Neurodynamic evaluation of hearing aid features using EEG correlates of listening effort

In this study, we propose a novel estimate of listening effort using electroencephalographic data. This method is a translation of our past findings, gained from the evoked electroencephalographic activity, to the oscillatory EEG activity. To test this technique, electroencephalographic data from experienced hearing aid users with moderate hearing loss were recorded, wearing hearing aids. The investigated hearing aid settings were: a directional microphone combined with a noise reduction algorithm in a medium and a strong setting, the noise reduction setting turned off, and a setting using omnidirectional microphones without any noise reduction. The results suggest that the electroencephalographic estimate of listening effort seems to be a useful tool to map the exerted effort of the participants. In addition, the results indicate that a directional processing mode can reduce the listening effort in multitalker listening situations

Reducing the Effect of Spurious Phase Variations in Neural Oscillatory Signals

The phase-reset model of oscillatory EEG activity has received a lot of attention in the last decades for decoding different cognitive processes. Based on this model, the ERPs are assumed to be generated as a result of phase reorganization in ongoing EEG. Alignment of the phase of neuronal activities can be observed within or between different assemblies of neurons across the brain. Phase synchronization has been used to explore and understand perception, attentional binding and considering it in the domain of neuronal correlates of consciousness. The importance of the topic and its vast exploration in different domains of the neuroscience presses the need for appropriate tools and methods for measuring the level of phase synchronization of neuronal activities. Measuring the level of instantaneous phase (IP) synchronization has been used extensively in numerous studies of ERPs as well as oscillatory activity for a better understanding of the underlying cognitive binding with regard to different set of stimulations such as auditory and visual. However, the reliability of results can be challenged as a result of noise artifact in IP. Phase distortion due to environmental noise artifacts as well as different pre-processing steps on signals can lead to generation of artificial phase jumps. One of such effects presented recently is the effect of low envelope on the IP of signal. It has been shown that as the instantaneous envelope of the analytic signal approaches zero, the variations in the phase increase, effectively leading to abrupt transitions in the phase. These abrupt transitions can distort the phase synchronization results as they are not related to any neurophysiological effect. These transitions are called spurious phase variation. In this study, we present a model to remove generated artificial phase variations due to the effect of low envelope. The proposed method is based on a simplified form of a Kalman smoother, that is able to model the IP behavior in narrow-bandpassed oscillatory signals. In this work we first explain the details of the proposed Kalman smoother for modeling the dynamics of the phase variations in narrow-bandpassed signals and then evaluate it on a set of synthetic signals. Finally, we apply the model on ongoing-EEG signals to assess the removal of spurious phase variations

Vestigial auriculomotor activity indicates the direction of auditory attention in humans

Unlike dogs and cats, people do not point their ears as they focus attention on novel, salient, or task-relevant stimuli. Our species may nevertheless have retained a vestigial pinna-orienting system that has persisted as a 'neural fossil’ within in the brain for about 25 million years. Consistent with this hypothesis, we demonstrate that the direction of auditory attention is reflected in sustained electrical activity of muscles within the vestigial auriculomotor system. Surface electromyograms (EMGs) were taken from muscles that either move the pinna or alter its shape. To assess reflexive, stimulus-driven attention we presented novel sounds from speakers at four different lateral locations while the participants silently read a boring text in front of them. To test voluntary, goal-directed attention we instructed participants to listen to a short story coming from one of these speakers, while ignoring a competing story from the corresponding speaker on the opposite side. In both experiments, EMG recordings showed larger activity at the ear on the side of the attended stimulus, but with slightly different patterns. Upward movement (perking) differed according to the lateral focus of attention only during voluntary orienting; rearward folding of the pinna’s upper-lateral edge exhibited such differences only during reflexive orienting. The existence of a pinna-orienting system in humans, one that is experimentally accessible, offers opportunities for basic as well as applied science

Notched-noise embedded frequency specific chirps for objective audiometry using auditory brainstem responses

It has been shown recently that chirp-evoked auditory brainstem responses (ABRs) show better performance than click stimulations, especially at low intensity levels. In this paper we present the development, test, and evaluation of a series of notched-noise embedded frequency specific chirps. ABRs were collected in healthy young control subjects using the developed stimuli. Results of the analysis of the corresponding ABRs using a time-scale phase synchronization stability (PSS) measure are also reported. The resultant wave V amplitude and latency measures showed a similar behavior as for values reported in literature. The PSS of frequency specific chirp-evoked ABRs reflected the presence of the wave V for all stimulation intensities. The scales that resulted in higher PSS are in line with previous findings, where ABRs evoked by broadband chirps were analyzed, and which stated that low frequency channels are better for the recognition and analysis of chirp-evoked ABRs. We conclude that the development and test of the series of notched-noise embedded frequency specific chirps allowed the assessment of frequency specific ABRs, showing an identifiable wave V for different intensity levels. Future work may include the development of a faster automatic recognition scheme for these frequency specific ABRs

