From the article:

"Strategy training was based on the principles of the Victorian Comprehensive Parkinson Disease Program (Australia), as documented in detail by Morris, Iansek, and Kirkwood.[6][8][21][22] Strategy training aimed to teach people how to use attention and to use the frontal cortical regions to compensate for movement disorders.[6][8]

This included teaching people with PD to plan in advance for forthcoming movements, mentally rehearse complex actions before they were performed, consciously focus on movements while they were being performed, breaking long or complex movement sequences down into component parts, avoiding dual task performance and using external visual and auditory cues to guide movements.[6][8]

External cues and attention strategies aimed to improve the size, speed, and sequencing of movements. Conventional musculoskeletal exercises aimed to improve strength, range of movement, posture, general fitness, and function, based on Schenkman's[13] protocols. This included lower limb and trunk strengthening exercises, spinal and lower limb flexibility exercises and receiving feedback on optimal postural alignment for a range of positions."

ANOTHER STUDY:

Article from 2000:
The role of sensory cues in the rehabilitation of parkinsonian patients: A comparison of two physical therapy protocols
Abstract

We devised a single-blind study to assess the role of providing external sensory cues in the rehabilitation of patients with idiopathic Parkinson's disease (PD). Twenty stable, nondemented patients with PD entered a 6-week rehabilitation program and were randomly assigned to two balanced protocols which were differentiated by the use of external sensory cues (non-cued vs cued). Patients were evaluated by a neurologist, who was blind to group membership, with the Unified Parkinson's Disease Rating Scale (UPDRS) at baseline, end of treatment, and after 6 weeks. Patient groups were comparable for age, disease duration, and severity. A significant reduction of UPDRS scores (activities of daily living and motor sections) was present after the rehabilitation phase in both groups. However, at follow up, while this clinical improvement had largely faded in the non-cuedgroup, mean UPDRS scores of the cued group were still significantly lower than baseline values. The incorporation of external sensory cues in the rehabilitation protocol can extend the short-term benefit of physical therapy in moderately disabled patients with PD, possibly as a result of the learning of new motor strategies. Cued physical therapy for PD should be targeted to compensate for the defective physiological mechanisms.

http://www3.interscience.wiley.com/j...08409/abstract
Full article:
http://www3.interscience.wiley.com/c...08409/PDFSTART

They used a metronome and visual cues, and some sensory cues that I don't understand. The therapy improved bradykinesia and balance.

They think cueing makes motor tasks less automatic and enables one to modify motor strategies to involve a "closed loop" performance. External cues help one to switch from one movement component to the next "compensating for a defective internal trigger from the pallidum to the supplementary motor area."

Cueing led to new "attentional strategies" which allowed for better movement.