Effects of Presentation Rate and Attention on Auditory Discrimination: A Comparison of Long-Latency Auditory Evoked Potentials in School-Aged Children and Adults

Decoding human speech requires both perception and integration of brief, successive auditory stimuli that enter the central nervous system as well as the allocation of attention to language-relevant signals. This study assesses the role of attention on processing rapid transient stimuli in adults and children. Cortical responses (EEG/ERPs), specifically mismatch negativity (MMN) responses, to paired tones (standard 100–100Hz; deviant 100–300Hz) separated by a 300, 70 or 10ms silent gap (ISI) were recorded under Ignore and Attend conditions in 21 adults and 23 children (6–11 years old). In adults, an attention-related enhancement was found for all rate conditions and laterality effects (L>R) were observed. In children, 2 auditory discrimination-related peaks were identified from the difference wave (deviant-standard): an early peak (eMMN) at about 100–300ms indexing sensory processing, and a later peak (LDN), at about 400–600ms, thought to reflect reorientation to the deviant stimuli or “second-look” processing. Results revealed differing patterns of activation and attention modulation for the eMMN in children as compared to the MMN in adults: The eMMN had a more frontal topography as compared to adults and attention played a significantly greater role in childrens’ rate processing. The pattern of findings for the LDN was consistent with hypothesized mechanisms related to further processing of complex stimuli. The differences between eMMN and LDN observed here support the premise that separate cognitive processes and mechanisms underlie these ERP peaks. These findings are the first to show that the eMMN and LDN differ under different temporal and attentional conditions, and that a more complete understanding of children’s responses to rapid successive auditory stimulation requires an examination of both peaks.     

The mismatch negativity for duration decrement of auditory stimuli in healthy subjects

The amplitude and latency of the mismatch negativity (MMN) elicited by occasional shorter-duration tones (25 and 50 ms) in a sequence of 75 ms standard tones were studied in 40 healthy subjects (9–84 years). The replicability and age dependence of the MMN-responses were determined. The 25 ms deviant tone evoked a clear response in 39 of the subjects, while the 50 ms deviant tone evoked an observable MMN only in 32 of the subjects. The MMN peak amplitude for the 25 ms deviants was significantly larger than for the 50 ms deviants. There was no significant difference in the peak latencies (measured from stimulus offset). For the 25 ms deviant, the amplitude diminished with increasing age. The MMN curves for the 25 ms deviant, measured on separate days in 14 subjects, looked very replicable. As a result of noise and filtering effect, the product-moment correlations were poor. The results indicate that the signal-to-noise ratio for the MMN to 25 ms deviants, obtained even in a 25 min recording session, is large enough for clinical use and individual diagnostics when undetectable (or very low amplitude) MMN is used as a sign of pathology. However, judged from the low correlation coefficients, despite the good replicability in visual evaluation, better methods for MMN quantification have to be used for clinical follow-up.     

Interstimulus interval and auditory event-related potentials in children: evidence for multiple generators

In the present study, the component structure of auditory event-related potentials (ERP) was studied in children of 7–9 years old by presenting stimuli with different interstimulus intervals (ISI). A short-term auditory sensory memory, as reflected by ISI effects on ERPs, was also studied. Auditory ERPs were recorded to brief unattended 1000 Hz frequent, `standard' and 1100 Hz rare, `deviant' (probability 0.1) tone stimuli with ISIs of 350, 700 and 1400 ms (in separate blocks). With the 350 ms-ISI, the ERP waveform to the standard stimulus consisted of P100-N250 peaks. With the two longer ISIs, in addition, the frontocentral N160 and N460 peaks were observed. Results suggested that N160, found with the longer ISIs, is a correlate of the adult auditory N1. In difference waves, obtained by subtracting ERP to standard stimuli from ERP to deviant stimuli, two negativities were revealed. The first was the mismatch negativity (MMN), which is elicited by any discriminable change in repetitive auditory input. The MMN data suggested that neural traces of auditory sensory memory lasted for at least 1400 ms, probably considerably longer, as no MMN attenuation was found across the ISIs used. The second, later negativity was similar to MMN in all aspects, except for the scalp distribution, which was posterior to that of the MMN.     

