This is Your Brain on Music – Professor Daniel Levitin

The Gestalt psychologists – von Ehrenfels, Max Wertheimer, Wolfgang Kohler, Kurt Koffka and others – were interested in the problem of configurations, that is, how it is that elements come together to form wholes, objects that are qualitatively different from the sum of their parts and cannot be understood in terms of their parts….

The Gestaltists wondered how it is that a melody – composed of a set of specific pitches – could retain its identity, its recognisability, even when all of its pitches changed…..

Play a melody using any set of pitches and so long as the relation between those pitches is held constant, it is the same melody.  Play it on different instruments and people still recognise it.  Play it at half speed or double speed, or impose all of these transformations at the same time and people still have no trouble recognising it as the original song.