The clinical utility of the hand-held tachistoscope.

A hand-held tachistoscope for use at the bedside was constructed and used to examine 40 normal controls and 170 psychiatric and neurological patients. This instrument quickly provided an index (perception time) which distinguished between idiopathic psychiatric illness and delirium, and between cortical and subcortical neuropathology. Slow perception time was seen in patients with delirium or cortical neuropathology.