Mismatch Negativity Latency and Cognitive Function in Schizophrenia

Background

The Mismatch Negativity (MMN) is an event-related potential (ERP) sensitive to early auditory deviance detection and has been shown to be reduced in schizophrenia patients. Moreover, MMN amplitude reduction to duration deviant tones was found to be related to functional outcomes particularly, to neuropsychological (working memory and verbal domains) and psychosocial measures. While MMN amplitude is thought to be correlated with deficits of early sensory processing, the functional significance of MMN latency remains unclear so far. The present study focused on the investigation of MMN in relation to neuropsychological function in schizophrenia.

Method

Forty schizophrenia patients and 16 healthy controls underwent a passive oddball paradigm (2400 binaural tones; 88% standards [1 kHz, 80 db, 80 ms], 11% frequency deviants [1.2 kHz], 11% duration deviants [40 ms]) and a neuropsychological test-battery. Patients were assessed with regard to clinical symptoms.

Results

Compared to healthy controls schizophrenia patients showed diminished MMN amplitude and shorter MMN latency to both deviants as well as an impaired neuropsychological test performance. Severity of positive symptoms was related to decreased MMN amplitude to duration deviants. Furthermore, enhanced verbal memory performance was associated with prolonged MMN latency to frequency deviants in patients.

Conclusion

The present study corroborates previous results of a diminished MMN amplitude and its association with positive symptoms in schizophrenia patients. Both, the findings of a shorter latency to duration and frequency deviants and the relationship of the latter with verbal memory in patients, emphasize the relevance of the temporal aspect of early auditory discrimination processing in schizophrenia.     

Short-term replicability of the mismatch negativity

The short-term replicability of the mismatch negativity (MMN) between two recording sessions spaced 2 h apart was evaluated at individual and group levels in a sample of 11 healthy adults. Subjects were presented with a random sequence of 1000 Hz standard (92%) and 1100 Hz deviant (8%) tones while they were reading a book. The N1 and P2 exogenous components to standard tones showed a fairly good individual and group replicability. There were no significant differences in the MMN amplitude and latency between the two sessions in the group of subjects as a whole. The individual replicability of the MMN was not as good as for the N1 to standards, reaching significance in only some of the electrodes. This result was, however, similar to that obtained for the N1 after deviant tones. The results indicate that the MMN has good replicability at the group level, and further that at the individual level, MMN replicability is similar to that of the N1 to deviants. This suggests that the number of summations should be increased in order to improve the clinical usefulness of the MMN.     

Auditory selective attention in middle-aged and elderly subjects: an event-related brain potential study

Reaction times (RTs) and event-related brain potentials (ERPs) were recorded in middle-aged (MA) and elderly (ELD) subjects performing an auditory selective attention task. Subjets attended to tone bursts of a specified pitch and ear of delivery and responded to occasional longer duration target tones (75 vs. 25 msec). Infrequent novel stimuli (computer synthesized sounds and digitized environmental noises) were also included in the stimulus sequence.No significant age-related differences were found in the speed or accuracy of target detection. However, in both groups, RTs were delayed (by more than 300 msec) to targets that followed novel sounds. The prolongation was greater following novel sounds in the attended ear, particularly in the ELD group.The effects of selective attention on ERPs to standard tones were isolated as negative difference waves (Nds) by subtracting ERPs to non-attended stimuli from ERPs to the same signals when attended. Nds had similar amplitudes, latencies of onset (60 msec), and distributions in ELD and MA groups. In both groups, Nd waves were more prominent following right ear stimulation, reflecting possible hemispheric asymmetries of generators in posterior temporal regions.The mismatch negativity (MMN) was isolated by subtracting ERPs to standard tones from ERPs to deviant stimuli. MMN amplitudes were reduced in the ELD group. There was also a significant change in MMN distribution with age: the MMN was larger over the right hemisphere for MA subjects but larger over the left for ELD subjects. Elderly subjects showed a trend toward smaller P3 amplitudes and delayed P3 latencies, but group differences did not reach statistical significance. ERPs to novel sounds were characterized by centrally distributed N2 and P3a components. Although the novel P3a was enhanced with attention, no novel Nd waves could be isolated. This suggests that novel sounds fell outside the focus of attention.     

