Target switching in 2D and 3D visual foraging reveals trade-offs between mental effort, travelling distance and movement speed.

Many everyday activities entail searching for multiple desired items and can be conceptualised as foraging. They require mental effort to keep each item in memory, while searching. An instantiation of such activities in experimental psychology is visual foraging, where people search for multiple target categories among distractors. In visual foraging, high frequencies of switching between selections of two different target categories suggest the use of mentally effortful strategies, which require sustained simultaneous use of working memory templates for each of them. As humans often strive to reduce mental effort in cognitive tasks, a key theoretical issue is the characterisation of what induces people to spontaneously increase the frequency of switching between target categories. In five experiments, we systematically manipulated variables in instances of foraging in 2D and 3D virtual reality environments to assess changes in target switching frequency and its determinants. Experiment 1 showed that humans switch more when foraging in large immersive navigational environments, than in visual arrays seen from a bird's eye view. Further experiments clarified that: 1) inter-target distance and movement speed are the critical determinants of strategy changes in a 2D small-scale environment; 2) distance affects the frequency of switching more than speed, in a 3D navigational environment. These results indicate that people spontaneously choose to endure mental costs to meet the demands of different naturalistic instances of foraging. They support theories postulating a flexible use of working memory templates.