Biomedical subjects

Hermann Ackermann

Publications and source records attributed to Hermann Ackermann.

At least 19 recordsLinked to original sources

PubMed2006

Sequential audiovisual interactions during speech perception: a whole-head MEG study.

Using whole-head magnetoencephalography (MEG), audiovisual (AV) interactions during speech perception (/ta/- and /pa/-syllables) were investigated in 20 subjects. Congruent AV events served as the 'standards' of an oddball design. The deviants encompassed incongruent /ta/-/pa/ configurations differing from the standards either in the acoustic or the visual domain. As an auditory non-speech control condition, the same video signals were synchronized with either one of two complex tones. As in natural speech, visual movement onset preceded acoustic signals by about 150 ms. First, the impact of visual information on auditorily evoked fields to non-speech sounds was determined. Larger facial movements (/pa/ versus /ta/) yielded enhanced early responses such as the M100 component, indicating, most presumably, anticipatory pre-activation of auditory cortex by visual motion cues. As a second step of analysis, mismatch fields (MMF) were calculated. Acoustic deviants elicited a typical MMF, peaking ca. 180 ms after stimulus onset, whereas visual deviants gave rise to later responses (220 ms) of a more posterior-medial source location. Finally, a late (275 ms), left-lateralized visually-induced MMF component, resembling the acoustic mismatch response, emerged during the speech condition, presumably reflecting phonetic/linguistic operations. There is mounting functional imaging evidence for an early impact of visual information on auditory cortical regions during speech perception. The present study suggests at least two successive AV interactions in association with syllable recognition tasks: early activation of auditory areas depending upon visual motion cues and a later speech-specific left-lateralized response mediated, conceivably, by backward-projections from multisensory areas.

Adult↗

PubMed2006

Functional significance of age-related differences in motor activation patterns.

Recent functional MRI (fMRI) studies have revealed an increased task-related activation in older subjects during a variety of cognitive or perceptual tasks, which may signal beneficial compensatory activity to counteract structural and neurochemical changes associated with aging. Under the assumption that incremental movement rates are associated with an increased functional demand on the motor system, we used fMRI and acoustically paced movements of the right index finger at six different frequencies (2.0, 2.5, 3.0, 4.0, 5.0 and 6.0 Hz) to investigate the behavioral significance of additionally recruited brain regions in a group of healthy, older subjects (mean age 66 +/- 8 years) compared with a group of young (mean age 23 +/- 7 years) subjects. The actual tapping frequency (F(1,14) = 0.049, P = 0.829), the tapping interval (F(1,14) = 0.043, P = 0.847), and the error rates (F(1,14) = 0.058, P = 0.743) did not differ significantly between both groups, whereas there was a significant increase in reaction time in the older subjects (F(1,14) = 281.786, P < or = 0.001). At all frequencies, the older subjects demonstrated significant overactivation within the ipsilateral sensorimotor and premotor cortex. However, we did not observe an increased age-related overactivation during higher movements rates in these or other motor regions. Moreover, the magnitude of the hemodynamic response in overactivated regions remained constant across all frequencies. In contrast to cognitive tasks, these findings indicate that an age-related overactivation within the motor system is not related to the functional demand and does not necessarily reflect reorganization to compensate for the neurobiological changes of aging.

Acoustic Stimulation↗

PubMed2006

Psychoacoustic studies on the processing of vocal interjections: how to disentangle lexical and prosodic information?

Both intonation (affective prosody) and lexical meaning of verbal utterances participate in the vocal expression of a speaker's emotional state, an important aspect of human communication. However, it is still a matter of debate how the information of these two 'channels' is integrated during speech perception. In order to further analyze the impact of affective prosody on lexical access, so-called interjections, i.e., short verbal emotional utterances, were investigated. The results of a series of psychoacoustic studies indicate the processing of emotional interjections to be mediated by a divided cognitive mechanism encompassing both lexical access and the encoding of prosodic data. Emotional interjections could be separated into elements with high- or low-lexical content. As concerns the former items, both prosodic and propositional cues have a significant influence upon recognition rates, whereas the processing of the low-lexical cognates rather solely depends upon prosodic information. Incongruencies between lexical and prosodic data structures compromise stimulus identification. Thus, the analysis of utterances characterized by a dissociation of the prosodic and lexical dimension revealed prosody to exert a stronger impact upon listeners' judgments than lexicality. Taken together, these findings indicate that both propositional and prosodic speech components closely interact during speech perception.

Brain↗

PubMed2005

Gamma-band activity over early sensory areas predicts detection of changes in audiovisual speech stimuli.

