Spectral factors in the perception of vowel quantity in Icelandic

Previous research has shown that the ratio of vowel to rhyme (vowel + consonant) duration is a major cue for quantity in Icelandic. In particular it serves as a higher-order invariant which enables the listener to disentangle those durational transformations of the speech signal which are "extrinsic" (e.g. due to changes in speaking rate) from those which are "intrinsic" to the phonemic message, involving a change of phonemic quantity. Previous research has been based on speech segment contrasts which are purely durational, involving vowels with a uniform spectrum whether phonemically long or short, such as [a] or [I]. This paper looks at the role of spectral factors in vowels which are spectrally dissimilar in their long and short varieties. It is shown that in these cases the spectral differences can be sufficiently great to override the previously established relational invariant for quantity. The implications of this finding for a model of quantity perception are discussed.