Med. Biol. Eng. & Cornput,, 1977, lS, 391-397
Portable clinical tracking-task instrument A. R. Potvin
J. A. D o e r r
Department of Biomedical Engineering, University of Texas at Arlington, Arlington, Tx. 76019, USA
LTV Aerospace, Grand Prairie, Tx., USA
J, T, Estes
W. W. Tourtellotte
Bell Helicopter, Hurst, Tx., USA
Neurology & Research Services, V.A. Wadsworth UCLA, USA
Hospital and
A b s t r a c t - - I t has been known that tracking tasks can be useful for detecting small but significant changes in neurological function. However the size, cost and complexity of the equipment have, to date, precluded their widespread use for evaluation of clinical trials. In development for nine years, a battery of tremour and tracking tasks has been designed and evaluated. It is portable, and easy to administer and score. It evaluates neurological functions associated with steadiness, reaction time, speed, and co-ordination of the upper extremities. Instrumentation includes a central electronics package with power supply and test timers, a digital data readout, a television display, a chart recorder, and position, force, and accelerometer transducers. Available tests include force steadiness, resting and sustention tremour, and random, sinusoid, step and critical tracking in pursuit and compensatory modes. Data analysis can be online or offline. Keywords--lnstrumentation. Neurophysiology, Tracking
1 Introduction
ONE purpose of a neurofunction laboratory is quantitatively to document and appraise modern treatment methods in neurology. A well equipped laboratory can considerably improve the evaluation of therapeutic trials by providing finer discrimination, increased precision, reliability, and validity, and improved reproducibility via standardisation at various centres. Quantitative tests are surely not intended to replace the physician but rather to measure objectively small changes in neurological function that are difficult to detect and document using the traditional classifications of mild, moderate, and severe dysfunction. Some important measurements taken in a neurofunction laboratory involve those of the upper extremities. The most important action of the upper extremities is prehensibility (grasping). It requires adequate strength of the grip, wrist, and shoulder; stamina; speed and co-ordination of movements (tracking); and proprioceptive and protective sensation (touch, pain, temperature). Adequate quantitative tests exist for measuring strength and sensation (e.g. POTVIN and TOURTELLOTTE, 1975), and clinically useful portable tests measuring tremour or steadiness have been developed (e.g. POTVIN et al., 1975a); however, except for special limited studies (e.g. REPA, et aL, 1975; DOMINO, et aL, 1972; POTVIN et aL, 1975b; STARK and IIDA, 1961; CASSELL, et al., 1973), state-of-the-art First received 7 June and in final form 1st October 1976
Medical and Biological Engineering & Computing
tracking-task batteries have not been used in clinics. In studies to date, unfortunately, equipment was specialised for a patient group, or was large in physical size, or required skilled technicians, o r was economically prohibitive to use clinically on a regular basis. What requirements should be met by a trackingtask battery for general clinical applications? Operation must be reliable and simple to use by paramedical personnel. The battery should contain a complete range of tests and test types. It should be compatible with a wide range of patient groups as well as normal subjects. The physical size of the instrumentation should be small to conserve clinical floor space and to minimise a patient's anxiety concerning apparatus. A clinical model should be portable and reasonably economical to duplicate. The data or measurements that the equipment yields must be reliable, valid and sufficiently sensitive to detect individual differences over a wide range of neurological function. In addition, the equipment should be capable of interfacing with optional equipment such as magnetic tape recorders, chart recorders, power-spectrum computers, or data-acquisition systems and have remoteoperating capabilities. Equipment meeting those requirements and measuring steadiness and tracking ability in a clinical situation are reported here. The instrumentation results from nine years of design, development, clinical evaluation and modification (ALBERS, et al., 1969, 1973; REPA et al., 1975; July 1977
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POTVIN et al., 1971, 1975a, 1975b, 1976a; DOMINO et aL, 1972). Circuit diagrams and instructions for developing duplicate equipment are available, and interested readers should contact the senior author. 2 Interface of patient and tracking tasks Tracking, as the name implies, is a type of testing that involves a subject's ability, through willed co-ordinated movements, to visually follow a target. Usual/y, an input signal is displayed on a cathode-ray tube, and an output signal is modified and controlled by a patient using a manually operated stick. By moving tb.e control stick, a patient tracks the displayed input signal. The interface of the human and tracking tasks can be represented by the control diagram shown in Fig. 1. The patient must bring the output into agreement with the input. In doing so, a patient may be described as an information-processing system operating on sensory inputs to produce an appropriate motor output. There are two display modes generally used in tracking. Compensatory tracking is one in which the patient sees only the error between the system output and input. Since the characteristics of the display and transducer are defined, both modes allow analysis of the patient, but the compensatory mode often provides for a simpler set of defining equations (McRuER et al., 1965). The system inputs, referred to as the foicing function, are usually constant, sine, square, sawtooth triangular or statistically random waveforms. The inputs are measurable and yield to mathematical analysis. The types of control sticks or transducers used vary in accordance with the particular function to be evaluated. BOWEN et al. (1972) had Parkinsonian patients track a moving target light with a photocell attached to the index figure. ALBERS et al. (1973), using a small rod, and Po'rv]N et al. (1975a), using a flat bar, generated an output signal proportional to the downward force applied to the stick. REPA et al. (1975) had subjects use a large position stick with horizontal motion and negligible dynamics. The present battery of tests includes a large position stick, a fiat bar force stick, and an accelerometer.
I
I~_
input
I
Critical task tracking represents another type of test (JE• et al., 1966, 1970). This test differs from other tracking tasks because the duration of the test is variable, no external forcing function is used, and the patient's own instability serves as an input, exciting increasingly unstable plant dynamics. The critical task yields a measure proportional to the maximum time delay over which a patient can effectively exert controlled movements (effective time delay). The test is analogous to driving a truck with no brakes down a steep, winding road. As time increases, staying on the road becomes more and more difficult until the truck finally runs off the road, and the test is over. The test measure is related to the distance travelled down the road. In several studies conducted to date, both patients and normal subjects have stated that this is a most enjoyable test and our group has found it to be a sensitive test for detecting reliably small changes in neurological function. (REPA et aL, 1975; POTVlN et al., 1975c; DOMINO et al., 1972). 3 Description of equipment The battery of tracking tasks contains random, sinusoid, step and critical tracking signals; force steadiness; and resting and sustention tremour measurements using an accelerometer. Most tests can be performed in a compensatory or pursuit mode, with visual feedback, using a position or a force control stick. Test timing can be either internal or remote, and data analysis can be online or offiine. The equipment used to implement the battery consists of a Panasonic 12in (30cm) diagonal black-and-white television set for visual display, an Astro-med 2-channel chart recorder, a force stick, a position stick, a piezo-resistive accelerometer (Endevco Model 2264-150), and an electronic interface package. The electronics package for the portable clinical tracking task battery contains four major subsystems: output transducers, display modes, tracking tests, and data processing. 4 Output transducers The laboratory-designed force stick (Fig. 2) is a rectangular bar with a 350~ strain-gauge bridge
su~ect (humon operator)
display
transducer dynami cs ond (pl ant) T
Fig. 1 Interface o f subject and tracking task - compensatory tracking . . . . . . . pursuit tracking
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July 1977
whose output is proportional to the downward force two lines superimposed by appropriate movements applied in grammes. The output of the force stick of the control stick. The distance between the two has a full scale deflection of 600g (adjustable from lines (i.e. the difference between the input signal 0 to 1400 g) on the display. Selection of the force and control stick output) is referred to as the patient's stick and its setting was influenced by ALBERS error signal. In a compensatory task, the target line remains stationary and centred on the oscilloet al. (1973) and POTVIN et al. (1975a). scope and the follower is controlled by the error (i.e. the patient sees only the error and is required to move the stick to minimise this error). Lines are used to depict the target and follower rather t h a n dots to minimise the possible effect of scotomas or otherwise poor vision accompanying some neurological disorders. In our experience, visual acuity is not a factor in tracking performance, except for extreme visual losses. The two lines can be switched from horizontal to vertical as required. At present, horizontal lines are used with the force-stick transducer and vertical lines are used with the position-stick transducer in order to maximise hand-eye compatibility. Amplifiers allow an appropriate voltage-amplitude interface with the visual display.
