Processing complex sentences in fluctuating noise: Intelligibility vs. cognitive resources
Rebecca Carroll & Esther Ruigendijk, University of Oldenburg
Processing speech in adverse listening conditions (e.g. background noise) has been shown to be more difficult than in acoustically well-controlled settings (Uslar et al. 2010, Carroll & Ruigendijk, subm.). Yet, fluctuating noise has been shown to increase intelligibility as compared to stationary noise, since silent intervals can be used for contextual information, which can make up for information ‘lost’ in noise (Wagener, Brand & Kollmeier 2006). However, we know little about the processing mechanisms involved in fluctuating noise. It is possible that it interacts with syntactic complexity, as noise itself adds load to working memory, which is also needed for difficult sentences (cf. Carroll & Ruigendijk, subm.).
We tested sentences of different complexity at three different measuring points in a reaction time study. Each trial was followed by a comprehension task. All stimuli were presented in fluctuating noise. Our material consists of V2 sentences (SVO, OVS) and embedded relative clauses (subject & object relatives), with or without canonical word order and with or without ambiguity. We also tested several cognitive measures to account for interindividual differences of the 21 normal-hearing native German participants.
Results show canonicity effects for OVS and reanalysis effects for ambiguous OVS sentences. Surprisingly, object relatives do not clearly show comparable structural effects. However, subdivision of participants shows that listeners who reached the correct interpretation do show canonicity effects, but listeners with below chance-level performance do not. We interpret this finding as a sign of shallow processing, which obscures the overall effects.
We also observe different processing mechanisms between SVO/OVS sentences and relative clauses. While the former strongly co-vary with the word span measure, the latter co-vary with the Stroop measure (indicative of susceptibility to interference). We argue for an interaction of bottom-up and top-down processes involved in processing complex sentences in fluctuating noise (intelligibility vs. higher-level processing and involvement of cognitive measures), which not only depend on the structural and acoustical make-up of the sentence but also on the characteristics of the interfering noise. While fluctuating noise may facilitate intelligibility (as compared to stationary noise as reported by Carroll & Ruigendijk, subm.) on an acoustic level, it can have a negative influence on structural processing on higher cognitive levels. That is, the relevant informational cues of a given structure are different and may thus be affected to different degrees. Parts of the processing of SVO/OVS sentences can be related to working memory, processing difficulties in relative clauses depends more on the susceptibility to interfering noise.