K. Zajdo

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

Abstract 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 F 0 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 Dutch- and 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.

Developmental vowel acquisition data obtained by a band‐filtering analysis method: Results from Hungarian children

A recently developed band‐filtering analysis method (van der Stelt et al., 2003, 2005; Zajdo et al., 2004) that minimizes the dependence of the results on fundamental frequency allows for a dependable identification of spectral measures in children’s vowels. In the scripts, selection of segments with certain acoustic features (e.g., sound quality, F0) is followed by the calculation of spectral envelopes between 0–7 kHz, resulting in 40 filter values per spectrum. An intensity matrix is produced with data from each 40 filters. Data reduction is achieved through prinicipal component analysis. Results indicate that the first two principal components are related to the F1 and F2 of vowels, both in adults (Pols, 1977) and children (Zajdo et al., 2005). Analyses of unlabeled vowel productions in Hungarian‐speaking children at 2; 0, 3; 0 and 4; 0 years show that the first two eigenvectors account for >50% of the variability in all age groups. By using these eigenvectors, age‐specific reference planes are created...