Spectrotemporal processing drives fast access to memory traces for spoken words.

The Mismatch Negativity (MMN) component of the event-related potentials is generated when a detectable spectrotemporal feature of the incoming sound does not match the sensory model set up by preceding repeated stimuli. MMN is enhanced at frontocentral scalp sites for deviant words when compared to acoustically similar deviant pseudowords, suggesting that automatic access to long-term memory traces for spoken words contributes to MMN generation. Does spectrotemporal feature matching also drive automatic lexical access? To test this, we recorded human auditory event-related potentials (ERPs) to disyllabic spoken words and pseudowords within a passive oddball paradigm. We first aimed at replicating the word-related MMN enhancement effect for Spanish, thereby adding to the available cross-linguistic evidence (e.g., Finnish, English). We then probed its resilience to spectrotemporal perturbation by inserting short (20 ms) and long (120 ms) silent gaps between first and second syllables of deviant and standard stimuli. A significantly enhanced, frontocentrally distributed MMN to deviant words was found for stimuli with no gap. The long gap yielded no deviant word MMN, showing that prior expectations of word form limits in a given language influence deviance detection processes. Crucially, the insertion of a short gap suppressed deviant word MMN enhancement at frontocentral sites. We propose that spectrotemporal point-wise matching constitutes a core mechanism for fast serial computations in audition and language, bridging sensory and long-term memory systems.

Top-down modulation of auditory processing: effects of sound context, musical expertise and attentional focus.

By recording auditory electrical brain potentials, we investigated whether the basic sound parameters (frequency, duration and intensity) are differentially encoded among speech vs. music sounds by musicians and non-musicians during different attentional demands. To this end, a pseudoword and an instrumental sound of comparable frequency and duration were presented. The accuracy of neural discrimination was tested by manipulations of frequency, duration and intensity. Additionally, the subjects' attentional focus was manipulated by instructions to ignore the sounds while watching a silent movie or to attentively discriminate the different sounds. In both musicians and non-musicians, the pre-attentively evoked mismatch negativity (MMN) component was larger to slight changes in music than in speech sounds. The MMN was also larger to intensity changes in music sounds and to duration changes in speech sounds. During attentional listening, all subjects more readily discriminated changes among speech sounds than among music sounds as indexed by the N2b response strength. Furthermore, during attentional listening, musicians displayed larger MMN and N2b than non-musicians for both music and speech sounds. Taken together, the data indicate that the discriminative abilities in human audition differ between music and speech sounds as a function of the sound-change context and the subjective familiarity of the sound parameters. These findings provide clear evidence for top-down modulatory effects in audition. In other words, the processing of sounds is realized by a dynamically adapting network considering type of sound, expertise and attentional demands, rather than by a strictly modularly organized stimulus-driven system.

Spatial auditory regularity encoding and prediction: Human middle-latency and long-latency auditory evoked potentials.

By encoding acoustic regularities present in the environment, the human brain can generate predictions of what is likely to occur next. Recent studies suggest that deviations from encoded regularities are detected within 10-50ms after stimulus onset, as indicated by electrophysiological effects in the middle latency response (MLR) range. This is upstream of previously known long-latency (LLR) signatures of deviance detection such as the mismatch negativity (MMN) component. In the present study, we created predictable and unpredictable contexts to investigate MLR and LLR signatures of the encoding of spatial auditory regularities and the generation of predictions from these regularities. Chirps were monaurally delivered in an either regular (predictable: left-right-left-right) or a random (unpredictable left/right alternation or repetition) manner. Occasional stimulus omissions occurred in both types of sequences. Results showed that the Na component (peaking at 34ms after stimulus onset) was attenuated for regular relative to random chirps, albeit no differences were observed for stimulus omission responses in the same latency range. In the LLR range, larger chirp-and omission-evoked responses were elicited for the regular than for the random condition, and predictability effects were more prominent over the right hemisphere. We discuss our findings in the framework of a hierarchical organization of spatial regularity encoding. This article is part of a Special Issue entitled SI: Prediction and Attention.

Electrophysiological indices of acute effects of ethanol on involuntary attention shifting.

