María-José Corral

Role of Mismatch Negativity and Novelty-P3 in Involuntary Auditory Attention

It has been proposed that the functional role of the mismatch negativity (MMN) generating process is to issue a call for focal attention toward any auditory change violating the preceding acoustic regularity. This paper reviews the evidence supporting such a functional role and outlines a model of how the attentional system controls the flow of bottom-up auditory information with regard to ongoing-task demands to organize goal-oriented behavior. Specifically, the data obtained in auditory-auditory and auditory-visual distraction paradigms demonstrated that the unexpected occurrence of deviant auditory stimuli or novel sounds captures attention involuntarily, as they distract current task performance. These data indicate that such a process of distraction takes place in three successive stages associated, respectively, to MMN, P3a/novelty-P3, and reorienting negativity (RON), and that the latter two are modulated by the demands of the task at hand.

Attention capture by auditory significant stimuli: semantic analysis follows attention switching.

Event‐related potentials (ERPs) were recorded from the scalp to investigate a long‐standing controversy in auditory attention research, namely when the ‘breakthrough of the unattended’ takes place in the human brain. Nine subjects classified visual stimuli appearing 300 ms after task‐irrelevant standard tones (80%, i.e. P = 0.8) or novel sounds (20%, i.e. P = 0.2) into odd/even categories. After the recording session, subjects scored the novel sounds as to whether they had any particular meaning (identifiable) or were perceived as a burst of noise (non‐identifiable), and performance and ERPs were analysed according to this classification. A control condition, in which the visual stimuli were presented with no sounds, showed that subjects covertly monitored the task‐irrelevant sounds during visual task‐performance, and a further condition, in which the auditory and visual stimuli appeared regardless of each other, made it possible to trace the processing of the distracters during allocation of attention outside the auditory environment. Results yielded identical N1‐enhancement for the two types of novel sounds, indicating similar attention switching triggered to these two types of unexpected sounds. However, there was a stronger orientating of attention towards identifiable novel sounds, as indicated both by behavioural distraction and by larger novelty‐P3. Furthermore, this stronger orientating of attention was due to the sounds being contingent on the visual stimuli, as no increase in novelty‐P3 to identifiable novel sounds was observed in the control condition, in which the sounds occurred outside the attentional set. Therefore, provided that the N1‐enhancement reflects a call for focal attention, and novelty‐P3 the effective orientating of attention towards the eliciting sounds, the present results suggest that semantic analysis of significant sounds occurs after a transitory switch of attention towards the eliciting stimuli. Moreover, as the novelty‐P3 increase in amplitude was observed only when subjects covertly monitored the sounds, the present data suggest that semantic analysis of irrelevant sounds depends on the top‐down cognitive influences of the attentional set.

When loading working memory reduces distraction: Behavioral and electrophysiological evidence from an auditory-visual distraction paradigm

The sensitivity of involuntary attention to top-down modulation was tested using an auditory-visual distraction task and a working memory (WM) load manipulation in subjects performing a simple visual classification task while ignoring contingent auditory stimulation. The sounds were repetitive standard tones (80%) and environmental novel sounds (20%). Distraction caused by the novel sounds was compared across a 1-back WM condition and a no-memory control condition, both involving the comparison of two digits. Event-related brain potentials (ERPs) to the sounds were recorded, and the N1/MMN (mismatch negativity), novelty-P3, and RON components were identified in the novel minus standard difference waveforms. Distraction was reduced in the WM condition, both behaviorally and as indexed by an attenuation of the late phase of the novelty-P3. The transient/change detection mechanism indexed by MMN was not affected by the WM manipulation. Sustained, slow frontal and parietal waveforms related to WM processes were found on the standard ERPs. The present results indicate that distraction caused by irrelevant novel sounds is reduced when a WM component is involved in the task, and that this modulation by WM load takes place at a late stage of the orienting response, all in all confirming that involuntary attention is under the control of top-down mechanisms. Moreover, as these results contradict predictions of the load theory of selective attention and cognitive control, it is suggested that the WM load effects on distraction depend on the nature of the distractor-target relationships.

An electrophysiological and behavioral investigation of involuntary attention towards auditory frequency, duration and intensity changes

