The aim of this study is to determine wether the threshold and pitch of falling glissandos are identical to those calculated for rising ones - and consequently to test the hypothesis that rising glissandos are less well perceived than falling ones. The results show a threshold between 18 and 19 Hz for a duration of 200 ms, with an initial frequency of 139 Hz. The pitch corresponds to the frequency of a point at two thirds of the duration of the vowel. These results confirm those obtained for rising glissandos. The above hypothesis is not verified. In conclusion, a model of hearing is proposed which account for the modes of perception of glissandos.