Investigating visual search mechanisms and enhancing the diagnostic potential of the trail making test using eTMT

Del Gatto, Claudia; Indraccolo, Allegra; Delogu, Franco; May, Maliea; Pedale, Tiziana; Brunetti, R. · 2025 · OpenAlex-citations

DOI: 10.1038/s41598-025-19125-0

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Summary

This study investigates the specific cognitive mechanisms underlying the Trail Making Test (TMT), a widely used assessment of executive function and visual search. While the TMT is often attributed to task-switching capabilities, the precise role of visual search dynamics, particularly the "display set-size effect" (the impact of distractor quantity on performance), remains debated. The authors hypothesized that previous research overlooked how the visual field’s complexity and the physical lines drawn by participants influence search efficiency. To address this, the researchers developed a new digital version of the test, the eTMT, designed to isolate variables such as visual clutter, target salience, and set-size reduction. The study employed two experiments, with the primary data presented from Experiment 1, which involved 69 right-handed participants. Using the eTMT, participants completed TMT-A (number sequencing) and TMT-B (alternating number-letter sequencing) under three distinct conditions: Standard (replicating the paper-and-pencil format with persistent connecting lines), No-Line (where connecting lines disappeared immediately after drawing, keeping all distractors visible), and Black Discs (where reached targets turned into black discs, removing the line and altering target salience). The experimental design allowed for the manipulation of visual clutter and the functional "cancellation" of previously selected items, enabling a direct comparison of how these factors affect reaction times and search strategies. The findings confirmed that the display set-size significantly influences TMT performance. The results supported the hypothesis that the connecting lines in the traditional TMT serve a functional role by effectively "canceling" or reducing the visual set-size of distractors. Consequently, the No-Line condition, which prevented this reduction, proved more difficult and resulted in slower performance compared to the Standard condition. Conversely, the Black Discs condition facilitated performance, suggesting that transforming reached targets into salient, dissimilar items allowed participants to filter them out more efficiently. The study also noted that these manipulations had a more pronounced impact on TMT-B, likely due to the additional cognitive load of task-switching, which heightens sensitivity to irrelevant visual information. The significance of this research lies in its refinement of the theoretical understanding of the TMT, shifting focus from general executive function to specific visual search mechanisms. By demonstrating that visual clutter and set-size are critical determinants of performance, the study validates the utility of digital adaptations like the eTMT. These tools offer a more granular assessment of cognitive processes, potentially enhancing the diagnostic precision of the TMT in clinical and research settings by isolating visual search deficits from other cognitive impairments.

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• visual search