We report a set of experiments demonstrating that the number of phonemes perceived in a stimulus depends on the native language of the listener. Comparing French and Japanese subjects we found that the phonotactic properties of the native language can induce subjects to insert "illusory" segments. In Experiment 1, we varied the duration of an inter-consonantal vowel [u] in stimuli such as ebuzo and found that unlike the French, Japanese listeners report that the vowel [u] is present even in stimuli in which the vowel is absent. In Experiment 2 and 3 using an ABX task, we show that Japanese subjects have trouble discriminating stimuli that contain an [u] vowel from stimuli in which the vowel is absent, e.g., (ebuzo vs. ebzo). However, they can easily discriminate items that contain one versus two [u] vowels, e.g., ebuzo vs. ebuuzo, a distinctive contrast in Japanese. Results for French subjects are reversed.