Psychologists have long appreciated that many real-world decisions require a balance of expediency and accuracy in gathering evidence. Often the best decisions are made when there is some lingering uncertainty. But how much? Depending on the situation, choosing the right amount of evidence can often be a fine line between making a rash decision and being indecisive. Psychologists have been reluctant to pursue studying peoples' abilities to judge the correct "threshold" for probabilistic decisions. There are two reasons for this: First, the question of a decision threshold, or "when should I stop gathering evidence?" is confounded by the larger issue of how subjects choose and integrate that evidence. Subjects may have a decision threshold that is consistently sub-optimal with respect to a model that does not consider cognitive constraints. However, subjects may actually be choosing the right amount of information given their own cognitive limitations. Second, it has been shown that people often use specific heuristics in making probabilistic decisions. In this case, defining a decision threshold would be largely dependent on the heuristic and task, thus preventing a study of decision thresholds that is widely applicable. The research presented here addresses both of these concerns. I defined a task where the ideal decision threshold is clearly defined, requiring some evidence, but not an exhaustive search. Furthermore, this threshold can be precisely manipulated by changes in the reward structure. Although it is possible to use a "sufficing" or sub-optimal heuristic, subjects are given a significant financial incentive to fully integrate as much evidence as possible. Lastly, and most importantly, a general model of people's cognitive limitations is applied to the traditional normative model. This enhancement allows a more refined study of humans' ability to place their decision threshold according to environmental conditions. / text

One of the goals of cognitive rehabilitation following traumatic brain injury is to help people perform everyday tasks. However, options for the rigorous assessment of everyday cognitive effectiveness after rehabilitation are limited. Performance on neuropsychological tests is only moderately correlated with everyday functioning, while previous measures of everyday functioning include only fairly general estimates of overall cognitive functioning. The aim of the current study was to develop an ecologically valid measure that captured a number of subdomains of executive functioning, using systematic behavioural observation of an everyday task. The initial phase of the research involved identifying an everyday task that was sufficiently complex to ensure that executive functioning was utilised in the completion of the task. Participants with traumatic brain injury were then asked to prepare chocolate brownies, using a recipe provided, and a hot drink. Participants were allowed to use any compensatory strategy to help complete the task. Participant performance was directly observed by an examiner and videotaped for subsequent inter-rater reliability. Two independent raters assessed nine components of executive functioning. During this phase, the examiner manuals were modified improving inter-rater reliability. The final version of the measure was then trialled with participants with and without traumatic brain injury. Final inter-rater reliability indicated the approach had merit. Significant and moderate correlations were found between traditional measures of executive functioning and the everyday task. This study employed systematic behavioural observation to obtain fine-grained information regarding a person’s cognitive functioning. With further development, this approach may prove useful for targeting and monitoring specific functional difficulties during cognitive rehabilitation.