In Brazilian Portuguese, minimal pairs are attested for the contrast between open- and close-mid vowels in stressed syllables. However, there are cases in which these two categories show free variation in this same context without semantic consequences. With the aim of verifying whether this phenomenon is reflected in representations stored in long term memory and used in perceptual processes, the results obtained by twelve Brazilian Portuguese native speakers in a classification task with back mid vowels [o] and [<img src="/img/revistas/delta/v25n2/a05img02.gif" align="absmiddle">] as stimuli were compared to the contrast between [o] and [u]. The degree to which those results predict vowel discrimination tasks was estimated. In comparison with the [u-o] continuum, a lower mean of the slopes of the classification curves and a looser relation between classification and discrimination results were observed for the [o-<img src="/img/revistas/delta/v25n2/a05img02.gif" align="absmiddle">] continuum. The results are interpreted as suggestive that the representations of the vowels [o] and [<img src="/img/revistas/delta/v25n2/a05img02.gif" align="absmiddle">] are less distinct from each other than the representations of [o] and [u].
mid vowels; speech perception; phonetic categories; contrast
