Attentional modulation in the detection of irrelevant deviance: a simultaneous ERP/fMRI study

Vowel-specific mismatch responses in the anterior superior temporal gyrus: an fMRI study

There have been many functional imaging studies that have investigated the neural correlates of speech perception by contrasting neural responses to speech and "speech-like" but unintelligible control stimuli. A potential drawback of this approach is that intelligibility is necessarily conflated with a change in the acoustic parameters of the stimuli. The approach we have adopted is to take advantage of the mismatch response elicited by an oddball paradigm to probe neural responses in temporal lobe structures to a parametrically varied set of deviants in order to identify brain regions involved in vowel processing. Thirteen normal subjects were scanned using a functional magnetic resonance imaging (fMRI) paradigm while they listened to continuous trains of auditory stimuli. Three classes of stimuli were used: 'vowel deviants' and two classes of control stimuli: one acoustically similar ('single formants') and the other distant (tones). The acoustic differences between the standard and deviants in both the vowel and single-formant classes were designed to match each other closely. The results revealed an effect of vowel deviance in the left anterior superior temporal gyrus (aSTG). This was most significant when comparing all vowel deviants to standards, irrespective of their psychoacoustic or physical deviance. We also identified a correlation between perceptual discrimination and deviant-related activity in the dominant superior temporal sulcus (STS), although this effect was not stimulus specific. The responses to vowel deviants were in brain regions implicated in the processing of intelligible or meaningful speech, part of the so-called auditory "what" processing stream. Neural components of this pathway would be expected to respond to sudden, perhaps unexpected changes in speech signal that result in a change to narrative meaning.

Gender differences in lateralization of mismatch negativity in dichotic listening tasks

OBJECTIVE

With the aim of investigating gender differences in the functional lateralization subserving preattentive processing of language stimuli, we compared auditory mismatch negativities (MMNs) using dichotic listening tasks.

METHODS

Forty-four healthy volunteers, including 23 males and 21 females, participated in the study. MMNs generated by pure-tone and phonetic stimuli were compared, to check for the existence of language-specific gender differences in lateralization. Both EEG amplitude and scalp current density (SCD) data were analyzed.

RESULTS

With phonetic MMNs, EEG findings revealed significantly larger amplitude in females than males, especially in the right hemisphere, while SCD findings revealed left hemisphere dominance and contralateral dominance in males alone. With pure-tone MMNs, no significant gender differences in hemispheric lateralization appeared in either EEG or SCD findings.

CONCLUSION

While males exhibited left-lateralized activation with phonetic MMNs, females exhibited more bilateral activity. Further, the contralateral dominance of the SCD distribution associated with the ear receiving deviant stimuli in males indicated that ipsilateral input as well as interhemispheric transfer across the corpus callosum to the ipsilateral side was more suppressed in males than in females.

SIGNIFICANCE

The findings of the present study suggest that functional lateralization subserving preattentive detection of phonetic change differs between the genders. These results underscore the significance of considering the gender differences in the study of MMN, especially when phonetic stimulus is adopted. Moreover, they support the view of Voyer and Flight [Voyer, D., Flight, J., 2001. Gender differences in laterality on a dichotic task: the influence of report strategies. Cortex 37, 345-362.] in that the gender difference in hemispheric lateralization of language function is observed in a well-managed-attention condition, which fits the condition adopted in the MMN measurement; subjects are required to focus attention to a distraction task and thereby ignore the phonetic stimuli that elicit MMN.

The cognitive locus of distraction by acoustic novelty in the cross-modal oddball task

Unexpected stimuli are often able to distract us away from a task at hand. The present study seeks to explore some of the mechanisms underpinning this phenomenon. Studies of involuntary attention capture using the oddball task have repeatedly shown that infrequent auditory changes in a series of otherwise repeating sounds trigger an automatic response to the novel or deviant stimulus. This attention capture has been shown to disrupt participants' behavioral performance in a primary task, even when distractors and targets are asynchronous and presented in distinct sensory modalities. This distraction effect is generally considered as a by-product of the capture of attention by the novel or deviant stimulus, but the exact cognitive locus of this effect and the interplay between attention capture and target processing has remained relatively ignored. The present study reports three behavioral experiments using a cross-modal oddball task to examine whether the distraction triggered by auditory novelty affects the processing of the target stimuli. Our results showed that variations in the demands placed on the visual analysis (Experiment 1) or categorical processing of the target (Experiment 2) did not impact on distraction. Instead, the cancellation of distraction by the presentation of an irrelevant visual stimulus presented immediately before the visual target (Experiment 3) suggested that distraction originated in the shifts of attention occurring between attention capture and the onset of the target processing. Possible accounts of these shifts are discussed.

