Objective: This study examined the effect of intensity level of presentation on scaling of speech intelligibility in speakers with and without dysarthria.
Patients and methods: A total of 50 utterances produced by speakers with dysarthria and healthy speakers were played to 60 listeners in four conditions, which consisted of two different presentation levels (‘high’ vs. ‘low’) and equalization of levels across utterances (‘adjusted’ vs. ‘unadjusted’). Speech intelligibility was scaled by using a direct magnitude estimation technique with and without modulus.
Results: A significant decrease in speech intelligibility was indicated when the stimuli were adjusted to have fixed intensity on the most intense vocalic nuclei of each word, while no significant change was found between ‘high’ and ‘low’ presentation level conditions.
Conclusion: The findings suggest that an increase in presentation level alone does not result in significant improvement in speech intelligibility ratings. The results are discussed by considering clinical implications in conducting speech therapy with emphasis on intensity variation.