Intermodal selective attention. I. Effects on event-related potentials to lateralized auditory and visual stimuli.

The effects of intermodal selective attention on event-related brain potentials (ERPs) were examined in 2 experiments. In experiment 1, auditory ERPs were compared (1) when subjects responded to easy and difficult-to-detect target tones in sequences of tone bursts; and (2) when they ignored the same auditory sequences and played a demanding video game. In experiment 2, auditory ERPs to tone bursts and visual ERPs to vertical line gratings were compared as subjects responded to difficult-to-detect targets in one modality or the other. Attention to auditory stimuli resulted in biphasic enhancements in auditory ERPs, the Nda (negative auditory difference wave, latency 120-160 msec) and the Pda (positive auditory difference wave, latency 200-240 msec) waves. These had longer latencies and somewhat different scalp distributions than N1 and P2 components evoked by non-attended tones. The Nda and Pda could be contrasted with the monophasic processing negativities typically found in dichotic selective attention tasks. Nda amplitudes were larger for difficult-to-detect targets (closely resembling standards) than for standards themselves, but no Ndas were recorded to highly deviant targets. Deviant auditory stimuli evoked mismatch negativities (MMNs) that persisted during visual attention. MMN amplitudes to difficult-to-detect deviants were enlarged with attention, but no change was found in MMN amplitudes to easy-to-detect deviants. In experiment 2 intermodal attention was associated with biphasic changes in visual ERPs over the posterior scalp: the occipital Pdv (100-130 msec), and contralateral-temporal Ndv (120-320 msec) deflections. Deviant visual stimuli also elicited mismatch negativity/N2b components, largest over the inferotemporal cortex contralateral to the stimulated visual field. Like the auditory MMN, the MMN increased in amplitude with attention, but it was also evident during attend auditory conditions. The results suggest that sustained, intermodal attention depends primarily in processing modulations in modality-specific cortex. We found no evidence of the participation of modality non-specific cortex. This excludes the possibility that intermodal attention depends on a single, supramodal attention system. The relatively long latency of intermodal effects suggests that they may depend on the reafferent (top down) modulation, and do not index "template matching" operations.     

Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch negativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repetition and change in a 6-year-old child undergoing presurgical evaluation for epilepsy. EEG was recorded from three bilateral sub-dural electrode strips located over lateral prefrontal areas during unattended auditory stimulation. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration tones and complex sounds (telephone buzz). In another condition, ERPs were recorded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any of the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections were recorded to both tones and phonemes over the right lateral prefrontal cortex. These responses were insensitive to the serial position of the repeating sound in the stimulus train. Deviant tones evoked an MMN peaking at around 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology but with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmann's area 45) is involved in early stages of processing repeating sounds and sound changes.     

The mismatch negativity to frequency deviant stimuli during natural sleep

Eight subjects spent a single night in the sleep laboratory. Event-related potentials (ERPs) were recorded during the presentation of two auditory ‘oddball’ stimulus conditions in which tonal frequency was manipulated. In the first condition, 1000 Hz ‘standard’ and 2000 Hz ‘deviant’ tones were presented. In the second condition, the deviant tone was reduced to 1050 Hz. In both conditions, deviant probability was 0.2. Stimuli were presented every 600 ms during wakefulness and stages 2, 4, and REM of sleep. A distinctive N1 wave was visible in both stimulus conditions when the subject was awake. The deviant stimuli elicited a ‘mismatch negativity’ (MMN) that inverted in polarity at the mastoid. In REM sleep, an N1 and a MMN were also elicited in both conditions. In the large deviance condition, the MMN had a slightly attenuated amplitude and was shorter in duration while in the small deviant condition, its peak latency was unusually early. Neither the N1 nor the MMN could be recorded in non-REM sleep.     

Separation of mismatch negativity and the N1 wave in the auditory cortex of the cat: a topographic study.

