Although the TMT is one of the most widely used measures in neuropsychological practice, it is culture-loaded because of reliance on the Latin alphabet, which has limited its application in Eastern populations 20]. The recent variant form of the TMT is the CTT, which is designed to minimize the influence of language and covers the full children-to-adult age range. It has allowed broader application for cross-cultural studies, while at the same time being similar to the original TMT in terms of neuropsychological sensitivity. However, studies have also suggested that there might be a large variability in performance on the CTT because of culture-bound factors. Familiarity with testing procedures and relevance of the applied techniques to real-life experience could affect task performance 15,18]. Besides, the possibility of a Stroop effect on CTT-B performance, as suggested by Spreen and Strauss1], may influence test performance in a way that makes the CTT-Part B a qualitatively different task in comparison to the classic TMT-Part B. Additionally, the CTT requires four color-printed record sheets which increases the cost accordingly.
The STT is another variant form of the original TMT. It was developed by Agnes Chan from the Chinese University of Hong Kong13]. In the current study, we analyzed the correlation between the STT with demographic variables in cognitively normal individuals, which showed a similar trend to the TMT 3,21,22,23,24,25]. The test loaded on both “rapid visual search” and “visuospatial sequencing” factors, as well as “cognitive set-shifting”. Factor analysis revealed that the STT-A and B correlated only moderately (r
0.522) with each other, suggesting that they measure somewhat different functions, which is similar to the original TMT. In addition to switching between squares and circles, Part B also includes more visual interferences and a longer path length. Hence, Part B requires more visual perceptual processing ability than Part A. Our factor analysis revealed that the STT-A reflected language and attention while the STT-B relied more on executive function and memory.
The trail test has been reported to be sensitive to neurological disorders such as closed-head injury, alcoholism and substance abuse. Studies have also found significant differences among AD, MCI and controls in the TMT26]. Similarly, in the current study, the STT-A and B distinguished well among AD, aMCI and controls. When age and education-stratified cut-off scores were adopted, the AUC of the ROC curves of the STT-A and B ranged from 0.816–0.913, and the sensitivity and specificity were also acceptable. We did not find any significant difference between the STT-A and B in differential validity.
The scoring of the original TMT has several indexes: (1) time in seconds required to complete each part1]; (2) derived indices from completion time: difference score
B-A, ratio score
B/A, Log ratio score
Log B: A, and proportional score
(B-A)/A 27]; (3) Errors: the number of wrong connections, including number of errors, near misses and corrections 26]; and (4) Prompts: the number of reminding times during connection 1]. Another scoring method sets a time limit on part B of 4 minutes. The respondent is scored 25 if he completes all the connections within 4 minutes. If not, his score is the number that he finished connecting 28,29]. However, the TMT is a neuropsychological test with a “floor effect”, which is the same in the STT. Almost all of the above indexes are not suitable in subjects who could not complete Part B. In our study, in cognitively normal controls, 1.5% subjects could not complete the STT-B. In patients with aMCI and mild AD, even more subjects failed in part B (4.8% and 30.4%). Therefore, we developed an index named “STT-1 min”, which means the number that participants correctly connect within the first one minute. Like the time for completion of the STT-A and STT-B, the STT-B-1 min index could distinguish well among AD, aMCI and controls. The “STT-1 min” is similar with the 25 point scoring method, but saves more time. As we know, both the original TMT and STT are time-consuming. In some AD patients, even more than 10 minutes is needed to complete part B. Adopting the “1 min” index as the score could save time for the test performance and improve efficiency at the same time.
In a sub-sample that completed both the STT and CTT, the STT-A was less than the CTT-A while the STT-B was greater than the CTT-B, which indicated that the interference burden in shape in the STT was heavier than that of color in the CTT. Meanwhile, our cognitively normal subjects spent more time to complete the STT-A and B compared with Americans or Japanese in the TMT-A and B 3,23]. The results suggest that the current STT is more difficult than the original TMT, and that the part B of the STT is harder than the CTT as well. This must be taken into consideration when comparing our data to western countries.
This study evaluated a new variant form of the TMT that fits the cultural background of the Chinese population. With a relatively large sample size, the performance of the cognitively normal older population on this new test was presented. The diagnostic value for identifying aMCI and AD with the STT was also evaluated. However, our study also had important limitations. Being a culture-fair test, we did not have data outside the Chinese population. Neither did we include younger subjects which made the data less standardized. In the future, an equivalence study of the TMT, CTT and STT among well-educated, bilingual Chinese population may have great implications for psychometric test development and clinical cultural neuropsychology.
In summary, the TMT is a sensitive test of visual search and sequencing. The STT is a meaningful attempt to create a “culture-fair” version of the TMT in addition to the CTT. Further validation studies are needed to extensively evaluate this test.