Tilo Kircher

Störungen in der Sprachverarbeitung finden sich bei Patienten mit Schizophrenie in ihrer ausgeprägtesten Form klinisch als „Konkretismus“, d. h. als Festhalten an der wörtlichen Bedeutung übertragener Begriffe („Der Apfel fällt nicht weit vom Stamm“). In leichter Ausprägung — d. h. in Form von Problemen beim Verstehen von sprachlichen Ausdrücken — findet sich dieses Phänomen bei fast allen Patienten; es gilt als einer der wichtigsten Prädiktoren für das Auftreten einer Psychose im Prodromalstadium.

It has been shown that social deficits contribute to psychopathology in schizophrenia, such as the bleulerian autism. A possible dysfunction in the mirror neuron system may be the reason for these deficits in the disorder. We wanted to better characterize the neural networks involved in the perception of social behavior. Fifteen healthy participants were presented with video clips of 8 seconds' duration depicting either (1) one actor manipulating an object, (2) two actors with only one manipulating an object or (3) two actors cooperating in manipulating an object and 2 other control conditions. Functional magnetic resonance imaging data were acquired during watching these videos. We found the perception of social cooperation is supported by a neural network comprising the precuneus, the temporoparietal junction (supramarginal gyrus, angular gyrus, BA 39/40), the middle temporal gyrus (including superior temporal sulcus) and frontal regions (medial frontal gyrus, inferior frontal gyrus). These areas form a complex network also being activated during theory of mind and cooperative behavior tasks. Its nodes overlap with those of the mirror neuron system. Consequently, both theory of mind abilities and mirror mechanisms are relevant in the perception and understanding of social cooperative behavior. We outline the consequences of these results for a further understanding of schizophrenic psychopathology with respect to social deficits and ego disturbances.

Language rhythm is assumed to involve an alternation of strong and weak
beats within a certain linguistic domain, although the beats are not
necessarily isochronously distributed in natural language. However, in
certain contexts, as for example in compound words, rhythmically induced
stress shifts occur in order to comply with the so-called Rhythm Rule
@Liberman1977. This rule operates when two stressed adjacent syllables
create a stress clash or adjacent unstressed syllables (stress lapse)
occur. Experimental studies on speech production, judgement of stress
perception, and event-related potentials (ERPs) @Bohn2013 have found
differences in production, ratings, and ERP components respectively,
between well-formed structures and rhythmic deviations. The present
study builds up on these findings by using functional magnetic resonance
imaging (fMRI) in order to localise rhythmic processing (within the
concept of Rhythm Rule) in the brain. Other fMRI studies on linguistic
stress found effects in the supplementary motor area, insula, precuneus,
superior temporal gyrus, parahippocampal gyrus, calcarine gyrus and
inferior frontal gyrus @Domahs2013, @Geiser2008, @Rothermich2013.
However, what other studies have not investigated yet is rhythm
processing in natural contexts, thus in the course of a story which is
not further controlled for a metrically isochronous speech rhythm. Here
we examine the hypotheses that a) well-formed structures are processed
differently than rhythmic deviations in compound words for German, b)
this happens in speech processing of stories in the absence of a
phonologically related task (implicit rhythm processing).

Our compounds consisted of three parts (A(BC)) that build a
premodifier-noun combination. The modifier was either a monosyllabic
noun (“*Holz*”, wood) or a bisyllabic noun (“*Pla*stik”, plastic) with
lexical stress on the initial syllable. The premodifier was followed by
a disyllabic noun bearing compound stress on the initial syllable in
isolation (“*Spiel*zeug”, toy ). When combining these two word
structures the premodifier bears overall compound stress and the initial
stress of the disyllabic noun should be shifted rightwards to its final
syllable, in order to be in accordance to the Rhythm Rule:
*Holz*-spiel-*zeug* (wooden toy(s)). On the other hand if the disyllabic
noun is combined with a preceding disyllabic noun bearing initial
stress, a shift is unnecessary allowing for the stress pattern:
*Pla*-stik-*spiel*-zeug (plastic toy(s)). The first condition we call
SHIFT and the second NO SHIFT. In contrast to these well-formed
conditions we induce rhythmically ill-formed conditions: CLASH for the
case that emph<span>Holz</span>-*spiel*-zeug keeps the initial stress of
its compounds and LAPSE when we introduce the unnecessary shift in
*Pla*-stik-spiel-*zeug*. We constructed 20 word pairs following the same
stress patterns as “Holz-/Plastikspielzeug” and embedded them in 20
two-minute long stories. Our focus when embedding the conditions was the
naturalness of the stories. For example, word-pair “Holzspielzeug” vs.
“Plastikspielzeug” would thus appear in the following context: ’The
clown made funny grimaces, reached into his red cloth bag and threw a
small *wooden toy* to the lady in the front row.’ vs. ’The toys, garden
chairs and pillows remained however outside. The mother wanted to tidy
up the *plastic toys* from the garden after dinner.’

