Rika Takegata

Independent processing of changes in auditory single features and feature conjunctions in humans as indexed by the mismatch negativity

The mismatch negativity (MMN), an event-related potential component of the EEG, is elicited by violations of auditory regularities In the present study, the stimulus blocks contained two types of standard tones, differing from each other in frequency and intensity. MMNs were recorded to three different types of deviant stimuli: (a) feature deviants, differing from standards in their perceived locus of origin; (b) conjunction deviants, having the frequency of one of the standards and the intensity of the other; (c) double deviants, differing from standards in both (a) and (b). The MMN to double deviants was similar to the sum of the MMNs to feature and conjunction deviants. This result indicates that changes in simple stimulus features and conjunction of features are processed independently by the automatic sound change detection system indexed by MMN.

Changes in acoustic features and their conjunctions are processed by separate neuronal populations

We investigated the relationship between the neuronal populations involved in detecting change in two acoustic features and their conjunction. Equivalent current dipole (ECD) models of the magnetic mismatch negativity (MMNm) generators were calculated for infrequent changes in pitch, perceived sound source location, and the conjunction of these two features. All of these three changes elicited MMNms that were generated in the vicinity of auditory cortex. The location of the ECD best describing the MMNm to the conjunction deviant was anterior to those for the MMNm responses elicited by either one of the constituent features. The present data thus suggest that at least partially separate neuronal populations are involved in detecting change in acoustic features and feature conjunctions.

Preattentive processing of spectral, temporal, and structural characteristics of acoustic regularities: a mismatch negativity study.

In the present study we investigated the relationship between detecting violations of structural regularities of tone sequences and detecting deviations from temporal regularities or repetitive spectral auditory stimulus features. Twelve subjects were presented with randomized sequences of two tones (differing both in frequency and intensity) delivered alternately to the left and right ears at a constant stimulus onset asynchrony (SOA). In separate blocks, occasional deviant stimuli broke one, two, or three of the following regularities: spatial alternation, the constancy of SOA, or the dominant frequency-intensity conjunctions. Unlike the mismatch negativity (MMN) elicited by alternation-plus-SOA deviants, the MMN elicited by alternation-plus-conjunction deviants was approximately equal to the sum of the two corresponding single-deviant MMNs. These results suggest that the preattentive change-detection system processes infrequent violations of the structural regularities of sound sequences together with changes in temporal regularities, but separately from changes in repetitive spectral sound features. The MMN elicited by the triple-deviant stimuli corroborated these conclusions.

Spectral and temporal stimulus characteristics in the processing of abstract auditory features

The processing of abstract stimulus features in the human brain was studied by presenting the subjects with frequent standard tone pairs and infrequent deviant tone pairs. Both pairs varied randomly over a wide frequency and/or intensity range, there being no physically constant standard stimulus. The common feature of the standard pairs was the direction of change within the pair, e.g. the second tone was louder in intensity and/or higher in frequency than the first tone. Deviant pairs, having opposite feature-change direction, elicited the mismatch-negativity (MMN) event-related potential component. MMN was similar to deviations in the direction of frequency and intensity changes and showed no additivity for simultaneous changes in both feature directions. Moreover, MMN was elicited even when the within-pair interval exceeded the 200 ms limit of auditory temporal integration. Results demonstrate that extraction of abstract features is not limited to frequency-based rules, nor is it dependent on temporal integration mechanisms. The lack of MMN additivity between violations of multiple abstract rules suggests that the processing of higher-order inva-riances differs from that of simple physical features.

Integrated neural representation of sound and temporal features in human auditory sensory memory: an event-related potential study

The present study explored the effect of varying stimulus onset asynchrony (SOA) on the pre-attentive detection of frequency changes indexed by the mismatch negativity (MMN). Reading subjects were presented with sequences of tones delivered at two SOAs. Each sequence included either one or both of the two SOAs. In sequences with two SOAs, the order of the SOAs was alternated or sequenced randomly. The MMN amplitude was larger in sequences with one SOA than in those with two. The order of SOAs (alternate or random) had no effect on the MMN. These results revealed that the processings of frequency and SOA are not independent, suggesting that sound features and the timing of stimulation delivering the sound can be encoded into a functionally integrated representation.

Parameter-specific modulation of the mismatch negativity to duration decrement and increment: evidence for asymmetric processes.

OBJECTIVE The mismatch negativity (MMN) component of event-related potentials (ERPs) reflects a change-detection process in the brain. The present study investigated whether stimulus parameters (sound type and duration) exert a differential influence on the MMN for a duration decrement and increment of an equal magnitude. Some asymmetries were reported in the previous studies; yet no systematical study has been conducted. METHODS ERPs were recorded from 16 healthy adults presented with repetitive standard sounds interspersed with duration changes (deviant sounds). In separate sequences, stimuli were vowels, music chord, sinusoid, or band-pass filtered white noise. The stimulus durations (standard/deviant) were either 200/120 ms or 400/240 ms for decrements, and vice versa for increments. RESULTS The MMN for the increments was abolished in the 400/240 ms condition, whereas the MMN for decrements was significant irrespective of the sound duration. The amplitude of the increment MMN paralleled with the spectral complexity of the stimulus sound, whereas that of the decrement MMN was larger for natural sounds than artificial sounds. CONCLUSIONS The observed interactions demonstrated asymmetries in the MMN for duration increment and decrement. SIGNIFICANCE The present findings suggest that the effects of stimulus parameters should be taken into account when comparing different studies, especially where clinical populations are involved, with one another.