Fig. 2 Instrument equipment 1 Signal-processing unit 2 Television-interface unit 3 Score display 4 Tracking display 5 Position transducer 6 Force transducer 7 Force preamplifier 8 Accelerometer 9 Acceleration preamplifier
The laboratory-designed position stick (Fig. 2) with a single-turn potentimeter is similar to the one used by REPA et al (1975) and is described by H~RZOG (1967). The transducer output of the position stick has an adjustable horizontal swing of at least _+90 ~ and is presently set at _+20 ~ which corresponds to + 102 mm deflection on the visual display. The accelerator (Figure 2) is presently used only to measure finger resting and sustension tremour. A highpass filter with the 3dB point at 0" 1 Hz is used to eliminate orientation (d.c.) shift in output
5 Visual-display modes F o r tracking, two lines are displayed on the television display. The longer of the two, called the target line, is controlled by the input signal during pursuit tracking. The shorter line, or follower, is controlled by the output of either control stick. During a pursuit task, the target moves about the screen, and the patient is instructed to keep the Medical and Biological Engineering & Computing
6 Tracking tasks 6.1 Step tracking Step tracking, usually with the position stick or force stick, is included in the battery of tests because it provides a somewhat simpler situation than continuous tracking for studying the timing aspects of motor responses. A square-wave generator utilising an operational-amplifier oscillator is employed to provide the forcing function for step tracking. Steps in the range 2.5-10 s (presently set at 4 s) are provided to allow for various patient disorders. In visual-pursuit tracking a 4 s step is the duration between jumps of the target line (i.e. the target will be one side of the screen for 4 s then jump to the other side). Although patients performing in this test know the direction of the next movement, they cannot predict with accuracy when movement will occur. Reaction times with fixed foreperiods of 944 ms were found to differ by an inconsequential 5 ms from those with random variabilities of 786 and 1070 m (SNODGRASS, 1969). According to Weber's Law (FixTs and POSNER, 1967), well practised subjects cannot be expected to estimate a 4 s foreperiod with accuracy greater than 10-20~. Thus our relatively unpractised patients should respond to a fixed 4 s interval in a manner consistent with response to a random interval between 3.2 and 4' 8 s. A laboratory pilot study (unpublished data) with random step intervals from 3 to 7 s supports this hypothesis. Over the years, many measures have been used to quantify step tracking. At present the most meaningful measures appear to be reaction time (latency from the input signal change to onset of patient's July 1977
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motion with the stick), maximum velocity of movement (strongly related to movement time), and phase-plane plots. First suggested by REPA (1972), the phase-plane plots are especially attractive to neurologists since they provide a spatial-temporal response record that appears to correlate highly with the classical finger-nose test. The graphical records preserve the interesting movement characteristic of this standard neurological examination test (PoTvIN et al., 1974a; REPA et aL, 1975).
filter to provide a mathematically random waveform, i.e. a waveform whose power spectrum is flat out to the desired cutoff frequency, thereby stimulating a white-noise output. Tracking is conducted using either the force stick or the position stick in either pursuit or compensatory modes. The online task measure is the filtered integrated absolute error (f.i.a.e.). The measure combines both the degree in which a patient overestimates or underestimates the target, as well as the length of time overestimating or underestimating takes place during a given trial. 6.2 Random tracking Although f.i.a.e, scores are adequate for statiRandom tracking requires the patient to ob- stically evaluating changes in neurological function; serve continuously the display signals and predict, offline error power-density spectra and crossprepare, and carry out appropriate movement correlation are often obtained for determining responses. The random-signal electronics consist whether a change in function is due to a change in of a pseudorandom pulse generator ('pseudo' predominant tremour amplitude (the 4-12 Hz implies that the pulse waveform is eventually region) or to both factors (ALBERS et al., 1973; periodic), and a 3" 8 pulse per second clock. The REPA et al., 1975). In a clinical study, the f.i.a.e, measure is quite pulse generator is a free-running 7-stage shift register fashioned from J-K flip-flops. The out- useful whenever the patient is used as his own puts of two stages are sent through an 'EXCUSIVE control. In our double-blind crossover studies oR' configuration into the first stage. The clock (TOURTELLOTTE et al., 1975; POTVIN et aL, 1975c; frequency and number of stages determine the DOMINO et aL, 1972; WALKER et al., 1972), imperiod of the pulse train (33 s). The pulse train provements in random-tracking ability are always is connected to a 4th-order Butterworth filter with found to correlate highly with decreases in tremour the 3dB cutoff points at 1.2 rad/s, and the output and increases in co-ordination control as measured of the filter is then amplified, level shifted, and by such tests as pencil rotation, peg rotation and fed into the system input. placement, alternate target hand tapping, rotary The frequency selected permits testing of a pursuit, Purdue pegboard, and a battery of simubroad cross-section of patients and normal subjects. lated activities of daily living tests. In a drug study, In a recent study (PoTvIN et al., 1976; 1977) it is far more important that a patient's overall 10 male and 10 female young adult normal sub- co-ordination improves than it is that his involunjects, 17 male multiple-sclerosis patients, and 18 tary movements improve, say at the expense of loss male Parkinson's-disease patients were evaluated in of voluntary-movement control. The f.i.a.e, is a 22 types of tracking tests. Included were three measure of overall co-ordination and, from other random signal tracking tests with bandwidths of tests or from offline cross-correlation or power 0.68, 1.22, and 1.94 rad/s. Each subject was spectral analysis of tracking data, the contributions tested once and retested one week later. The test of voluntary and involuntary co-ordination to the with 1.22 rad/s bandwidth was found reliable and Li.a.e. score can be assessed readily. valid, and relatively easy for almost all patients In our recent study (PoxvIN et al., 1976; 1977), to perform. Young adult normal subjects performed briefly described above, tracking-task measurements, this test precisely. The 0.68 rad/s bandwidth test historically most meaningful for assessing performwas judged too slow to maintain proper motivation ance in normal subjects (such as describing function and sustained competitive effort by normal subjects, parameters, the linear correlation coefficient or whereas the 1-94 rad/s bandwidth was judged too coherence between subject output and input forcing difficult, somewhat discouraging, and hence less function, remnant, phase lag, power match etc.)reliable for patients with moderate and moderate- were found neither reliable nor valid for Parkin, to-severe disability. However, our group considers sonian or multiple-sclerosis patients. Moderately such patients ideal for use as subjects in clinical disabled patients have 4 0 ~ or more of their outtrials. To evaluate the efficacy of treatment in a put power uncorrelated with the input power as clinical trial, it is important that tests and measures compared with 3 - 2 0 ~ in normal subjects. Such be reliable and valid over a range of human function large deviations from linear performance effectively from severe disability to supernormal performance. preclude the use of powerful well developed and For this reason, our group has selected the 1.22 useful measures applicable to normal subjects. tad/s bandwidth random forcing function. Instead, the best clinically useful measure for According to GIBSON (1966), the clock frequency random-tracking tests from 38 considered was the of the pulse generator should be approximately absolute value of the highpass filtered error wave20 times the cutoff frequency of the Butterworth form or f.i.a.e. ( e ( t ) - ~ ) . 394
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6.3 Sine tracking A sinusoid was chosen as the third forcing function with frequencies ranging from 0.05 to 0.2 Hz (presently set at 0.09 Hz). Sine tracking is easier than step or random tracking and allows observation of smooth continuous predictable movements in trained subjects. The sine wave is generated by integrating a square-wave oscillator and rounding the resulting triangle waveform with a paralleldiode combination. Sine-tracking tests are conducted in the same manner as the random-tracking tests, and the same measures are utilised.
