Validation of cognitive and neuromuscular latencies using an iPad-based tool to quantify simple reaction times in asymptomatic subjects

Abstract

Context: Simple reaction times (SRTs), measured in milliseconds (msec), are equal to the sum of subject-dependent latencies that occur during cognitive processing and neuromuscular responses to a preprogrammed stimulus presented to a subject. SRTs have the advantage of being a relatively pure, neurologically driven motor/sensory task that provides a clinician with a generalized assessment of functional deficits. SRTs are easily obtained, and studies have reported that the average number of finger-taps during a 10-s interval can be utilized to distinguish between patients with mild traumatic brain injury (TBI) and healthy controls.

Objectives: A stimulus/response SRT protocol, utilizing an iPad-based tool, was utilized to see if differentiation and quantification of individual components of cognitive latency (CL) and neuromuscular latency (NL) from a subject's total SRT could be accomplished. The study hypothesis was that cognitive latencies, related to a specific cognitive challenge, would remain constant even as latencies due to neuromuscular challenges changed.

Methods: Two categories of SRT tests were utilized. The first was a simple finger tapping test (FTT), without any cognitive involvement, that was designed to quantify pure NL. The second test was a choice test (CT) that was characterized by the addition of a cognitive task to the FTT. The objective of the FTT was for the subject to simply tap a single target positioned on the iPad screen as fast as possible over an interval of 10 s. Measurement of the SRT began when a target was displayed and ended when the target was tapped. Two levels of challenge for the FTT and CT tests were presented to the subjects: a small random displacement (SD) of the target of up to 6 mm, and a large random displacement (LD) of the target of up to 24 mm. It was expected that the magnitude of the SRT (FTT) would be directly related to the magnitude of the displacement of the target due to kinematic response characteristics of the hand and arm.

Results: To validate the study hypothesis, CL for both small and large displacements was calculated by subtracting the respective NL from the total SRT. Utilizing a repeated measures t-test analysis utilizing SPSS, a significant difference between CL (SD) and CL (LD) at p=0.696 was not observed.

Conclusions: Differentiation and quantification of individual components of CL and NL from a subject's total SRT was accomplished. An Apple iPad Pro was selected as a platform for our study because: (1) it is readily available, affordable, and programmable; (2) it meets a requirement for portability; and (3) it allows the modification/addition of test parameters to meet future needs. The ability to quantify the extent of cognitive and neuromuscular dysfunction in the TBI patient is an essential component of developing an effective treatment plan.

Keywords: cognitive dysfunction; neuromuscular dysfunction; simple reaction time; traumatic brain injury.