This study investigates the importance of source spectrum slopes in the perception of phonation by White Hmong listeners. In White Hmong, non-modal phonation (breathy or creaky voice) accompanies certain lexical tones, but its importance in tonal contrasts is unclear. In this study, native listeners participated in two perception tasks, in which they were asked to identify the word they heard. In the _rst task, participants heard natural stimuli with manipulated F0 and duration (phonation unchanged). Results indicate that phonation is important in identifying the breathy tone, but not the creaky tone. Thus, breathiness can be viewed as contrastive in White Hmong. Next, to understand which parts of the source spectrum listeners use to perceive contrastive breathy phonation, source spectrum slopes were manipulated in the second task to create stimuli ranging from modal to breathy sounding, with F0 held constant. Results indicate that changes in H1-H2 (di_erence in amplitude between the _rst and second harmonics) and H2-H4 (di_erence in amplitude between the second and fourth harmonics) are independently important for distinguishing breathy from modal phonation, consistent with the view that the percept of breathiness is inuenced by a steep drop in harmonic energy in the lower frequencies
