When originally published, the article by Czapka et al, included the wrong caption for Fig 2. The publication indicates that Fig 2 shows data for heterogeneous groups when in fact it shows data for homogenous groups.
The correct figure and caption is shown below

Fig. 2. Mean response latencies (with error bars indicating standard errors) of the A) go/nogo task, B) BST and C) N-back for the homogenous groups (monolinguals - dark bars and multilinguals - light bars).
A corrigendum has been previously published incorrectly stating that the problem lies with Fig 1. Fig 1 is correct in the original published article