Poster D83, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall
The environment makes a difference: Disrupted processing of speech sounds within natural auditory environment is reflected in the left auditory cortical activity
Hanna Renvall1, Sebastian Silfverberg1, Lauri Jahkola1, Riitta Salmelin1;1Aalto University
Introduction Humans can automatically attend and react to behaviorally relevant perceptual features such as speech in our natural environment. The special nature of attended speech stimuli has been under intensive scrutiny in several recent neuroimaging studies. These studies have shown that higher-order auditory areas track the spectrotemporal features of attended speech signals (Kerlin et al. 2010; Ding and Simon 2012; Mesgarani and Chang 2012; Vander Ghinst et al. 2016) while suppressing those of unattended speech (Puvvada and Simon, 2017). Here we addressed whether the speech-specific cortical processes would be affected by simultaneously presented, unattended non-speech natural sounds. For this, we used superimposed speech and environmental sound excerpts. We hypothesized that the cortical activity to speech would be modified by the simultaneously presented environmental sounds, and such modulation would depend on the semantic agreement of the attended sounds and the auditory surroundings. Methods In our magnetoencephalography (MEG) study, 18 native Finnish-speaking subjects were presented with auditory “miniscenes” that consisted of superimposed 4- to 6-word sentences and short fragments of auditory environments. The sentences were modified so that the last word of the sentence was—on the basis of extensive behavioral testing—either i) highly expected and semantically appropriate, ii) improbable but semantically appropriate, or iii) semantically inappropriate. The superimposed environmental sounds were selected to match the expected last word or not, and they consisted of e.g. sounds of traffic, household, animal calls, and non-speech human sounds. The combined sounds were presented with +10 dB speech-to-environmental sound intensity ratios. At this intensity ratio, both sound excerpts within the stimuli were clearly distinguishable. The subjects were instructed to attend to the sentences and respond with a finger lift when they heard a predefined target word at any position in a sentence (7% of the stimuli). Brain activity was recorded with a 306-channel neuromagnetometer (Vectorview, Neuromag Ltd). Results The inappropriate sentence-final words evoked a significantly stronger sustained response (> 400 ms) than expected final words, especially in the left temporal areas. At 550-700 ms after the final word onset, the size of this effect was influenced by whether the auditory surroundings matched the expected or the actual (inappropriate) final word: when the auditory environment matched the presented inappropriate sentence ending, the amplitude of the sustained MEG response was smaller than when the auditory environment agreed with the expected (but not presented) word (p = 0.001). Conclusions The present results suggest strong top-down modulation from the natural, unattended auditory surroundings for processing of attended speech sounds. Such processes are likely to play an important role in real-life-like auditory environments, and appear to rely on the activation of the predominantly left auditory cortex at around 550-700 ms after the stimulus onset.
Themes: Speech Perception, Perception: Auditory
Method: Electrophysiology (MEG/EEG/ECOG)