Visual search as a tool for a quick and reliable assessment of cognitive functions in patients with multiple sclerosis

Abstract

Background: Despite the high frequency of cognitive impairment in multiple sclerosis, its assessment has not gained entrance into clinical routine yet, due to lack of time-saving and suitable tests for patients with multiple sclerosis.

Objective: The aim of the study was to compare the paradigm of visual search with neuropsychological standard tests, in order to identify the test that discriminates best between patients with multiple sclerosis and healthy individuals concerning cognitive functions, without being susceptible to practice effects.

Methods: Patients with relapsing remitting multiple sclerosis (n = 38) and age-and gender-matched healthy individuals (n = 40) were tested with common neuropsychological tests and a computer-based visual search task, whereby a target stimulus has to be detected amongst distracting stimuli on a touch screen. Twenty-eight of the healthy individuals were re-tested in order to determine potential practice effects.

Results: Mean reaction time reflecting visual attention and movement time indicating motor execution in the visual search task discriminated best between healthy individuals and patients with multiple sclerosis, without practice effects.

Conclusions: Visual search is a promising instrument for the assessment of cognitive functions and potentially cognitive changes in patients with multiple sclerosis thanks to its good discriminatory power and insusceptibility to practice effects.

Figure 1. Illustration of the visual search tasks.

A: single feature search – colour. The red X has to be found amongst several green Xs varying in number. B: feature conjunction search. The red X has to be found amongst green Xs and red Ys varying in number. C: difficult feature search – orientation. A white backslash (\) has to be found amongst white slashes (/) varying in number.

Figure 2. The sequence of a trial using the example of the single feature search.

At the beginning, a central fixation cross was displayed along with the instruction to hold down the start button. Participants had to press a button on a Serial Response Box (Psychology Software Tools, Inc., Pittsburgh, PA). At the moment of button press, the stimuli appeared on the screen. The participants were instructed to visually search the target, and release the button only after they had detected the target. Next they should touch the target on the screen. The trial was completed (and the next trial initiated) when the touch screen detected a touch or when more than 3000 milliseconds (ms) had elapsed since button release. Trials, that were aborted because no touch was registered within the 3000 ms time window, were excluded from the analysis.

Figure 3. Receiver-Operator-Characteristic-Curves of the tests with significant group differences.

Abbreviations: PASAT-3’’: Paced Auditory Serial Addition Test-3 seconds; RT: Reaction time; MT: Movement time. For reasons of clarity, only the curves of the combined mean RT and mean MT of all three visual search tasks are displayed.