Attentional and linguistic interactions in speech perception

The role of attention in speech comprehension is not well understood. We used fMRI to study the neural correlates of auditory word, pseudoword, and nonspeech (spectrally rotated speech) perception during a bimodal (auditory, visual) selective attention task. In three conditions, Attend Auditory (ignore visual), Ignore Auditory (attend visual), and Visual (no auditory stimulation), 28 subjects performed a one-back matching task in the assigned attended modality. The visual task, attending to rapidly presented Japanese characters, was designed to be highly demanding in order to prevent attention to the simultaneously presented auditory stimuli. Regardless of stimulus type, attention to the auditory channel enhanced activation by the auditory stimuli (Attend Auditory>Ignore Auditory) in bilateral posterior superior temporal regions and left inferior frontal cortex. Across attentional conditions, there were main effects of speech processing (word+pseudoword>rotated speech) in left orbitofrontal cortex and several posterior right hemisphere regions, though these areas also showed strong interactions with attention (larger speech effects in the Attend Auditory than in the Ignore Auditory condition) and no significant speech effects in the Ignore Auditory condition. Several other regions, including the postcentral gyri, left supramarginal gyrus, and temporal lobes bilaterally, showed similar interactions due to the presence of speech effects only in the Attend Auditory condition. Main effects of lexicality (word>pseudoword) were isolated to a small region of the left lateral prefrontal cortex. Examination of this region showed significant word>pseudoword activation only in the Attend Auditory condition. Several other brain regions, including left ventromedial frontal lobe, left dorsal prefrontal cortex, and left middle temporal gyrus, showed Attention x Lexicality interactions due to the presence of lexical activation only in the Attend Auditory condition. These results support a model in which neutral speech presented in an unattended sensory channel undergoes relatively little processing beyond the early perceptual level. Specifically, processing of phonetic and lexical-semantic information appears to be very limited in such circumstances, consistent with prior behavioral studies.

Unmixing concurrent EEG-fMRI with parallel independent component analysis

Concurrent event-related EEG-fMRI recordings pick up volume-conducted and hemodynamically convoluted signals from latent neural sources that are spatially and temporally mixed across the brain, i.e. the observed data in both modalities represent multiple, simultaneously active, regionally overlapping neuronal mass responses. This mixing process decreases the sensitivity of voxel-by-voxel prediction of hemodynamic activation by the EEG when multiple sources contribute to either the predictor and/or the response variables. In order to address this problem, we used independent component analysis (ICA) to recover maps from the fMRI and timecourses from the EEG, and matched these components across the modalities by correlating their trial-to-trial modulation. The analysis was implemented as a group-level ICA that extracts a single set of components from the data and directly allows for population inferences about consistently expressed function-relevant spatiotemporal responses. We illustrate the utility of this method by extracting a previously undetected but relevant EEG-fMRI component from a concurrent auditory target detection experiment.

Difficulty of discrimination modulates attentional capture for deviant information

It has been reported that an increased difficulty of discrimination between standard and target enhances P3a for typical nontarget. To elucidate the mechanism of this effect on deviant processing, the P300 event-related brain potential (ERP) was elicited using a visual three-stimulus oddball paradigm (standard circle, .70, target circle, .15, and nontarget/target square, .15). Four task conditions were defined by a combination of two category types of rare square (nontarget or target) and two levels of discrimination difficulty between standard and target circles (easy or difficult). In the difficult conditions, P3a was elicited by both nontarget and target square. Our findings suggest that the difficulty of discrimination between standard and target enhances attentional capture, rather than inhibition, for deviant information. This study has implications for understanding the attentional mechanisms of deviant processing.

Auditory event-related potentials and cognitive function of preterm children at five years of age

OBJECTIVE

In our previous study, auditory event-related potentials (AERPs) in preterm 1-year-old children had a positive deflection at 150-350 ms that correlated positively with their 2-year neurodevelopmental outcome. In a study of the same subjects at age 5, our aim was to assess AERPs and their relationship to neuropsychological test results.

METHODS

Preterm small (SGA, n=13), appropriate for gestational age (AGA, n=15), and control (n=13) children were assessed with an Easy paradigm presenting a large frequency change accompanied with occasional novel sounds, and a Challenging paradigm presenting small frequency and duration changes with a rapid rate. The preterm children underwent neurocognitive tests.

RESULTS

Easy paradigm. The P1 response to frequency deviant was smaller and MMN larger in the preterm than in the control children. Challenging paradigm. The P1 response to standard, frequency, and duration deviants was smaller in the preterm than in the control children. The N2 response to frequency deviant was larger in the preterm than in the control children. AGA and SGA children had similar AERPs. The P1, N2, and MMN amplitudes correlated with verbal IQ and NEPSY language subtests.

CONCLUSIONS

Small P1 response(s) appears to be typical for preterm children.

SIGNIFICANCE

Small P1 response in preterm children may suggest altered primary auditory processing.

Neurophysiological indices of attention to speech in children with specific language impairment

OBJECTIVE

The aim was to determine whether children with specific language impairment (SLI) differed from children with typical language development (TLD) in their allocation of attention to speech sounds.

