Kazunari Ikeda

Asymmetrical mismatch negativity in humans as determined by phonetic but not physical difference.

A two-tone oddball procedure was employed to examine the effect of a phonemic category on the mismatch negativity (MMN). One of the stimuli was a phoneme prototype of Japanese /e/, and the other, [e/ö], which was perceived by Japanese participants as showing deviance from typicality but is nonetheless included in the category /e/. As control stimuli, a pair of pure tones (1940 and 1794 Hz), corresponding to the F2 frequencies of /e/ and [e/ö], respectively, was presented within the same oddball procedure. The MMN for deviant [e/ö] revealed greater amplitude than that of deviant /e/, although there was no significant difference in amplitude between the pure tones. The results suggest that a phonemic category determines the auditory sensory memory.

ERP Evaluation of Auditory Sensory Memory Systems in Adults with Intellectual Disability

Auditory sensory memory stage can be functionally divided into two subsystems; transient-detector system and permanent feature-detector system (). We assessed these systems in persons with intellectual disability by measuring event-related potentials (ERPs) N1 and mismatch negativity (MMN), which reflect the two auditory subsystems, respectively. Added to these, P3a (an ERP reflecting stage after sensory memory) was evaluated. Either synthesized vowels or simple tones were delivered during a passive oddball paradigm to adults with and without intellectual disability. ERPs were recorded from midline scalp sites (Fz, Cz, and Pz). Relative to control group, participants with the disability exhibited greater N1 latency and less MMN amplitude. The results for N1 amplitude and MMN latency were basically comparable between both groups. IQ scores in participants with the disability revealed no significant relation with N1 and MMN measures, whereas the IQ scores tended to increase significantly as P3a latency reduced. These outcomes suggest that persons with intellectual disability might own discrete malfunctions for the two detector systems in auditory sensory-memory stage. Moreover, the processes following sensory memory might be partly related to a determinant of mental development.

Automatic auditory processing and event-related brain potentials in persons with mental retardation.

Measuring event-related brain potentials, this study examined automatic auditory processing in adults with and without mental retardation. Using an auditory oddball paradigm under an inattentive condition, we anticipated that an enhanced negative potential would be followed by a relatively small positive potential. The former was considered as the mismatch negativity and the latter as the P3a. Retarded adults (1 woman, 6 men, defined as a range of moderate to profound retardation) and 8 nonretarded (2 women, 6 men) adults participated. The mismatch negativity showed smaller amplitudes and greater latencies for retarded persons than those for nonretarded adults, whereas the P3a for the groups was comparable. The results may suggest malfunction of automatic auditory change-detection of the brain in mentally retarded persons.

Distinctive MMN relative to sound types in adults with intellectual disability

The effect of stimulus characteristics (vowel vs pure tone) upon mismatch negativity (MMN) was compared between adults with intellectual disability and healthy controls. Either vowels (synthesized vowels /e/ and /o/) or pure tones (1940 and 851 Hz corresponding to the F2 frequencies of /e/ and /o/, respectively) were presented using an oddball procedure. Both groups showed identical results in latency (vowel MMN>pure tone MMN) and less amplitudes for vowels. However, the disabled group demonstrated amplitude attenuation regardless of the stimulus type, although the vowel MMN amplitude showed a descending trend with age in both groups. These results suggest that auditory sensory memory in intellectual disability might have an insufficient capacity yet share a property common to controls.

An ignoring task improves validity of cortical evoked response audiometry.

This study examined the basis for introducing an ignoring task during cortical evoked response audiometry (CERA) using the N1-P2 response. Healthy hearing participants were assigned to two groups with and without an ignoring task (ignoring and listening groups) during CERA whose outcomes were compared with the pure-tone audiometry (PTA) in response to tone frequencies at 500–4000 Hz. The ignoring but not the listening group exhibited positive correlations between the PTA and CERA thresholds, and further showed negative correlations between the PTA threshold and the N1-P2 amplitude as the tone intensity decreased particularly for lower tone frequencies. Within the healthy hearing levels at least, conducting an ignoring task is thus considered to improve the validity of CERA for lower tone frequencies.

