The mismatch negativity: an index of cognitive decline in neuropsychiatric and neurological diseases and in ageing.

Cognitive impairment is a core element shared by a large number of different neurological and neuropsychiatric diseases. Irrespective of their different aetiologies and symptomatologies, most appear to converge at the functional deficiency of the auditory-frontal cortex network of auditory discrimination, which indexes cognitive impairment shared by these abnormalities. This auditory-frontal cortical deficiency, and hence cognitive decline, can now be objectively measured with the mismatch negativity and its magnetic equivalent.

Sources of non-physiologic noise in simultaneous EEG-fMRI data: a phantom study.

Simultaneous EEG-fMRI studies require an understanding of the noise characteristics of the acquisition environment so that appropriate pre-processing steps may be taken to remove known artifacts from the data stream. Using a phantom approach, we have developed a general methodology for characterizing non-physiologic noise in EEG signal and demonstrate the use of this methodology for a specific MR scanner and EEG data acquisition system configuration. Our results show the δ frequency band is significantly impacted by baseline drift or baseline correction algorithms while the β and γ bands are impacted by residual gradient artifact and gradient corrections.

Mismatch negativity with visual-only and audiovisual speech.

The functional organization of cortical speech processing is thought to be hierarchical, increasing in complexity and proceeding from primary sensory areas centrifugally. The current study used the mismatch negativity (MMN) obtained with electrophysiology (EEG) to investigate the early latency period of visual speech processing under both visual-only (VO) and audiovisual (AV) conditions. Current density reconstruction (CDR) methods were used to model the cortical MMN generator locations.

Spatiotemporal dynamics of audiovisual speech processing.

The cortical processing of auditory-alone, visual-alone, and audiovisual speech information is temporally and spatially distributed, and functional magnetic resonance imaging (fMRI) cannot adequately resolve its temporal dynamics. In order to investigate a hypothesized spatiotemporal organization for audiovisual speech processing circuits, event-related potentials (ERPs) were recorded using electroencephalography (EEG). Stimuli were congruent audiovisual/ba/, incongruent auditory/ba/synchronized with visual/ga/, auditory-only/ba/, and visual-only/ba/and/ga/.

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.

Simultaneous 3-T fMRI and high-density recording of human auditory evoked potentials.

We acquired simultaneous high-field (3 T) functional magnetic resonance imaging (fMRI) and high-density (64- and 128-channel) EEG using a sparse sampling technique to measure auditory cortical activity generated by right ear stimulus presentation. Using dipole source localization, we showed that the anatomical location of the grand mean equivalent dipole of auditory evoked potentials (AEPs) and the center of gravity of fMRI activity were in good agreement in the horizontal plane. However, the grand mean equivalent dipole was located significantly superior in the cortex compared to fMRI activity.

Subtitled videos and mismatch negativity (MMN) investigations of spoken word processing.

The purpose of this study was to determine whether the presence of subtitles on a distracting, silent video affects the automatic mismatch negativity (MMN) response to simple tones, consonant-vowel (CV) nonwords, or CV words. Two experiments were conducted in this study, each including ten healthy young adult subjects. Experiment 1 investigated the effects of subtitles on the MMN response to simple tones (differing in frequency, duration, and intensity) and speech stimuli (CV nonwords and CV words with a /d/-/g/ contrast).

Automatic auditory processing of english words as indexed by the mismatch negativity, using a multiple deviant paradigm.

Objective: The aim of this study was to investigate mismatch negativity (MMN) responses to a variety of speech stimuli (/de:/, /ge:/, /deI/ "day", and /geI/ "gay") in a multiple deviant paradigm. It was hypothesized that all speech stimulus contrasts in the multiple deviant paradigm, including the fine acoustic speech contrast [d/g], would elicit robust MMN responses and that consonant vowel (CV) real word deviants (e.g.

Processing of English words with fine acoustic contrasts and simple tones: a mismatch negativity study.

The purpose of this study was to compare the robustness of the event-related potential (ERP) response, called the mismatch negativity (MMN), when elicited by simple tone stimuli (differing in frequency, duration, or intensity) and speech stimuli (CV nonword contrast /de:/ vs. /ge:/ and CV word contrast /del/ vs. /gel/).

Differential ear effects of profound unilateral deafness on the adult human central auditory system.

This study investigates the effects of profound acquired unilateral deafness on the adult human central auditory system by analyzing long-latency auditory evoked potentials (AEPs) with dipole source modeling methods. AEPs, elicited by clicks presented to the intact ear in 19 adult subjects with profound unilateral deafness and monaurally to each ear in eight adult normal-hearing controls, were recorded with a 31-channel system. The responses in the 70-210 ms time window, encompassing the N1b/P2 and Ta/Tb components of the AEPs, were modeled by a vertically and a laterally oriented dipole source in each hemisphere.

Auditory-evoked potential studies of cortical maturation in normal hearing and implanted children: correlations with changes in structure and speech perception.

Human auditory system maturation as assessed by means of auditory-evoked potential recording is compared to maturation of axon neurofilaments and some critical stages in speech perception. The parallels strongly suggest that the emergence of the N1 component reflects the maturation of the axons in layer II and upper layer III of the auditory cortex. This is also the time period during which the perception of speech in noise and degraded speech markedly improves.

Maturation of human central auditory system activity: the T-complex.

Objective: The purpose of this study was to evaluate and describe the maturation of a set of auditory evoked potentials (AEPs) described as the T-complex from a large group of children, adolescents, and young adults who ranged in age from 5 to 20 years of age.

Methods: The AEPs evoked by brief trains of clicks presented to the left ear were measured at 30 scalp-electrode locations. Analyses focused on age-related latency and amplitude changes in the T-complex recorded at the temporal electrode sites T3 and T5 over the left hemisphere and T4 and T6 over the right hemisphere.

The neurophysiology of auditory perception: from single units to evoked potentials.

Evoked electric potential and magnetic field studies have the immense benefit that they can be conducted in awake, behaving humans and can be directly correlated with aspects of perception. As such, they are powerful objective indicators of perceptual properties. However, given a set of evoked potential and/or evoked field waveforms and their source locations, obtained for an exhaustive set of stimuli and stimulus contrasts, is it possible to determine blindly, i.

Visual speech perception without primary auditory cortex activation.

Speech perception is conventionally thought to be an auditory function, but humans often use their eyes to perceive speech. We investigated whether visual speech perception depends on processing by the primary auditory cortex in hearing adults. In a functional magnetic resonance imaging experiment, a pulse-tone was presented contrasted with gradient noise.

Maturation of human central auditory system activity: separating auditory evoked potentials by dipole source modeling.

Objectives: Previous studies have shown that observed patterns of auditory evoked potential (AEP) maturation depend on the scalp location of the recording electrodes. Dipole source modeling incorporates the AEP information recorded at all electrode locations. This should provide a more robust description of auditory system maturation based on age-related changes in AEPs.