Pitch fluctuations in accurate and inaccurate singers: are they the same?

The research presented here attempts to explore the fine-control of pitch during singing among accurate occasional singers and individuals whose singing reflects a Vocal Pitch Imitation Deficit (VPID). Most past research addresses individual differences at the level of entire sung notes or melodies. By contrast, in the present research we addressed whether VPID singers differ from accurate singers with respect to the way to reach, maintain, and stop a sung tone.
In order to describe the “scoops” at the beginning and ends of tone, as well as other forms of instability, we adapted the model of Large et al. (2002), originally designed to model entrainment of timing during synchronization. This model was applied to 1461 notes performed by 12 VPID and 17 accurate singers from the database of Pfordresher and Mantell (2014). Finally, the parameter values across the VPID and accurate singers were compared.
The results showed that the model fits tones performed by accurate and VPID singers similarly well. As expected, the median pitch across the entire sung note deviated from the target to imitate for VPID singers; at the same time, the proportion of these deviations that were overshoots (“sharp”) versus undershoots (“flat”) were the same for VPID and accurate singers (2/3rd under and 1/3rd above). Thus accurate and VPID singers differ in the magnitude but not the type of overall deviation they exhibit. Whereas no difference occurred between the singers regarding the direction of the scoop (up or down) at the start and the end of the tone, the amplitude of the scoops was significantly different between VPID and accurate singers.
The present study highlights the difficulty of VPID singers to reach and stop a sung tone, which supports the hypothesis of a fine motor control deficit in this population. Furthermore, the pitch fluctuations described by the model would have to be investigated in research on pitch accuracy perception.