Perceptual Temporal Asymmetry Associated with Distinct ON and OFF Responses to Time-Varying Sounds with Rising versus Falling Intensity: A Magnetoencephalography Study.

This magnetoencephalography (MEG) study investigated evoked ON and OFF responses to ramped and damped sounds in normal-hearing human adults. Two pairs of stimuli that differed in spectral complexity were used in a passive listening task; each pair contained identical acoustical properties except for the intensity envelope. Behavioral duration judgment was conducted in separate sessions, which replicated the perceptual bias in favour of the ramped sounds and the effect of spectral complexity on perceived duration asymmetry. MEG results showed similar cortical sites for the ON and OFF responses. There was a dominant ON response with stronger phase-locking factor (PLF) in the alpha (8-14 Hz) and theta (4-8 Hz) bands for the damped sounds. In contrast, the OFF response for sounds with rising intensity was associated with stronger PLF in the gamma band (30-70 Hz). Exploratory correlation analysis showed that the OFF response in the left auditory cortex was a good predictor of the perceived temporal asymmetry for the spectrally simpler pair. The results indicate distinct asymmetry in ON and OFF responses and neural oscillation patterns associated with the dynamic intensity changes, which provides important preliminary data for future studies to examine how the auditory system develops such an asymmetry as a function of age and learning experience and whether the absence of asymmetry or abnormal ON and OFF responses can be taken as a biomarker for certain neurological conditions associated with auditory processing deficits.

Neural correlates of auditory scale illusion.

The auditory illusory perception "scale illusion" occurs when ascending and descending musical scale tones are delivered in a dichotic manner, such that the higher or lower tone at each instant is presented alternately to the right and left ears. Resulting tone sequences have a zigzag pitch in one ear and the reversed (zagzig) pitch in the other ear. Most listeners hear illusory smooth pitch sequences of up-down and down-up streams in the two ears separated in higher and lower halves of the scale. Although many behavioral studies have been conducted, how and where in the brain the illusory percept is formed have not been elucidated. In this study, we conducted functional magnetic resonance imaging using sequential tones that induced scale illusion (ILL) and those that mimicked the percept of scale illusion (PCP), and we compared the activation responses evoked by those stimuli by region-of-interest analysis. We examined the effects of adaptation, i.e., the attenuation of response that occurs when close-frequency sounds are repeated, which might interfere with the changes in activation by the illusion process. Results of the activation difference of the two stimuli, measured at varied tempi of tone presentation, in the superior temporal auditory cortex were not explained by adaptation. Instead, excess activation of the ILL stimulus from the PCP stimulus at moderate tempi (83 and 126 bpm) was significant in the posterior auditory cortex with rightward superiority, while significant prefrontal activation was dominant at the highest tempo (245 bpm). We suggest that the area of the planum temporale posterior to the primary auditory cortex is mainly involved in the illusion formation, and that the illusion-related process is strongly dependent on the rate of tone presentation.

Ambiguity involving two illusory melodies induced by a simple configuration of tones.

Auditory scene analysis is essential in daily life to extract necessary information from complex acoustic environment and also from intricate development of music compositions. Auditory illusions and ambiguity are important factors in auditory scene analysis and have been studied extensively. We here report a novel form of ambiguity involving two illusory melodies implied by a very simple stimulus consisting of two sustained tones of different frequencies and an intermittently repeated tone of a frequency between the sustained tones. The measured time elapsed before a first perception change showed that illusion, ambiguity and disambiguation actually took place. We anticipate that the proposed illusion and ambiguity will provide a well-controlled approach for behavioral and neurophysiological studies of music recognition because of the simplicity of stimulus.

Neurophysiological correlates of different moods and feelings induced by chords and harmonized scales revealed by fMRI.

Activated brain areas in response to major, minor, augmented and diminished chords as well as to major and minor harmonized scales were investigated by fMRI. The activated areas for the chord experiments included regions related to emotion processing. Results of the scale experimnts were less straightforward than those of the chord experiments. Possible relationship between the known functions of the areas activated by each category of stimuli and the behavioral (emotinal) effects of the category was discussed.