6.4 Critical tracking The test battery includes the critical task modified from the one developed by JEX et al. (1966). This task does not require extensive learning and has been shown to be reliable. The task is used with no external forcing function, since the patient's own motor noise serves as the input to excite the increasingly unstable controlled element. The plant dynamics include a lst-order divergent pole, and thus is an unstable system. The pole is moved to the right at a known rate, causing the patient to maintain a zero over the pole to stabilise the overall system. The pole is initially set at 1 rad/s and is moved to the right initially at a rate of 0.02 rad/s and later at a rate of 0 . 0 5 r a d / s . Throughout, the patient attempts to minimise the error signal. When the test becomes difficult for the patient and the error exceeds 10% of the visual display, the rate by which the pole is moved to the right is decreased to obtain a more accurate measure of the point of instability for the overall system. The length of time spent in the task at 0" 02 or 0" 05 rad/s is not related to the test measure. Instead, the best measure is taken as the inverse of the value of the pole when the error exceeds the size of the visual display, and is called the effective time delay. As such, the measure reflects a patient's transport delays and central nervous system latencies, average neuromuscular delay, and predictive ability (JEX et aL, 1966). As previously mentioned, measures such as describing-function parameters or linear correlation coefficients are not applicable for even moderately disabled neurology patients, and cross-correlation phase-lag measures are relatively unreliable (POTVIN et aL, 1976; 1977). However, the critical tracking test provides a unique and effective way to measure transport and central-nervous-system delays, and the measurement can be obtained easily, online. 6.5 Steadiness tracking Another task in the battery is called force steadiness. In this task there is no input signal and only the dynamics of the force stick are used. The patient is required to maintain a constant load on the Medical and Biological Engineering & Computing
force stick which can be adjusted for 200 to 1400 g (presently set at 300 g). In this task, the television display is set in the horizontal mode and the target line is centred on the screen. The patient must again superimpose the two lines. Depending upon test instructions, the arm may either be supported or unsupported on the bench. As with random and sinusoid tracking, the measurements used for steadiness tracking are filtered integrated absolute error and error power-density spectra.
6.6 Tremour A piezoresistive accelerometer is mounted over the dorsum of the index finger to obtain measures of resting tremour and sustention tremour. The f.i.a.e. scores are obtained as an online measurement with power-density spectra often taken offiine. The task requires no input signal, and the patient's concentration on tremour can be minimised, if desired, by requiring backward counting and removing the visual display. The Parkinsonian tremour often increases considerably with backward counting (PoTVIN et al., 1975b). The tremour tests and the force-steadiness tests measure different aspects of motor control. The force-steadiness tests require visual acuity and concentration to maintain a load as steady as possible, whereas the tremour tests do not require maintenance of a load and visual acuity and concentration can be eliminated. Thus one set of tests attempts to measure unlimited unconcerned tremours, while the other attempts to measure tremours that cannot be wilfully controlled during the execution of a skilled motor task. 7 Data processing The tracking-task battery generates various data signals that can be used for online and offline analysis. While online measurements are adequate for routine clinical studies, offiine measurements are often necessary for research studies, such as studies investigating the mechanism of tremour, environmental factors affecting upper-extremity motor limb control etc. The online filtered integrated absolute-error score, representing the total area under the absoluteerror curve over the test's time period, provides a relative measure of neurological function. The integrator can be adjusted to avoid component saturation during the longer test durations (range is 10-120 s). The score computed and displayed digitally must be calibrated for each test duration and control stick used. For a given study, the test duration is fixed and only three constants are needed, one for each output transducer. Continuous signals are available for offline analysis including error (equal to input minus output), absolute error, input signal, and output signal. July 1977
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8 Discussion Serious developmental research in human tracking began during the second World War by controlsystems engineers to aid in making practical design decisions concerning tank-turret and anti-aircraft gunnery operation. Tracking was later applied to aircraft control, automobile control, and more recently to spacecraft control (McRUER and KLEIN, 1975; McRtlER et al., 1965; YOUNG and STARK, 1965). However, the control engineer was primarily concerned with modelling the behaviour of the human operator as a part of the overall closed-loopcontrol system. Yet the techniques and equations used readily describe the human's combined sensory decision-making and motor behaviour as a component in the system, thereby describing certain aspects of neurological function. Control engineers have long recognised the applicability of tracking tasks to clinical trials, but have seldom found the clinical opportunity. Conversely, clinicians have also recognised the need for quantitatively evaluating upper-extremity function but have not had the means to implement tests. The advent of sophisticated, reliable, yet inexpensive semiconductors and the formal emergence of biomedical engineering has permitted realisation of the clinical need. Tests in the present tracking-task battery have been in design, development, clinical evaluation, and modification since 1966. Early versions of the present battery of tests have been involved in five clinical drug trials to date and numerous evaluation studies involving patients and normal subjects. A review of the long-term development of a neurofunction laboratory can be found elsewhere (PoTvIN et al., 1974b; POTVIN and TOURTELLOTTE, 1975). Included in the review are applications in neuropharmacological trials and reports on the reliability and validity of tracking tasks. This report is limited to a description of equipment presently in use for measuring tracking behaviour comprehensively and easily in a clinical setting. In a typical neurofunction laboratory study, only a small subset of the available tracking tests are utilised. F o r example, in a Parkinsonian levodopa study (SINEMET| presently underway, the tracking tasks include: 10 critical tracking trials with position stick, three 20 s compensatory random tracking trials with position stick, three 20 s pursuit sinetracking trials with position stick, 12 steps of step tracking with position stick, three forcesteadiness trials in a supported position and three in an unsupported position with the force stick, three resting-tremour trials, and three sustentiontremour trials. Including test instructions and limited practice for a knowledgeable patient (i.e., one who has been tested previously), the tracking tests can be administered in approximately 20 to 30 min. Other tests conducted by the patient in the Neurofunction Laboratory take approximately 1.5 h (PoTvIN and TOURTELLOTTE, 1975). 396
