Measuring auditory event-related potentials at the external ear canal: A demonstrative study using a new electrode and error-feedback paradigm.

Although ear canal electroencephalogram (EEG) recording has received interest from basic and applied research communities, evidence on how it can be implemented in practice is limited. The present study involving eight male participants including the authors presents the utility of our ear canal electrode and method by demonstrating both comparability of ear canal EEG to those at nearby sites and distinctiveness that ear canal event-related potentials (ERPs) could have. For this purpose, we used the balanced noncephalic electrode reference and an experimental paradigm with an error-feedback sound. Clear auditory ERPs were detected at the ear canal sites with a sufficiently low noise level comparable with those at conventional sites. The N1c, a temporal maximum subcomponent, spread over the bilateral temporal sites, including the ear canals and earlobes. While consecutive signals are generally highly similar between the ear canal and the earlobe, the N1c was larger at the ear canal than the earlobe, as demonstrated by the conventional frequentist and the hierarchical Bayesian modelling approaches. Although an evident caveat is that our sample was limited in terms of size and sex, the general capability indicates that the structure of our ear canal electrode provides EEG measurement that can be used in basic and applied settings. Our experimental method can also be an ERP-based test that conveniently assesses the capability of existing and future ear canal electrodes. The distinctive nature of the ERPs to the error-feedback sound may be utilized to examine the basic aspects of auditory ERPs and to test the processes involved in feedback-guided behaviour of participants.

The N400 and late occipital positivity in processing dynamic facial expressions with natural emotional voice.

People require multimodal emotional interactions to live in a social environment. Several studies using dynamic facial expressions and emotional voices have reported that multimodal emotional incongruency evokes an early sensory component of event-related potentials (ERPs), while others have found a late cognitive component. The integration mechanism of two different results remains unclear. We speculate that it is semantic analysis in a multimodal integration framework that evokes the late ERP component. An electrophysiological experiment was conducted using emotionally congruent or incongruent dynamic faces and natural voices to promote semantic analysis. To investigate the top-down modulation of the ERP component, attention was manipulated via two tasks that directed participants to attend to facial versus vocal expressions. Our results revealed interactions between facial and vocal emotional expressions, manifested as modulations of the auditory N400 ERP amplitudes but not N1 and P2 amplitudes, for incongruent emotional face-voice combinations only in the face-attentive task. A late occipital positive potential amplitude emerged only during the voice-attentive task. Overall, these findings support the idea that semantic analysis is a key factor in evoking the late cognitive component. The task effect for these ERPs suggests that top-down attention alters not only the amplitude of ERP but also the ERP component per se. Our results implicate a principle of emotional face-voice processing in the brain that may underlie complex audiovisual interactions in everyday communication.

Event-related potentials using the auditory novel paradigm in patients with myotonic dystrophy.

Many neuropsychological disorders, especially attentional abnormality, are present in patients with myotonic dystrophy type 1 (DM1), but the underlying mechanisms remain unclear. This study aimed to evaluate attention function by auditory event-related potential (ERP) P3a (novelty paradigm) in DM1 patients. A total of 10 young DM1 patients (mean age 30.4 years) and 14 age-matched normal controls participated in this study. ERPs were recorded using an auditory novel paradigm, consisting of three types of stimuli, i.e., standard sound (70%), target sound (20%), and various novel sounds (10%), and participants pressed buttons to the target sounds. ERP components P3b after the target stimuli and P3a following the novel stimuli were analyzed. Correlations of neuropsychological evaluations with the amplitudes and latencies of P3b and P3a were analyzed in DM1 patients. We found that P3a latency was significantly delayed in patients with DM1 compared with normal controls, although the latency and amplitude of P3b in DM1 patients were comparable with those in normal controls. The achievement rates of both the Symbol Digit Modality Test and the Paced Auditory Serial Addition Test were significantly correlated with P3a amplitude, as well as P3b amplitude. These results suggest that ERPs, including P3a and P3b, provide important insights into the physiological basis of neuropsychological abnormalities in patients with DM1, especially from the viewpoint of the frontal lobe and attention function.

