What happens within and in between notes?
Most of the research in the psychology of music dealing with expression is concerned with the discrete aspects of music performance, and mainly concentrates on the study of piano music. However, in wind instruments and most notable in voice, that what happens during and in between the notes is sometimes more relevant then the realization of the note onsets themselves.

The animation below shows the data of repeated performances (as sung by a soprano) of the same transition (notes 5 and 6 of the melody from C. Saint-Saens "Le Cygne" ). Three of the repetitions are very similar, both to the eye and the ear, the fourth is quite different. Nevertheless, it is amazing how much control musicians have over these minute modulations of pitch.

The full text and more animations can be found in the transcript of the ICMPC 1996 Keynote address on vibrato and portamento.