As with its predecessors, the battery of tracking tasks reported herein has been carefully evaluated (PoTvlN et al., 1975c; 1976; 1977; REPA et al., 1975) and found to be reliable and valid. The tracking tasks not only expand capability in a neurofunction laboratory, but their increased sensitivity eliminates the need for many other tests of upper-extremity function (POTVIN and TOURTELI OTTE, 1975). The total cost of the equipment (parts only) is approximately $300 for the electronics package, $100 for a television set, $265 for an accelerometer, and $750 for a 2-channel chart recorder. The chart recorder is actually an expendable option, since measurements of step-tracking-movement time and reaction time could easily be implemented as part of the electronics package for approximately $100 in parts. Thus, excluding technician assembly time, the entire battery can be constructed for $765. Acknowledgment--This work was supported in part by NSF grant GK32-630, UTA organised research funds and by a grant from Merck, Sharp & Dohme Inc. References ALBERS, J. W., TOURTELLOTE,W. W., PEW, R. W., and POTVlN, A. R. (1969) Quantification of motor performance in the clinical neurological examination. Proceedings of the 8th International Conference on Medical & Biological Engineering and the 22nd Annual Conference on Engineering in Medicine & Biology. 4-12. ALBERS, J. W., POTVIN, A. R., TOURTELLOTTE, W. W., PEW, R. W., and STRIBLEY,R. S. (1973). Quantification of hand tremour in the clinical neurological examination. IEEE Trans. BME-20, 27-37. BOWEN,F. P., HOLHN,M. M., and YAHR,M. D. (1972). Cerebral dominance in relation to tracking and tapping performance in patients with Parkinsonism. Neurology, 22, 32 CASSELL, K., SHAW, K., and STERN, G., (1973). A computerised tracking technique for the assessment of Parkinsonism motor disabilities l~rain, 96, 815-826. DOMINO, E. F., ALBERS, J. W., POTVIN, A. R., REPA, B. S., and TOURTELLOTTE,W. W. (1972). Effects of d-amphetamine on quantitative measures of motor performance. Clin. Pharm. Ther. 13, 251-257. FITTS, P. M., and POSNER, M. I. (1967). Human performance. Brooks/Cole, Calif. GILSON,R. (1966). Some results of amplitude distribution experiments on shift-register generated pseudorandom noise. IEEE Trans., EC, 926--927. HERZOG, J. W. (1967). Operation manual: variable dynamics control stick. Private communication, University of Michigan. JEx, H. R., and ALLAN,R. W. (1970). Research on a new human dynamic response test battery. Sixth Annual Conference on Manual Control. Wright-Patterson AFB, Ohio. JEX, H. R., McDoNNELL, J. D., and PHATAH,A. V. (1966). A critical tracking task for manual control research. IEEE Trans, HFE-7, 138-145. McRuEg, D. T., DUNSTAN, G., KRENDEL, E., and REISENER, W. (1965). Human pilot dynamics in compensatory systems-theory, models and experiments with controlled element and forcing function variations
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AFFDL-TR-65-15.
McRuER, D. T., and KLEIN, R., (1975). Effects of auto-
W. W. (1976) Analysis of tracking task measures applicable to normal and pathological subjects. 29th Annual Conference on Engineering in Medicine & Biology, Boston. POTVIN, A. R., CROSIER, W. G., and TOURTELLOTTE, W. W. (1977) Analysis of clinically relevant tracking task measures. Manuscript in preparation. REPA, B. S. (1972). The use of a tracking test battery in the quantitative evaluation of neurological function. Ph.D. thesis, University of Michigan. REPA, B. S., ALBERS,J. W., POTVIN,A. R., and TOURTELLOTTE,W. W. (1975). Application of tracking tasks in the nenrofunction laboratory. Technical Report, VA Wadsworth Hospital Center. SNODGRASS, J. G. (1969). Foreperiod effects in simple reaction time: anticipation or expectancy? J. Exp. Psychol. 79, 1-19. STARK, t., and IIDA, M. (1961) Dynamical response of the movement coordination of patients with Parkinson syndrome. Research Laboratory of Electronics, Quarterly Progress Report 63, Massachusetts Institute of Technology. TOURTELLOTTE, W. W., POTVIN, A. R., HIRSCH, S. B.,
mobile steering characteristics on driver vehicle system dynamics in regulation tasks. Eleventh Annual Conference on Manual Control. Ames Research Center, 408-439. POTVIN, A. R., ALBERS, J. W., TOURTELLOTTE,W. W., PEW, R. W., and SNYDER, D. N. (1971). The development of clinicalinstruments for measuring steadiness. 24th Annual Conference on Engineering in Medicine & Biology. 104. POTVIN, A. R., and TOURTELLOTTE, W. W. (1974a). Cybernetics: a quantitative clinical neurological approach. Proceedings of the International Conference on Systems, Man & Cybernetics, Dallas, 191-196. POTVIN, A. R., ALBERS, J. W., REPA, B. S., HENDERSON, W. G., WALKER,J. E. STRIBLEY,R. F., PEW, R. W., and TOURTELLOTTE, W W (1974b). Quantitative evaluation of neuropharmacological trials. Clin Pharm. Therap. 15, 229-241. POTVlN, A. R., and TOURTELLOTTE,W. W. (1975). The neurological examination: advancements in its quantification. Arch. Phys. Med. Rehab. 56, 425-437. MORGAN, A., HENDERSON, W. G., SCHOELLHAMMER, POTVIN, A. R., STRIBLEY,R. F., PEW, R. W., ALBERS, H., and RICHARDS, S. I. (1975) MK-130 versus CoJ. W., and TOURTELLOTTE,W. W. (1975a). A battery gentin in a clinical trial: a double blind-cross-over of tests for evaluating steadiness in clinical trials. study. Technical Report, VA Wadsworth Hospital Med. & Biol. Eng. 13, 914-922. Center. POTVIN, A. R., TOURTELLOTTE,W. W., SNYDER,D. N., WALKER, J. E., POTVIN, A. R., TOURTELLOTTE, W. W., HENDERSON, W. G., and ALBERS, J. W., (1975b). ALBERS, S. W., REPA, B. S., HENDERSON,W. G. and Validity of quantitative tests measuring tremour. SNYDER, D. N. (1972) Amantadine and levo-dopa in Am. J. Phys. Med. 54, 243-252. the treatment of Parkinson's disease. Clin. Pharm. POTVIN, A. R., SALAMY,J. G., CROSIER, W. G., JONES, Therap. 13, 28-36. K. W., and DOER_R, J. A. (1975c). Effects of seco- YOUNG, L. R., and STARK,L. (1975) Biological control barbitol on performance upon arousal from stage 4 systems--a critical review and evaluation: developsleep. AppL Neurophysiol. 38, 240-250. ments in manual control. National Aeronautics & POTVIN, A. R., CROSIER, W. G., and TOURTELLOTTE, Space Administration Report CR-190.
Appariel portable de d6pistage en clinique Sommaire---I1 est bien connu que le d6pistage peut servir /l d6tecter les variations faibles, bien que significatives, des fonctions neurologiques. Toutefois, la taille, le coot et la complexit6 des 6quipements ont, jusqu'ici, emp~ch6 leur application g6n6ralis6e pour l'6valuation des tests cliniques. Neuf ans de travaux de mise au point ont abouti b. l'6tude et l'6valuation d'une batterie de d6pistage et de d6tection de tremblements. Elle est portable, et facile h utiliser. Elle 6value les fonctions neurologiques correspondant ~t la r6gularit6, le temps de r6action, la vitesse et la coordination des extr6mit6s sup6rieures du corps. Les appareils de mesure comprennent un groupe 61ectronique central avec unit6 d'alimentation et minuteries de test, un affichage de donn6es num6riques un tube cathodique de visualisation, un enregistreur ~t bande, ainsi que des transducteurs de position, de force et d'acc616rom~tres. Les tests pr6vus comportent, entre autres, la r6gularit6 de la force, le tremblement au repos et en sustentation, ainsi que le d6pistage al6atoire, sinusoidale, pas-h-pas et critique en modes de poursuite et de compensation. L'analyse des donn6es peut se faire en mode direct ou autonome.
