Infants adapt to speaking rate differences in word segmentation

Throughout their development, infants are exposed to varying speaking rates. Thus, it is important to determine whether they are able to adapt to speech at varying rates and recognize target words from continuous speech despite speaking rate differences. To address this question, a series of four experiments were conducted to test whether infants can recognize words in continuous speech when rate is variable. In addition, the underlying mechanisms that infants may use to cope with variations induced by different speaking rates were also examined. Specifically, using the Headturn Preference procedure [Jusczyk and Aslin (1995). Cognitive Psychol. 29, 1-23], infants were familiarized with normal-rate passages containing two trisyllabic target words (e.g., elephants and dinosaurs), and tested with familiar (elephants and dinosaurs) and unfamiliar (crocodiles and platypus) words embedded in normal-rate (experiment 1), fast-rate (experiments 2 and 3), or slow-rate passages (experiment 4). The results indicate that 14-month-olds, but not 11-month-olds, recognized target words in passages with a fast speaking rate. In addition, findings suggest that infants used context to normalize speech across different speaking rates.

Slow speech rate effects on stuttering preschoolers with disordered phonology

To study the effects of clinicians' slow rate on the speech of children who stutter with and without a concomitant phonological disorder, an A-B-A-B single case design was used with six clinician-child dyads, where B = Clinician's slow speech rate model. Two boys and one girl, aged 49-54 months, stuttering with disordered phonology (S + DP), were compared to three boys aged 42-50 months, stuttering with normal phonology (S + NP). Articulation rates were measured in phones per second (pps) in clinician-child adjacent utterance pairs. The S + NP dyads showed improved fluency in the B condition through a larger effect size, higher mean baseline stutter reductions and lower percentages of non-overlapping data than did the S + DP dyads. The S + DP girl showed relatively improved fluency in the B condition. S + DP children showed no articulation rate alignment (Range: 16% decrease to a 1.2% increase), whereas S + NP children averaged a 20% pps rate reduction (Range: 19.6-25.4% decrease), aligning with their clinicians who averaged a 38% pps rate reduction from baseline. The S + DP group spoke significantly (z = -4.63; p < 0.00) slower at baseline (Mdn = 6.9 pps; SE = 0.07 pps) than S + NP children in previously published samples (Mdn = 9.8 pps; SE = 0.22 pps). Results suggest that a slow rate model alone is not effective for facilitating fluency in S + DP boys with time since onset of about 2 years.