If the sensitivity to phonetic contrasts is dominated by acoustic/phonetic characteristics of the input signal one would expect the same sensitivity for the same contrast in two groups of subjects speaking different languages containing identical phonetic categories. However, if there is a top-down influence of the language-specific phonological system implemented in the speaker's mental lexicon, one would expect a differential sensitivity for identical phonetic contrasts when contrastive phonological features are different. Here we use the differential assignment of the phonological feature LOW in Bengali and German to some of the vowels varying along the LOW-HIGH dimension (from [a] to [u]). The contrast sensitivity was examined by means of the mismatch negativity (MMN). Vowel pairs were presented to groups of Bengali and German subjects as standard and deviant and had therefore the same phonetic contrast for both groups. In some experimental blocks, standard and deviant contained conflicting phonological features for Bengali speakers but non-conflicting features for speakers of German. Only in these blocks a differential MMN between the two groups was observed. In control conditions, where standard and deviant formed a conflicting LOW-HIGH contrast for both groups, MMNs were not different. This study provides neurobiological evidence for a top-down influence of the language-specific phonological system on the perception of phonetic contrasts.