The Attentional Blink (AB) refers to a period of approximately 500ms when, following the correct report of a first target (T1), report of a second target (T2) is disrupted. Despite the theoretical basis of this effect remaining contentious, researchers have applied the paradigm to specific populations such as individuals with dyslexia in order to examine the temporal nature of attention within this population. The series of experiments reported in this thesis aimed to develop methods capable of controlling for individual differences in factors potentially unrelated to the AB, which may, however, be interfering with the interpretation of the applied research. This highlighted four factors which could be estimated and controlled in an AB investigation: practice effects, target duration, intertarget interval (ITI), and task foreperiod. Investigation of practice effects suggested that these could be attenuated by providing a sufficiently demanding task. Overall, it appeared that practice led to enhanced task-preparation. Under conditions of high task difficulty, as set by modifying target exposure duration, there was not a significant change in AB accuracy across a series of 700 trials. Target exposure duration was varied to establish target equality between observers. By reducing or extending the exposure duration, target accuracy could be set at a fixed level of correct report between observers. Therefore, speed of processing could be estimated and examined between observers; but most importantly, it could be factored out of the AB effect. In a similar manner to target exposure duration, ITI was estimated and controlled. This was most easily estimated using a minimalist AB design using a fixation cross, T1 and a backward mask, and T2 and a backward mask. Utilising the established target exposure duration, the temporal lag between targets could be modified so that T2 accuracy was set to a criterion level. Task foreperiod, the time between fixation offset and T1 onset, was equated in similar fashion. The AB pattern could now be estimated with inter-target lags set to fixed proportions of the value established in the step controlling for ITI. In estimating and controlling for each of these factors, a task preparatory model of the AB was necessary to adequately account for a significantly attenuated AB effect when foreperiod was held constant. Two factors were found to be critical: the development of 'task-set', defined as opting to complete one task over another; and 'perceptual-set', defined as preparation to receive the physical attributes of the to-be-processed stimuli including modality and intensity as well as spatial and temporal location. The conclusion of the investigation posits that in commonly applied AB methodologies, there are a number of factors unrelated to the AB effect which, when unaccounted for, contaminate the effect. If valid conclusions regarding group differences in the AB per se are going to be established, these unrelated factors should be ruled out as sources of between group differences.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2007|