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Age differences in sensitivity, response bias, and reaction time on a visual discrimination task.

Twelve young adults (age 21-25 years) and twelve older adults (age 57-65 years) performed a visual discrimination task (parallel lines) in which the following factors were manipulated: the difference in the length of the lines (3% and 9%), signal exposure duration (150, 750, and 2000 ms), and presentation modality (simultaneous and successive). The effect of repeating the task over three blocks was also controlled. Reaction time, sensitivity (d'), the decision criterion (beta), and the level of confidence the subjects had in their responses were measured and analyzed. The reaction time of the older subjects was longer than for younger ones. The difference remained constant across conditions. Signal detection analysis indicated that the ability to discriminate, as measured by d', was the same, on the whole, in the two age groups, but the sensitivity of the older was more affected by signal exposure duration than that of their younger counterparts. Contrary to what might have been expected, the older subjects used a more risky decision criterion than the younger subjects (preferring false alarms to omissions) and did not have significantly less confidence in their responses. Task repetition led to reduced reaction times and to a slightly higher level of confidence, but no age-related effects were found. The findings suggest that, in addition to a perceptual compensatory component, the longer reaction times of the older subjects include a decision-making component not necessary for their level of discrimination accuracy. The outcome of a lower criterion in the older group supports other findings according to which a more conservative decision strategy is not a general, systematic feature of the aged.