The dual-task paradigm is widely used in studying the interaction between visual search and working memory. A number of studies showed that holding items in working memory delays the overall response time (RT) in visual search, but it does not affect the efficiency of search (i.e., the slope of the RT × set size function). Why the memory load merely affects the overall RT? Some researchers proposed that this load-effect on overall RT may be caused by factors that only affect response selection processes, while others argued that it may reflect the effect of visual working memory load on visual search. This study investigated the two competing hypotheses by measuring the threshold stimulus exposure duration (TSED) for successfully fulfilling a search task. Experiment 1 replicated the large overall RT difference with the RT method but only found a small though reliable overall TSED difference with the TSED method. Experiment 2, with better controls, found no TSED difference by manipulating the visual working memory load. Experiment 3 showed that the TSED is not influenced by processes in the response selection stage. The present findings suggest that the overall stimulus processing time in visual search is not affected by visual working memory load and that the effect of memory load on overall RT is largely due to factors affecting response selection alone.

No abstract

Space perception is systematically biased. Few theories of spatial bias address the possible functional advantages of mechanisms that produce spatial biases. The scale expansion hypothesis proposes that many spatial biases are due to the perceptual expansion of visual angles, which acts somewhat like a natural magnifying glass in vision. The present study examined the idea that visual expansion may improve motor precision (i.e., reduce motor variability) in movements when using closed-loop control but not when using open-loop control. Experiment 1 tested this idea in an online tracking task (closed-loop control), whereas Experiment 2 tested it in a fast-hitting task (open-loop control). The results were consistent with the hypothesis. To rule out the effect of the task difference (i.e., tracking vs. fast hitting), Experiment 3 examined the effect of visual expansion on the variability of motor performance in a line-reproduction task. The control type (closed-loop or open-loop) was manipulated by the form of visual feedback (online or offline). The results were again consistent with the present assumption. Taken together, the present data suggest that perceptual expansion in vision improves motor control precision when using closed-loop control (but not when using open-loop control), which supports the scale-expansion hypothesis. In addition, the present findings also improve our understanding of how visual error amplification affects motor control.