Backward masking in bipolar affective disorder

1. 1. When an informational stimulus, the target, is followed closely in time by a noninformational stimulus, the mask, the visual system's processing of the informational stimulus is disturbed. This disturbance is known as backward visual masking. 2. 2. Transient and sustained visual pathways detect different characteristics of a visual stimulus, at different times in early visual information processing, and have unique anatomic distribution with regard to retinal origin, thalamic and cortical projections. 3. 3. Backward masking occurs by two mechanisms. Interruption occurs when activity in the transient channels of the mask disrupt activity in the sustained channels of the target. Integration occurs when activity in the sustained channels of the mask disrupt activity of the sustained channels of the target. 4. 4. Characteristics of the mask—energy, location, or the time presented after the target— can be altered to enhance interruption or integration. Interruption is a bell-shaped function of, and integration is an exponential function of, visual performance and interstimulus interval. 5. 5. An impairment in backward masking is present in bipolar subjects during manic episodes, is not related to the presence of psychotic symptoms, and persists when mania resolves. Lithium appears to have a detrimental effect on backward masking.