Is there a structural limit to 'branch' recursively between more than two tasks?

The term 'branching' refers to processes needed for successful reuptake of a task after interruption by another task. Based on a model of human prefrontal cognitive architecture, it has been postulated that people cannot branch recursively between more than two tasks due to a capacity limit built into the cognitive architecture (Koechlin and Hyafil in Science 318:594-598, 2007). As an alternative to a structural limit for recursive branching between more than two tasks we put forward the hypothesis that working memory capacity is the limiting factor in recursive branching. We tested this hypothesis by independently varying working memory load and number of recursive branching steps. Successful branching between up to four tasks was observed, as long as working memory load was kept low. Our data, thus, do not support the proposition of a structural limit to recursive branching beyond two tasks. Instead, they suggest that working memory capacity limit is the most important factor that limits the capacity for branching. We further observed that the requirement to retain task sets and task contents additively contributed to the difficulty of recursive branching. In a broader context, our data thus support working memory models that conceptualize working memory and executive functions not as separate modules, but as tightly interactive processes.