Effects of temporal grouping on the memory representation of inter-tone relationships.

The length of silence between successive sounds is a dominant cue for temporal grouping of sounds. The present study tested whether the sensory memory representation of inter-tone relationships is dependent on the grouping of tones within a single stream of sound. Subjects were presented with sequences of two alternating tones that differed from each other in frequency. Perception of a sequence made up of tone-pairs was promoted by alternating a short and a long inter-tone interval. Occasional tone repetitions fell either within one tone-pair or across two pairs. We found that detecting tone repetitions was slower for across- than within-pair repetitions (Experiment 1). Also the amplitude of the mismatch negativity (MMN) event-related potential was lower for across-pair repetitions compared with that measured in the control isochronous sequences (Experiment 2). This attenuation of the MMN-amplitude could not be explained by the inter-tone interval differences that existed between the paired and the isochronous conditions (Experiment 3). These results demonstrate that temporal grouping affects the sensory memory representation of inter-tone relationships within a single sound stream.

Common neural mechanism for processing onset-to-onset intervals and silent gaps in sound sequences

Stimulus onset asynchrony (SOA) and inter-stimulus interval (ISI) are important factors in the perceptual organization of sound sequences. The present study tested whether these two temporal parameters are independently processed in the auditory system. Independence was studied by testing the additivity of mismatch negativity (MMN). Four conditions differing in their temporal regularities were administered: (1) constant SOA and ISI, (2) constant SOA and variable ISI, (3) constant ISI and variable SOA, and (4) variable SOA and ISI. The MMN elicited by simultaneous deviance from the constant SOA and ISI (Condition 1) was compared with an additive model calculated from the MMNs elicited in the other conditions. The amplitude of the MMN in Condition 1 was significantly larger than that of the modeled MMN, suggesting that SOA and ISI are processed by interactive or common neural mechanisms.

Transitional Probabilities Are Prioritized over Stimulus/Pattern Probabilities in Auditory Deviance Detection: Memory Basis for Predictive Sound Processing

Representations encoding the probabilities of auditory events do not directly support predictive processing. In contrast, information about the probability with which a given sound follows another (transitional probability) allows predictions of upcoming sounds. We tested whether behavioral and cortical auditory deviance detection (the latter indexed by the mismatch negativity event-related potential) relies on probabilities of sound patterns or on transitional probabilities. We presented healthy adult volunteers with three types of rare tone-triplets among frequent standard triplets of high-low-high (H-L-H) or L-H-L pitch structure: proximity deviant (H-H-H/L-L-L), reversal deviant (L-H-L/H-L-H), and first-tone deviant (L-L-H/H-H-L). If deviance detection was based on pattern probability, reversal and first-tone deviants should be detected with similar latency because both differ from the standard at the first pattern position. If deviance detection was based on transitional probabilities, then reversal deviants should be the most difficult to detect because, unlike the other two deviants, they contain no low-probability pitch transitions. The data clearly showed that both behavioral and cortical auditory deviance detection uses transitional probabilities. Thus, the memory traces underlying cortical deviance detection may provide a link between stimulus probability-based change/novelty detectors operating at lower levels of the auditory system and higher auditory cognitive functions that involve predictive processing. SIGNIFICANCE STATEMENT Our research presents the first definite evidence for the auditory system prioritizing transitional probabilities over probabilities of individual sensory events. Forming representations for transitional probabilities paves the way for predictions of upcoming sounds. Several recent theories suggest that predictive processing provides the general basis of human perception, including important auditory functions, such as auditory scene analysis. Our results demonstrate that the memory traces underlying cortical deviance detection form a link between stimulus probability-based change/novelty detectors operating at lower levels of the auditory system and higher auditory cognitive functions that involve predictive processing.

A Paradigm to Measure Mismatch Negativity Responses to Phonetic and Acoustic Changes in Parallel

The mismatch negativity (MMN) of the event-related potential has been purported to be an objective index of central auditory processing. The present study tested a new paradigm to measure the MMN responses to phonological changes in parallel with those to simple acoustic changes. Stimulus sequences consisted of repetitive consonant-vowel syllables interspersed with infrequent phonetic changes (in place of articulation or voicing) and repetitive sinusoidal tones with occasional acoustic changes (in frequency or duration). The speech and tone stimuli were delivered to the opposite ears (right and left, respectively) at a stimulus onset asynchrony (SOA) of 300 ms. The MMNs elicited in this new paradigm were compared with those measured in a conventional paradigm, in which the speech and tone stimuli were presented in separate sequences at an identical speech-speech or tone-tone SOA (600 ms) of the new paradigm. The MMNs elicited in the two paradigms had a similar morphology and topography, although the MMNs measured with the new paradigm were slightly smaller for 3 out of 4 types of deviants. The results suggest that the new paradigm enables the measurement of reliable MMNs to phonetic changes in parallel with those to acoustic changes.