Auditory stimulus discrimination recorded in dogs, as indicated by mismatch negativity (MMN)

Dog cognition research tends to rely on behavioural response, which can be confounded by obedience or motivation, as the primary means of indexing dog cognitive abilities. A physiological method of measuring dog cognitive processing would be instructive and could complement behavioural response. Electroencephalogram (EEG) has been used in humans to study stimulus processing, which results in waveforms called event-related potentials (ERPs). One ERP component, mismatch negativity (MMN), is a negative deflection approximately 160-200 ms after stimulus onset, which may be related to change detection from echoic sensory memory. We adapted a minimally invasive technique to record MMN in dogs. Dogs were exposed to an auditory oddball paradigm in which deviant tones (10% probability) were pseudo-randomly interspersed throughout an 8 min sequence of standard tones (90% probability). A significant difference in MMN ERP amplitude was observed after the deviant tone in comparison to the standard tone, t₅ = −2.98, p = 0.03. This difference, attributed to discrimination of an unexpected stimulus in a series of expected stimuli, was not observed when both tones occurred 50% of the time, t₁ = −0.82, p > 0.05. Dogs showed no evidence of pain or distress at any point. We believe this is the first illustration of MMN in a group of dogs and anticipate that this technique may provide valuable insights in cognitive tasks such as object discrimination.     

The Characteristic and Changes of the Event-Related Potentials (ERP) and Brain Topographic Maps before and after Treatment with rTMS in Subjective Tinnitus Patients

Objectives

To compare the event-related potentials (ERPs) and brain topographic maps characteristic and change in normal controls and subjective tinnitus patients before and after repetitive transcranial magnetic stimulation (rTMS) treatment.

Methods and Participants

The ERPs and brain topographic maps elicited by target stimulus were compared before and after 1-week treatment with rTMS in 20 subjective tinnitus patients and 16 healthy controls.

Results

Before rTMS, target stimulus elicited a larger N1 component than the standard stimuli (repeating sounds)in control group but not in tinnitus patients. Instead, the tinnitus group pre-treatment exhibited larger amplitude of N1 in response to standard stimuli than to deviant stimuli. Furthermore tinnitus patients had smaller mismatch negativity (MMN) and late discriminative negativity (LDN)component at Fz compared with the control group. After rTMS treatment, tinnitus patients showed increased N1 response to deviant stimuli and larger MMN and LDN compared with pre-treatment. The topographic maps for the tinnitus group before rTMS -treatment demonstrated global asymmetry between the left and right cerebral hemispheres with more negative activities in left side and more positive activities in right side. In contrast, the brain topographic maps for patients after rTMS-treatment and controls seem roughly symmetrical. The ERP amplitudes and brain topographic maps in post-treatment patient group showed no significant difference with those in controls.

Conclusions

The characterical changes in ERP and brain topographic maps in tinnitus patients maybe related with the electrophysiological mechanism of tinnitus induction and development. It can be used as an objective biomarker for the evaluation of auditory central in subjective tinnitus patients. These findings support the notion that rTMS treatment in tinnitus patients may exert a beneficial effect.     

Auditory event-related potentials to deviant stimuli during drowsiness and stage 2 sleep

Twelve subjects were tested using a 3-tone auditory oddball paradigm consisting of a standard 1000 Hz tone (P = 80%) and two deviants, namely, a 1200 Hz tone and a 2000 Hz tone (both P = 10%). Testing took place in 3 conditions: (1) attend, in which the subject had to count one of the deviant tones; (2) ignore, in which the subject read a book; and (3) sleep, in which the subject was encouraged to go to sleep during presentation of the tones.In the awake conditions stimulus deviance elicited mismatch negativity (MMN) and P3. During drowsiness, no separate mismatch negativity (MMN) could be detected, but the 2000 Hz tone evoked a broad fronto-central early negative deflection, suggesting an overlap of N₁ and MMN. In the same condition, P210, N330 and P430 appeared, all being sensitive to magnitude of deviance. During stage 2, the P210, N330 and P430 amplitudes increased, most notably to the large deviant.These data indicate that differential processing of auditory inputs is maintained during drowsiness and stage 2 sleep, but do not support the notion that MMN or P3 activity comparable to the waking state occurs to oddball stimuli during this stage. It is hypothesised that during light sleep, scanning of the environment is performed by a different system than in the awake state and that during drowsiness a gradual switch between these two systems takes place.     