Ein tragbares, klinisches Eingrenzungsinstrument Zusammenfassung--Es ist bekannt, dab Eingrenzungsaufgaben ftir das Auffinden geringfiigiger, jedoch bedeutsamer .~nderungen in der neurologischen Funktion ntitzlich sein k6nnen. Gr613e, Kosten und Kompliziertheit der Ausriistung haben ihre weitgehende Anwendung zur Auswertung klinischer Versuche jedoch bisher verhindert. In neunj~ihriger Entwicklungsarbeit ist nunmehr eine Zitterund Spureneingrenzungsbatterie entwickelt und ausgewertet worden. Sie ist tragbar und leicht zu benutzen. Sie wertet neurologische Funktionen in Verbindung mit Bestandigkeit, Reaktionszeit, Geschwindigkeit mad Koordinierung der oberen Extremitaten aus. Die Instrumentenausstattung schlieBt ein zentrales Elektronik-Paket mit Netzteil und Prtifzeitschaltern, eine digitale Datenauslesung, eine Fernsehanzeige, einen Streifenblattschreiber sowie Positions-, Kraft- und Beschleunigungsmesser-Wandler ein. Die verfiigbaren Tests umfassen Kraftbest~ndigkeit, Ruhe- und Aushaltezittern mad wahllose-, sinus~ihnliche-, stufenartige- und kritische Spureneingrenzung in Verfolgungs- und Ausgleichs~ Die Datenanalyse kann systemabh~ingig oder systemunabh~ngig erfolgen.
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Portable clinical tracking-task instrument A. R. Potvin
J. A. D o e r r
Department of Biomedical Engineering, University of Texas at Arlington, Arlington, Tx. 76019, USA
LTV Aerospace, Grand Prairie, Tx., USA
J, T, Estes
W. W. Tourtellotte
Bell Helicopter, Hurst, Tx., USA
Neurology & Research Services, V.A. Wadsworth UCLA, USA
Hospital and
A b s t r a c t - - I t has been known that tracking tasks can be useful for detecting small but significant changes in neurological function. However the size, cost and complexity of the equipment have, to date, precluded their widespread use for evaluation of clinical trials. In development for nine years, a battery of tremour and tracking tasks has been designed and evaluated. It is portable, and easy to administer and score. It evaluates neurological functions associated with steadiness, reaction time, speed, and co-ordination of the upper extremities. Instrumentation includes a central electronics package with power supply and test timers, a digital data readout, a television display, a chart recorder, and position, force, and accelerometer transducers. Available tests include force steadiness, resting and sustention tremour, and random, sinusoid, step and critical tracking in pursuit and compensatory modes. Data analysis can be online or offline. Keywords--lnstrumentation. Neurophysiology, Tracking
1 Introduction
ONE purpose of a neurofunction laboratory is quantitatively to document and appraise modern treatment methods in neurology. A well equipped laboratory can considerably improve the evaluation of therapeutic trials by providing finer discrimination, increased precision, reliability, and validity, and improved reproducibility via standardisation at various centres. Quantitative tests are surely not intended to replace the physician but rather to measure objectively small changes in neurological function that are difficult to detect and document using the traditional classifications of mild, moderate, and severe dysfunction. Some important measurements taken in a neurofunction laboratory involve those of the upper extremities. The most important action of the upper extremities is prehensibility (grasping). It requires adequate strength of the grip, wrist, and shoulder; stamina; speed and co-ordination of movements (tracking); and proprioceptive and protective sensation (touch, pain, temperature). Adequate quantitative tests exist for measuring strength and sensation (e.g. POTVIN and TOURTELLOTTE, 1975), and clinically useful portable tests measuring tremour or steadiness have been developed (e.g. POTVIN et al., 1975a); however, except for special limited studies (e.g. REPA, et aL, 1975; DOMINO, et aL, 1972; POTVIN et aL, 1975b; STARK and IIDA, 1961; CASSELL, et al., 1973), state-of-the-art First received 7 June and in final form 1st October 1976
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tracking-task batteries have not been used in clinics. In studies to date, unfortunately, equipment was specialised for a patient group, or was large in physical size, or required skilled technicians, o r was economically prohibitive to use clinically on a regular basis. What requirements should be met by a trackingtask battery for general clinical applications? Operation must be reliable and simple to use by paramedical personnel. The battery should contain a complete range of tests and test types. It should be compatible with a wide range of patient groups as well as normal subjects. The physical size of the instrumentation should be small to conserve clinical floor space and to minimise a patient's anxiety concerning apparatus. A clinical model should be portable and reasonably economical to duplicate. The data or measurements that the equipment yields must be reliable, valid and sufficiently sensitive to detect individual differences over a wide range of neurological function. In addition, the equipment should be capable of interfacing with optional equipment such as magnetic tape recorders, chart recorders, power-spectrum computers, or data-acquisition systems and have remoteoperating capabilities. Equipment meeting those requirements and measuring steadiness and tracking ability in a clinical situation are reported here. The instrumentation results from nine years of design, development, clinical evaluation and modification (ALBERS, et al., 1969, 1973; REPA et al., 1975; July 1977
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POTVIN et al., 1971, 1975a, 1975b, 1976a; DOMINO et aL, 1972). Circuit diagrams and instructions for developing duplicate equipment are available, and interested readers should contact the senior author. 2 Interface of patient and tracking tasks Tracking, as the name implies, is a type of testing that involves a subject's ability, through willed co-ordinated movements, to visually follow a target. Usual/y, an input signal is displayed on a cathode-ray tube, and an output signal is modified and controlled by a patient using a manually operated stick. By moving tb.e control stick, a patient tracks the displayed input signal. The interface of the human and tracking tasks can be represented by the control diagram shown in Fig. 1. The patient must bring the output into agreement with the input. In doing so, a patient may be described as an information-processing system operating on sensory inputs to produce an appropriate motor output. There are two display modes generally used in tracking. Compensatory tracking is one in which the patient sees only the error between the system output and input. Since the characteristics of the display and transducer are defined, both modes allow analysis of the patient, but the compensatory mode often provides for a simpler set of defining equations (McRuER et al., 1965). The system inputs, referred to as the foicing function, are usually constant, sine, square, sawtooth triangular or statistically random waveforms. The inputs are measurable and yield to mathematical analysis. The types of control sticks or transducers used vary in accordance with the particular function to be evaluated. BOWEN et al. (1972) had Parkinsonian patients track a moving target light with a photocell attached to the index figure. ALBERS et al. (1973), using a small rod, and Po'rv]N et al. (1975a), using a flat bar, generated an output signal proportional to the downward force applied to the stick. REPA et al. (1975) had subjects use a large position stick with horizontal motion and negligible dynamics. The present battery of tests includes a large position stick, a fiat bar force stick, and an accelerometer.