Oscillatory activity in the gamma-band range in human magneto- and electroencephalogram is thought to reflect the oscillatory synchronization of cortical networks. Findings of enhanced gamma-band activity (GBA) during cognitive processes like gestalt perception, attention and memory have led to the notion that GBA may reflect the activation of internal object representations. However, there is little direct evidence suggesting that GBA is related to subjective perceptual experience. In the present study, magnetoencephalogram was recorded during an audiovisual oddball paradigm with infrequent visual (auditory /ta/ + visual /pa/) or acoustic deviants (auditory /pa/ + visual /ta/) interspersed in a sequence of frequent audiovisual standard stimuli (auditory /ta/ + visual /ta/). Sixteen human subjects had to respond to perceived acoustic changes which could be produced either by real acoustic or illusory (visual) deviants. Statistical probability mapping served to identify correlations between oscillatory activity in response to visual and acoustic deviants, respectively, and the detection rates for either type of deviant. The perception of illusory acoustic changes induced by visual deviants was closely associated with gamma-band amplitude at approximately 80 Hz between 250 and 350 ms over midline occipital cortex. In contrast, the detection of real acoustic deviants correlated positively with induced GBA at approximately 42 Hz between 200 and 300 ms over left superior temporal cortex and negatively with evoked gamma responses at approximately 41 Hz between 220 and 240 ms over occipital areas. These findings support the relevance of high-frequency oscillatory activity over early sensory areas for perceptual experience.

Adult↗

PubMed2005

The cerebral control of speech tempo: opposite relationship between speaking rate and BOLD signal changes at striatal and cerebellar structures.

So far, only sparse data on the cerebral organization of speech motor control are available. In order to further delineate the neural basis of articulatory functions, fMRI measurements were performed during self-paced syllable repetitions at six different frequencies (2-6 Hz). Bilateral hemodynamic main effects, calculated across all syllable rates considered, emerged within sensorimotor cortex, putamen, thalamus and cerebellum. At the level of the caudatum and the anterior insula, activation was found restricted to the left side. The computation of rate-to-response functions of the BOLD signal revealed a negative linear relationship between syllable frequency and response magnitude within the striatum whereas cortical areas and cerebellar hemispheres exhibited an opposite activation pattern. Dysarthric patients with basal ganglia disorders show unimpaired or even accelerated speaking rate whereas, in contrast, cerebellar dysfunctions give rise to slowed speech tempo which does not fall below a rate of about 3 Hz. The observed rate-to-response profiles of the BOLD signal thus might help to elucidate the pathophysiological mechanisms of dysarthric deficits in central motor disorders.

Acoustic Stimulation↗

PubMed2005

Selective influences of cross-modal spatial-cues on preattentive auditory processing: a whole-head magnetoencephalography study.

The processing streams of the various sensory modalities are known to interact within the central nervous system. These interactions differ depending on the level of stimulus representation and attention. The current study focused on cross-sensory influences on stimulus change detection during unattended auditory processing. We employed an oddball paradigm to assess cortical processing using whole-head magnetoencephalography (MEG) in 20 volunteers. While subjects performed distraction tasks of varying difficulties, auditory duration deviants were applied randomly to the left or the right ear preceded (200-400 ms) by oculomotor, static visual, or flow field co-stimulation at either side. Mismatch fields were recorded over both hemispheres. Changes in gaze direction and static visual stimuli elicited the most reliable enhancement of deviance detection at the same side (most prominent at the right auditory cortex). Under both conditions, the lateralized unattended and unpredictive pre-cues acted analogously to shifts in selective attention, but were not reduced by attentional load. Thus, the early cognitive representation of sounds seems to reflect automatic cross-modal interference. Preattentive multisensory integration may provide the neuronal basis for orienting reactions to objects in space and thus for voluntary control of selective attention.

Acoustic Stimulation↗

PubMed2005

Spatial auditory attention is modulated by tactile priming.

Previous studies have shown that cross-modal processing affects perception at a variety of neuronal levels. In this study, event-related brain responses were recorded via whole-head magnetoencephalography (MEG). Spatial auditory attention was directed via tactile pre-cues (primes) to one of four locations in the peripersonal space (left and right hand versus face). Auditory stimuli were white noise bursts, convoluted with head-related transfer functions, which ensured spatial perception of the four locations. Tactile primes (200-300 ms prior to acoustic onset) were applied randomly to one of these locations. Attentional load was controlled by three different visual distraction tasks. The auditory P50m (about 50 ms after stimulus onset) showed a significant "proximity" effect (larger responses to face stimulation as well as a "contralaterality" effect between side of stimulation and hemisphere). The tactile primes essentially reduced both the P50m and N100m components. However, facial tactile pre-stimulation yielded an enhanced ipsilateral N100m. These results show that earlier responses are mainly governed by exogenous stimulus properties whereas cross-sensory interaction is spatially selective at a later (endogenous) processing stage.

