Danish is a quantity language in which the length of vowels is either short or long. This study investigates vowel length in order to determine the degree to which we can ascribe the conventional categorical tag to vowel quantity perception. In a pilot study (n = 18) the gradual shortening of long vowels was identified as methodologically preferable for deriving stimuli continua, as complete identification functions could be fitted to the mean data. We employed this method to derive stimuli for identification and discrimination experiments (n = 32) that included the words used in the pilot and another word pair. This pair has phonetically similar variation in vowel duration although, due to recent language change, quantity is no longer contrastive. Results from the phonologically contrastive word pairs showed sigmoidal identification functions and discrimination peaks in the middle of the continua, while the identification slope for the non-contrastive pair was approximately linear and there was no clear discrimination peak. These differences show that the perception of speech contrasts is influenced by the linguistic experience of listeners as well as auditory and articulatory factors.