Selective adaptation in sentence comprehension: Evidence from event-related brain potentials.

In this study, two event-related potential experiments were conducted to investigate whether readers adapt their expectations to morphosyntactically (Experiment 1) or semantically (Experiment 2) anomalous sentences when they are repeatedly exposed to them. To address this issue, we experimentally manipulated the probability of occurrence of grammatical sentences and syntactically and semantically anomalous sentences through experiments. For the low probability block, anomalous sentences were presented less frequently than grammatical sentences (with a ratio of 1 to 4), while they were presented as frequently as grammatical sentences in the equal probability block. Experiment 1 revealed a smaller P600 effect for morphosyntactic violations in the equal probability block than in the low probability block. Linear mixed-effects models were used to examine how the size of the P600 effect changed as the experiment went along. The results showed that the smaller P600 effect of the equal probability block resulted from an amplitude's decline in morphosyntactically violated sentences over the course of the experiment, suggesting an adaptation to morphosyntactic violations. In Experiment 2, semantically anomalous sentences elicited a larger N400 effect than their semantically natural counterparts regardless of probability manipulation. Little evidence was found in favour of adaptation to semantic violations in that the processing cost associated with the N400 did not decrease over the course of the experiment. Therefore, a dynamic aspect of language-processing system was demonstrated in this study. We will discuss why the language-processing system shows a selective adaptation to morphosyntactic violations.

A newly developed free software tool set for averaging electroencephalogram implemented in the Perl programming language.

BACKGROUND: Considering the need for daily activity analysis of older adults, development of easy-to-use, free electroencephalogram (EEG) analysis tools are desired in order to decrease barriers to accessing this technology and increase the entry of a wide range of new researchers. NEW METHOD: We describe a newly developed tool set for EEG analysis, enabling import, average, waveform display and iso-potential scalp topographies, utilizing the programming language Perl. RESULTS: The basic processing, including average, display waveforms, and isopotential scalp topography was implemented in the current system. The validation was examined by making difference waveforms between the results using the current analysis system and a commercial software.Comparison with Existing Method(s): The current software tool set consists of free software. The scripts are easily editable by any user and there are no black boxes. CONCLUSIONS: The currently reported procedures provide an easy-to-begin, flexible, readable, easy-to-modify basic tool set for EEG analysis and is expected to recruit new EEG researchers.

Certain non-isochronous sound trains are perceived as more isochronous when they start on beat.

Perceiving the duration of neighboring time intervals is vital for rhythm perception. We discovered a phenomenon in which the perceived equality/inequality of neighboring time intervals in a sound sequence is changed by its metrical interpretation. The target sound sequence consisted of eight short sound bursts marking seven neighboring time intervals, which were repetitions of two durations (T1 and T2) presented in alternation (T1-T2-T1-T2 …). There were three tempos, which corresponded to T1 + T2 being 210, 420, and 630 ms. The physical difference between T1 and T2 (T1 - T2) was varied systematically for each tempo in the ranges of -100 to 100 ms (when T1 + T2 was 210 or 420 ms) or -150 to 150 ms (when T1 + T2 was 630 ms). Participants reported the level of perceived equality/inequality of these neighboring time intervals. For each target sequence, four isochronous lower-pitched preceding sounds were added at different phases so that the beginning of either T1 (Beat-on-T1 condition) or T2 (Beat-on-T2 condition) coincided with the beat induced by these preceding sounds. When T2 was longer than T1 by up to 60 ms, the neighboring time intervals of the same target sequence were perceived as more "equal" in the Beat-on-T1 condition compared with the Beat-on-T2 condition. Such a difference in the perceived equality/inequality appeared significantly only at the intermediate tempo of T1 + T2 = 420 ms. The difference in equality/inequality perception at limited temporal conditions could be accounted for by the occurrence of an illusion in time perception called time-shrinking.

