fNIRS Shows that Object Relative Clauses are More Difficult to Process
than Subject Relative Clauses in Turkish
It was suggested that processing subject relative clauses (SRCs) are
universally easier than processing object relative clauses (ORCs) based
on the studies carried out in head-initial languages such as English,
and German. However, studies carried out in head-final languages such as
Chinese and Basque refuted this claim. Turkish is also a head-final
language. Existing relative clause processing literature in Turkish is
based solely on behavioural metrics. Even though an ORC processing
disadvantage was suggested for Turkish, the results were not conclusive.
Therefore, we aimed to investigate the neural dynamics of relative
clause processing in Turkish. We asked 14 native Turkish speakers to
answer Yes/No questions about 24 sentences each containing either SRC or
ORC while their prefrontal hemodynamic activity was recorded with fNIRS.
Our findings revealed hemodynamic activity in the lateral portions of
the left prefrontal cortex in both conditions. However, hemodynamic
activity was more widespread in prefrontal regions for ORC than SRC.
Even though the behavioural metrics failed to produce a significant
difference between SRC and ORC conditions, direct ORC>SRC
contrast revealed significant activity in left and right DLPFC, which
are known to be involved in language processing and conflict monitoring
related processes, respectively. Our findings indicate that processing
ORCs are more difficult and require further prefrontal resources than
processing SRCs in Turkish, thus refuting the head-directionality based
explanations of relative clause processing asymmetries.