I
I~_
input
I
Critical task tracking represents another type of test (JE• et al., 1966, 1970). This test differs from other tracking tasks because the duration of the test is variable, no external forcing function is used, and the patient's own instability serves as an input, exciting increasingly unstable plant dynamics. The critical task yields a measure proportional to the maximum time delay over which a patient can effectively exert controlled movements (effective time delay). The test is analogous to driving a truck with no brakes down a steep, winding road. As time increases, staying on the road becomes more and more difficult until the truck finally runs off the road, and the test is over. The test measure is related to the distance travelled down the road. In several studies conducted to date, both patients and normal subjects have stated that this is a most enjoyable test and our group has found it to be a sensitive test for detecting reliably small changes in neurological function. (REPA et aL, 1975; POTVlN et al., 1975c; DOMINO et al., 1972). 3 Description of equipment The battery of tracking tasks contains random, sinusoid, step and critical tracking signals; force steadiness; and resting and sustention tremour measurements using an accelerometer. Most tests can be performed in a compensatory or pursuit mode, with visual feedback, using a position or a force control stick. Test timing can be either internal or remote, and data analysis can be online or offiine. The equipment used to implement the battery consists of a Panasonic 12in (30cm) diagonal black-and-white television set for visual display, an Astro-med 2-channel chart recorder, a force stick, a position stick, a piezo-resistive accelerometer (Endevco Model 2264-150), and an electronic interface package. The electronics package for the portable clinical tracking task battery contains four major subsystems: output transducers, display modes, tracking tests, and data processing. 4 Output transducers The laboratory-designed force stick (Fig. 2) is a rectangular bar with a 350~ strain-gauge bridge
su~ect (humon operator)
display
transducer dynami cs ond (pl ant) T
Fig. 1 Interface o f subject and tracking task - compensatory tracking . . . . . . . pursuit tracking
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whose output is proportional to the downward force two lines superimposed by appropriate movements applied in grammes. The output of the force stick of the control stick. The distance between the two has a full scale deflection of 600g (adjustable from lines (i.e. the difference between the input signal 0 to 1400 g) on the display. Selection of the force and control stick output) is referred to as the patient's stick and its setting was influenced by ALBERS error signal. In a compensatory task, the target line remains stationary and centred on the oscilloet al. (1973) and POTVIN et al. (1975a). scope and the follower is controlled by the error (i.e. the patient sees only the error and is required to move the stick to minimise this error). Lines are used to depict the target and follower rather t h a n dots to minimise the possible effect of scotomas or otherwise poor vision accompanying some neurological disorders. In our experience, visual acuity is not a factor in tracking performance, except for extreme visual losses. The two lines can be switched from horizontal to vertical as required. At present, horizontal lines are used with the force-stick transducer and vertical lines are used with the position-stick transducer in order to maximise hand-eye compatibility. Amplifiers allow an appropriate voltage-amplitude interface with the visual display.
Fig. 2 Instrument equipment 1 Signal-processing unit 2 Television-interface unit 3 Score display 4 Tracking display 5 Position transducer 6 Force transducer 7 Force preamplifier 8 Accelerometer 9 Acceleration preamplifier
The laboratory-designed position stick (Fig. 2) with a single-turn potentimeter is similar to the one used by REPA et al (1975) and is described by H~RZOG (1967). The transducer output of the position stick has an adjustable horizontal swing of at least _+90 ~ and is presently set at _+20 ~ which corresponds to + 102 mm deflection on the visual display. The accelerator (Figure 2) is presently used only to measure finger resting and sustension tremour. A highpass filter with the 3dB point at 0" 1 Hz is used to eliminate orientation (d.c.) shift in output
5 Visual-display modes F o r tracking, two lines are displayed on the television display. The longer of the two, called the target line, is controlled by the input signal during pursuit tracking. The shorter line, or follower, is controlled by the output of either control stick. During a pursuit task, the target moves about the screen, and the patient is instructed to keep the Medical and Biological Engineering & Computing
6 Tracking tasks 6.1 Step tracking Step tracking, usually with the position stick or force stick, is included in the battery of tests because it provides a somewhat simpler situation than continuous tracking for studying the timing aspects of motor responses. A square-wave generator utilising an operational-amplifier oscillator is employed to provide the forcing function for step tracking. Steps in the range 2.5-10 s (presently set at 4 s) are provided to allow for various patient disorders. In visual-pursuit tracking a 4 s step is the duration between jumps of the target line (i.e. the target will be one side of the screen for 4 s then jump to the other side). Although patients performing in this test know the direction of the next movement, they cannot predict with accuracy when movement will occur. Reaction times with fixed foreperiods of 944 ms were found to differ by an inconsequential 5 ms from those with random variabilities of 786 and 1070 m (SNODGRASS, 1969). According to Weber's Law (FixTs and POSNER, 1967), well practised subjects cannot be expected to estimate a 4 s foreperiod with accuracy greater than 10-20~. Thus our relatively unpractised patients should respond to a fixed 4 s interval in a manner consistent with response to a random interval between 3.2 and 4' 8 s. A laboratory pilot study (unpublished data) with random step intervals from 3 to 7 s supports this hypothesis. Over the years, many measures have been used to quantify step tracking. At present the most meaningful measures appear to be reaction time (latency from the input signal change to onset of patient's July 1977
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motion with the stick), maximum velocity of movement (strongly related to movement time), and phase-plane plots. First suggested by REPA (1972), the phase-plane plots are especially attractive to neurologists since they provide a spatial-temporal response record that appears to correlate highly with the classical finger-nose test. The graphical records preserve the interesting movement characteristic of this standard neurological examination test (PoTvIN et al., 1974a; REPA et aL, 1975).
