Recently, with a data set dating back to my time in Angela Friederici’s department, we proposed the idea that auditory signal degradation would affect the exact configuration of activity along the main processing streams of language, in the superior temporal and inferior frontal cortex. We tentatively coined this process “upstream delegation”: The activations that were driven by increasing syntactic demands, with the challenge of decreasing signal quality coming on top, were all of a sudden found more “upstream” from where we had located them with improvingsignal quality.
Category: Auditory Neuroscience
There will be two poster presentations at SFN in Washington, DC., on the topic of auditory predictions in speech perception. The first poster, authored by Alexandra Bendixen, Mathias Scharinger, and Jonas Obleser, summarizes as follows:
Speech signals are often compromised by disruptions originating from external (e.g., masking noise) or internal (e.g., sluggish articulation) sources. Speech comprehension thus entails detecting and replacing missing information based on predictive and restorative mechanisms. The nature of the underlying neural mechanisms is not yet well understood. In the present study, we investigated the detection of missing information by occasionally omitting the final consonants of the German words “Lachs” (salmon) or “Latz” (bib), resulting in the syllable “La” (no semantic meaning). In three different conditions, stimulus presentation was set up so that subjects expected only the word “Lachs” (condition 1), only the word “Latz” (condition 2), or the words “Lachs” or “Latz” with equal probability (condition 3). Thus essentially, the final segment was predictable in conditions 1 and 2, but unpredictable in condition 3. Stimuli were presented outside the focus of attention while subjects were watching a silent video. Brain responses were measured with multi-channel electroencephalogram (EEG) recordings. In all conditions, an omission response was elicited from 125 to 165 ms after the expected onset of the final segment. The omission response shared characteristics of the omission mismatch negativity (MMN) with generators in auditory cortical areas. Critically, the omission response was enhanced in amplitude in the two predictable conditions (1, 2) compared to the unpredictable condition (3). Violating a strong prediction thus elicited a more pronounced omission response. Consistent with a predictive coding account, the processing of missing linguistic information appears to be modulated by predictive context.
The second poster looks at similar material, but contrasts coronal [t] with dorsal [k], yielding interesting asymmetries in MMN responses:
Research in auditory neuroscience has lead to a better understanding of the neural bases of speech perception, but the representational nature of speech sounds within words is still a matter of debate. Electrophysiological research on single speech sounds provided evidence for abstract representational units that comprise information about both acoustic structure and articulator configuration (Phillips et al., 2000), thereby referring to phonological categories. Here, we test the processing of word-final consonants differing in their place of articulation (coronal [ts] vs. dorsal [ks]) and acoustic structure, as seen in the time-varying formant (resonance) frequencies. The respective consonants distinguish between the German nouns Latz (bib) and Lachs (salmon), recorded from a female native speaker. Initial consonant-vowel sequences were averaged across the two nouns in order to avoid coarticulatory cues before the release of the consonants. Latz and Lachs served as standard and deviant in a passive oddball paradigm, while the EEG from 20 participants was recorded. The change from standard [ts] to deviant [ks] and vice versa was accompanied by a discernible Mismatch Negativity (MMN) response (Näätänen et al., 2007). This response showed an intriguing asymmetry, as seen in a main effect condition (deviant Latz vs. deviant Lachs, F(1,1920) = 291.84, p < 0.001) of an omnibus mixed-effect model. Crucially, the MMN for the deviant Latz was on average more negative than the MMN for the deviant Lachs from 135 to 185 ms post deviance onset (p < 0.001). We interpret these findings as reflecting a difference in phonological specificity: Following Eulitz and Lahiri, 2004, we assume coronal segments ([ts]) to have less specific (‘featurally underspecified’) representations than dorsal segments ([ks]). While in standard position, Lachs activated a memory trace with a more specific final consonant for which the deviant provided a stronger mismatch than vice versa, i.e. when Latz activated a memory trace with a less specific final consonant. Our results support a model of speech perception where sensory information is processed in terms of discrete units independent of higher lexical properties, as the asymmetry cannot be explained by differences in lexical surface frequencies between Latz and Lachs (both log-frequencies of 0.69). We can also rule out a frequency effect on the segmental level. Thus, it appears that speech perception involves a level of processing where individual segmental representations within words are evaluated.
We are happy to announce that our paper “Asymmetries in the processing of vowel height” will be appearing in the Journal of Speech, Language, & Hearing Research, authored by Philip Monahan, William Idsardi and Mathias Scharinger. A short summary is given below:
[Update]Purpose: Speech perception can be described as the transformation of continuous acoustic information into discrete memory representations. Therefore, research on neural representations of speech sounds is particularly important for a better understanding of this transformation. Speech perception models make specific assumptions regarding the representation of mid vowels (e.g., []) that are articulated with a neutral position in regard to height. One hypothesis is that their representation is less specific than the representation of vowels with a more specific position (e.g., [æ]).
Method: In a magnetoencephalography study, we tested the underspecification of mid vowel in American English. Using a mismatch negativity (MMN) paradigm, mid and low lax vowels ([]/[æ]), and high and low lax vowels ([I]/[æ]), were opposed, and M100/N1 dipole source parameters as well as MMN latency and amplitude were examined.
Results: Larger MMNs occurred when the mid vowel [] was a deviant to the standard [æ], a result consistent with less specific representations for mid vowels. MMNs of equal magnitude were elicited in the high–low comparison, consistent with more specific representations for both high and low vowels. M100 dipole locations support early vowel categorization on the basis of linguistically relevant acoustic–phonetic features.
