| Summary: | 碩士 === 長庚大學 === 臨床行為科學研究所 === 97 === Impulsivity is a complex construct. Pathological impulsivity is a common feature of many psychiatric disorders. Psychologists with different theoretical persuasions tend to define the construct differently. In the realm of behavioural approach, “impulsivity” has generally been regarded as “intolerance of delayed gratification”, that is, when choosing between a smaller reinforcer presented after a shorter delay and a larger reinforcer presented after a longer delay, choice of the former is regarded as being ‘impulsive’, and choice of the latter as being ‘self-controlled’.
Ho, Mobini, Chiang, Bradshaw, & Szabadi（1999）proposed one multiplicative hyperbolic model of impulsivity, which assumes that the subjective value of a reinforcer is modulated by the interplay between its size, delay and the odds against its occurrence. The evidence accumulated from animal studies has been in agreement with the hypotheses and predictions postulated by the model. The present study attempted to test the clinical applicability of the model by examining the performance of substance users on intertemporal behavioural tasks. In addition, recent studies indicated that impulsivity and executive functions may share common neural bases, which pit against each other in terms of overt behavioral expressions. Therefore, the present study also intended to investigate if impusivity would be exacerbated in participants with impaired intellectual or executive functions.
In the present study, we recruited 31 healthy male adults by advertisements, and 56 male substance users from Taipei Retention Center. The healthy volunteers were used as a standardized group in order to define the impaired scores for the neuropsychological assessment of the substance users. Based on their scores for a fluid intelligence test and the tests of executive functions, all substance users were allocated to the impaired group (n = 29) and non-impaired group (n = 27), respectively. And then, the responses on various impulsivity measures were compared between the two groups.
The results showed that the scores for the healthy participants significantly differed from those for the substance users on the Category Fluency Test and the Chinese Graded Word Reading Test. With regard to the substance use groups, the scores for the fluid intelligence test and verbal learning test in the impaired group were significantly inferior to those for the non-impaired group. In addition, the impaired group revealed signficantly higher impulsive traits on two self-reported questionnaires and showed higher tendency for impulsive choices on the behavioral tasks. The present results suggest that lower fluid intellegence in substance users may yield higher impulsivity. And, the model proposed by Ho et al.（1999） is also applicable to substance users. However, while the impulsivity parameter K, proposed by Ho et al.’s (1999) is nearly identical across two different tasks in the case of non-impaired group, similar trend cannot be obersvered in the case of the impaired group.
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