  The Trail Making Test (TMT) is one of the most popular neuropsychological
tests in the clinical assessment of executive functions (EF) and research in a
wide range of clinical conditions. In addition to its sensitivity to executive
dysfunction, the TMT presents several strengths: it is simple and intuitive, it
is easy to understand for patients, and has a short administration. However, it
has important limitations. First, the underlying EFs articulated during the
task are not well discriminated, which makes it a test with low specificity.
Second, the traditional pen-and-paper version presents one trial per condition
which introduces high variability. Third, only the total time is quantified,
which does not allow for a detailed analysis. Fourth, it has a fixed spatial
configuration per condition. In the present study we designed a computerized
version of the TMT (cTMT) to overcome its main limitations. Eye and hand
positions are simultaneously measured with high resolution, several trials are
acquired, and spatial configuration of the targets is controlled. Our results
showed a very similar performance profile compared to the traditional TMT.
Moreover, it revealed similarities and differences in eye movements between the
two parts of the task. Most importantly, we found an internal working memory
measure of the cTMT based on hand and eye movements that showed an association
to a validated working memory task. Additionally, we found another internal
measure of the TMT, also based on hand and eye movements, that we propose as a
potential marker of inhibitory control. Our results showed that executive
functions can be studied in more detail using traditional tests combined with
powerful digital setups. Finally, our study paved the way for a detailed
analysis of other complex tasks used for clinical evaluation, providing a
deeper understanding of the processes underlying its resolution.