Evoked magnetoencephalographic responses to omission of a tone in a musical scale.

The musical scale is a basis for melodies and can be a simple melody by itself. The present study investigated magnetoencephalographic (MEG) responses to omissions of one tone out of the C major scale. The tone preceding the omitted "target" tone was either prolonged or repeated. In another series, the tone after the target tone was repeated. In "normal" oddball experiments, the complete C major scale was presented more frequently than an incomplete scale lacking one tone, and in "reverse" oddball experiments, the roles were exchanged. In the normal oddball experiments, omission of any tone produced a response significantly different in amplitude from the standard response in the group of non-musicians, although the responses differed depending on the types of omission. The leading tone (B in the C major scale) was shown to elicit a large response when omitted and also when its presence was emphasized. The Reverse oddball experiments showed that repeated presentation of an incomplete scale lacking one tone temporarily reduced the influence of the complete scale but could not even temporarily replace it working as "standard." In addition, an auxiliary study was done to see possible influence of rhythmic variations.

fMRI measurement of brain activities to major and minor chords and cadence sequences.

Brain activities to major and minor chords and to major and minor cadence sequences were measured by sparse scanning fMRI. Areas activated by major and minor chords and cadence sequences were examined. Some of them are known to be related to emotion, motivation, arousal or reward. In general, minor chords activated larger areas of brain regions than major chords. Some activated areas have not been especially associated with emotion or music processing. Cadence results are somewhat ambiguous probably due to the control sequence used. Also individual differences were considerable in both experiments.

Auditory MEG responses to removal of a tone in C major scale measured in a pair of reciprocal oddball schemes.

The C major scale was used either as frequent or as infrequent stimulus in the oddball auditory evoked field measurement where the other stimulus was constructed by removing one the tones in the scale. Multivariate statistical analysis was employed to judge whether there was a significant difference between the responses to complete and incomplete scales in each subject for each 'target' tone which was removed in an incomplete scale. Incomplete scales lacking, especially E, or B caused responses in both of the two oddball schemes but less significantly when used as frequent stimuli indicating that the complete major scale stored in the long term memory retained its influence as 'reference' stimulus even when presented with a smaller probability.

Neural signatures of phonetic learning in adulthood: a magnetoencephalography study.

The present study used magnetoencephalography (MEG) to examine perceptual learning of American English /r/ and /l/ categories by Japanese adults who had limited English exposure. A training software program was developed based on the principles of infant phonetic learning, featuring systematic acoustic exaggeration, multi-talker variability, visible articulation, and adaptive listening. The program was designed to help Japanese listeners utilize an acoustic dimension relevant for phonemic categorization of /r-l/ in English. Although training did not produce native-like phonetic boundary along the /r-l/ synthetic continuum in the second language learners, success was seen in highly significant identification improvement over twelve training sessions and transfer of learning to novel stimuli. Consistent with behavioral results, pre-post MEG measures showed not only enhanced neural sensitivity to the /r-l/ distinction in the left-hemisphere mismatch field (MMF) response but also bilateral decreases in equivalent current dipole (ECD) cluster and duration measures for stimulus coding in the inferior parietal region. The learning-induced increases in neural sensitivity and efficiency were also found in distributed source analysis using Minimum Current Estimates (MCE). Furthermore, the pre-post changes exhibited significant brain-behavior correlations between speech discrimination scores and MMF amplitudes as well as between the behavioral scores and ECD measures of neural efficiency. Together, the data provide corroborating evidence that substantial neural plasticity for second-language learning in adulthood can be induced with adaptive and enriched linguistic exposure. Like the MMF, the ECD cluster and duration measures are sensitive neural markers of phonetic learning.

Stochastic resonance in auditory steady-state responses in a magnetoencephalogram.