We measured behavior and event-related brain potentials (ERPs) in 12 subjects performing on an audio-visual distraction paradigm to investigate the cerebral mechanisms of involuntary attention towards stimulus changes in the acoustic environment. Subjects classified odd/even numbers presented on a computer screen 300 ms after the occurrence of a task-irrelevant auditory stimulus, by pressing the corresponding response button. Auditory stimuli were standard tones (600 Hz, 200 ms, 85 dB; P=0.8) or deviant tones (P=0.2), these differing from the standard either in frequency (700 Hz), duration (50 ms) or intensity (79 dB), in separate blocks. In comparison to performance to visual stimuli following the standard tones, reaction time increased by 24 ms (F(1,11)=10.91, P<0.01) and hit rate decreased by 4.6% (F(1,11)=35.47, P<0.001) to visual stimuli following the deviant tones, indicating behavioral distraction. ERPs revealed the mismatch negativity (MMN) elicited to deviant tones, which was larger for the duration deviant than for the frequency and intensity deviants (F(2,22)=19.43, P<0.001, epsilon =0.83), and which had different scalp distribution for all three deviant conditions (F(16,176)=2.40, P<0.05, epsilon =0.12). As the shorter duration and softer intensity deviant tones were unlikely to engage fresh neurons responding to their specific physical features, the present results indicate that a genuine change detection mechanism is involved in triggering attention switching towards sound changes, and suggest a largely distributed neural network of the auditory cortex underlying such involuntary attention switching.

Abnormal speech sound representation in persistent developmental stuttering.

Objectives: To determine whether adults with persistent developmental stuttering (PDS) have auditory perceptual deficits. Methods: The authors compared the mismatch negativity (MMN) event–related brain potential elicited to simple tone (frequency and duration) and phonetic contrasts in a sample of PDS subjects with that recorded in a sample of paired fluent control subjects. Results: Subjects with developmental stuttering had normal MMN to simple tone contrasts but a significant supratemporal left-lateralized enhancement of this electrophysiologic response to phonetic contrasts. In addition, the enhanced MMN correlated positively with speech disfluency as self-rated by the subjects. Conclusions: Individuals with persistent developmental stuttering have abnormal permanent traces for speech sounds, and their abnormal speech sound representation may underlie their speech disorder. The link between abnormal speech neural traces of the auditory cortex and speech disfluency supports the relevance of speech perception mechanisms to speech production.

Auditory event-related potentials as a function of abstract change magnitude.

Event-related potentials were recorded in healthy volunteers to test the accuracy of the human brain to extract, preattentively, auditory abstract rules. The abstract rule was determined by the frequency relationship between two pure tones forming a pair. The standard pairs had identical tone frequency, whereas the deviant pairs had the second tone two, four, six or eight musical steps higher or lower in frequency than the first one. All abstract changes elicited mismatch negativity, which was not affected by the magnitude of change. However, the subsequent P3a increased as a function of the magnitude of the abstract change. These results suggest that mismatch negativity detects violations of abstract rules, and the amount of violation is analyzed in subsequent stages of auditory processing.

Reduced novelty-P3 associated with increased behavioral distractibility in schizophrenia.

Behavioral and electrophysiological brain responses were used to examine the relationship between the vulnerability to distraction and the orienting response in schizophrenia. Nineteen schizophrenics and nineteen matched healthy controls were instructed to ignore task-irrelevant auditory stimuli while they classified capital letters and digits. The auditory sequences contained repetitive standard tones occasionally replaced by complex novel sounds. Relative to controls, patients showed an increased behavioral distraction, as indicated by a larger response time increase caused by novel sounds, and a disturbance in the attention orienting toward distracting stimuli, as indicated by a reduced novelty-P3. This behavioral-electrophysiological dissociation may stem from a limited pool of available resources. Thus, the few attentional resources directed toward novel stimuli would be sufficient to cause an important decrease of the similarly reduced amount of resources assigned to task-relevant stimuli, resulting in a striking impairment of the ongoing task performance.

Effects of sound location on visual task performance and electrophysiological measures of distraction

Novel sounds embedded in a repetitive stream of auditory stimuli impair performance of the visual task at hand. Parmentier et al. suggested that this distraction effect might be because of the shifting cost of moving attention from the task-irrelevant (auditory) to the task-relevant (visual) channel, or from their shifting of spatial locations. Here, the source location of the sounds in an audio-visual distraction paradigm was varied systematically (headphones and 0, −18, −72, 18, and 72°), and the results revealed significant distracting effects of novel sounds occurring in the headphone and the right location conditions. This supports the assumption that in the behavioral cost observed in the audio-visual distraction paradigm a spatial shift of attention is involved.

Individual differences in sequence learning and auditory pattern sensitivity as revealed with evoked potentials

Research on motor sequence acquisition has shown significant differences between learners. Learners who develop explicit knowledge respond faster than non‐explicit ones and they show larger amplitude in event‐related brain potentials to sequence deviants. There is evidence that memory span correlates with the amount of sequence learned, but the specific mechanisms subserving such differences are still unknown. Recently, it has been observed that performance of explicit learners, but not of non‐explicit ones, improves when presented with auditory action effects. Accordingly, differences between learners might be related to differences in auditory rhythm perception. To test this hypothesis, the mismatch negativity (MMN)‐evoked potential elicited to stimuli violating stimulus alternation (i.e. low pitch, high pitch) was recorded in explicit and non‐explicit sequence learners. Results confirmed our prediction: explicit learners showed larger amplitude of the MMN to the violation of the auditory rhythm, suggesting new theoretical implications to account for individual differences in sequential action control.