filter to provide a mathematically random waveform, i.e. a waveform whose power spectrum is flat out to the desired cutoff frequency, thereby stimulating a white-noise output. Tracking is conducted using either the force stick or the position stick in either pursuit or compensatory modes. The online task measure is the filtered integrated absolute error (f.i.a.e.). The measure combines both the degree in which a patient overestimates or underestimates the target, as well as the length of time overestimating or underestimating takes place during a given trial. 6.2 Random tracking Although f.i.a.e, scores are adequate for statiRandom tracking requires the patient to ob- stically evaluating changes in neurological function; serve continuously the display signals and predict, offline error power-density spectra and crossprepare, and carry out appropriate movement correlation are often obtained for determining responses. The random-signal electronics consist whether a change in function is due to a change in of a pseudorandom pulse generator ('pseudo' predominant tremour amplitude (the 4-12 Hz implies that the pulse waveform is eventually region) or to both factors (ALBERS et al., 1973; periodic), and a 3" 8 pulse per second clock. The REPA et al., 1975). In a clinical study, the f.i.a.e, measure is quite pulse generator is a free-running 7-stage shift register fashioned from J-K flip-flops. The out- useful whenever the patient is used as his own puts of two stages are sent through an 'EXCUSIVE control. In our double-blind crossover studies oR' configuration into the first stage. The clock (TOURTELLOTTE et al., 1975; POTVIN et aL, 1975c; frequency and number of stages determine the DOMINO et aL, 1972; WALKER et al., 1972), imperiod of the pulse train (33 s). The pulse train provements in random-tracking ability are always is connected to a 4th-order Butterworth filter with found to correlate highly with decreases in tremour the 3dB cutoff points at 1.2 rad/s, and the output and increases in co-ordination control as measured of the filter is then amplified, level shifted, and by such tests as pencil rotation, peg rotation and fed into the system input. placement, alternate target hand tapping, rotary The frequency selected permits testing of a pursuit, Purdue pegboard, and a battery of simubroad cross-section of patients and normal subjects. lated activities of daily living tests. In a drug study, In a recent study (PoTvIN et al., 1976; 1977) it is far more important that a patient's overall 10 male and 10 female young adult normal sub- co-ordination improves than it is that his involunjects, 17 male multiple-sclerosis patients, and 18 tary movements improve, say at the expense of loss male Parkinson's-disease patients were evaluated in of voluntary-movement control. The f.i.a.e, is a 22 types of tracking tests. Included were three measure of overall co-ordination and, from other random signal tracking tests with bandwidths of tests or from offline cross-correlation or power 0.68, 1.22, and 1.94 rad/s. Each subject was spectral analysis of tracking data, the contributions tested once and retested one week later. The test of voluntary and involuntary co-ordination to the with 1.22 rad/s bandwidth was found reliable and Li.a.e. score can be assessed readily. valid, and relatively easy for almost all patients In our recent study (PoxvIN et al., 1976; 1977), to perform. Young adult normal subjects performed briefly described above, tracking-task measurements, this test precisely. The 0.68 rad/s bandwidth test historically most meaningful for assessing performwas judged too slow to maintain proper motivation ance in normal subjects (such as describing function and sustained competitive effort by normal subjects, parameters, the linear correlation coefficient or whereas the 1-94 rad/s bandwidth was judged too coherence between subject output and input forcing difficult, somewhat discouraging, and hence less function, remnant, phase lag, power match etc.)reliable for patients with moderate and moderate- were found neither reliable nor valid for Parkin, to-severe disability. However, our group considers sonian or multiple-sclerosis patients. Moderately such patients ideal for use as subjects in clinical disabled patients have 4 0 ~ or more of their outtrials. To evaluate the efficacy of treatment in a put power uncorrelated with the input power as clinical trial, it is important that tests and measures compared with 3 - 2 0 ~ in normal subjects. Such be reliable and valid over a range of human function large deviations from linear performance effectively from severe disability to supernormal performance. preclude the use of powerful well developed and For this reason, our group has selected the 1.22 useful measures applicable to normal subjects. tad/s bandwidth random forcing function. Instead, the best clinically useful measure for According to GIBSON (1966), the clock frequency random-tracking tests from 38 considered was the of the pulse generator should be approximately absolute value of the highpass filtered error wave20 times the cutoff frequency of the Butterworth form or f.i.a.e. ( e ( t ) - ~ ) . 394
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6.3 Sine tracking A sinusoid was chosen as the third forcing function with frequencies ranging from 0.05 to 0.2 Hz (presently set at 0.09 Hz). Sine tracking is easier than step or random tracking and allows observation of smooth continuous predictable movements in trained subjects. The sine wave is generated by integrating a square-wave oscillator and rounding the resulting triangle waveform with a paralleldiode combination. Sine-tracking tests are conducted in the same manner as the random-tracking tests, and the same measures are utilised.
6.4 Critical tracking The test battery includes the critical task modified from the one developed by JEX et al. (1966). This task does not require extensive learning and has been shown to be reliable. The task is used with no external forcing function, since the patient's own motor noise serves as the input to excite the increasingly unstable controlled element. The plant dynamics include a lst-order divergent pole, and thus is an unstable system. The pole is moved to the right at a known rate, causing the patient to maintain a zero over the pole to stabilise the overall system. The pole is initially set at 1 rad/s and is moved to the right initially at a rate of 0.02 rad/s and later at a rate of 0 . 0 5 r a d / s . Throughout, the patient attempts to minimise the error signal. When the test becomes difficult for the patient and the error exceeds 10% of the visual display, the rate by which the pole is moved to the right is decreased to obtain a more accurate measure of the point of instability for the overall system. The length of time spent in the task at 0" 02 or 0" 05 rad/s is not related to the test measure. Instead, the best measure is taken as the inverse of the value of the pole when the error exceeds the size of the visual display, and is called the effective time delay. As such, the measure reflects a patient's transport delays and central nervous system latencies, average neuromuscular delay, and predictive ability (JEX et aL, 1966). As previously mentioned, measures such as describing-function parameters or linear correlation coefficients are not applicable for even moderately disabled neurology patients, and cross-correlation phase-lag measures are relatively unreliable (POTVIN et aL, 1976; 1977). However, the critical tracking test provides a unique and effective way to measure transport and central-nervous-system delays, and the measurement can be obtained easily, online. 6.5 Steadiness tracking Another task in the battery is called force steadiness. In this task there is no input signal and only the dynamics of the force stick are used. The patient is required to maintain a constant load on the Medical and Biological Engineering & Computing
force stick which can be adjusted for 200 to 1400 g (presently set at 300 g). In this task, the television display is set in the horizontal mode and the target line is centred on the screen. The patient must again superimpose the two lines. Depending upon test instructions, the arm may either be supported or unsupported on the bench. As with random and sinusoid tracking, the measurements used for steadiness tracking are filtered integrated absolute error and error power-density spectra.
