Salthouse, T. A.
(2011). What cognitive abilities are involved in trail-making performance?
Intelligence, 39(4), 222-232.
In this paper, the renowned scholar
Salthouse attempted to find out what cognitive abilities are involved in the
TMT test. The research was done with
adults. Will children's results be the
same? That's an interesting question.
Salthouse is a professor of
psychology in Virginia University, where he studies the process of cognitive
aging. He published 10 books and over
250 chapters and papers.
Salthouse used a slightly different
version of the TMT test than the version most of us are familiar with. This version, the Connections test, has 49
circles containing numbers or letters in each stage of the task. Like in the TMT test, one has to connect
numbers only, numbers alternating with letters (1-A-2-B-3-C etc.) and letters
only (A-B-C…this part does not exist in all familiar versions). One of the differences between the
Connections test and the TMT test is that in the Connections test the
influences of visual search and hand movements have been minimized since the
"targets" (the circles one has to reach in the sequence performed)
are close together and not widely scattered on
the page. Another difference is that one
gets 20 seconds to work on each page, instead of measuring the time needed to
complete the page. Research has shown
that the Connections test is loaded with the same factors as the TMT test. This means that the tests are highly
equivalent.
Despite their simplicity,
researchers think that TMT tests reflect a wide variety of cognitive processes
including attention, visual search and scanning, sequencing and shifting,
psychomotor speed, abstraction, flexibility, the ability to perform and to
alter a plan for action, and an ability to keep two lines of thought in mind
simultaneously.
Some scholars argue that performance
in the TMT reflects executive functions.
Salthouse writes that since there is a very close connection between
fluid ability and executive functions, it can be predicted that fluid ability will
affect performance on the TMT. Other
scholars argue that working memory affects performance in the TMT because of
the need to keep track of the number and letter sequences. Since there is a very strong empirical
relation between fluid ability and working memory, Salthouse asked himself if
working memory has a unique contribution to performance in the TMT, beyond the presumed contributions of
processing speed and fluid ability.
The study was done with a large
sample of adults aged 18 to 98 (I admire 98 year olds who are willing to
participate in such studies!). The
participants performed the Connections test and tests measuring fluid ability,
long term memory, processing speed and vocabulary.
Like
other studies, this study reveals unpleasant facts about the influence of aging on
cognitive abilities, and one ray of hope.
As we can see in the attached figure, fluid
ability, long term memory and processing speed deteriorate from the age of 20
(participants in this study were recruited through advertisement. In each age group – in each decade, there
were between 220 and 830 subjects.
Generally, the participants in this study performed better on the tests
than normative samples). Vocabulary is
the ray of hope. Vocabulary keeps rising between ages 20 to 65,
and then it deteriorates slightly, but remains in the average level.
The difference in processing speed between part A and part
B of the Connections test was smaller at the older ages (performance speed in part
A deteriorated faster than performance speed in part B, and thus
the two parts came closer together).
In part A, processing speed affected
performance more than fluid ability, which also affected performance
significantly. In part B, the results
were reversed: fluid ability affected
performance more than processing speed, which also affected performance
significantly. The difference in
performance speed between part A and part B was affected only by processing
speed. People with a high processing
speed had a larger difference between speed of performance in part A and part B
than people with low processing speed.
Here we can see something odd – inferences
about relations of cognitive abilities on Connections performance vary
depending on the particular measure of performance examined. Performance on the Connections test was affected in a moderate to a large
degree by processing speed in parts A and B.
Processing speed probably affects performance because of the need for
fast response on both parts. Performance
in the Connections test was affected in a moderate to a large degree by fluid
ability, both in part A and in part B. Fluid
ability probably affects performance because of the need to keep one's place in
the current sequence while one looks for the next element in the sequence. This is required on both parts of the
test. There was a special relation
between fluid ability and performance in part B. This means that fluid ability affects the
ability to switch between sequences. There was no relation of fluid ability with the
difference score (B–A)
measure. The difference score reflected mainly processing speed.
There was
no significant relation between working memory and performance on the
Connections test. I think that working memory was assessed here with very
complex tasks, resembling fluid tasks.
This may be the reason for the lack of influence of working memory on
the performance on the TMT beyond the influence of fluid ability.
Other studies, like this of Hoelzle, also found
that the TMT test measures processing speed (and not working memory)
