Vowel labelling in a pluricentric language Flemish and Dutch labellers at work

Labelling speech sounds, i.e. classifying them into particular linguistic categories , can be influenced by several linguistic and extralinguistic factors, such as the emotional and physical condition of the speaker, the level of expertise and concentration of the labeller, and the quality and loudness of the recordings and labelling speech of children, non-native speakers or computers is more difficult than interpreting speech of adult native speakers (e.g. van Heuven & van Houten 1985). In addition, the regional background of the labellers influences the results of a labelling task. Most relevant research has focused on the influence of the labeller's mother tongue. Native speakers of a language are better at identifying vowels of their language than non-native speakers are (e.g. van Zanten & van Heuven 1984). In a vowel labelling task, the mother tongue of the labeller seems to be even more influential than the mother tongue of the speaker (Wang & van Heuven 2004). Furthermore, the responses (" labels ") of native speakers are more consistent than those of non-native speakers (van Heuven et al. 1985, van Heuven & van Houten 1989). In phonological terms: the listener's mother tongue influences the location of the phoneme boundaries (Janson 1979). Dialectologists have repeatedly drawn attention to the possible effect of the dialectal background of transcribers on the reliability of transcriptions (e.g. did not find significant differences between listeners, who were all native speakers of American English, from Chicago and Oklahoma. However, Janson (1981) showed that the location of the boundary between two vowels can actually be different for labellers with a different dialectal background.