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TABLE IV. Descriptive data for closure duration To, pressure difference in the closure Pd, pressure atclosure Pc, and pressure at release Pr. To and Pd are the two measures used to n from ; Pd=Pr−Pc. Eachcell in the first three rows shows the group mean standard deviation. The last row provides the ratio of the5 year olds to the adults means and standard deviations calculated separately.Closure duration ToPressure differencePdPressure at closurePcPressure at releasePr/b/ /p/ /b/ /p/ /b/ /p/ /b/ /p/5 year olds 106.7 17.9 113.7 21.4 4.9 1.9 5.2 1.8 2.5 0.8 3.4 1.1 7.4 2.0 8.6 1.910 year olds 86.7 17.9 82.9 18.0 3.9 0.9 4.4 0.7 2.4 0.8 3.9 1.5 6.3 1.2 8.3 1.8Woman 75.5 10.4 75.6 9.6 2.7 0.9 2.9 1.2 1.7 0.5 2.9 0.9 4.3 1.1 5.8 1.5Ratio: 5 yearolds to women1.4 1.7 1.5 2.2 1.8 2.1 1.8 1.5 1.5 1.6 1.2 1.2 1.7 1.8 1.5 1.3tions for were also fairly large here refer back to Fig. 4.Review of the women’s data showed four cases in whichindividuals had values at or lower than Müller and Brown’saverages. The same was true for one 10 year old. Thus, thecurrent adult data overlap with those of Müller and Brown,and appear to be generally consistent with the results of theearlier study. Section IV raises some issues concerning which may explain the wide variation in even in adultspeakers.IV. DISCUSSIONA. Age and stop consonant voicingPast studies have found that children up to 6 years ofage produce fewer voiced stops and less closure voicing thanadults e.g., Barton and Macken, 1980; Kewley-Port and Preston1974; Smith, 1979; Zlatin and Koenigsknecht, 1976.Qualitatively, the current data showed the least /b/ voicingand the largest number of devoiced /b/ productions in the5 year olds, but age effects did not reach significance for anyof the voicing measures. Four factors should be consideredin interpreting this result: a nature of the voicing contrast inEnglish; b phonetic context; c age of the children; and dsample size.Given that closure voicing is not obligatory in stressed,syllable-initial contexts in American English e.g., Liskerand Abramson, 1964; Zlatin, 1974, all speakers have theoption of producing voiceless unaspirated stops, which maybe motorically less demanding Kewley-Port and Preston,1974. At the same time, the intervocalic frame in which thetarget consonants appeared here tends to facilitate closurevoicing. Children might be particularly susceptible to factorsfavoring devoicing Westbury and Keating, 1986, but to ascribea lack of significant age effects here to the intervocaliccontext would be to assert that children have a stronger positionalbias toward voicing. Given smaller vocal tract sizesand higher phonation threshold pressures in children, there isno reason to think they should be more likely to voice in anintervocalic position than adults. That is, the phonetic contextmay have predisposed all speakers to produce voicedstop closures, but this should not have made age differencesless likely.More likely is that the children’s ages and the groupsizes had the effect of minimizing age effects. Past developmentalstudies of consonant voicing have mostly concentratedon very young children. The requirements of the experimentaltask used here precluded recording childrenyounger than about 4 years, and the younger group includedindividuals nearing their sixth birthday. These children werethus at the upper end of the age range at which group differenceshave been demonstrated. The intensive within-speakerprocessing here also limited group sizes. Finally, the childrenshowed considerable intersubject variability, as has oftenbeen observed e.g., Eguchi and Hirsh, 1969; Kent and Forner,1980. With a larger sample size, the mean group differencesmay have outweighed the within-group variability toproduce a significant age effect e.g., Kirk, 1999.In contrast to the 5 year olds, the 10 year olds werequalitatively as well as statistically comparable to the womenin their voicing measures. Although a few studies have reportedVOTs for voiced stops in children of this age KentFIG. 5. Differences between values of /p/ and /b/ for each speaker.FIG. 6. Results of correlations Pearson’s r values between and durationof closure voicing for each speaker. Asterisks mark speakers for whom thecorrelation was significant at p0.002.1084 J. Acoust. Soc. Am., Vol. 123, No. 2, February 2008 L. L. Koenig and J. C. Lucero: Voicing and intraoral pressure