||Features are phonological transforms of natural boundaries
Features are differential units: not categories but differences between categories. Starting from the differential nature of the features, the best candidates for instantiating them are the perceptual boundaries evidenced in the study of speech. We showed that place-of-articulation perception is based on psychoacoustic boundaries in the neutral vocalic context. Also, we found that the contextual changes of the place boundaries follow a radial movement around a central point corresponding to the neutral vowel. Further, the perceptual boundaries relative to vowel and consonant place of articulation contrasts coincided after rotation of the acoustic space. Taken together these findings suggest that place perception refers to a "Radial" representation of the vocal tract with psychoacoustic boundaries as central reference.