Dose-related effects of ethanol (placebo, 0.30, and 0.60 g/kg) on behavioral and event-related brain potential (ERP) indices of involuntary attention shifting of audition were investigated. ERPs were recorded from 11 healthy social drinkers during a forced-choice reaction-time (RT) task. Subjects were presented with 100 and 200 ms tones (P = 0.50 for each) with a constant inter-stimulus interval (ISI) of 1 s. The task was to press either of two buttons, depending on the tone duration. The majority of the tones ("standards") were of 700 Hz (P = 0.82). Occasionally, however, the frequency of the tones changed, deviating either slightly (750 Hz), moderately (900 Hz), or widely (1200 Hz; P = 0.06 for each) from the standard frequency. In accordance with previous findings, the task-irrelevant frequency deviations prolonged the RT. This RT prolongation was attenuated by alcohol with the 0.3 g/kg dose, thus suggesting less distraction by irrelevant stimulus deviations under the influence of ethanol. Furthermore, the P3a, reflecting involuntary attention shifting, was suppressed by alcohol even with the 0.3 g/kg dose. These findings demonstrate a detrimental effect of alcohol on involuntary attention shifting, evident with doses considerably smaller than previously described, and still juridically acceptable in road traffic in most countries.

Behavioral and electrophysiological effects of task-irrelevant sound change: a new distraction paradigm.

A distraction paradigm was utilized that is suited to yield reliable auditory distraction on an individual level even with rather small frequency deviances (7%). Distraction to these tiny deviants was achieved by embedding task-relevant aspects and task-irrelevant, distracting aspects of stimulation into the same perceptual object. Event-related potential (ERP) and behavioral effects of this newly developed paradigm were determined. Subjects received tones that could be of short or long duration equiprobably. They were instructed to press a response button to long-duration tones (targets). In oddball blocks, tones could be of standard frequency or of low-probability (p=0.1), deviant frequency. The task-irrelevant frequency deviants elicited MMN, N2b, and P3a components, and caused impoverished behavioral performance to targets. The usage of tiny distractors permits an interpretation of auditory distraction in terms of attention switching due to a particular memory-related change-detection process. On the basis of the results from an additional condition in which tones were of 10 different frequencies (involving those frequencies which served as standard and deviant in oddball blocks), it is argued that one important prerequisite for linking the neural mechanisms reflected in change-related brain waves to behavioral distraction effects may be regarded as fulfilled. The robustness of the distraction effects to tiny deviations was confirmed in two control experiments.

A comparison of auditory and visual distraction effects: behavioral and event-related indices.

Infrequent task-irrelevant deviations in the frequency of a tone may distract our attention away from the processing of task-relevant tone duration. The distraction obtained in the auditory paradigm is reflected in prolonged reaction times in duration discrimination and in P3a. The P3a is followed by a late negative component, which may be related to a re-orienting process following distraction (RON, re-orienting negativity). The present study aimed at comparing effects of the auditory and a corresponding visual distraction paradigm. Distraction elicited a deviance-related negativity which revealed a modality-specific distribution. It was followed by P3a (350-ms post-stimulus) and by RON (500-ms post-stimulus). RON did not occur with long-duration visual stimuli indicating a difference in visual and auditory distraction. Moreover, the results suggest that in both tasks irrelevant deviants were detected by modality-specific processes which caused an attention shift.

Activation of the auditory pre-attentive change detection system by tone repetitions with fast stimulation rate.

The human automatic pre-attentive change detection system indexed by the mismatch negativity (MMN) component of the auditory event-related brain potential is known to be highly adaptive. The present study showed that even infrequent repetitions of tones can elicit MMN, independently of attention, when tones of varying frequency are rapidly presented in an isochronous rhythm. This demonstrates that frequency variation can be extracted as an invariant feature of the acoustic environment revealing the capacity for adaptation of the auditory pre-attentive change detection system. It is argued that this capacity is related to the temporal-window of integration.

Automaticity and attention: investigating automatic processing in texture segmentation with event-related brain potentials.

The present article deals with the question of automaticity and/or plasticity of processes in early vision. The detection of irregularities in an otherwise homogeneous surrounding, as studied in texture segmentation tasks, is considered an example of an automatic process in the processing of visual information. Participants in texture segmentation experiments are usually instructed to respond to the texture stimuli, i.e. attention is completely allocated towards them. Automaticity, however, would imply that processing takes also place when no attention is allocated to the texture stimuli and participants, e.g. perform another primary task. We investigated the automaticity of texture segmentation by recording Event-related potentials which allow to investigate processing also when no overt response is given. Three experiments investigated the role of attention in texture segmentation by varying task relevance of the texture stimuli. Participants had to either discriminate homogeneous or inhomogeneous textures or had to perform a different primary task of varying complexity. Two components were found to be sensitive to texture segmentation, a posterior N2 and a positivity within the P3 time interval. Both components were also observed when texture segmentation was task-irrelevant. However, while the posterior N2 was not affected by the complexity of the primary task and thus showed some degree of automaticity, the P3 was found to be dependent on the attentional resources left over by the primary task.

