Exploring the acoustic vowel space in two-year-old children: Results for Dutch and Hungarian

In the last decade, there has been an increasing interest in exploring patterns of vowel acquisition in young children. Traditionally, researchers attempt to estimate formant values of vowel realizations via acoustic measurements. However, these techniques have yielded questionable results, due primarily to a low sampling rate of the spectrum caused by a high fundamental frequency in young children s speech. Additionally, the researcher s knowledge about the intended vowel quality affects the decision pertaining to vowel formants. A frequency domain band filtering analysis method that minimizes the dependence of the results on F0 is developed to measure the spectral envelopes in children s utterances automatically, and is applied to existing utterance data sets of Dutch and Hungarian. One further advantage of the current method is that it selects a maximum of 10 measurement points along the length of the utterance. Data reduction of all filter outputs is achieved via Principal Component Analysis (PCA). By using the first 2 eigenvectors, a reference plane is created. The first two eigenvectors account for 54.2 vs. 58.6% in the Dutch and Hungarian data sets, respectively. Next, a common reference plane for Dutch and Hungarian two-year-olds is constructed by balancing the number of utterances that are analyzed per language. Perceptually judged as being correctly pronounced corner vowels of Dutchand Hungarian-speaking two-year-old boys were mapped onto this common Dutch–Hungarian reference plane. The band filtering method has shown to be robust with regard to signal-to-noise ratios and to the differences in numbers of measurements. 2005 Published by Elsevier B.V.