Frequency Change Detection in Human Auditory Cortex

We offer a model of how human cortex detects changes in the auditory environment. Auditory change detection has recently been the object of intense investigation via the mismatch negativity (MMN). MMN is a preattentive response to sudden changes in stimulation, measured noninvasively in the electroencephalogram (EEG) and the magnetoencephalogram (MEG). It is elicited in the oddball paradigm, where infrequent deviant tones intersperse a series of repetitive standard tones. However, little apart from the participation of tonotopically organized auditory cortex is known about the neural mechanisms underlying change detection and the MMN. In the present study, we investigate how poststimulus inhibition might account for MMN and compare the effects of adaptation with those of lateral inhibition in a model describing tonotopically organized cortex. To test the predictions of our model, we performed MEG and EEG measurements on human subjects and used both small- (<1/3 octave) and large- (>5 octaves) frequency differences between the standard and deviant tones. The experimental results bear out the prediction that MMN is due to both adaptation and lateral inhibition. Finally, we suggest that MMN might serve as a probe of what stimulus features are mapped by human auditory cortex.     

Auditory ERPs to stimulus deviance in an awake chimpanzee (Pan troglodytes): towards hominid cognitive neurosciences

Background

For decades, the chimpanzee, phylogenetically closest to humans, has been analyzed intensively in comparative cognitive studies. Other than the accumulation of behavioral data, the neural basis for cognitive processing in the chimpanzee remains to be clarified. To increase our knowledge on the evolutionary and neural basis of human cognition, comparative neurophysiological studies exploring endogenous neural activities in the awake state are needed. However, to date, such studies have rarely been reported in non-human hominid species, due to the practical difficulties in conducting non-invasive measurements on awake individuals.

Methodology/Principal Findings

We measured auditory event-related potentials (ERPs) of a fully awake chimpanzee, with reference to a well-documented component of human studies, namely mismatch negativity (MMN). In response to infrequent, deviant tones that were delivered in a uniform sound stream, a comparable ERP component could be detected as negative deflections in early latencies.

Conclusions/Significance

The present study reports the MMN-like component in a chimpanzee for the first time. In human studies, various ERP components, including MMN, are well-documented indicators of cognitive and neural processing. The results of the present study validate the use of non-invasive ERP measurements for studies on cognitive and neural processing in chimpanzees, and open the way for future studies comparing endogenous neural activities between humans and chimpanzees. This signifies an essential step in hominid cognitive neurosciences.     

Mismatch negativity in the brain evoked potentials induced by short duration acoustic stimuli in adolescents in the norm and those with attention deficit

The effect of stimulus duration on the mismatch negativity of the auditory event-related potentials was studied in healthy children and those with attention-deficit symptoms. The minimum stimulus duration with which a MMN was elicited by frequency deviant was 50 ms in healthy children. The MMN was absent with shorter stimuli (11 ms and 30 ms). These parametres are close to those in adults. As to children with attention-deficit symptoms the MMN was insignificant with all tested stimulus durations (11 ms, 30 ms, 50 ms).     

Answering six questions in extracting children��s mismatch negativity through combining wavelet decomposition and independent component analysis

This study combines wavelet decomposition and independent component analysis (ICA) to extract mismatch negativity (MMN) from electroencephalography (EEG) recordings. As MMN is a small event-related potential (ERP), a systematic ICA based approach is designed, exploiting MMN’s temporal, frequency and spatial information. Moreover, this study answers which type of EEG recordings is more appropriate for ICA to extract MMN, what kind of the preprocessing is beneficial for ICA decomposition, which algorithm of ICA can be chosen to decompose EEG recordings under the selected type, how to determine the desired independent component extracted by ICA, how to improve the accuracy of the back projection of the selected independent component in the electrode field, and what can be finally obtained with the application of ICA. Results showed that the proposed method extracted MMN with better properties than those estimated by difference wave only using temporal information or ICA only using spatial information. The better properties mean that the deviant with larger magnitude of deviance to repeated stimuli in the oddball paradigm can elicit MMN with larger peak amplitude and shorter latency. As other ERPs also have the similar information exploited here, the proposed method can be used to study other ERPs.     

