Discrimination of differences in digitally manipulated phoneme length during speech.

The present study investigated differences in the thresholds of phoneme duration in word and sentence contexts by participants' sex. In the word condition, 27 participants listened to two pairs of words in a dual pair discrimination task. One pair contained the same durations of /s/, and the other pair contained different durations of /s/. Participants were to select the pair which contained different durations of /s/ in the words. In the sentence condition, the other set of 27 participants listened to two pairs of sentences and selected the pair containing different durations of /s/ in the sentences. Throughout these tasks, the participants' just-noticeable-difference and trials-to-completion were analyzed. The results showed that the participants demonstrated better performance in detecting just-noticeable-difference in the sentence condition than in the word condition. In addition, a sex difference was found in just-noticeable-difference in both conditions with better performance in men than women. No significant differences in trials-to-completion were found in either condition.

The effects of duration and frequency of occurrence of voiceless fricatives on listeners' perceptions of sound prolongations.

UNLABELLED: The present study examined listeners' identification and rating of words in passages as stuttered when the duration and frequency of occurrence of sound prolongations were manipulated. Thirty-six participants listened to a 219-word passage containing voiceless fricatives digitally increased from their normal durations to 200, 300, and 420ms. Listeners heard one of three passages that contained 5%, 10% or 15% altered stimuli within the passage. In Condition 1, listeners identified words considered stuttered. In Condition 2, listeners rated specifically selected words in the passage relative to the extent they considered the words stuttered. The results showed that (1) both the duration and the frequency of occurrence of the altered phonemes within the paragraph length material had an impact on listeners' perception of words identified as a sound prolongation; (2) listeners gave significantly higher ratings in Condition 2 than Condition 1 when determining if a word was stuttered or produced fluently. The implications of these results are discussed. LEARNING OUTCOMES: After reading this article, the reader will be able to: (1) Describe the past literature on listener perceptions of stuttering. (2) Differentiate between listener's perceptions of sound prolongations that are altered in duration and frequency of occurrence. (3) Describe how paragraph-length speech material compares to past research that has used isolated utterances.

The effect of amplitude modulation on intelligibility of time-varying sinusoidal speech in children and adults.

Although researchers are currently studying auditory object formation in adults, little is known about the development of this phenomenon in children. Amplitude modulation has been suggested as one of the characteristics of the speech signal that allows auditory grouping. In this experiment, we evaluated children (4 to 13 years of age) and adults to examine whether children's ability to use amplitude modulation (AM) in perception of time-varying sinusoidal (TVS) sentences is different from that of adults, and whether there are developmental changes. We evaluated performance on recognition of TVS sentences (unmodulated, amplitude-comodulated at 25, 50, 100, and 200 Hz, and amplitude-modulated using conflicting frequencies). Overall, the youngest children performed more poorly than did older children and adults. However, difference scores, defined as the percentage of phonemes correct in a given modulation condition minus the percentage correct for the unmodulated condition, showed no significant effects of age. Unlike the findings of previous studies (Carrell & Opie, 1992), these results support the ability of modulation with conflicting frequencies to improve intelligibility. The present study provides evidence that children and adults receive the same benefits (or decrements) from amplitude modulation.

Listeners' identification and discrimination of digitally manipulated sounds as prolongations.

The present study had two main purposes. One was to examine if listeners perceive gradually increasing durations of a voiceless fricative categorically ("fluent" versus "stuttered") or continuously (gradient perception from fluent to stuttered). The second purpose was to investigate whether there are gender differences in how listeners perceive various duration of sounds as "prolongations." Forty-four listeners were instructed to rate the duration of the // in the word "shape" produced by a normally fluent speaker. The target word was embedded in the middle of an experimental phrase and the initial // sound was digitally manipulated to create a range of fluent to stuttered sounds. This was accomplished by creating 20 ms stepwise increments for sounds ranging from 120 to 500 ms in duration. Listeners were instructed to give a rating of 1 for a fluent word and a rating of 100 for a stuttered word. The results showed listeners perceived the range of sounds continuously. Also, there was a significant gender difference in that males rated fluent sounds higher than females but female listeners rated stuttered sounds higher than males. The implications of these results are discussed.