OBJECTIVE: The amplitude distribution of the frequency mismatch negativity (MMN) and that of P1 and N1 components were investigated in cats to reveal their sources in the auditory areas of the neocortex. METHODS: Pure tone stimuli were given in a passive oddball paradigm with different degrees of deviance between the standard and deviant tones. Amplitude maps of event-related potential (ERP) components were generated from the responses, recorded in awake, freely moving animals by a chronically implanted epidural electrode matrix, covering both the primary and secondary auditory fields. RESULTS: The P1 and N1 components appeared with highest amplitude on the middle ectosylvian gyrus, while the amplitude maximum of the MMN was ventral and rostral to them on the AII area. Both the latency and the peak amplitude of the MMN depended on the degree of deviance. CONCLUSIONS: The MMN is generated in the rostroventral part of the secondary auditory area, well separated from the sources of the P1 and N1 components.     

Mismatch negativity in paranoid, schizotypal, and antisocial personality disorders.

AIMS: The mismatch negativity (MMN) to frequency deviant tones has yielded conflicting results in patients with schizophrenia. This might be because Axis I schizophrenia overlaps with Axis II diagnoses such as paranoid or schizotypal personality disorders. This study was designed to address this issue. METHODS: We evaluated the auditory MMN to frequency deviance in 17 patients with paranoid, 15 schizotypal, and 16 antisocial personality disorders. These were compared to 25 healthy subjects. RESULTS: N1 to both deviant and standard tones was shorter in the paranoid group when compared to healthy controls. MMN latencies were shorter at Fz, Cz, and Pz in the paranoid group when compared to healthy controls, schizotypal, and antisocial groups. MMN amplitudes were higher at Fz and Cz in the schizotypal and antisocial groups when compared to healthy controls and the paranoid group. CONCLUSIONS: Patients with paranoid personality disorder had faster automatic detection of auditory stimuli and of their change, but normal inhibition of irrelevant stimuli. By contrast, patients with schizotypal and antisocial personality disorders had normal discrimination of the auditory stimuli, but might have a deficit in inhibition on irrelevant stimuli. Our results might help differentiate these personality types, and clarify some MMN findings in schizophrenia.     

The mismatch negativity and the P3a components of the auditory event-related potentials in autistic low-functioning subjects.

OBJECTIVE: In order to understand better the psychophysiological basis of auditory processing abnormalities in autism, we decided to study two automatic components of the auditory event-related potentials (ERPs): the mismatch negativity (MMN)--a component of the ERP which is recorded when, during repetitive auditory stimulation, rare changes are introduced--and the novelty-related P3a which is recorded as a response to unexpected novel events occurring in a sequence of repetitive stimuli. METHODS: Ten male subjects, mean age 12.3 years (SD 4.95), affected by autism and mental retardation were admitted to this study. All patients were also mentally retarded. Ten normal male subjects, mean age 12.2 years (SD 3.94), were used as controls. Auditory evoked potentials were recorded from 19 scalp electrodes (10-20 system), and stimuli were presented in sequences consisting of 2000 tones (70 dB, ISI=800 ms). Three types of stimuli were presented: (1) standard stimuli (1000 Hz tones, 80% of total stimuli), (2) deviant stimuli (1300 Hz tones, 10% of total stimuli), and (3) novel stimuli (complex and non-monotonal, 10% of total stimuli). To quantify the MMN, the evoked response to the standard tones was subtracted from the corresponding deviant stimulus response and its amplitude and latency at peak were measured over Fz, Cz and Pz; similarly, the P3a component of the ERP was obtained by subtracting the response to the standard tone from that to the novel stimuli and its amplitude and latency at peak were measured over Fz, Cz and Pz. Also, the amplitude and latency at peak for the N1 component of the auditory evoked potential obtained with the standard stimuli were measured over Fz, Cz and Pz. The correlation between age and MMN and P3a amplitude was also analyzed. RESULTS: N1 showed significantly shorter latencies in the autistic groups. MMN elicited by deviant stimuli, but not that elicited by novel stimuli, was found to be significantly larger in autistic children than in normal controls. P3a showed higher amplitude in autistic subjects than in normal controls during childhood; the opposite was observed during young adulthood. DISCUSSION: Our findings indicate that significant changes in ERPs can also be seen in non-cooperative individuals with autism and mental retardation, which might be different from the changes already reported for high-functioning autistic subjects and deserve further insight. These changes show developmental modifications that should be taken into consideration when analyzing data from autistic subjects.     