Color-specific filtering of rival binocular inputs induced by priming1

:  In a situation where the two eyes separately receive two dissimilar images such as a blue square and a red square, the brain is forced to resolve competitive interpretations of the visual inputs. Earlier studies have indicated that adaptation to one of two rival images can control the following competitive perception. Consistent with those studies, the present experiments revealed that immediately after a brief presentation of a color (priming stimulation) to the two eyes, subjects dominantly perceived the other color out of the chromatic rivalry. This effect showed an interocular transfer even if indirect monocular priming was employed, but the filtering out of a primed color did not occur when an unprimed rival image was removed from the other eye. These facts suggest that binocular feature-detection processes in the human visual system might be responsible for the priming effect on rival images.

Binaural interaction in human auditory brainstem response compared for tone-pips and rectangular clicks under conditions of auditory and visual attention.

Binaural interaction in the auditory brainstem response (ABR) represents the discrepancy between the binaural waveform and the sum of monaural ones. A typical ABR binaural interaction in humans is a reduction of the binaural amplitude compared to the monaural sum at the wave-V latency, i.e., the DN1 component. It has been considered that the DN1 is mainly elicited by high frequency components of stimuli whereas some studies have shown the contribution of low-to-middle frequency components to the DN1. To examine this issue, the present study compared the ABR binaural interaction elicited by tone pips (1 kHz, 10-ms duration) with the one by clicks (a rectangular wave, 0.1-ms duration) presented at 80 dB peak equivalent SPL and a fixed stimulus onset interval (180 ms). The DN1 due to tone pips was vulnerable compared to the click-evoked DN1. The pip-evoked DN1 was significantly detected under auditory attention whereas it failed to reach significance under visual attention. The click-evoked DN1 was robustly present for the two attention conditions. The current results might confirm the high frequency sound contribution to the DN1 elicitation.

Attention-related modulation of auditory brainstem responses during contralateral noise exposure.

As determinants facilitating attention-related modulation of the auditory brainstem response (ABR), two experimental factors were examined: (i) auditory discrimination; and (ii) contralateral masking intensity. Tone pips at 80 dB sound pressure level were presented to the left ear via either single-tone exposures or oddball exposures, whereas white noise was delivered continuously to the right ear at variable intensities (none – 80 dB sound pressure level). Participants each conducted two tasks during stimulation, either reading a book (ignoring task) or detecting target tones (attentive task). Task-related modulation within the ABR range was found only during oddball exposures at contralateral masking intensities greater than or equal to 60 dB. Attention-related modulation of ABR can thus be detected reliably during auditory discrimination under contralateral masking of sufficient intensity.

Concentrated pitch discrimination modulates auditory brainstem responses during contralateral noise exposure

This study examined a notion that auditory discrimination is a requisite for attention-related modulation of the auditory brainstem response (ABR) during contralateral noise exposure. Given that the right ear was exposed continuously with white noise at an intensity of 60–80 dB sound pressure level, tone pips at 80 dB sound pressure level were delivered to the left ear through either single-stimulus or oddball procedures. Participants conducted reading (ignoring task) and counting target tones (attentive task) during stimulation. The oddball but not the single-stimulus procedures elicited task-related modulations in both early (ABR) and late (processing negativity) event-related potentials simultaneously. The elicitation of the attention-related ABR modulation during contralateral noise exposure is thus considered to require auditory discrimination and have the corticofugal nature evidently.

ATTENTION EFFECTS AT AUDITORY PERIPHERY DERIVED FROM HUMAN SCALP POTENTIALS: DISPLACEMENT MEASURE OF POTENTIALS

It is known in humans that electrophysiological measures such as the auditory brainstem response (ABR) are difficult to identify the attention effect at the auditory periphery, whereas the centrifugal effect has been detected by measuring otoacoustic emissions. This research developed a measure responsive to the shift of human scalp potentials within a brief post-stimulus period (13 ms), that is, displacement percentage, and applied it to an experiment to retrieve the peripheral attention effect. In the present experimental paradigm, tone pips were exposed to the left ear whereas the other ear was masked by white noise. Twelve participants each conducted two conditions of either ignoring or attending to the tone pips. Relative to averaged scalp potentials in the ignoring condition, the shift of the potentials was found within early component range during the attentive condition, and displacement percentage then revealed a significant magnitude difference between the two conditions. These results suggest that, using a measure representing the potential shift itself, the peripheral effect of attention can be detected from human scalp potentials.