Resultados Comparativos Grupo Control y Grupo Experimental

The prediction that depression would have a negative impact on STM was not supported in either the median or quartile split analyses, despite past research finding STM impairment in depression for both younger and older adults. There was a small interaction between Depression and Age for the letter- number sequencing working memory task, but no effects or interactions for the reading span task. The interaction in the letter-number sequencing task was from superior performance in the younger adults with high depression when compared with the low depression group, while the older adults with high depression had inferior performance compared to their low depression counterparts. This increase in letter-number sequencing score in the high level of depression may be attributable to the increasing difficulty of the task interrupting rumination and directing attentional resources back to the working memory task. The slight deterioration in performance in the high depression older adult group is supported by previous research, although the difference between groups in the present study is not as marked as in previous studies. The prediction that time-based prospective memory would be affected by depression was partially supported by a small effect in the quartile analysis, with performance in the high depression groups being inferior to that of the low depression groups.

The memory moderators, processing speed and IQ, were investigated, as were anxiety and stress. While there were no effects or interactions for Verbal Processing Speed, there were some small interactions for Visual Processing Speed with Depression and Age for the recall task, and for Depression, Age and Visual Processing Speed for the reading span task. From the interactions, it

appears that visual processing speed may have a potentially protective role in recall performance and late-life depression. Yet for the reading span task, a high visual processing speed for those in the high depression (and high stress) groups was a disadvantage (as opposed to an advantage for the low depression groups). There was also a small Depression x IQ interaction for the reading span task, with IQ providing the greatest benefit to those in the high depression groups. There was a medium Depression x IQ interaction for the time-based prospective memory task, in which high IQ tended to provide a greater advantage to those in the high depression groups when compared to the low depression groups. These results are difficult to interpret in light of past research due to a lack of studies investigating interactions between depression, memory, processing speed, and IQ in this manner.

There were small Anxiety x Age and Stress x Age interactions for the letter- number sequencing task, which followed the same pattern as for the small Depression x Age interaction. These results appeared inconsistent with the minimal research available on anxiety, stress, and working memory. Processing Speed and IQ were also investigated with Anxiety and Stress. The results were similar to those seen for Depression, with a small Anxiety x Visual Processing Speed interaction for the recall task and a medium effect for the Stress x Visual Processing Speed interaction for the reading span task. Past research on stress, depression, and processing speed found that only cognitive interference (such as from rumination) predicted performance on working memory and processing speed tasks, not perceived stress or depression. There were no noteworthy interactions for Verbal Processing Speed or IQ with either Anxiety or Stress.

There are several implications of the present research. Firstly, the effects of age on memory are far greater than any effects of depression. Secondly, the present study has highlighted the overlap between the constructs of depression, anxiety, and stress, which are known to have high correlations with one another. The results from the present study support a theoretical shift back to

the investigation of the constructs of depression, anxiety, and stress, and their individual utility. The difficulties of investigating these as separate constructs can be seen in the correlations between measures of these constructs. The correlations between tests purporting to measure the same construct (such as depression) are relatively weak when the correlations between measures of depression, anxiety, and stress are considered.

There is a parallel process occurring with tests of memory constructs such as working memory. There are many tests claiming to assess working memory, yet the correlations between such tests can be low. The results when using differing tests of depression and working memory may be strikingly different. Attempting to compare differing results from differing tests may be responsible for the inconsistency seen in previous studies.

There are some limitations to this study. The sample size was calculated using expected medium effect sizes, but as most of the effects in the present study were small, there was insufficient power to detect their significance. In hindsight, it may have been more theoretically useful to have looked at attention and investigated the allocation of attentional resources or inhibitory control theory. It is expected that similar problems would have arisen in terms of measurement as attention also falls prey to having multiple definitions and tests. The age bands used caused statistical difficulties and do not allow for any generalisation to middle adulthood. Finally, the study used an epidemiological design which led to low depression scores and a reduced range of scores. It may be that depression affects memory after it reaches a critical capacity that was not accessed in this study, and replication using participants meeting the diagnostic criteria for a Major Depressive Episode may lead to different results.