Acoustic Stimulation↗

PubMed2005

MEG responses to rippled noise and Huggins pitch reveal similar cortical representations.

The onset of pitch within an ongoing noise signal evokes a particular brain activity, the pitch onset response (POR). Using whole-head MEG, PORs to iterated rippled noise (IRN) and Huggins pitch (HP), representing prototypical pitch-in-noise signals, were measured in twenty subjects during a pitch identification task (333 Hz, 400 Hz, randomized). HP and IRN yielded similar responses, lateralized to the left hemisphere and peaking about 180 ms after pitch onset. The initial phase (140 ms) showed stronger activations to 400 than to 333 Hz whereas later stages (200-300 ms) showed target vs nontarget effects. These results suggest, first, that different pitches converge into a common cortical representation and, second, that the POR encompasses various successive processing stages.

Acoustic Stimulation↗

PubMed2005

Functional MRI localizing in the cerebellum.

Mapping of cerebellar function by functional MRI now enables us not only to re-establish older anatomic findings of somatotopic representations but to gain new insights in the function of the cerebellum and its intimate relations of cerebral regions to serving sensorimotor function, sensory discrimination, and cognitive processing. Consequently, it will change our understanding of neurologic and psychologic failures in patients with inborn errors or neurodegenerative diseases or after neurosurgical procedures.

Brain Mapping↗

PubMed2004

Hearing lips: gamma-band activity during audiovisual speech perception.

Auditory pattern changes have been shown to elicit increases in magnetoencephalographic gamma-band activity (GBA) over left inferior frontal cortex, forming part of the putative auditory ventral "what" processing stream. The present study employed a McGurk-type paradigm to assess whether GBA would be associated with subjectively perceived changes even when auditory stimuli remain unchanged. Magnetoencephalograms were recorded in 16 human subjects during audiovisual mismatch perception. Both infrequent visual (auditory /ta/ + visual /pa/) and acoustic deviants (auditory/pa/ + visual /ta/) were compared with frequent audiovisual standards (auditory /ta/ and visual /ta/). Statistical probability mapping revealed spectral amplitude increases at approximately 75 and approximately 78 Hz to visual deviants. GBA to visual deviants peaked 160 ms after auditory stimulus onset over posterior parietal cortex, at 270 ms over occipital areas and at 320 ms over left inferior frontal cortex. The latter GBA enhancement was consistent with the increase observed previously to pure acoustic mismatch, supporting a role of left inferior frontal cortex for the representation of perceived auditory pattern change. The preceding gamma-band changes over posterior areas may reflect processing of incongruent lip movements in visual motion areas and back-projections to earlier visual cortex.

Adult↗

PubMed2004

Transient and phase-locked evoked magnetic fields in response to periodic acoustic signals.

Using whole-head MEG, time course and hemispheric lateralization effects of phase-locked brain responses to complex periodic acoustic signals (stimulus frequency 13, 22, 40, 67, or 111 Hz) were determined based on a dipole analysis approach. Apart from systematic rate-induced changes in amplitude and shape of the transient evoked magnetic fields (M50, M100), phase-locked brain activity emerged, being more pronounced over the right as compared to the left hemisphere. Furthermore, this MEG component showed a consistent phase angle across subjects, indicating active synchronization mechanisms within auditory cortex that operate upon afferent input. Conceivably, these early side-differences in periodicity encoding contribute to or even snowball into hemispheric lateralization effects of higher-order aspects of central-auditory processing such as melody perception.

Acoustic Stimulation↗

PubMed2004

Discrimination of temporal information at the cerebellum: functional magnetic resonance imaging of nonverbal auditory memory.

Until recently, the cerebellum was held to play its chief role in motor control. By contrast, Keele and Ivry (1990) proposed that it may subserve time estimation within the perceptual domain as well. In accordance with this suggestion, speech perception requiring minute differentiation of time intervals was found compromised by cerebellar pathology a subsequent functional magnetic resonance imaging (fMRI) study found hemodynamic activation of the right neocerebellum under these conditions. In the current fMRI investigation a non-speech task involving duration storage and comparison yielded significant hemodynamic responses within the lateral Crus I area of the right cerebellar hemisphere. Concomitantly, a left prefrontal cluster was observed. The present fMRI study employed single-shot double-echo echo-planar imaging (EPI) to reduce image distortion and acquisition time with whole-brain coverage (TE = 28 and 66 ms, TR = 5 s, 28 slices, TA = 2.8 s). Twelve healthy subjects performed two tasks: identifying pauses between tones as "short" or "long" (30-130 ms) and deciding which of two successive pauses was longer. The activation pattern in the discrimination task was analogous to that seen during speech perception and verbal working memory (WM) tasks. We suggest that the storage of precise temporal structures relies on a cerebellar-prefrontal loop. This network allows for temporal organization of verbal sequences and phoneme encoding based on durational operations in a linguistic context.