METHODS

Event-related potentials were recorded to non-target speech sounds in two tasks (passive-watch a video and attend to target tones among speech sounds) in two experiments, one using 50-ms duration vowels and the second using 250-ms vowels. The difference in ERPs across tasks was examined in the latency range of the early negative difference wave (Nd) found in adults. Analyses of the data using selected superior and inferior sites were compared to those using electrical field power (i.e., global field power or GFP). The topography of the ERP at the maximum GFP was also examined.

RESULTS

A negative difference, comparable to the adult Nd, was observed in the attend compared to the passive task for both types of analysis, suggesting allocation of attentional resources to processing the speech stimuli in the attend task. Children with TLD also showed greater negativity than those with SLI in the passive task for the long vowels, suggesting that they allocated more attentional resources to processing the speech in this task than the SLI group. This effect was only significant using the GFP analysis and was seen as smaller GFP for the TLD than SLI group. The SLI group also showed significantly later latency than the TLD group in reaching the maximum GFP. In addition, a significantly greater proportion of children with SLI compared to those with typical language showed left-greater-than-right frontocentral amplitude at the latency determined from each child's maximum GFP peak.

CONCLUSIONS

Children generally showed greater attention to speech sounds when attention is directed to the auditory modality compared to the visual modality. However, children with TLD, unlike SLI, also appear to devote some attentional resources to speech even in a task in which they are instructed to attend to visual information and ignore the speech.

SIGNIFICANCE

These findings suggest that children with SLI have limited attentional resources, that they are poorer at dividing attention, or that they are less automatic in allocating resources to speech compared to children with typically developing language skills.

The Frontal Generator of the Mismatch Negativity Revisited

The mismatch negativity (MMN) is an event-related brain potential elicited by the occurrence of a rare event (deviance) in an otherwise regular acoustic environment, and is assumed to reflect a preattentive mechanism for change detection. A widely adopted model holds that MMN has main generators in the superior temporal planes bilaterally, which are responsible for the sensory memory part of change detection, as well as frontal lobe sources responsible for triggering an attention shift upon change detection. Whereas the temporal sources have been documented in numerous studies across species and methodologies, much less is known about the frontal sources. The present review examines the current state of the evidence for their existence, location, and possible function. It confirms that the frontal generator is still a less consistent finding in MMN research than the temporal generator. There is clear evidence from scalp EEG and, especially, current source density studies for the existence of an MMN generator that is functionally distinct from the main supratemporal generator of the MMN. Evidence from fMRI, PET, optical imaging, EEG source imaging, and lesion studies implicates mainly the inferior frontal and possibly also the medial frontal cortex. However, these results should be taken with caution because of the paucity of support from more direct measures like intracranial recordings and MEG, and the negative findings from several fMRI and PET, as well as EEG source imaging studies. Recent studies also raise questions about the exact role of the frontal generator in triggering an attention shift. Delineating the exact cortical locations of frontal MMN generators, the conditions under which they are activated and, consequently, their function, remains an acute challenge.

Direct evidence for differential roles of temporal and frontal components of auditory change detection

Automatic change detection is a fundamental capacity of the human brain. In audition, this capacity is indexed by the mismatch negativity (MMN) event-related potential, which is putatively supported by a network consisting of superior temporal and frontal nodes. The aim of this study was to elucidate the roles of these nodes within the neural network of change detection. We used a dichotic paradigm in which subjects (N=14) attended targets defined by either pitch or spatial location in one auditory stream while the MMN was measured in response to unattended deviants of pitch and spatial location in the other stream. The frontal and temporal components of the MMN were examined using current source density (CSD) measurements. Competition for processing resources nearly eliminated the temporal CSD mismatch response, in a highly feature-specific manner: the response to spatial location deviants was reduced when the target dimension was spatial location but not when it was pitch, whereas the reverse occurred for pitch deviants. In contrast, the frontal CSD mismatch response was neither affected by competition nor by general attention demands. Thus, within the network of change detection, the temporal generators are specifically associated with processing feature-specific information, whereas the role of the frontal generators remains unclear. Moreover, the results are inconsistent with a serial model in which the frontal generator is contingent on activation of the temporal generator.

Heschl's gyrus, posterior superior temporal gyrus, and mid-ventrolateral prefrontal cortex have different roles in the detection of acoustic changes

A part of the auditory system automatically detects changes in the acoustic environment. This preattentional process has been studied extensively, yet its cerebral origins have not been determined with sufficient accuracy to allow comparison to established anatomical and functional parcellations. Here we used event-related functional MRI and EEG in a parametric experimental design to determine the cortical areas in individual brains that participate in the detection of acoustic changes. Our results suggest that automatic change processing consists of at least three stages: initial detection in the primary auditory cortex, detailed analysis in the posterior superior temporal gyrus and planum temporale, and judgment of sufficient novelty for the allocation of attentional resources in the mid-ventrolateral prefrontal cortex.