The psychological theory of rhythm has its beginnings in the work of Herbart,[1] who inaugurated the treatment of rhythm as a species of time perception and suggested an explanation of its emotional effects.  While Herbart had simply pointed out the effect of a whole rhythmic series in giving rise to an emotion of expectation, delay, or haste, Lotze[2] applied the principle severally to each unit group (each foot) in the rhythm, and made the emotional effect of rhythm depend on these alternate feelings of strain, expectation, and satisfaction produced by every repetition of the unit group.  Vierordt[3] did the first experimental work on rhythm, determining the period of greatest regularity in the tapping of rhythms.  But the first important experiments were carried on by von Bruecke.[4] By tapping out rhythms on a kymograph, he determined the well-known ‘Taktgleichheit’ of the feet in scanned verse, and noted a number of facts about the time relations of the different unit groups.  Mach[5] added to the previous knowledge about rhythm certain observations on the subjective accentuation of an objectively uniform series, and specially he noted that the process is involuntary.  With a much clearer understanding of the facts of rhythm than his predecessors had had, he really provided the foundation for the theories which follow.  His most important contribution, for some time overlooked, was his emphasis of the essentially motor nature of the phenomena of rhythm, and his motor theory therefor.

   [1] Herbart, J.F.:  ‘Psychol.  Untersuchungen’ (Saemmt.  Werk,
   herausgeg. von Hartenstein), Leipzig, 1850-2, Bd.  VII., S. 291
   ff.

   [2] Lotze, R.H.:  ‘Geschichte der AEsthetik,’ Muenchen, 1863, S.
   487 ff.

   [3] Vierordt, K.:  ‘Untersuchungen ueber d.  Zeitsinn,’ Tuebingen,
   1868.

   [4] von Bruecke, E.W.:  ’Die physiol.  Grundlagen d.
   neuhochdeutschen Verskunst,’ Wien, 1871.

   [5] Mach, Ernst:  ‘Unters. ue. d.  Zeitsinn d.  Ohres,’ Wiener
   Sitz.  Ber., mathem. naturw.  Classe, 1865, Bd. 51, II., S. 133.
   Beitraege zur Physiol. d.  Sinnesorgane, S. 104 ff.

Many of the recent theories of rhythm are based on Wundt’s analysis.  The work of Wundt and Dietze,[6] was concerned with rhythmic series; but it may be noted that the ‘span of consciousness’ and the ‘synthetic activity of consciousness’ were the subjects actually under investigation.  Rhythm was considered as a special temporal form of this ‘psychic synthesis.’  There are three different elements in a sound series, declared these writers, which contribute to this synthesis:  qualitative changes, intensive changes and melodic changes.  Of these the intensive changes are the most important.  Every increase in intensity, that is, every beat (’Hebung’) is followed by a decrease, and the next increase which follows is recognized as a repetition of the preceding beat and as the forerunner of the beat which is to follow.