. To test ideas in controlled conditions, we asked observers to perform a simple matching task involving the rapid sequential presentation of pairs of visual patterns and the subsequent decision as whether the two patterns in a pair were the same or different. We recorded the response times of observers as well as a neural feature which predicts incorrect decisions and, thus, indirectly indicates the confidence of the decisions made by the observers. We then built a composite neuro-behavioural feature which optimally combines the two measures. For group decisions, we uses a majority rule and three rules which weigh the decisions of each observer based on response times and our neural and neuro-behavioural features. Results indicate that the integration of behavioural responses and neural features can significantly improve accuracy when compared with the majority rule. An analysis of event-related potentials indicates that substantial differences are present in the proximity of the response for correct and incorrect trials, further corroborating the idea of using hybrids of brain-computer interfaces and traditional strategies for improving decision making.

Novel Protocols for P300-Based Brain–Computer Interfaces

The oddball protocol is often used in brain-computer interfaces (BCIs) to induce P300 ERPs, although, recently, some issues have been shown to detrimentally effect its performance. In this paper, we study a new periodic protocol and explore whether it can compete with the standard oddball protocol within the context of a BCI mouse. We found that the new protocol consistently and significantly outperforms the standard oddball protocol in relation to information transfer rates (33 bits/min for the former and 22 bits/min for the latter, measured at 90% accuracy) as well as P300 amplitudes. Furthermore, we performed a comparison of two periodic protocols with two less conventional oddball-like protocols that reveals the importance of the interactions between task and sequence in determining the success of a protocol.