Browsing by Author "Sahari, Elisa"

Aims. Speech processing has largely been studied in relatively simple paradigms, which do not take into account the variety of conditions people face in everyday situations. Yet, during natural conversations there are many factors that can affect the way we process speech, such as varying listening conditions, context of the conversation and visual information a listener receives from the speaker´s face. A recent study examined how speech is processed in natural situations by considering different listening conditions and availability of visual information. Participants selectively attended to audio-visual conversations among other speech, while the audio-visual quality of conversations were modulated. Selective attention to the conversations increased activity in the speech processing areas of the superior temporal lobe and in the cortical attention network, but also in the posterior cingulate and orbitofrontal cortex. Previously, the latter brain areas have been associated with socio-emotional processing. Therefore, it was assumed that the conversations might create a strong enough social context to activate these areas. The aim of the present research was to study whether these areas are activated due to the social context of conversations. This was examined by breaking the coherent plot of the conversations. Furthermore, the present study aimed at clarifying how the coherence of conversations facilitates speech processing. The present study also aimed to replicate previous results associated with modulations of audio-visual quality of perceived speech. Methods. Functional magnetic resonance imaging data were collected from 20 adult participants, while the participants viewed audio-visual conversations. The amount of contextual information was modulated by breaking the coherent plots of conversations. Furthermore, the auditory and visual quality of speech were modulated. Also, to increase need for cognitive control while processing the conversations, a speech audiobook was presented in the background. Results and conclusions. Attention to audio-visual speech activated cortical areas related to speech processing in temporal lobe and inferior frontal gyrus and areas related to attention in frontal lobe, as well as the medial brain areas assumed to be involved in social processing. The coherence of conversations did not modulate activations in the latter areas, implying that these areas were not activated due to social processing, but perhaps due to conceptual processing. The coherence of conversations increased activity in posterior superior temporal gyrus and temporal pole suggesting that a coherent context facilitates speech processing in both earlier and later phases of speech processing, possibly due to semantic priming. Modulation of audio-visual quality enhanced activity mainly in the same brain areas as in the previous study while increasing activation in the auditory cortex.