Adult↗

PubMed2004

Time course and hemispheric lateralization effects of complex pitch processing: evoked magnetic fields in response to rippled noise stimuli.

To delineate the time course and processing stages of pitch encoding at the level of the supratemporal plane, the present study recorded evoked magnetic fields in response to rippled noise (RN) stimuli. RN largely masks simple tonotopic representations and addresses pitch processing within the temporal domain (periodicity encoding). Four dichotic stimulus types (111 or 133 Hz RN at one ear, white noise to the other one) were applied in randomized order during either visual distraction or selective auditory attention. Strictly periodic signals, noise-like events, and mixtures of both signals served as control conditions. (1) Attention-dependent ear x hemisphere interactions were observed within the time domain of the M50 field, indicating early streaming of auditory information. (2) M100 responses to strictly periodic stimuli were found lateralized to the right hemisphere. Furthermore, the higher-pitched stimuli yielded enhanced activation as compared to the lower-pitch signals (pitch scaling), conceivably reflecting sensory memory operations. (3) Besides right-hemisphere pitch scaling, the relatively late M100 component in association with the RN condition (latency = 136 ms) showed significantly stronger field strengths over the left hemisphere. Control experiments revealed this lateralization effect to be related to noise rather than pitch processing. Furthermore, subtle noise variations interacted with signal periodicity. Obviously, thus, complex task demands such as RN encoding give rise to functional segregation of auditory processing across the two hemispheres (left hemisphere: noise, right hemisphere: periodicity representation). The observed noise/periodicity interactions, furthermore, might reflect pitch-synchronous spectral evaluation at the level of the left supratemporal plane, triggered by right-hemisphere representation of signal periodicity.

Acoustic Stimulation↗

PubMed2004

The contribution of the insula to motor aspects of speech production: a review and a hypothesis.

Based on clinical and functional imaging data, the left anterior insula has been assumed to support prearticulatory functions of speech motor control such as the "programming" of vocal tract gestures. In order to further elucidate this model, a recent functional magnetic resonance imaging (fMRI) study of our group (Riecker, Ackermann, Wildgruber, Dogil, & Grodd, 200) investigated both overt (aloud) and covert (silent) production of highly overlearned word strings ("automatic speech"), based on the suggestion that "inner speech" might provide a "window" into preparatory motor activities (Jeannerod, 1994). As a control condition, subjects were asked to reproduce a nonlyrical tune. In contrast to hemodynamic responses within motor cortex and cerebellum, activation of the intrasylvian cortex turned out to be bound to overt task performance. Rather than prearticulatory processes, these findings suggest the left insula to contribute to the actual coordination of the up to 100 muscles engaged in articulation and phonation. Conceivably, the association of speech production with intrasylvian cortex might have evolved within the framework of phylogenetically older connections between the insula and limbic structures, on the one hand, and nonspeech functions of the upper midline musculature such as swallowing, on the other. Whereas (overt) speech tasks predominantly elicit activation within left anterior insula, reproduction of a nonlyrical tune yielded an opposite response pattern. Conceivably, the opposite distributional pattern of speaking and singing at the level of intrasylvian cortex reflects operation of the two hemispheres across different time domains ("double filtering by frequency theory": left hemisphere=segmental information, right hemisphere=intonation contours of verbal utterances and musical melodies; ). In line with this suggestion, a further study of our group (Ackermann et al., 2001) provided first evidence that differential hemispheric filtering might be bound to insular cortex.

Brain Mapping↗

PubMed2004

Mismatch negativity responses in schizophrenia: a combined fMRI and whole-head MEG study.

