The present study investigates the longstanding question of whether visual and auditory WM draws on a single capacity or their own individual capacities. Past research has provided evidence for multiple WM capacities independent of sensory modality, but findings have been inconsistent. The measurement of capacity has also been relatively vague in the past. Therefore, the sample size model, a precise and quantitative model, was used to model the proportion of correct responses as a capacity metric.
Research Questions / Hypotheses
It is hypothesised that if WM is best characterised as a single capacity, the sample size model would better fit the data. Conversely, if WM capacity is best characterised as multiple independent capacities, the independent capacities model would better fit the data.
Eighteen participants signed up for the study and nine were excluded from the analysis due to incompleteness of both sessions.
Participants were asked to report what they saw or heard after being presented with a display containing up to two visual and two auditory stimuli. The program informs them whether their response was accurate or inaccurate as they go along. There is a block of training trials at the beginning of the session which allowed participants to get habituated to the stimuli and the expectations of the experiment. Each session takes about 40 to 60 minutes to complete.
The global values of AIC demonstrate that the proportion of correct and incorrect responses predicted by the sample size model had a better fit than the power law model and the independent capacities model. When the AIC values were compared on a participant-by-participant basis, the sample size model better predicted the proportion of correct and incorrect responses compared to the power law model and the independent capacities model for five out of eight participants.
The findings of our study show that performance across set size was consistent with the predictions of the sample size model which assumes a single WM capacity. That being said, there are still some questions to address in the future such as the role of attention in WM capacity allocation.The results of this study will be communicated in the form of an honours thesis.