Evoked potential correlates of stimulus deviance during wakefulness and sleep in cat--animal model of mismatch negativity

Auditory evoked potentials (EPs) elicited by standard (STs) and deviant tones (DTs) of different probabilities were studied in freely moving cats during wakefulness and sleep. A large double peaked negativity, so-called mismatch negativity (MMN), was evoked by the unattended low probability DTs. The EPs recorded from the AI and AII areas of the auditory cortex showed more dynamic changes than the vertex and association cortical responses. The amplitude of the MMN was inversely proportional to the probability of DTs. The latency of the MMN showed dependence both on the location of the recording site and on the probability of DTs. During slow wave sleep (SWS) the MMN of increased latency could be evoked only at the lowest probabilities. The cortical distribution of the MMN changed in the SWS.     

Overnight changes in waking auditory evoked potential amplitude reflect altered sleep homeostasis in major depression

Goldstein MR, Plante DT, Hulse BK, Sarasso S, Landsness EC, Tononi G, Benca RM. Overnight changes in waking auditory evoked potential amplitude reflect altered sleep homeostasis in major depression. Objective: Sleep homeostasis is altered in major depressive disorder (MDD). Pre‐ to postsleep decline in waking auditory evoked potential (AEP) amplitude has been correlated with sleep slow wave activity (SWA), suggesting that overnight changes in waking AEP amplitude are homeostatically regulated in healthy individuals. This study investigated whether the overnight change in waking AEP amplitude and its relation to SWA is altered in MDD. Method: Using 256‐channel high‐density electroencephalography, all‐night sleep polysomnography and single‐tone waking AEPs pre‐ and postsleep were collected in 15 healthy controls (HC) and 15 non‐medicated individuals with MDD. Results: N1 and P2 amplitudes of the waking AEP declined after sleep in the HC group, but not in MDD. The reduction in N1 amplitude also correlated with fronto‐central SWA in the HC group, but a comparable relationship was not found in MDD, despite equivalent SWA between groups. No pre‐ to postsleep differences were found for N1 or P2 latencies in either group. These findings were not confounded by varying levels of alertness or differences in sleep variables between groups. Conclusion: MDD involves altered sleep homeostasis as measured by the overnight change in waking AEP amplitude. Future research is required to determine the clinical implications of these findings.     

Surface auditory evoked potentials in the unrestrained rat: component definition

Auditory evoked potentials (AEPs) to click and pure tone stimuli were recorded in unrestrained, unanesthetized rats. The middle latency rat AEPs (N17, P23, N38) had midline scalp distributions similar to human MAEPs and were recorded to within 15 dB above BAEP threshold. In contrast to human MAEPs, rat MAEPs were decreased in amplitude at high stimulation rates and only the N17 component was unaltered by slow wave sleep. The longer latency N50, N80 and P130 components had several response properties comparable to human N100-P200 vertex potentials. These included restricted midline fronto-central scalp distributions, progressive increases in amplitude at ISIs up to 4-8 sec and marked attenuation during slow wave sleep. The frequency sensitivity of the rat AEP revealed a decreased response to pure tones below 4 kHz but robust responses for stimuli up to at least 45 kHz. There was a notch in the rat audiogram with decremented component amplitudes to pure tone stimuli centered at 35 kHz. When equated for intensity, click and pure tone stimuli in the range of the rats maximal audiometric sensitivity (8-20 kHz) generated comparable AEP components. These results provide normative data on rat surface recorded AEPs. It is suggested that these surface recorded rat AEPs are generated by subcortical neural systems involved in the detection of auditory transients.     

Modulation of mismatch negativity by stimulus deviance and modality of attention

We studied the effect of attention on the processing of auditory sensory inputs by means of the mismatch negativity (MMN) potential, which can be derived from event-related EEG. A series of frequent standard and rare deviant auditory stimuli were presented to 20 healthy subjects in two recording sessions about five weeks apart. Deviant stimuli were either low or highly deviant as compared to the standard stimulus. While MMN was recorded, subjects were performing a visual and, subsequently, an auditory discrimination task. Directing attention towards the auditory task was associated with increased MMN amplitude only in response to low deviant stimuli and only in the first recording session. No change of MMN amplitude was found when directing attention towards the visual task or when MMN was recorded in response to highly deviant auditory stimuli. The latter may trigger an involuntary switch of attention, thereby overwriting the effect of task-directed attention. Conversely, the effects of attention on the processing of low deviant stimuli appear to be fragile and diminish with increasing automaticity of task execution.     