OBJECTIVE: Mismatch negativity is an event-related brain response sensitive to deviations within a sequence of repetitive auditory stimuli. It is thought to reflect short-term sensory memory and is independent of higher-level cognitive processes. Mismatch negativity response is diminished in patients with schizophrenia. Little is known about the mechanisms of this decreased response, the contribution of the different hemispheres, and its locus of generation. METHOD: Patients with schizophrenia (N=12) and matched comparison subjects (N=12) were studied. A novel design to measure mismatch negativity responses to deviant auditory stimuli was generated by using the switching noises from the functional magnetic resonance imaging (fMRI) scanner, thus avoiding any interfering background sound. Stimuli included deviants of amplitude (9 dB lower) and duration (76 msec shorter) presented in a random sequence. The scanner noise was recorded and applied to the same subjects in a whole-head magnetoencephalography (MEG) device. Neuromagnetic and hemodynamic responses to the identical stimuli were compared between the patients and comparison subjects. RESULTS: As expected, neuromagnetic mismatch fields were smaller in the patient group. More specifically, a lateralization to the right for duration deviance was only found in comparison subjects. For the relative amplitude of the blood-oxygen-level-dependent signal (measured with fMRI), differences emerged in the secondary (planum temporale), but not primary (Heschl's gyrus), auditory cortex. Duration deviants achieved a right hemispheric advantage only in the comparison group. A significantly stronger lateralization to the left was found for the deviant amplitude stimuli in the patients. CONCLUSIONS: The data support the view of altered hemispheric interactions in the formation of the short-term memory traces necessary for the integration of auditory stimuli. This process is predominantly mediated by the planum temporale (secondary auditory cortex). Altered interaction of regions within the superior temporal plane and across hemispheres could be in part responsible for language-mediated cognitive (e.g., verbal memory) and psychopathological (hallucinations, formal thought disorder) symptoms in schizophrenia.

Adult↗

PubMed2004

Temporal organization of "internal speech" as a basis for cerebellar modulation of cognitive functions.

The sequencing of smooth and rhythmically "sculptured" words and phrases at a speaker's habitual speech rate (4 Hz to 6 Hz) critically depends on the cerebellum. Besides overt performance, the cerebellum also seems to organize the syllabic structure of "auditory verbal imagery" or "internal speech"--that is, a prearticulatory but otherwise fully elaborated and temporally organized representation of verbal utterances. As a consequence, cerebellar disorders may compromise cognitive operations that involve a speech code, such as verbal working memory, or disrupt cognitive processes that encompass linguistic mediation. Besides the temporal organization of syllable strings at a prearticulatory level, cerebellar patients are impaired in speech perception tasks requiring the encoding of durational parameters of the acoustic signal. The hemodynamic responses associated with these two aspects of verbal-acoustic communication--internal speech and speech perception--were found to be organized along the rostro-caudal direction within paravermal aspects of the superior right cerebellar hemisphere. Those areas of the right cerebellar hemisphere thus might provide a common platform for the computation of temporal aspects of verbal utterances in the domains of both speech production and perception.

Brain↗

PubMed2003

The right supratemporal plane hears the distance of objects: neuromagnetic correlates of virtual reality.

The neural mechanisms of auditory distance perception, a function of great biological importance, are poorly understood. Where not overruled by conflicting factors such as echoes or visual input, sound intensity is perceived as conveying distance information. We recorded neuromagnetic responses to amplitude variations over both supratemporal planes, with and without auditory spatial simulations. In the absence of other cues for distance, including those provided by auditory virtual reality, amplitude changes elicited enhanced preattentive responses over the right temporal lobe, indicating hemispheric lateralization of the 'where' pathway in the human. Lesion studies in monkeys and humans have shown that the rostral part of the right superior temporal cortex contributes to spatial awareness in the visual domain. Our data indicate that the distance to a sound source is processed within the adjacent right auditory cortex, thus extending the recent model of a right-hemisphere temporal multisensory matrix that subserves the integration of space-related data across visual and auditory modalities.

Adult↗

PubMed2003

Reconstruction of extended cortical sources for EEG and MEG based on a Monte-Carlo-Markov-chain estimator.

A new procedure to model extended cortical sources from EEG and MEG recordings based on a probabilistic approach is presented. The method (SPMECS) was implemented within the framework of maximum likelihood estimators. Neuronal activity generating EEG or MEG signals was characterized by the number of sources and their location and extension. Based on the noise distribution of the measured data, source configurations were associated with the according value of the likelihood function. To find the most likely source, i.e., the maximum likelihood estimator, and its level of confidence, a stochastic solver (Metropolis algorithm) was applied. The method presented supports the incorporation of virtually any constraint, e.g., based on physiological and anatomical a priori knowledge. Thus, ambiguity of the ill-posed inverse problem was reduced considerably by confining sources to the cortical surface extracted from individual MR images. The influence of different levels and types of noise on the outcome was investigated by means of simulations. Somatosensory evoked magnetic fields analyzed by the method presented suggest that larger extended cortical areas are involved in the processing of combined finger stimulation as compared to single finger stimulation.

Algorithms↗