Dark condition normalization of smooth pursuit tracking: evidence of cerebellar dysfunction in psychosis.

Smooth pursuit tracking performance was evaluated in psychotic (n = 20) and normal control subjects (n = 20) during light and dark testing conditions using computer-based analyses of electrographically recorded tracking patterns. Previously reported impaired tracking in psychotics tested under light conditions was reaffirmed. However, the tracking patterns of patients during the dark condition not only resembled those of controls under similar conditions, but were no longer significantly different from controls' light condition performance. Among several possible bases for these results which are considered, the involvement of cerebellar dysfunction in these patients is emphasized.