Odd sound processing in the sleeping brain

How does the sleeping brain process external stimuli, and in particular, up to which extent does the sleeping brain detect and process modifications in its sensory environment? In order to address this issue, we investigated brain reactivity to simple auditory stimulations during sleep in young healthy subjects. Electroencephalogram signal was acquired continuously during a whole night of sleep while a classical oddball paradigm with duration deviance was applied. In all sleep stages, except Sleep Stage 4, a mismatch negativity (MMN) was unquestionably found in response to deviant tones, revealing for the first time preserved sensory memory processing during almost the whole night. Surprisingly, during Sleep Stage 2 and paradoxical sleep, both P3a-like and P3b-like components were identified after the MMN, whereas a P3a alone followed the MMN in wakefulness and in Sleep Stage 1. This totally new result suggests elaborated processing of external stimulation during sleep. We propose that the P3b-like response could be associated to an active processing of the deviant tone in the dream's consciousness.     

Finding the right control: The mismatch negativity under investigation

ObjectiveWhen investigating auditory perceptual regularity processing, mismatch negativity (MMN) is commonly used. MMN is computed as a difference signal between the event-related potentials (ERPs) elicited by repeated standard tones and rarely occurring deviant tones. This procedure leads to an underestimation of the N1 component elicited by standards compared to the N1 to deviants which might affect the MMN. Consequently, a random control design was previously introduced. This design, however, overestimates the N1 to the deviant. Here, we developed a new paradigm that avoids previous drawbacks.MethodsWe designed a regular cascadic sequence as a control to the deviant. ERPs were measured while presenting conventional oddball blocks (standards, deviants), random control blocks and a cascadic control block.ResultsMMN was observed in each difference signal. Regarding the N1, standards elicited smallest amplitudes. The N1 for the deviant and the cascadic control was comparable. The largest N1 was elicited by the random control.ConclusionStandards underestimate N1 refractoriness effects in the responses to deviants, while random control tones overestimate. Cascadic control tones, however, provide a reasonable estimation for the N1.SignificanceThe new cascadic control design is suitable to investigate auditory perceptual regularity processes while controlling for N1 refractoriness effects.     

The vanishing point of the mismatch negativity at sleep onset.

OBJECTIVE: To determine when the mismatch negativity (MMN) disappears at sleep onset, event-related potentials (ERPs) were recorded continuously from wakefulness to sleep. METHODS: Ten healthy young students were told to fall asleep ignoring the tones presented through a loudspeaker above their head. Standard (1000 Hz, P=0.90), high deviant (1200 Hz, P=0.05), and low deviant (1050 Hz, P=0.05) tones were presented in a quasirandom order with a fixed stimulus onset asynchrony of 500 ms. ERP waveforms were obtained separately for 5 successive stages characterized by typical electroencephalographic (EEG) patterns of the sleep onset period. The EEG staging was made manually with very short (5 s) scoring epochs. RESULTS: The MMN appeared in wakefulness and in the early phase of stage 1 sleep (EEG stage II) but disappeared when low-voltage theta waves emerged after alpha flattening (EEG stage III). Instead, P240 and N360 developed particularly for high deviant tones. CONCLUSIONS: Concurrently with the disappearance of alpha waves, the automatic change detection system in wakefulness seems to stop operating and a different sleep-specific system becomes dominant.     

Effects of sleep onset on the mismatch negativity (MMN) to frequency deviants using a rapid rate of presentation

