The task is probably best described from the text:
Attentional resources are limited and constrain the capacity to process information. In particular, there is a limit to how quickly attention can be allocated and reallocated to a different object or parts of the same object. This limitation becomes particularly evident when considering that the visual world is intrinsically organized in a hierarchical manner. For instance, a forest has trees, and a tree in turn is composed of leaves. This example reflects the ubiquitous embedded relation between global and local parts present in the world. When attending to the global shape of an object, such as a tree, there is less attention available to attend to the fine grained detail, such as the leaves, and redirecting attention between levels – from the global shape to the local details or vice versa - is known to be inherently slow. In psychophysical tests subjects are typically much faster in detecting the global pattern than the local detail; this phenomenon known as the “global precedence effect”.
From the discussion:
Meditators did not only exhibit a strongly reduced global precedence effect, they were also overall much faster than controls, with an average advantage of more than 100 ms. This effect cannot be explained by a speed-accuracy trade-off in the meditator population, as accuracy was overall very high and comparable between groups. Altogether, these results suggest increased speed of processing along with improvements in the distribution of attentional resources in the meditator population.