Preattentive periodicity detection in auditory patterns as governed by time and intensity information.

The present study demonstrated that the mismatch negativity (MMN), generated by the brain's preattentive detection of a sound change, is elicited by infrequent reversals of two consecutive tones differing in intensity. When tones were presented in a pairwise manner, the MMN was time-locked to the onset of the intensity reversal. When the tones were continuously presented, the MMN was elicited by an irregular loud tone succeeding a regular loud tone but not by an irregular soft tone following a regular soft tone. Results suggest that the preattentive construction of auditory units is primarily governed by the timing of tone presentation but that it may also utilize intensity information, when no sufficient timing information is available.

Automatic detection of frequency change is invariant over a large intensity range.

The influence of stimulus intensity on the automatic detection of frequency change was studied. Ten human subjects were presented with a high-probability standard tone (700 Hz) and a low-probability deviant tone (750 Hz). In a between-block design, the intensity of the auditory stimuli was varied over a 40 dB range. The frequency deviant elicited the mismatch negativity (MMN), an event-related brain potential component indicative of automatic change detection in the auditory cortex. The MMN for a frequency change was even elicited in low-intensity blocks and it did not significantly vary with intensity. These results suggest that the frequency MMN is sensitive to the informational content of a change not to the total amount of stimulus energy. Furthermore, the data imply that an efficient encoding of frequency information, which underlies the change detection mechanism, takes place even with weak sensory stimulation.

Mismatch response of the human brain to changes in sound location.

WE investigated whether the enhanced negativity of the human event-related brain potential elicited by changes in auditory lateralization is due to a higher-order change-detection process or whether it can be explained exclusively in terms of selective sensory adaptation. Infrequent changes in lateralization of a repetitive standard tone, generated by changes in interaural time differences, elicited a frontocentrally distributed negative brain wave in the 100-250 ms range relative to stimulus onset. This brain wave was also elicited when possible sensory adaptation was prevented by controlling for the state of refractoriness of location-specific neurones. The results demonstrate that changes in lateralization elicit a genuine mismatch negativity (MMN), indicating the activity of an automatic higher-order change-detection process.

Attentional orienting and reorienting is indicated by human event-related brain potentials.

We investigated event-related potential indications for the orienting towards task-irrelevant, distracting aspects of stimulation and for the subsequent reorienting towards task-related aspects of stimulation. An identical experimental protocol was run in three conditions manipulating the task relevance of the sounds. As to be expected, distractors elicited the MMN (reflecting the brain's pre-attentive change detection) in each condition (even when the sounds were ignored) and subsequent N2b and P3 (reflecting orienting towards the distractor) when the sounds were attended. A late negativity was confined to a condition in which subjects discriminating long from short sounds were distracted by task-irrelevant frequency deviations. The 'reorienting negativity' (RON) probably reflects processes in the context of reorienting towards task-relevant aspects of stimulation following distraction.

Neural representation for the temporal structure of sound patterns.

Responses to infrequently exchanging two segments of a complex tonal pattern were tested for the presence of the mismatch negativity event-related brain potential component. This component is elicited when an auditory stimulus differs from the sensory memory trace of the previously presented repetitive sound. Because the segments exchanged in the tonal pattern differed from each other only in their durations, the elicitation of the mismatch response revealed that the temporal structure of sound patterns is encoded in the traces underlying the mismatch process. Results showing that the mismatch response was elicited even when the tonal patterns were presented continuously (i.e. without silent intervals separating successive patterns) demonstrate the automatic detection of periodicity in the acoustic stream.

Effects of transient spatial attention on auditory event-related potentials.

Event-related potentials (ERPs) were recorded in subjects receiving left- and right-ear tones while they shifted attention to the left or right on a trial-by-trial basis. ERPs at attended compared with unattended tones revealed an enhanced negativity consisting of an early part that was parietally distributed and a later part with a frontocentral distribution. It may be concluded that these ERP modulations reflect the selection of auditory stimuli according to spatial criteria within a transient spatial attention situation. Furthermore, the attention-related negativity was not reduced for long inter-stimulus intervals (10 s) suggesting that prior stimulus exposure is not a basic requirement for eliciting attention-related negativity in the auditory modality.

