Coincident timing by nondisabled, mentally retarded, and traumatic brain-injured individuals under varying target-exposure conditions.

Coincident timing by 15 nondisabled individuals, 15 mentally retarded and 15 traumatically brain injured was measured under varying target-exposure conditions. Absolute constant error, constant error, and variable error were analyzed in separate repeated-measures analyses of variance for early performance (first block of practice), late performance (last block of practice), and retention (last block of retention). Subjects with mental retardation displayed the least accurate and most variable coincident-timing responses. Nondisabled subjects were most influenced by target-exposure time; subjects with traumatic brain injury were most influenced by target-viewing distance; and subjects with mental retardation were most influenced by a combination of target velocity and target-viewing distance. Subjects with mental retardation displayed a too-early response bias, while nondisabled subjects tended to have a too-late response bias. Individuals with traumatic brain injury had a variable response bias.