This study examined the effects of sleep onset-the transition from a waking, conscious state to one of sleep and unconsciousness-on the mismatch negativity (MMN) following frequency deviants when a rapid rate of stimulus presentation is employed. The MMN is thought to reflect a brief-lasting sensory memory. Rapid rates of stimulus presentation should guard the sensory memory from fading. A 1,000 Hz standard stimulus was presented every 150 ms. At random, on 6.6% of the trials, the standard was changed to either a large 2,000 or a small 1,100 Hz deviant. During alert wakefulness (when subject ignored the stimuli and read a book), the large deviant elicited a larger deviant related negativity (DRN) than did the small deviant. This negativity may be a composite of both N1 and MMN activity while that following the small deviant is probably a 'true' MMN. The large deviant continued to elicit a DRN in relaxed wakefulness (eyes closed) and Stages 1 and 2 of sleep, although it was much reduced in amplitude. A significant MMN was recorded for the small deviant only in alert wakefulness. The failure to observe an MMN to small deviance and the attenuation of the DRN to large deviance at sleep onset therefore is probably not due to a decay of sensory memory. It is more likely that cortical encoding of both the standard and deviant is weakened during sleep onset because of prior thalamic inhibition of sensory input.     

Measuring duration mismatch negativity.

OBJECTIVE: Automatic comparisons of sound duration in auditory sensory memory are typically investigated by comparing event-related potentials (ERPs) to standard and deviant stimuli presented in oddball blocks. Deviants elicit mismatch negativity (MMN). This procedure might overestimate an MMN contribution reflecting automatic sensory memory processes because of differential states of refractoriness of respectively recruited neural populations [Neuroreport 1996;7:3005; Psychophysiology 2001;38:723]. Here, memory-comparison-based Duration MMN contributions were investigated using various experimental protocols. METHODS: Memory-comparison-based first-order Duration MMN was investigated using 4 blocked conditions: (a) descending Deviant (100 ms, P=0.14), 150 ms Standard; (b) reverse ascending Deviant (150 ms), 100 ms Standard; (c) Control comprised of 7 equiprobable durations between 25 and 175 ms; and additionally (d) equiprobable tones between 100 and 400 ms. Using the former 3 conditions, Deviants, Standards and Controls were physically identical. RESULTS: Comparing Deviants and Controls excluded potential refractoriness effects, and a decomposition of memory-comparison-based MMN and residual MMN was demonstrated. Genuine Duration MMN was also obtained in the deviant-standard-reverse comparison. CONCLUSIONS: Using a blocked control condition yielded equivalent results to reversing the role of deviant and standard in two separate oddball blocks. Using the reverse ascending deviant condition is thus sufficient as a control.     

Spatial Properties of Mismatch Negativity in Patients with Disorders of Consciousness

In recent decades, event-related potentials have been used for the clinical electrophysiological assessment of patients with disorders of consciousness (DOCs). In this paper, an oddball paradigm with two types of frequency-deviant stimulus (standard stimuli were pure tones of 1000 Hz; small deviant stimuli were pure tones of 1050 Hz; large deviant stimuli were pure tones of 1200 Hz) was applied to elicit mismatch negativity (MMN) in 30 patients with DOCs diagnosed using the JFK Coma Recovery Scale-Revised (CRS-R). The results showed that the peak amplitudes of MMN elicited by both large and small deviant stimuli were significantly different from baseline. In terms of the spatial properties of MMN, a significant interaction effect between conditions (small and large deviant stimuli) and electrode nodes was centered at the frontocentral area. Furthermore, correlation coefficients were calculated between MMN amplitudes and CRS-R scores for each electrode among all participants to generate topographic maps. Meanwhile, a significant negative correlation between the MMN amplitudes elicited by large deviant stimuli and the CRS-R scores was also found at the frontocentral area. In consequence, our results combine the above spatial properties of MMN in patients with DOCs, and provide a more precise location (frontocentral area) at which to evaluate the correlation between clinical electrophysiological assessment and the level of consciousness.     

Impaired temporal lobe processing of preattentive auditory discrimination in schizophrenia

Feature-specific stimulus discrimination related to short-term auditory sensory memory can be studied electrophysiologically using a specific event-related potential (ERP) component termed mismatch negativity (MMN), which is generated in the auditory cortex, indexing automatic comparison of the existing memory trace to incoming novel stimuli. Previous results with electroencephalography (EEG) and magnetoencephalography (MEG) suggest that schizophrenia patients have attenuated MMN response and that preattentive auditory processing preceding MMN appears to be functionally asymmetric in schizophrenia. Here we studied parallel MMN activity of the hemispheres using a whole-head MEG by presenting stimulus blocks consisting of frequent standard and infrequent deviant tones to 15 schizophrenia patients and 19 healthy control subjects. Auditory evoked fields (AEFs) were recorded simultaneously over both auditory cortices. The equivalent current dipole (ECD) modeling revealed that patients had significant MMNm reduction (magnetic counterpart of MMN) in both temporal lobes. In addition, patients had significantly delayed MMNm in the left but not in the right hemisphere to ipsilateral auditory stimuli. These results suggest that patients with schizophrenia have impaired auditory processing in the temporal lobes underlying preattentive stimulus discrimination that is also selectively delayed in the left hemisphere.     

