Researches Upon The Cognitive Mechanisms Underlying The Limitations Of Working Memory Span

To investigate the cognitive mechanisms underlying the limitations of working memory span, the author designed two experiments to carry out the research, with undergraduate and graduate being the subjects. Experiment 1 was done to examine the resource constraint hypothesis, memory decay hypothesis and switching mechanism hypothesis concerning the limitations of working memory span. Firstly, to test the resource constraint hypothesis, the author manipulated the cognitive load of the processing component (hereinafter referred to as processing load) by designing two types of working memory span tasks with different difficulty, one being continuous operation span task and the other de-de-de span task. In the continuous operation span task, some participants were asked to maintain consonant English letters while performing simple arithmetic operations; the others were required to maintain the same letters while reading aloud the syllable de presented continuously in de-de-de span task. Secondly, to test the memory decay hypothesis, the retention duration was also manipulated and this was achieved by varying the number of sign-operand pairs in continuous span task and the number of de syllables in de-de-de span task. Finally, to test the switching mechanism hypothesis, all the participants were required to complete a switching efficiency task before performing working memory span tasks. Adopting completely randomized factorial design, 80 undergraduates and graduates were randomly assigned to the four treatments. Two-way (processing load×retention duration) analyses of variance on the span data revealed that, there was a main significant effect of processing load, with de-de-de span being predominantly greater than continuous operation span, and that neither the retention duration nor the interaction between processing load and retention duration had a significant effect. Correlation analysis between switching cost and working memory span was also carried out, which indicated that there was no significant relationship between them.In Experiment 2, to investigate the impacts of the processing load, the memory load (referred to as the cognitive load of storage component) and the similarity between processing and storage stimuli upon working memory span, the author designed two kinds of working memory span tasks, one being reading letter span task and the other reading digit span task. The manipulation of the processing load was achieved by asking participants to read letters or digits; to manipulate the memory load, participants were asked to maintain letters or digits; and the manipulation of the similarity between processing and storage stimuli was accessed by requiring participants to maintain letters or digits while reading them. Adopting mixed factorial design with processing task being between-subject factor and memory task within-subject factor, 42 undergraduates and graduates were randomly assigned to the two working memory span tasks. Two-way (processing load×memory load) repetition analyses of variance on the span data revealed that, processing load had no effect on working memory span, while memory load had a main significant effect, i.e., memory load of letters being higher than that of digits, working memory span was significantly greater for maintaining digits than for letters. The interaction between processing and storage stimuli was also highly significant. Simple-effect test found that under digit memory conditions, reading letter span was superior to reading digit span; while under letter memory conditions, reading digit span was superior to reading letter span.The results implicated that although memory decay and switching mechanism had no effect upon working memory span, processing load played an important role in working memory span when the processing load was only manipulated, and that adults'working memory span was not constrained by processing load but by memory load when the processing and storage load was simutaneously controlled, and that the similarity between processing and storage stimuli had a great effect upon working memory span.