David Huron
Music Perception, Vol. 7, No. 4 (1990) pp. 385-394.
Existing research has shown that single-voice entries in polyphonic music are more easily perceived than single-voice exits. A study of 195 assorted musical works reveals a marked asymmetry between voice entries and exits. Specifically, voices tend to be added one at a time, while voice exits tend to occur several at a time. This practice is consistent with the hypothesis that voice entries and exits are perceptually important points in musical works and that composers avoid single-voice exits because they are less likely to be perceived.