Hypophonia or low speech intensity is one of the most common speech deficits associated with Parkinson’s disease (PD)
(Adams & Dykstra, 2009; Duffy, 2013). It has been suggested that a deficit in the perception of speech loudness may play a
causal role in the hypophonia of PD (Ho, Bradshaw, & Iansek, 2000; Kwan & Whitehill, 2011). Ho et al. (2000) proposed that
in PD there is an abnormal integration of the sensation of one’s own loudness during the motor output of speech intensity.
Thus, the hypophonia of PD is hypothesized to be the result of a sensorimotor integration disorder