Stimulus timing by people with Parkinson's disease.

Previous literature suggests that Parkinson's disease is marked by deficits in timed behaviour. However, the majority of studies of central timing mechanisms in patients with Parkinson's disease have used timing tasks with a motor component. Since the motor abnormalities are a defining feature of the condition, the status of timing in Parkinson's disease remains uncertain. Data are reported from patients with mild to moderate Parkinson's disease (both on and off medication) and age- and IQ-matched controls on a range of stimulus timing tasks without counting. Tasks used were temporal generalization, bisection, threshold determination, verbal estimation, and a memory for duration task. Performance of patients was generally "normal" on all tasks, but significant differences from performance of controls were found on the memory for duration task. Among the "normal" effects noted were arithmetic mean bisection, asymmetric temporal generalization gradients, and subjective shortening on the memory for duration task. The results suggest (a) that some previous reports of timing "deficits" in Parkinson's patients were possibly due to the use of tasks requiring a timed manual response and (b) small differences between patients and controls may be found on tasks where two stimuli are presented on each trial, whether patients are on medication or off it.

Auditory cues can modify the gait of persons with early-stage Parkinson's disease: a method for enhancing parkinsonian walking performance?

OBJECTIVE: To investigate whether systematically adjusting the rate of auditory cues induces corresponding modulations of the temporal and spatial parameters of gait of patients with early-stage Parkinson's disease. DESIGN: Subjects performed a series of 15 9-metre walks along a level floor under uncued and four cued conditions; the order of cued conditions was randomized. SETTING: A physiotherapy gymnasium, Manchester, UK. SUBJECTS: Eleven subjects with early-stage idiopathic Parkinson's disease. INTERVENTIONS: Preferred pace was established from the initial three uncued walks. The rate of auditory cues delivered throughout subsequent walks was systematically adjusted for each subject, representing 85, 92.5, 107.5 and 115% of their mean cadence at preferred walking pace. MAIN OUTCOME MEASURES: Mean cadence, mean stride length and mean velocity. RESULTS: Repeated measures ANOVA indicated that the mean velocity and mean cadence of subjects' gait significantly (p < or = 0.01) increased relative to baseline values at cue rates of 115 and 107.5% of cadence at preferred pace and decreased at cue rate of 85%. Mean stride length was unaffected by variations in cue rate. CONCLUSION: The rate of auditory cues, within the range tested, can modulate cadence and thus velocity of gait of subjects with early-stage Parkinson's disease. The provision of auditory cues provides a potential strategy for enhancing walking performance in these patients.

Tactile inhibition of return: non-ocular response inhibition and mode of response.

Inhibition of return (IOR) refers to the slowing of responses to stimuli presented at the same location as a preceding cue. However, the cue-target paradigm used in most previous studies may have overestimated the contribution of eye movement programming to IOR, due to the existence of manual response inhibition effects. This confound can be circumvented by using a target-target paradigm in which participants respond to all stimuli. Here, we compared IOR magnitude from tactile cue-target and target-target tasks involving identical interstimulus intervals of 1,400 and 1,800 ms. Reaction times were measured using a foot pedal toe-lift response and a vocal response. Tactile IOR was observed using both modes of response, demonstrating IOR for the first time using a non-spatial, vocal response. Moreover, IOR effects were significantly smaller in target-target compared to cue-target conditions, thereby confirming the existence of the response inhibition confound.