OBJECTIVE: To see whether stochastic resonance can be triggered in the auditory steady-state responses (ASSRs) in a magnetoencephalogram (MEG). METHODS: We measured ASSRs to 1kHz sinusoidal tone modulated at 40Hz with various intensities of white noise and obtained its power and degree of phase synchrony. RESULTS: Group statistics showed a significant enhancement in phase synchrony of ASSR by the presence of white noise of appropriate intensity. Tests on individual subjects showed that the data of four out of nine subjects exhibited enhancements in power or phase synchrony. CONCLUSIONS: The ASSRs exhibit stochastic resonance of the so-called I-type (I for information) shown in phase synchrony when responding to modulated sinusoidal sound superimposed with weak white noise. SIGNIFICANCE: The gamma-band component and other oscillatory components in the brain activity have been recently ascribed by some researchers to the result of stochastic resonance caused by internal noise in the brain. Therefore the presence of stochastic resonance in ASSRs may be evidence to the hypothesis that ASSRs are related to the ongoing gamma-band component.

Multiplicative correction of subject effect as preprocessing for analysis of variance.

The procedure of repeated-measures ANOVA assumes the linear model in which effects of both subjects and experimental conditions are additive. However, in electroencephalography and magnetoencephalography, there may be situations where subject effects should be considered to be multiplicative in amplitude. We propose a simple method to normalize such data by multiplying each subject's response by a subject-specific constant. This paper derives ANOVA tables for such normalized data. Present simulations show that this method performs ANOVA effectively including multiple comparisons provided that the data follows the multiplicative model.

Comparison of mismatch fields elicited by changes in tonal and atonal sequences.

Mismatch fields in magnetoencephalogram were recorded in ;ignore' condition while presenting combinations of standard and deviant tone sequences to the subjects to investigate how the structure of musical scale is represented in the brain function. Both tonal (having a key) and atonal sequences were employed to see the influence of tonality in eliciting mismatch fields. Mismatch fields were larger when the subject encountered the deviant sequence associated with the tonal sequence than with the atonal sequence suggesting connection between auditory cortical activity and recognition of 'key'.

Effect of magnetic bead agglomeration on Cytomagnetometric measurements.

Magnetic twisting cytometry (MTC) is a novel tool to measure cytoskeleton-associated cell functions by the use of ferromagnetic microbeads. Magnetic beads are either incorporated by living cells by phagocytic processes or attached to integrin receptors to the cell membrane. The magnetic beads are magnetized and aligned in a strong magnetic field pulse. The application of twisting forces allows to investigate mechanical properties (stiffness, viscoelasticity) of the cytoskeleton of living cells by analyzing the magnetic cell field. Incorporated magnetic beads undergo intracellular transport processes, which result in a loss of particle alignment and in a decay of the remanent magnetic cell field. This process, called relaxation, depends on the mechanical cytoskeletal properties and can directly visualize the intracellular energy of cellular transport processes. The preparation of spherical monodisperse ferromagnetic beads made it possible to understand the above-described processes using mathematical models. Experimental conditions with many magnetic particles per cell enhances the formation of aggregates because of the attractive forces between magnetic spheres, resulting in a change of magnetic properties and of hydrodynamic behavior. Due to mutual magnetization, the remanent magnetic moment of an aggregate is stronger compared to the same number of single particles. This implies a higher cell field. Additionally the relaxation is retarded because of the change in shape factor and in volume, which also implies a faulty estimation of intracellular transport energy. Magnetic particle twisting is less influenced. In summary, valuable cytomagnetometric measurements have to be done with less than one particle per macrophage to ensure low probability of multiple particles per cell.

A complex-valued version of Nagumo-Sato model of a single neuron and its behavior.

The Nagumo-Sato model of a single neuron was extended so that it can handle complex numbers and the behavior of the complex-valued model was investigated. The model neuron receives its past outputs through a complex-valued weight and fires when the absolute value of the membrane potential exceeds a threshold. Some of the basic features of the model, such as associated with fixed points and period-two orbits, were derived. The main purpose of the paper is to show the model's chaotic behavior which is the result of the extension to the complex numbers and different from that of the original real-valued model. The apparently chaotic orbits were numerically shown to have positive Lyapunov exponents and high sensitivity to the initial conditions. Some of the chaotic orbits seem to be related to the saddles of period-two and their associated stable and unstable manifolds.