We obtained images (3T) of 20 healthy right-handed German monolinguals
(9 male) employing a 2x2 design: well-formedness (rhythmically
well-formed vs. ill-formed) x rhythm-trigger (monosyllabic vs.
disyllabic premodifier). Subjects were instructed to listen carefully
and were asked two comprehension questions after each story. On the
group level we analysed the data in the 2x2 design mentioned above. Our
critical events were the whole compound words. We report clusters of
p\<.005 and volumes of at least 72 voxels (Monte Carlo corrected).

For the main effect of well-formedness we found effects in the left
cuneus, precuneus and calcarine gyrus. For the main effect of
rhythm-trigger we found no significant differences at this
supra-threshold level, which was expected since we did not hypothesise
an effect of the length of the premodifier. Our main finding is the
interaction of well-formedness and rhythmic-trigger in the precentral
gyrus bilaterally and in the right supplementary motor area (SMA). Since
the interaction was significant we calculated theoretically motivated
pairwise contrasts within one rhythmic trigger level. For the
monosyllabic premodifier CLASH vs. SHIFT revealed no significant
clusters, but, interestingly, the opposite contrast (SHIFT vs. CLASH)
showed differences in the right superior frontal gyrus, right inferior
frontal gyrus (rIFG, BA 45), right lingual and calcarine gyrus,
bilateral precentral gyrus (BA6,BA4), left precentral gyrus (BA3a). For
the bisyllabic premodifier LAPSE vs. NO SHIFT activated significantly
the left inferior temporal gyrus, left parahippocampal gyrus, left
insula, bilateral superior temporal gyrus (STG), right pre- and
postcentral gyrus. NOSHIFT vs. LAPSE activated significantly the right
lingual gyrus and the calcarine gyrus bilaterally. We finally compared
the two rhythmically ill-formed structures LAPSE vs. CLASH and found
significant activation in the right supplementary motor area and
premotor cortex.

Our findings are in line with previous fMRI findings on rhythmic
processing. Firstly, the superior temporal gyrus is robustly involved in
rhythmic processing irrespective of the task of the study: semantic and
metric task @Rothermich2013, speech perception of violated vs. correctly
stressed words @Domahs2013 and in explicit and implicit isochronous
speech rhythm tasks @Geiser2008. To this we can add with our
careful-listening task comparable to the semantic task of
@Rothermich2013. Our contribution is that we found activations for the
implicit task of careful listening which have only been found for
explicit tasks before: these include the left insula, the bilateral
precentral gyrus, the precuneus and the parahippocampal gyrus. Lastly,
the activation in the supplementary motor areas completes the picture of
rhythm processing regions in the brain. This finding is of special
interest since it was strong for the comparison within rhythmically
ill-formed conditions LAPSE vs. CLASH. This might be due to the fact
that stress lapse structures contain two violations, i.e. a deviation
from word stress which is not rhythmically licensed, while the clash
structures contain only a rhythmically deviation but keep the original
word stress.

The differences in activations found for well-formedness show that even
in implicit rhythmical processing the language parser is sensitive to
subtle deviations in the alternation of strong and weak beats. This is
particularly evident in the STG activation associated with the
processing of linguistic prosody, SMA activation which has been
suggested to be involved in temporal aspects of the processing of
sequences of strong and weak syllables, and IFG activation associated
with tasks requiring more demanding processing of suprasegmental cues.

Bohn, K., Knaus, J., Wiese, R., & Domahs, U. The influence of rhythmic
(ir) regularities on speech processing: Evidence from an ERP study on
German phrases. Neuropsychologia, 51(4), 760-771 (2013). Domahs, U.,
Klein, E., Huber, W., & Domahs, F. Good, bad and ugly word stress–fMRI
evidence for foot structure driven processing of prosodic violations.
Brain and language, 125(3), 272-282 (2013). Geiser, E., Zaehle, T.,
Jancke, L., & Meyer, M. The neural correlate of speech rhythm as
evidenced by metrical speech processing. Journal of Cognitive
Neuroscience, 20(3), 541-552 (2008). Liberman, M., & Prince, A. On
stress and linguistic rhythm. Linguistic inquiry, 249-336 (1977).
Rothermich, K., & Kotz, S. A. Predictions in speech comprehension: fMRI
evidence on the meter–semantic interface. Neuroimage, 70, 89-100 (2013).