Representation and Processing of Lexical Tone and Tonal Variants: Evidence from the Mismatch Negativity

Pronunciation variation is ubiquitous in the speech signal. Different models of lexical representation have been put forward to deal with speech variability, which differ in the level as well as the nature of mental representation. We present the first mismatch negativity (MMN) study investigating the effect of allophonic variation on the mental representation and neural processing of lexical tones. Native speakers of Standard Chinese (SC) participated in an oddball electroencephalography (EEG) experiment. All stimuli have the same segments (ma) but different lexical tones: level [T1], rising [T2], and dipping [T3]. In connected speech with a T3T3 sequence, the first T3 may undergo allophonic change and is produced with a rising pitch contour (T3V), similar to the lexical T2 pitch contour. Four oddball conditions were constructed (T1/T3, T3/T1, T2/T3, T3/T2; standard/deviant). All four conditions elicited MMN effects, with the T1–T3 pair eliciting comparable MMNs, but the T2–T3 pair asymmetrical MMN effects. There were significantly greater and earlier MMN effects in the T2/T3 condition than that in the reversed T3/T2 condition. Furthermore, the T3/T2 condition showed more rightward MMN effects than the T2/T3 condition and the T1–T3 pair. Such asymmetries suggest co-activation of long-term memory representations of both T3 and T3V when T3 serves as the standard. The acoustic similarity between the activated T3V (by the standard T3) and the incoming deviant stimulus T2 induces acoustic processing of the tonal contrast in the T3/T2 condition, similar to that of within-category lexical tone processing, which is in contrast to the processing of between-category lexical tones observed in the T2/T3, T1/T3, and T3/T1 conditions.     

Effects of pre- and postnatal exposure to extremely low-frequency electric fields on mismatch negativity component of the auditory event-related potentials: Relation to oxidative stress

ABSTRACT

In our previous study, the developmental effects of extremely low-frequency electric fields (ELF-EF) on visual and somatosensory evoked potentials in adult rats were studied. There is no study so far examining the effects of 50 Hz electric field (EF) on mismatch negativity (MMN) recordings after exposure of rats during development. Therefore, our present study aimed to investigate MMN and oxidative brain damage in rats exposed to EF (12 kV/m, 1 h/day). Rats were divided into four groups, namely control (C), prenatal (Pr), postnatal (Po), and prenatal+postnatal (PP). Pregnant rats of Pr and PP groups were exposed to EF during pregnancy. Following birth, rats of PP and Po groups were exposed to EF for three months. After exposure to EF, MMN was recorded by electrodes positioned stereotaxically to the surface of the dura, and then brain tissues were removed for histological and biochemical analyses. The MMN amplitude was higher to deviant tones than to standard tones. It was decreased in all experimental groups compared with the C group. 4-Hydroxy-2-nonenal (4-HNE) levels were significantly increased in the Po group with respect to the C group, whereas they were significantly decreased in the PP group compared with Pr and Po groups. Protein carbonyl levels were significantly decreased in the PP group compared with C, Pr, and Po groups. EF decreased MMN amplitudes were possibly induced by lipid peroxidation.     

Neuromagnetic evidence for early auditory restoration of fundamental pitch

Background

Understanding the time course of how listeners reconstruct a missing fundamental component in an auditory stimulus remains elusive. We report MEG evidence that the missing fundamental component of a complex auditory stimulus is recovered in auditory cortex within 100 ms post stimulus onset.

Methodology

Two outside tones of four-tone complex stimuli were held constant (1200 Hz and 2400 Hz), while two inside tones were systematically modulated (between 1300 Hz and 2300 Hz), such that the restored fundamental (also knows as “virtual pitch”) changed from 100 Hz to 600 Hz. Constructing the auditory stimuli in this manner controls for a number of spectral properties known to modulate the neuromagnetic signal. The tone complex stimuli only diverged on the value of the missing fundamental component.

Principal Findings

We compared the M100 latencies of these tone complexes to the M100 latencies elicited by their respective pure tone (spectral pitch) counterparts. The M100 latencies for the tone complexes matched their pure sinusoid counterparts, while also replicating the M100 temporal latency response curve found in previous studies.

Conclusions

Our findings suggest that listeners are reconstructing the inferred pitch by roughly 100 ms after stimulus onset and are consistent with previous electrophysiological research suggesting that the inferential pitch is perceived in early auditory cortex.     

