Resultados de la muestra

There is some evidence that more complex tasks are associated with reduced estimations o f task duration, even in the context of similar levels of timing accuracy. This was apparent in experiments 1 from the control subjects on the error task and from SMH in both error and interrupted tasks. Similarly, in experiment 3 SMH significantly under­ estimated the duration of the complex sort relative to the simple sort task. Results from experiment 2 were generally internally consistent in so far as a tendency to under­ estimate duration verbally was associated with the likelihood of overestimating duration by method of time production. Again, there was a tendency for SMH to under-estimate standard task duration relative to controls, though showing no difference from them in timing accuracy. By contrast, there was a tendency in experiment 3 for controls to be more accurate then SMH in estimating the simple sort task.

In general, SMH did not show significant impairments in timing accuracy despite being tested over periods of time which Kinsboume and Hicks (1990) suggested should result in performance decrements from amnesic subjects. The results could therefore be interpreted as showing a much greater intact window of psychological time which could be monitored accurately by SMH (as suggested by Shaw and Aggelton,1994). Yet Shaw and Aggelton (1994) reported normal timing accuracy amongst post-encephalitic amnesics for up to one minute only; the experimental task durations employed above may reasonably be expected to have exceeded SMH’s relatively intact short-term memory capacity. An alternative explanation for the results lies in a possible response bias in relation to the durations of the different tasks employed. Task durations comprised one minute (experiment 3), two minutes (experiment 1) and four minutes (experiment 2). Examination of her verbatim responses revealed that SMH tended to

give verbal estimates around the two to three minute mark and that “a couple of minutes" was her modal response. This would certainly account for her tendency to grossly overestimate tasks of one minute’s duration (experiment 3) while tending to underestimate tasks of four minutes (experiment 2).

The data also reveal a tendency for more complex information processing demands or task interruptions to be associated with a reduction of estimated duration from SMH, to a greater extent than shown by the controls (experiments 1 and 3). Again this is only evident for tasks o f one or two minutes’ duration and the statistical validation of these effects is weak. Nevertheless, given the small data sets involved and the risk of type II errors it is probably unwise at this stage to disregard trends in the data. A provisional interpretation of the above experiments is that SMH shows a tendency to experience short-intervals of time (ie. 1-2 minutes) as passing slowly but her amnesic deficit renders it difficult for her to have any awareness of temporal passage over longer periods and she relies on a fixed response set. In this context it is interesting to note that Shaw and Aggleton’s (1994) study revealed a significant correlation between time estimation and performance on the cognitive estimates test for their seven Korsakoff’s amnesics but not the three post-encephalitic cases.

9.3 Towards understanding psychological time in amnesia

In a neuropsychological context the above results are broadly in keeping with those reported from other memory-impaired subjects, suggesting that attention to time may be compromised, especially during performance of complex tasks. Such activities may either be timed less accurately or under-estimated or both. In some respects SMH did not demonstrate the grossly impaired awareness of time that she displayed in everyday contexts. Nevertheless, the experimental studies yielded some interesting observations. In experiment 1, both SMH and the controls underestimated the more demanding error lexical decision task compared to the non error version. This suggests that all the subjects were sensitive to the detrimental effect of extra task demands upon concurrent timing. Only SMH however, also showed this effect on the interrupted task. This

sensitivity after brain damage to task interruptions was also raised in chapter 6. In experiment 3 SMH also showed a significant reduction in timing distortion with the more complex sorting task (resulting in greater accuracy than on the simple sorting version) which is consistent with an effect of increased task demands detracting attention from timing. Although it has been suggested that this result is due to a response bias, the fact that the response bias is operative is still testimony to the fact that SMH’s timing is disturbed to a greater extent than for controls by increases in task demands.

The absence of more significant timing deficits from SMH is interpreted largely as a consequence o f experimental design. The procedures employed did not control for the possible compensatory strategies adopted by SMH for intervals longer than the one minute which seemed to exceed her concurrent timing ability. Thus she appeared to give plausible, almost colloquial, responses for several tasks which may be seen as an adaptive strategy in its own right for someone who was disoriented in time. Such a strategy entails a degree of reasoning ability and in less formal circumstances (when time is unlikely to be measured to the nearest second, as it was in the experiments) then it would undoubtedly have been very effective. In terms of the cognitive skills which contribute to psychological time, this suggests that SMH was able to deploy some reasoning skills to good effect. Thus she was able to utilise comprehension of temporal terms (related to semantic memory) to infer solutions to problems (utilising executive skills). In addition, there were other indications of a role for semantic memory processes in SMH’s temporal awareness. For example, despite having little appreciation of the passage of time over periods of several hours, she could still tell the time (presumably due to intact semantic memory - see chapter 11) and compensated reasonably well by this means.

In summary, the results provide further evidence that time estimation studies with individuals with severe cognitive dysfunction do not readily equate to the results from healthy samples. The present investigations lends credence to the view that estimated time is not based solely on experience but incorporates other factors such as expectation.

past knowledge, plausibility and reasoning. It therefore becomes difficult to encapsulate the results within an single model of time experience. Further discussion of these conceptual issues is left until the final chapter 14, the next two chapters consider in more detail the role of memory in psychological time.

Chapter 10

Memory and Psychological Time: