Contrast sensitivity is increased in a case of nonparkinsonian freezing gait.

We measured spatiotemporal contrast sensitivity and gait variables in a 60-year-old man who had spontaneous episodes of freezing gait without any sign of rigidity or tremor. One major factor triggering freezing was the characteristics of visual space, as freezing episodes occurred during spontaneous walking and passing through apertures and never during walking with eyes closed. Initiation and maintenance of locomotion were greatly facilitated when transverse stripes with optimal intervals were placed on the ground in front of the patient. On the other hand, contrast sensitivity to low-to-intermediate spatiotemporal frequencies was increased in this patient when compared with that of elderly controls. These data suggest that hypersensitivity to visual stimulation and to modifications of the visual environment, associated with abnormal ocular motor behavior, can be one factor leading to the freezing gait phenomenon, which could be called "hypersensitivity braking" and be considered as a sensorimotor disorder.