Inter-participant variabilities and sample sizes in P300 and P600.

Reliably and efficiently detecting physiological differences between conditions of interest is of importance in psychophysiology. In particular, when it comes to the observation of relatively small differences, such as a P600 effect, a language-related brain potential elicited by ungrammatical sentences compared to grammatical sentences, inter-participant variability is a critical factor since a larger inter-participant variability decreases statistical significance, and therefore increases the necessary sample size. The present study investigated how stable individual P600s are, at which sample sizes the P600 becomes stable, and how many participants are necessary to observe a P600 effect. P600s were recorded from 48 participants, as well as P300 (P3b) from 40 participants for comparison. Unlike the P3b effect, which had an approximately 10 µV difference between the target and standard stimuli, P600 increased in amplitude by only 1.4-1.7 µV at Pz during the processing of ungrammatical sentences relative to the grammatical counterparts. The sample size analysis suggests that 20 to 30 participants are needed to detect a P600 effect at Pz, and the distribution of variances does not change significantly with a larger sample size.

Discrete cortical regions associated with the musical beauty of major and minor chords.

Previous research has demonstrated that the degree of aesthetic pleasure a person experiences correlates with the activation of reward functions in the brain. However, it is unclear whether different affective qualities and the perceptions of beauty that they evoke correspond to specific areas of brain activation. Major and minor musical keys induce two types of affective qualities--bright/happy and dark/sad--that both evoke aesthetic pleasure. In the present study, we used positron emission tomography to demonstrate that the two musical keys (major and minor) activate distinct brain areas. Minor consonant chords perceived as beautiful strongly activated the right striatum, which has been assumed to play an important role in reward and emotion processing, whereas major consonant chords perceived as beautiful induced significant activity in the left middle temporal gyrus, which is believed to be related to coherent and orderly information processing. These results suggest that major and minor keys, both of which are perceived as beautiful, are processed differently in the brain.

Electrophysiological correlates of absolute pitch and relative pitch.

The temporal and spatial characteristics of the cortical processes responsible for absolute pitch (AP) and relative pitch (RP) were investigated by multi-channel event-related potentials (ERPs). Compared to listening, pitch-naming of tones in non-possessors of AP elicited three ERP components (P3b, parietal positive slow wave, frontal negative slow wave) over parietal and frontal scalp between 300 and 900 ms in latency, representing the cortical processes for RP. Possessors of AP elicited a unique left posterior-temporal negativity ('AP negativity') at 150 ms in both listening and pitch-naming conditions, representing the cortical processes for AP that were triggered by pitch input irrespective of the task the subjects were asked to perform. Congruency of auditory Stroop stimuli modulated the amplitudes of parietal positive slow wave (non-possessors of AP) and 'AP negativity' (possessors of AP), confirming that these components reflect the verbal labeling or pitch-to-pitch-name associative transformation that is central to pitch-naming. These results are consistent with the hypothesis that AP is subserved by neuronal processes in the left auditory association cortex that occur earlier and more automatically than the processes for RP, which involve broader areas of the cortex over longer periods of time.

An ERP study of sensory mismatch expressions in Japanese.

Combinations of different sensory words produce mismatch expressions like smooth color and red touch in contrast to normal expressions like red color and smooth touch. Concerning these sensory mismatch expressions, results of three experiments are reported. Experiment 1 revealed that (i) mismatch expressions were less comprehensible than normal expressions, and that (ii) there were two patterns among mismatch expressions: the high-comprehensible mismatch expression (HighCME, e.g., smooth color) and the low-comprehensible mismatch expression (LowCME, e.g., red touch). Experiment 2 revealed that the mismatch expressions produced a significantly greater N400 amplitude than the normal expressions. Experiment 3 implied that the difference between High/LowCME was reflected in a later latency band or in a topographical difference of N400, although the statistical significance was marginal. It is argued that the processes to integrate linguistic elements (e.g., combining adjectives and nouns) are not homogeneous.