Surprisingly, once education and CESD were controlled for on the working memory span test, age did not contribute significantly to the prediction of the variance. This is in contrast to a wealth of research that has established that declines in working memory are associated with aging. There are several possible reasons for these contradictory findings. One possibility is that because only older adults were used in this study, there was not enough variance in performance or in age for age to be predictive; i.e., because the data were only examined at one end of the age and performance continuum, the relationship may not have been apparent. This possible explanation is further strengthened by the fact that the range of performance on the memory task was quite small. This task provides scores in a short range, from 2 to 6, and it is possible that this range is too small to make age-related differences apparent in a sample consisting of all older individuals.
Interestingly, FVC was able to explain 18% of the variance in performance on the memory span task. This finding suggests that this measure of pulmonary function may be related to working memory span. Another explanation relates to the fact that FVC has also been shown to be related to timed walk dis-tance. While neither 6-min walk distance nor Vo2peak entered into the equation for the prediction of working memory span, there was a significant correlation between each of these two variables and the FVC (6-min walk distance, r = 0.55 and p < 0.01; V02peak, r = 0.57 and p < 0.01). Therefore, the fact that FVC entered into the equation may be more of a problem of multicollinearity among FVC, 6-min walk distance, and V02peak than the fact that FVC is predictive of working memory span. Additionally, it is probably worthy of mention that while these results are indicative of a statistically significant relationship, they cannot ascertain the level of practical significance. Therefore, while this measure of pulmonary function was a statistical predictor of memory span, it is unlikely that it is a meaningful predictor from a practical standpoint.
The ability to inhibit a response was not predicted by any of the variables assessed in this study. It is somewhat surprising that age was not associated with accuracy of performance because this relationship has been established in the past. However, there are two likely explanations for these contradictory findings. First, it is possible that inhibition abilities in a COPD population are not affected by age. Second, it is possible that the variations made to simplify the stopping task made it less sensitive to age-related differences in performance. The design of this research does not allow us to clearly identify the reason for these findings. However, examination of the accuracy of responses by the participants suggests that the second explanation is most viable because there was very little variance in the accuracy of performance on this task, with most participants performing at a level of 60% accuracy.