Superior pre-attentive auditory processing in musicians.

The present study focuses on influences of long-term experience on auditory processing, providing the first evidence for pre-attentively superior auditory processing in musicians. This was revealed by the brain's automatic change-detection response, which is reflected electrically as the mismatch negativity (MMN) and generated by the operation of sensoric (echoic) memory, the earliest cognitive memory system. Major chords and single tones were presented to both professional violinists and non-musicians under ignore and attend conditions. Slightly impure chords, presented among perfect major chords elicited a distinct MMN in professional musicians, but not in non-musicians. This demonstrates that compared to non-musicians, musicians are superior in pre-attentively extracting more information out of musically relevant stimuli. Since effects of long-term experience on pre-attentive auditory processing have so far been reported for language-specific phonemes only, results indicate that sensory memory mechanisms can be modulated by training on a more general level.

Attentive and pre-attentive periodicity analysis in auditory memory: an event-related brain potential study.

In an event-related potential (ERP) study we presented human subjects with streams of repetitive white noise (semi-periodic noise) under attend and ignore conditions to investigate whether the perception of the periodicity with short cycle-lengths is due to lower level, pre-attentive sensory memory processing or higher level, attentive working memory processing. The ERPs of both conditions reveal N1-like deflections that are time locked on the semi-periodic noise suggesting that the processing of the periodicity is due to a pre-attentive rather than an attentive process. The topography of the deflections suggests that its generators are located in the supratemporal plane. Additionally, the ERPs elicited by infrequent disruptions in the periodicity show differences between the conditions suggesting that the detection of disruptions in periodicity is facilitated by attention.

Effects of consciousness on human brain waves following binocular rivalry.

When the two eyes of an observer are exposed to conflicting stimuli, they enter into binocular rivalry and the two possible percepts will alternate in dominance. We investigated neural activity and its time course following binocular rivalry by measuring human event-related brain potentials to transitions from rivalrous to non-rivalrous stimulation. When these changes did not entail a change in conscious perception they elicited a markedly attenuated N1 component and a delayed and attenuated P3 peak as compared to percept-incompatible changes and non-rivalrous control conditions. These results suggest that in humans binocular rivalry is resolved at latest in extrastriate visual areas.

Facilitation of visual search at new positions: a behavioral and ERP study of new object capture.

Visual search was studied in two consecutive displays. Display 1 items changed identity whilst retaining their positions when the additional items appeared in Display 2. In the New condition, the target appeared at one of the new positions, whereas in the Old condition, the target appeared at one of the old positions. Responses were faster and accuracy increased in the New condition. Event-related brain potentials revealed an Old-New difference 400 ms after Display 2 onset for the smaller set size, suggesting that subjects had a holistic impression that the target was absent at a new position. A posteriorly distributed processing difference between both conditions was manifest at around 1200 ms, suggesting a bias for search at new positions.

Development of a memory trace for a complex sound in the human brain.

The development of a memory trace for a complex, unfamiliar sound in the human brain was studied by repeatedly presenting reading subjects with this sound ('standard') which was occasionally replaced by a slightly different sound ('deviant'). Deviants did not elicit the mismatch negativity, an index of automatic change detection in auditory cortex, in the beginning but did later during the session. This result reflects a gradual 'sharpening' of sensory information encoded in the memory trace: the representation of the standard stimulus eventually became precise enough to enable the cortical change-detector mechanism to detect a slight different stimulus.

Differentiating ERAN and MMN: an ERP study.

In the present study, the early right-anterior negativity (ERAN) elicited by harmonically inappropriate chords during listening to music was compared to the frequency mismatch negativity (MMN) and the abstract-feature MMN. Results revealed that the amplitude of the ERAN, in contrast to the MMN, is specifically dependent on the degree of harmonic appropriateness. Thus, the ERAN is correlated with the cognitive processing of complex rule-based information, i.e. with the application of music-syntactic rules. Moreover, results showed that the ERAN, compared to the abstract-feature MMN, had both a longer latency, and a larger amplitude. The combined findings indicate that ERAN and MMN reflect different mechanisms of pre-attentive irregularity detection, and that, although both components have several features in common, the ERAN does not easily fit into the classical MMN framework. The present ERPs thus provide evidence for a differentiation of cognitive processes underlying the fast and pre-attentive processing of auditory information.