WORKING-MEMORY AND STIMULUS-INDEPENDENT THOUGHT - EFFECTS OF MEMORY LOAD AND PRESENTATION RATE

When not engaged in demanding tasks, we commonly experience streams of thoughts and images quite unrelated to immediate sensory input. Such stimulus-independent (SI) thoughts may be troublesome, as in worry, insomnia and depression. Previous research within a working memory paradigm suggested that SI thought production depended on central executive control resources. To explore this hypothesis further, we examined the interference with SI thought production resulting from shadowing auditorily presented digits compared to remembering them. Effects of stimulus presentation rate and size of memory load were also examined. At slow presentation rates, remembering produced more interference than shadowing. For shadowing, faster presentation produced greater interference than slow presentation. In remembering, interference was not substantially affected by size of memory load, was greater when subjects reported greater awareness of task stimuli, and was restricted to thoughts forming parts of connected sequences. The results are consistent with the view that production of connected sequences of SI thoughts depends on central executive control resources, that tasks interfere with thoughts to the extent that they make continuous demands on these resources, and that high subjective awareness of task stimuli is a marker that these resources are deployed to task management rather than thought production. The results are not consistent with Antrobus' view that interference with SI thoughts by tasks is simply a function of the rate of processing information from external sources required by the task.