Mismatch field to tone pairs: neuromagnetic evidence for temporal integration at the sensory level

The mismatch field (MMF) to minor pitch changes in two experimental conditions was studied. Standard tones of 1000 Hz and deviant tones of 1050 Hz both of 50 ms duration were delivered in single tone condition. Paired tones of the same duration were used in the paired tone condition. The standard tone pair consisted of two 1000 Hz tones, whereas the deviant tone pair was composed of a 1000 Hz tone in the first position and a 1050 Hz tone in the second position with a silent interval of 15 ms between the two. Standards of 90% and deviants of 10% probability were presented in random order and with a randomized interstimulus interval between 600 and 900 ms. The source analysis showed a more lateral location for the MMF obtained in the paired tone condition (MMF.P) compared to the MMF elicited by the single deviants (MMF.S). The source location of both the MMF.P and MMF.S turned out to be significantly anterior relative to the sources of the M100. The increased stimulus repetition in the paired tone condition (two times more stimuli than in the single tone condition) lead to a strong suppression of the field amplitude and of the dipole moment of the M100, while this effect could not be seen for the MMF. The data demonstrate a fundamental difference between the processes reflected by the M100 and the MMF: while the M100 represents the processing of every individual tone, the MMF reflects the change detection of the paired stimuli as unitary events, forming a perceptual group. The different sources of the MMF.P and MMF.S also support an integrated processing of the paired stimuli.     

Processing of Continuously Provided Punishment and Reward in Children with ADHD and the Modulating Effects of Stimulant Medication: An ERP Study

Objectives

Current models of ADHD suggest abnormal reward and punishment sensitivity, but the exact mechanisms are unclear. This study aims to investigate effects of continuous reward and punishment on the processing of performance feedback in children with ADHD and the modulating effects of stimulant medication.

Methods

15 Methylphenidate (Mph)-treated and 15 Mph-free children of the ADHD-combined type and 17 control children performed a selective attention task with three feedback conditions: no-feedback, gain and loss. Event Related Potentials (ERPs) time-locked to feedback and errors were computed.

Results

All groups performed more accurately with gain and loss than without feedback. Feedback-related ERPs demonstrated no group differences in the feedback P2, but an enhanced late positive potential (LPP) to feedback stimuli (both gains and losses) for Mph-free children with ADHD compared to controls. Feedback-related ERPs in Mph-treated children with ADHD were similar to controls. Correlational analyses in the ADHD groups revealed that the severity of inattention problems correlated negatively with the feedback P2 amplitude and positively with the LPP to losses and omitted gains.

Conclusions

The early selective attention for rewarding and punishing feedback was relatively intact in children with ADHD, but the late feedback processing was deviant (increased feedback LPP). This may explain the often observed positive effects of continuous reinforcement on performance and behaviour in children with ADHD. However, these group findings cannot be generalised to all individuals with the ADHD, because the feedback-related ERPs were associated with the severity of the inattention problems. Children with ADHD-combined type with more inattention problems showed both deviant early attentional selection of feedback stimuli, and deviant late processing of non-reward and punishment.     

Evoked potentials in the brain of adolescents in norm and those with attention deficit during recognition of short-term acoustic stimuli

The effect of stimulus duration on auditory event-related potentials and performance of oddball task was studied in normal children and those with attention-deficit symptoms. Mismatch negativity was absent on presentation of short-term (11 ms) stimuli and present with longer stimuli (50 ms). The adolescents with deficit of attention performed much worse (errors of omission) with the short stimuli. The RT was significantly larger in subjects with attention-deficit with all types of tested stimulus duration. They also manifested a smaller P3b amplitude in response to task-relevant deviant stimuli and larger N2b peaks in response to the standard stimuli. It was possible to differentiate between the MMN and the N2b components owing to the fact that the MMN was absent with shorter stimuli. The findings suggest that there is a deficit in processing of sensory information at the cortical level in subjects with the attention-deficit symptoms.     

规律短音中极短间隔短音诱发的失匹配负电位

失匹配负电位是听觉事件相关电位的一个成分,它由一系列重复的,同性质的“标准刺激”的物理性质稍有偏离的“偏差刺激”所诱发,在规律性的标准刺激中,偶然的物理性质稍有偏离的刺激,如频率,强度,久度等的些微变化均可诱发ＭＭＮ。偶然地给于时间上“过早出现”的同样刺激,即频率,强度,久度完全相同,只是在规律性的标准刺激中过早地出现的刺激,作为偏差刺激,也可以诱发出ＮＮＭ。本研究在恒定刺激间隔ＩＳＩ＝６００ｍｓ