Age-Related Changes in Sensitivity to Relative Reward Frequency

Older adults, younger adults, and children completed a signal-detection task which involved discriminating between two pattern types. Correct identifications of one pattern were reinforced three times more often than identification of the other. Performance was analyzed in terms of reaction time, accuracy (discriminability), and bias toward the more frequently reinforced alternative. The children had the fastest reaction times and the lowest discriminability scores. The younger adults were the most accurate at discriminating between the stimuli. The group of older adults had the slowest reaction times and showed the smallest response bias toward the more frequently reinforced alternative. Increasing task difficulty increased reaction times for the adult subjects, and reduced discriminability and response bias across all three groups. The results are consistent with an age-related reduction in sensitivity to the frequency of reinforcement. It is generally accepted that the outcomes or consequences of a person's behaviour influence their future actions. Behaviour which is rewarded occurs more often, while punishment decreases the frequency of the behaviour it follows. Allowing for some developmental changes in sensitivity to different characteristics of outcomes (Mischel, 1984), these rules are assumed to apply across the lifespan. Evidence is accumulating, however, to suggest that older adults may be less influenced by the outcomes of their behaviour than younger generations. In a critical review of the literature on probabilistic information processing and age, Sanford (1978) reported that the response patterns of older adults were less susceptible to reward manipulations than those of younger adults. For example, under conditions where participants were financially rewarded for correct guessing, younger adults showed the classical tendency toward maximization. Older adults failed to show such matching. Furthermore, increasing the magnitude of the rewards had no effect on the older participants' behaviour. Sanford (1978) concluded that the behaviour of older adults was characterized by "a reduced response to simple payoffs" (p 386). Most of the research addressing age-related differences in response to reinforcement has focused on the extent to which reward promotes learning or skill acquisition; that is, cognitive or motor skill training. These studies have been of two types: comparisons of the performance of older adults under reinforced and nonreinforced conditions and, comparisons of the performance of younger and older adults on tasks incorporating external reward for performance. For the most part the results of these studies suggest external rewards do not enhance the performance of older adults (over and above the effects of practice), or that the effects are small. Beach and Tennant (1992) compared the motor skill performance of older adults receiving either positive reinforcement or statements of personal importance with that of a control group. Reinforcement had no effect on the performance of older adults. Hill, Storandt, and Simeone (1990) assessed the effect of memory skills training and/or external reward on the free recall performance of older adults. Although both skills training and reward enhanced word recall, the effect was greater for skills training. Combining skills training with incentives was no more effective than skills training alone. As no younger adult comparision groups were included in these studies it is not clear if these results reflect the participants age, or some aspect of the tasks they completed. In one of the few studies which directly compared the effects of reinforcement on skill acquisition in younger and older adults, Bellucci and Hoyer (1975) demonstrated that older adults were less influenced by rewards than their younger counterparts. Using a simple speeded performance task (digit symbol), they found younger women receiving noncontingent reinforcement improved more across trials than younger women in the control condition (no reinforcement) and also more than older women, irrespective of condition. …