1 The importance of spectro-temporal modulation cues in conveying tonal information for 2 lexical tones was assessed in native-Mandarin and native-French adult listeners using a 3 lexical-tone discrimination task. The fundamental frequency (F0) of Thai tones was either 4 degraded using an 8-band vocoder that reduced fine spectral details and frequency-modulation 5 cues, or extracted and used to modulate the F0 of click trains. Mandarin listeners scored lower 6 than French listeners in the discrimination of vocoded lexical tones. For click trains, Mandarin 7 listeners outperformed French listeners. These preliminary results suggest that the perceptual 8 weight of the fine spectro-temporal modulation cues conveying F0 information is enhanced 9 for adults speaking a tonal language.