Conclusion: We take our results to reflect an abstract long-term representation of vowels that do not include redundant specifications at very early stages of processing the speech signal. Moreover, the dipole locations indicate extraction of distinctive features and their mapping onto representationally faithful cortical locations (i.e., a feature map).
The paper is available here.
References
- Scharinger M, Monahan PJ, Idsardi WJ. Asymmetries in the processing of vowel height. J Speech Lang Hear Res. 2012 Jun;55(3):903–18. PMID: 22232394. [Open with Read]
Obleser, J., Weisz, N. (in press) Suppressed alpha oscillations predict intelligibility of speech and its acoustic details. Cerebral Cortex.
[Update]Paper is available here.
References
- Obleser J, Weisz N. Suppressed alpha oscillations predict intelligibility of speech and its acoustic details. Cereb Cortex. 2012 Nov;22(11):2466–77. PMID: 22100354. [Open with Read]
I am also delighted to report the fruits of a very recent collaboration with Nathan Weisz and his OBOB lab at the University of Konstanz, Germany.
Alpha Rhythms in Audition: Cognitive and Clinical Perspectives
In this review paper, which appears in the new, exciting “Frontiers in Psychology” journal, we sum the recent evidence that alpha oscillations (here broadly defined from 6 to 13 Hz) are playing a very interesting role in the auditory system, just as they do in the visual and the somatosensory system.
In essence, we back Ole Jensen’s and others’ quite parimonious idea of alpha as a functional inhibition / gating system across cortical areas.
From our own lab, preliminary data from two recent experiments is included: On the role of alpha osillations as a potential marker for speech intelligibility and its acoustic determinants, as well as on speech degradation and working memory load and their combined reflection in alpha power increases.
NB — the final pdf is still lacking, and Front Psychol is still not listed in PubMed. This should not stop you from submitting to their exciting new journals, as the review process is very fair and efficient and the outreach via free availability promises to be considerable.
References
- Weisz N, Hartmann T, Müller N, Lorenz I, Obleser J. Alpha rhythms in audition: cognitive and clinical perspectives. Front Psychol. 2011 Apr 26;2:73. PMID: 21687444. [Open with Read]
A new paper is about to appear in Neuroimage on the interaction of syntactic complexity and acoustic degradation.
It is written by myself, PhD student Lars Meyer, and Angela Friederici. In a way, the paper brings together one of Angela’s main research questions (which brain circuits mediate the processing of syntax?) with a long-standing interest of mine, that is, how do adverse listening situations affect the comprehension of speech.
The paper is entitled
Dynamic assignment of neural resources in auditory comprehension of complex sentences
The paper first establishes that acoustic variants of increasingly complex sentences essentially behave like written versions of these sentences.
The data then neatly show that processing challenging (but legal) syntax under various levels of degradation has a very different effect on the neural circuits involved than profiting from semantics: While the latter has been shown previously to involve more widespread, heteromodal brain areas, the double demand of increasingly complex syntax and an increasingly degraded speech signal (from which the complex syntax has to be parsed) elicit an “upstream” shift of activation back to less abstract processing areas in the superior temporal and prefrontal/frontal cortex.
We tentatively have termed this process “upstream delegation”. We have also tried and established a slightly unusual method to do justice to the fMRI activation data: We have included all z‑scores gathered along certain spatial dimensions, irrespective of whether they were sub- or suprathreshold, and have treated them as distributions. Check it out and let us know what you think.
References
- Obleser J, Meyer L, Friederici AD. Dynamic assignment of neural resources in auditory comprehension of complex sentences. Neuroimage. 2011 Jun 15;56(4):2310–20. PMID: 21421059. [Open with Read]
This went online just a day before Christmas:
Neuromagnetic evidence for a featural distinction of English consonants: Sensor- and source-space data
by Mathias Scharinger, Jennifer Merickel, Joshua Riley, and William Idsardi
http://dx.doi.org/10.1016/j.bandl.2010.11.002
We wanted to look at featural (categorical) place of articulation distinctions in English consonants, and selected labial and coronal fricatives and glides for an MMN study. In this study, we looked at sensor- and source-space effects of labial deviants preceded by coronal standards and coronal deviants preceded by labial standards, across the two manners of articulation, i.e. fricatives and glides. Note that there are rather dramatic acoustic differences between these manners of articulation: uncorrelated noise through narrow constriction vs. vowel-like sound with typical resonance frequencies. We found consistent place-of-articulation effects, independent of manner of articulation: labial deviants produced larger MMN, contra a directional hypothesis of underspecification, and dipole source locations followed the Obleser-gradient in that labials elicited N1m dipoles anterior to dipoles of coronals in auditory cortex.
References
- Scharinger M, Merickel J, Riley J, Idsardi WJ. Neuromagnetic evidence for a featural distinction of English consonants: sensor- and source-space data. Brain Lang. 2011 Feb;116(2):71–82. PMID: 21185073. [Open with Read]
Late 2010 was particularly good to us:
Multiple brain signatures of integration in the comprehension of degraded speech
by Jonas Obleser and Sonja Kotz, in NeuroImage.
The final pdf will hopefully be available online very soon. Meanwhile the figure below captures our main results:
References
- Obleser J, Kotz SA. Multiple brain signatures of integration in the comprehension of degraded speech. Neuroimage. 2011 Mar 15;55(2):713–23. PMID: 21172443. [Open with Read]