Bitemporal lesions dissociate auditory evoked potentials and perception

We studied auditory evoked potentials (AEPs) in an 82-year-old female patient who became suddenly deaf following the second of two strokes. The patient showed markedly elevated pure tone thresholds, was unable to discriminate sounds and could not understand speech. Brain-stem auditory evoked potentials (BAEPs) were normal. CT scans revealed bilateral lesions of the superior temporal plane which included auditory cortex. Two experiments were performed. In the first, tones, complex sounds and speech stimuli were presented at intensities above and below the patient's perceptual threshold. P1, N1 and P2 components were elicited by each of the stimuli--whether or not they were perceived. In particular, stimuli presented below threshold evoked large amplitude, short latency responses comparable to those produced in a control subject. In a second experiment, the refractory properties of the N1-P2 were examined using trains of tones. They were also found to be similar to those of normal subjects. Shifts in the pitch of the tones near the end of the train (when refractory effects were maximal) evoked N1-P2s with enhanced amplitudes, although the change in pitch was not perceived by the patient. In both experiments AEP scalp topographies were normal. The results suggest that bitemporal lesions of auditory cortex can dissociate auditory perception and long-latency auditory evoked potentials. A review of evoked potential studies of cortical deafness suggests that the neural circuits responsible for N1-P2 generation lie in close proximity to those necessary for auditory perception.     

Electrophysiological evidence of abnormal activation of the cerebral network of involuntary attention in alcoholism.

OBJECTIVE: Increased distractibility is a common impairment in alcoholism, but objective evidence has remained elusive. Here, a task designed to investigate with event-related brain potentials (ERPs) the neural mechanism underlying distraction was used to show abnormal involuntary orienting of attention in chronic alcoholism. METHODS: Fifteen alcoholics and 17 matched healthy controls were instructed to ignore auditory stimuli while concentrating in the discrimination of immediately following visual stimuli. The auditory sequences contained repetitive standard tones occasionally replaced by deviant tones of slightly higher frequency, or by complex novel sounds. RESULTS: Deviant tones and novel sounds distracted visual performance, i.e. increased reaction time to visual stimuli, similarly in patients and controls. Compared to controls, however, alcoholics showed ERP abnormalities, i.e. enhanced P3a amplitudes over the left frontal region, and a positive posterior deflection instead of the frontally distributed reorienting negativity (RON). CONCLUSIONS: The enhanced P3a to novelty and subsequent positive wave instead of RON in alcoholics suggests encoding into working memory of task-irrelevant auditory events and provides neurophysiological markers of impaired involuntary attention mechanisms in chronic alcoholism.     

Mismatch negativity of higher amplitude for melodic ascendance than descendance

The auditory system prefers, presumably because of evolutionary adaptation, melodically upward over downward steps in sound frequency. The mismatch negativity (MMN) of event-related potentials (ERPs) to auditory oddball stimuli, an index of preattentive auditory change detection, is also augmented for the upward relative to the downward steps. We aimed to test whether this melodic MMN asymmetry shows specificity to the oddball stimuli. Auditory ERPs were recorded in adult humans during a visual task. In an oddball condition, a repeated 400 Hz tone was occasionally (P=0.01) replaced either by a 380 Hz or by a 420 Hz tone. In a same-rate condition, the tones of the three frequencies occurred at equal probabilities (P=0.33). In the oddball condition, frontally augmented ERPs of negative polarity (MMN) were found to be of higher amplitude for the 420 Hz tone than for the 380 Hz tone. In the same-rate condition, ERPs did not distinguish between the tones. The findings associate the melodic MMN asymmetry with the neural detection of oddball tones in particular.