Reducing the Effect of Spurious Phase Variations in Neural Oscillatory Signals

The phase-reset model of oscillatory EEG activity has received a lot of attention in the last decades for decoding different cognitive processes. Based on this model, the ERPs are assumed to be generated as a result of phase reorganization in ongoing EEG. Alignment of the phase of neuronal activities can be observed within or between different assemblies of neurons across the brain. Phase synchronization has been used to explore and understand perception, attentional binding and considering it in the domain of neuronal correlates of consciousness. The importance of the topic and its vast exploration in different domains of the neuroscience presses the need for appropriate tools and methods for measuring the level of phase synchronization of neuronal activities. Measuring the level of instantaneous phase (IP) synchronization has been used extensively in numerous studies of ERPs as well as oscillatory activity for a better understanding of the underlying cognitive binding with regard to different set of stimulations such as auditory and visual. However, the reliability of results can be challenged as a result of noise artifact in IP. Phase distortion due to environmental noise artifacts as well as different pre-processing steps on signals can lead to generation of artificial phase jumps. One of such effects presented recently is the effect of low envelope on the IP of signal. It has been shown that as the instantaneous envelope of the analytic signal approaches zero, the variations in the phase increase, effectively leading to abrupt transitions in the phase. These abrupt transitions can distort the phase synchronization results as they are not related to any neurophysiological effect. These transitions are called spurious phase variation. In this study, we present a model to remove generated artificial phase variations due to the effect of low envelope. The proposed method is based on a simplified form of a Kalman smoother, that is able to model the IP behavior in narrow-bandpassed oscillatory signals. In this work we first explain the details of the proposed Kalman smoother for modeling the dynamics of the phase variations in narrow-bandpassed signals and then evaluate it on a set of synthetic signals. Finally, we apply the model on ongoing-EEG signals to assess the removal of spurious phase variations

The role of attention in immersion: The two–competitor model

Currently, we face an exponentially increasing interest in immersion, especially sensory–driven immersion, mainly due to the rapid development of ideas and business models centered around a digital virtual universe as well as the increasing availability of affordable immersive technologies for education, communication, and entertainment. However, a clear definition of ‘immersion’, in terms of established neurocognitive concepts and measurable properties, remains elusive, slowing research on the human side of immersive interfaces.To address this problem, we propose a conceptual, taxonomic model of attention in immersion. We argue (a) modeling immersion theoretically as well as studying immersion experimentally requires a detailed characterization of the role of attention in immersion, even though (b) attention, while necessary, cannot be a sufficient condition for defining immersion. Our broader goal is to characterize immersion in terms that will be compatible with established psychophysiolgical measures that could then in principle be used for the assessment and eventually the optimization of an immersive experience. We start from the perspective that immersion requires the projection of attention to an induced reality, and build on accepted taxonomies of different modes of attention for the development of our two–competitor model. The two–competitor model allows for a quantitative implementation and has an easy graphical interpretation. It helps to highlight the important link between different modes of attention and affect in studying immersion

Speech induced binaural beats: Electrophysiological assessment of binaural interaction

This paper introduces and evaluates a speech signal manipulation scheme that generates transient speech induced binaural beats (SBBs). These SBBs can only be perceived when different signals are presented dichotically (to both ears). Event-related potentials were recorded in 22 normal-hearing subjects. Dichotic stimulus presentation reliably evoked auditory late responses (ALRs) in all subjects using such manipulated signals. As control measurements, diotic stimulation modalities were presented to confirm that the ALRs were not evoked by the speech signal itself or that the signal manipulation scheme created audible artifacts. Since diotic measurements evoked no ALRs, responses from dichotic stimulation are a pure correlate of binaural interaction. While there are several auditory stimuli (mostly modulated sinusoids or noise) that share this characteristic, none of them are based on running speech. Because SBBs can be added to any arbitrary speech signal, they could easily be combined with psychoacoustic tests, for example speech reception thresholds, adding an objective measure of binaural interaction

Gabor frame phase stability analysis of chirp evoked auditory brainstem responses

We have shown that click evoked auditory brainstem response (ABR) single sweeps can be efficiently processed using a novelty detection paradigm. In this paradigm, the diagnostic system is self-adjusted to the individual measurement setting using the spontaneous activity. ABRs as a large-scale reflection of a stimulus locked neuronal group synchronization at the brainstem level are detected as novel instance - novel as compared to the spontaneous activity which does not exhibit a regular stimulus locked synchronization. In this paper we propose for the first time Gabor frame operators as an efficient feature extraction technique for ABR single sweeps. In particular, we use this decomposition technique to derive the Gabor frame phase stability (GFPS) of sweep sequences of click and chirp evoked ABRs. We show that the GFPS represents a robust feature of ABRs and that GFPS of chirp evoked ABRs provides a stable discrimination of the spontaneous activity from stimulations above the hearing threshold with a minimum number of sweeps, even at low stimulation intensities. This is the first study that is directed to a single sweep analysis of chirp evoked ABRs. We conclude that our study reinforces the use of chirp stimulations for the fast hearing threshold detection. The presented method might be used in expert based diagnostic procedures directly or for the ultra-fast detection of the hearing threshold by cojoint systems with a computational decision making stage according to the novelty detection paradigm