Browsing by Subject "intelligibility"

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  • Hakonen, Maria; May, Patrick J. C.; Jaaskelainen, Iiro P.; Jokinen, Emma; Sams, Mikko; Tiitinen, Hannu (2017)
    Introduction: We examined which brain areas are involved in the comprehension of acoustically distorted speech using an experimental paradigm where the same distorted sentence can be perceived at different levels of intelligibility. This change in intelligibility occurs via a single intervening presentation of the intact version of the sentence, and the effect lasts at least on the order of minutes. Since the acoustic structure of the distorted stimulus is kept fixed and only intelligibility is varied, this allows one to study brain activity related to speech comprehension specifically. Methods: In a functional magnetic resonance imaging (fMRI) experiment, a stimulus set contained a block of six distorted sentences. This was followed by the intact counterparts of the sentences, after which the sentences were presented in distorted form again. A total of 18 such sets were presented to 20 human subjects. Results: The blood oxygenation level dependent (BOLD)-responses elicited by the distorted sentences which came after the disambiguating, intact sentences were contrasted with the responses to the sentences presented before disambiguation. This revealed increased activity in the bilateral frontal pole, the dorsal anterior cingulate/paracingulate cortex, and the right frontal operculum. Decreased BOLD responses were observed in the posterior insula, Heschl's gyrus, and the posterior superior temporal sulcus. Conclusions: The brain areas that showed BOLD-enhancement for increased sentence comprehension have been associated with executive functions and with the mapping of incoming sensory information to representations stored in episodic memory. Thus, the comprehension of acoustically distorted speech may be associated with the engagement of memory-related subsystems. Further, activity in the primary auditory cortex was modulated by prior experience, possibly in a predictive coding framework. Our results suggest that memory biases the perception of ambiguous sensory information toward interpretations that have the highest probability to be correct based on previous experience.
  • Kallio, Heini (Helsingfors universitet, 2012)
    The main aim of this study was to examine the effects of different acoustic features on the perception of clear news speech. Additional goal was to increase knowledge on informational clear speech, more closely the Finnish plain language radio news speech. Plain language news is produced by the national Finnish broadcasting station for listeners with Finnish as a second language. Clear speech in news reading was not previously studied in Finnish and therefore the theoretical aspects were obtained from several studies on clear speech, intelligibility and prosody. Clear speech research has revealed many acoustic-phonetic changes made by speakers attempting to clarify their speech. Features like slower speech rate, wider F0 range, higher mean F0 and increased intensity are said to be characteristic to clear speech. In plain language news slower speech rate and appropriate phrasing are significant. The study consisted of two experiments: a listening experiment and acoustic analysis. The purpose of the listening experiment was to study how speech rate, clarity, pleasantness and intelligibility of different news readers were perceived by listeners with different linguistic background. Ratings of news speech from professional plain news readers were obtained from 15 non-native learners of Finnish and 15 native Finnish listeners. Factors that varied were speech rate (normal versus slow) and speaker (two males and two females). Acoustic analysis was made to study differences between news readers on speech rate, articulation rate, fundamental frequency, prosodic phrasing and voice quality. Measurements were made from news samples with two addressed speaking rates. The relations between the rating results of two subject groups and acoustic features were studied using ordinal logistic regression model. The intelligibility ratings of non-native listeners were affected by linguistic contents and therefore were not reliable for statistical testing. However, results showed that fundamental speech rates and articulation rates affected the perception of clarity. Voice quality had an effect on perceived pleasantness. Methods for measuring intelligibility should be studied further. Also the relations between acoustic features as well as perceived qualities of speech should be studied further. This study can be seen as preliminary study for upcoming research on Finnish clear news speech. The focus of this study was on fundamental acoustic features. In addition to suggested improvements, wider analysis on segmental level acoustics is recommended.