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   A NOVEL PORTABLE VISUOMOTOR MANUAL REACTION TIME TEST 1  Hogene Kim, 3 James T. Eckner, 3 James K. Richardson, 1,2 James A. Ashton-Miller 1 Department of Biomedical Engineering, 2 Department of Mechanical Engineering 3 Physical Medicine and Rehabilitation, University of Michigan Health System, University of Michigan, Ann Arbor, Michigan Email:, Website: INTRODUCTION There is a need for a simple, portable, and inexpensive clinical test of reaction time in at least two areas of medicine. In geriatrics manual simple reaction time (SRT) is significantly increased in elderly fallers [1]; and manual choice reaction time (CRT) differentiates between elderly fallers and non-fallers [2]. Similarly, the ability of the elderly to drive safely is predicted by their SRT and visual motion sensitivity [3]. In the area of sport-related concussion, the return-to-play issue is a current topic of concern: it is known that concussed football players and boxers have shown prolonged SRT compared to controls several days after complete symptom resolution [4]. Currently, SRT as well as CRT measurement typically involves a laptop and neuropsychological testing software that are too expensive to be widely available for testing younger athletes, who are the most prone of all athletes to sport-related concussion [5]. In high schools SRT has long been measured inexpensively via the “catch the ruler” test (asking a student to catch a ruler that is suddenly released, measuring the drop height and calculating the visuomotor SRT). We automated and extended this visuomotor manual SRT apparatus to measure SRT and CRT. We then used the method to test the null hypothesis that there is no gender difference in visuomotor SRT or CRT in young healthy adults. METHODS The apparatus is an elongated member equipped with LED for visual cues, an accelerometer, microcontroller and LCD display. The device can measure simple response time and choice response time (via a “Go - No Go” paradigm). Twenty two healthy adults (12 females, 10 males, age: F: 23.9±7.7 years, M: 27.7±9.0 years; height: F: 169.4±7.4 cm, M: 179.3±6.9 cm; weight: F: 69.2±10.7 kg, M: 74±6.7 kg) were recruited for this study The subjects stood with their dominant forearm resting on a horizontal surface with the wrist positioned at the edge of the surface. The examiner holds the device vertically and releases it after a random time interval for the subject to catch as quickly as possible using a pinch grip. This gives the Simple Response Time, henceforth termed SRT-D (where D denotes measured by the device, in ms). In the CRT test, the LED illuminates upon acceleration onset; the subject catches the device as quickly as possible if the LED illuminates, but lets it fall if the LED does not illuminate. The CRT, hence forth termed the Choice Response Time (CRT-D) is reported in ms units after each trial via the LCD display. One optoelectric camera (Optotrak Certus) recorded the apparatus and finger kinematics at 500 Hz using one marker on the apparatus body and two markers on the tip of index finger and thumb. Electromyographic (EMG) activities in finger flexor muscles were sampled at 2 kHz to find the onset of EMG activity in target muscle group. To validate the method the subject’s response was partitioned into three intervals using measurements independent of the device: a) Pre-motor time (PMT): from the onset of device acceleration to the onset of agonist EMG activity. b) Electromechanical delay (EMD): from the onset of depolarization of the agonist muscle group to the acceleration onset of the fingers c) Movement Time (MVT): from acceleration onset of the finger to the first instant when device velocity returns to zero.  Technically, the sum of a) and b) are the reaction time, and the sum of a), b) and c) is the response time. Finally, minimum response times were defined as the [mean-3.29*SD] point for the SRT data, and a similar point for the CRT-D data after logarithmic transformation of the skewed data and back- transformation to the srcinal scale. The mean-3.29*SD corresponds to the minimum in one out of 1,000 trials. RESULTS AND DISCUSSION Figure 1. Simple Response Time Test – Sample device, finger kinematics, and finger flexor muscle activity for a female subject, showing SRT-D, PMT, EMD, and MVT. SRT-D was within 5-10 ms of the sum of PMT+EMD+MVT showing construct validity. The difference was due to the use of the acceleration onset/offset by the device, and the device velocity onset/offset for the kinematic measurements. Table 1 summarizes results of SRT and CRT tests. There was no significant gender difference in SRT-D or CRT-D (effect size <0.23). A power analysis showed that sample sizes of 235 subjects would be needed in each group to demonstrate a significant gender difference. CRT-D was significantly longer than SRT-D (P<0.0001). The estimated minimum response times for the SRT-D and CRT-D are found in Table 2. The correlation between SRT-D and the reaction time (PMT+EMD) was 0.910. Table 2. Minimum visuomotor estimated human visuomotor manual response times (in ms) by test Group SRT-D CRT-D Female 91.0 127.4 Male 90.0 122.7 CONCLUSIONS 1)   No significant gender differences were found in SRT-D or CRT-D. 2)   This inexpensive apparatus and method was validated using independent measures. REFERENCES 1. Lord SR, et al.  J Am Geriatr Soc. 39 :1194–1200, 1991 2. Lord SR, et al. Gerontology. 42 : 199–203, 1996 3. Wood, JM ., J Am Geriatr Soc   56 :986–993, 2008. 4.   Warden, DL, et al.  Neurology   57 (3): 524 ‐ 6. 2001 5. Theye, F. et al., Clin Med Res   2 (3):165 ‐ 71. , 2004 ACKNOWLEDGEMENTS Public Health Service grants: R01 AG 026569 & P30 AG 024824 Table 1. Summary of mean (SD) reaction and response times (in ms) for the SRT and CRT tests measured using the device as well as standard kinesiological techniques involving electromyography and kinematics. Gender Simple Reaction Time (SRT) Test Choice Reaction Time (CRT) Test PMT EMD MVT SRT-D* PMT EMD MVT CRT-D **  Female 118  (23) 13  (7) 46  (12) 165  (25) 180 (52)  12 (12) 57 (21) 235 (54)  Male 123  (24) 11 ( 11) 40 (9) 162  (25) 174 (48) 15 (14) 54 (23) 230 (51) * p-value = 0.236, **p-value = 0.1220 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7-50050100150T 0  T 3 SRT-D    D  e  v   i  c  e   A  c  c  e   l  e  r  a   t   i  o  n   (  m   /  s    2    ) 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7-0.500.5T 1 PMT    E   M   G   (   V   ) 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7-101   T 2  T 4 EMD    F   i  n  g  e  r   V  e   l  o  c   i   t  y   (  m   /  s   )  ThumbIndex1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7-6-4-202T 0  T 5 MVT    D  e  v   i  c  e   V  e   l  o  c   i   t  y   (  m   /  s   ) Time (sec)
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