6.6 Tremour A piezoresistive accelerometer is mounted over the dorsum of the index finger to obtain measures of resting tremour and sustention tremour. The f.i.a.e. scores are obtained as an online measurement with power-density spectra often taken offiine. The task requires no input signal, and the patient's concentration on tremour can be minimised, if desired, by requiring backward counting and removing the visual display. The Parkinsonian tremour often increases considerably with backward counting (PoTVIN et al., 1975b). The tremour tests and the force-steadiness tests measure different aspects of motor control. The force-steadiness tests require visual acuity and concentration to maintain a load as steady as possible, whereas the tremour tests do not require maintenance of a load and visual acuity and concentration can be eliminated. Thus one set of tests attempts to measure unlimited unconcerned tremours, while the other attempts to measure tremours that cannot be wilfully controlled during the execution of a skilled motor task. 7 Data processing The tracking-task battery generates various data signals that can be used for online and offline analysis. While online measurements are adequate for routine clinical studies, offiine measurements are often necessary for research studies, such as studies investigating the mechanism of tremour, environmental factors affecting upper-extremity motor limb control etc. The online filtered integrated absolute-error score, representing the total area under the absoluteerror curve over the test's time period, provides a relative measure of neurological function. The integrator can be adjusted to avoid component saturation during the longer test durations (range is 10-120 s). The score computed and displayed digitally must be calibrated for each test duration and control stick used. For a given study, the test duration is fixed and only three constants are needed, one for each output transducer. Continuous signals are available for offline analysis including error (equal to input minus output), absolute error, input signal, and output signal. July 1977
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8 Discussion Serious developmental research in human tracking began during the second World War by controlsystems engineers to aid in making practical design decisions concerning tank-turret and anti-aircraft gunnery operation. Tracking was later applied to aircraft control, automobile control, and more recently to spacecraft control (McRUER and KLEIN, 1975; McRtlER et al., 1965; YOUNG and STARK, 1965). However, the control engineer was primarily concerned with modelling the behaviour of the human operator as a part of the overall closed-loopcontrol system. Yet the techniques and equations used readily describe the human's combined sensory decision-making and motor behaviour as a component in the system, thereby describing certain aspects of neurological function. Control engineers have long recognised the applicability of tracking tasks to clinical trials, but have seldom found the clinical opportunity. Conversely, clinicians have also recognised the need for quantitatively evaluating upper-extremity function but have not had the means to implement tests. The advent of sophisticated, reliable, yet inexpensive semiconductors and the formal emergence of biomedical engineering has permitted realisation of the clinical need. Tests in the present tracking-task battery have been in design, development, clinical evaluation, and modification since 1966. Early versions of the present battery of tests have been involved in five clinical drug trials to date and numerous evaluation studies involving patients and normal subjects. A review of the long-term development of a neurofunction laboratory can be found elsewhere (PoTvIN et al., 1974b; POTVIN and TOURTELLOTTE, 1975). Included in the review are applications in neuropharmacological trials and reports on the reliability and validity of tracking tasks. This report is limited to a description of equipment presently in use for measuring tracking behaviour comprehensively and easily in a clinical setting. In a typical neurofunction laboratory study, only a small subset of the available tracking tests are utilised. F o r example, in a Parkinsonian levodopa study (SINEMET| presently underway, the tracking tasks include: 10 critical tracking trials with position stick, three 20 s compensatory random tracking trials with position stick, three 20 s pursuit sinetracking trials with position stick, 12 steps of step tracking with position stick, three forcesteadiness trials in a supported position and three in an unsupported position with the force stick, three resting-tremour trials, and three sustentiontremour trials. Including test instructions and limited practice for a knowledgeable patient (i.e., one who has been tested previously), the tracking tests can be administered in approximately 20 to 30 min. Other tests conducted by the patient in the Neurofunction Laboratory take approximately 1.5 h (PoTvIN and TOURTELLOTTE, 1975). 396
As with its predecessors, the battery of tracking tasks reported herein has been carefully evaluated (PoTvlN et al., 1975c; 1976; 1977; REPA et al., 1975) and found to be reliable and valid. The tracking tasks not only expand capability in a neurofunction laboratory, but their increased sensitivity eliminates the need for many other tests of upper-extremity function (POTVIN and TOURTELI OTTE, 1975). The total cost of the equipment (parts only) is approximately $300 for the electronics package, $100 for a television set, $265 for an accelerometer, and $750 for a 2-channel chart recorder. The chart recorder is actually an expendable option, since measurements of step-tracking-movement time and reaction time could easily be implemented as part of the electronics package for approximately $100 in parts. Thus, excluding technician assembly time, the entire battery can be constructed for $765. Acknowledgment--This work was supported in part by NSF grant GK32-630, UTA organised research funds and by a grant from Merck, Sharp & Dohme Inc. References ALBERS, J. W., TOURTELLOTE,W. W., PEW, R. W., and POTVlN, A. R. (1969) Quantification of motor performance in the clinical neurological examination. Proceedings of the 8th International Conference on Medical & Biological Engineering and the 22nd Annual Conference on Engineering in Medicine & Biology. 4-12. ALBERS, J. W., POTVIN, A. R., TOURTELLOTTE, W. W., PEW, R. W., and STRIBLEY,R. S. (1973). Quantification of hand tremour in the clinical neurological examination. IEEE Trans. BME-20, 27-37. BOWEN,F. P., HOLHN,M. M., and YAHR,M. D. (1972). Cerebral dominance in relation to tracking and tapping performance in patients with Parkinsonism. Neurology, 22, 32 CASSELL, K., SHAW, K., and STERN, G., (1973). A computerised tracking technique for the assessment of Parkinsonism motor disabilities l~rain, 96, 815-826. DOMINO, E. F., ALBERS, J. W., POTVIN, A. R., REPA, B. S., and TOURTELLOTTE,W. W. (1972). Effects of d-amphetamine on quantitative measures of motor performance. Clin. Pharm. Ther. 13, 251-257. FITTS, P. M., and POSNER, M. I. (1967). Human performance. Brooks/Cole, Calif. GILSON,R. (1966). Some results of amplitude distribution experiments on shift-register generated pseudorandom noise. IEEE Trans., EC, 926--927. HERZOG, J. W. (1967). Operation manual: variable dynamics control stick. Private communication, University of Michigan. JEx, H. R., and ALLAN,R. W. (1970). Research on a new human dynamic response test battery. Sixth Annual Conference on Manual Control. Wright-Patterson AFB, Ohio. JEX, H. R., McDoNNELL, J. D., and PHATAH,A. V. (1966). A critical tracking task for manual control research. IEEE Trans, HFE-7, 138-145. McRuEg, D. T., DUNSTAN, G., KRENDEL, E., and REISENER, W. (1965). Human pilot dynamics in compensatory systems-theory, models and experiments with controlled element and forcing function variations
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AFFDL-TR-65-15.
McRuER, D. T., and KLEIN, R., (1975). Effects of auto-
W. W. (1976) Analysis of tracking task measures applicable to normal and pathological subjects. 29th Annual Conference on Engineering in Medicine & Biology, Boston. POTVIN, A. R., CROSIER, W. G., and TOURTELLOTTE, W. W. (1977) Analysis of clinically relevant tracking task measures. Manuscript in preparation. REPA, B. S. (1972). The use of a tracking test battery in the quantitative evaluation of neurological function. Ph.D. thesis, University of Michigan. REPA, B. S., ALBERS,J. W., POTVIN,A. R., and TOURTELLOTTE,W. W. (1975). Application of tracking tasks in the nenrofunction laboratory. Technical Report, VA Wadsworth Hospital Center. SNODGRASS, J. G. (1969). Foreperiod effects in simple reaction time: anticipation or expectancy? J. Exp. Psychol. 79, 1-19. STARK, t., and IIDA, M. (1961) Dynamical response of the movement coordination of patients with Parkinson syndrome. Research Laboratory of Electronics, Quarterly Progress Report 63, Massachusetts Institute of Technology. TOURTELLOTTE, W. W., POTVIN, A. R., HIRSCH, S. B.,
mobile steering characteristics on driver vehicle system dynamics in regulation tasks. Eleventh Annual Conference on Manual Control. Ames Research Center, 408-439. POTVIN, A. R., ALBERS, J. W., TOURTELLOTTE,W. W., PEW, R. W., and SNYDER, D. N. (1971). The development of clinicalinstruments for measuring steadiness. 24th Annual Conference on Engineering in Medicine & Biology. 104. POTVIN, A. R., and TOURTELLOTTE, W. W. (1974a). Cybernetics: a quantitative clinical neurological approach. Proceedings of the International Conference on Systems, Man & Cybernetics, Dallas, 191-196. POTVIN, A. R., ALBERS, J. W., REPA, B. S., HENDERSON, W. G., WALKER,J. E. STRIBLEY,R. F., PEW, R. W., and TOURTELLOTTE, W W (1974b). Quantitative evaluation of neuropharmacological trials. Clin Pharm. Therap. 15, 229-241. POTVlN, A. R., and TOURTELLOTTE,W. W. (1975). The neurological examination: advancements in its quantification. Arch. Phys. Med. Rehab. 56, 425-437. MORGAN, A., HENDERSON, W. G., SCHOELLHAMMER, POTVIN, A. R., STRIBLEY,R. F., PEW, R. W., ALBERS, H., and RICHARDS, S. I. (1975) MK-130 versus CoJ. W., and TOURTELLOTTE,W. W. (1975a). A battery gentin in a clinical trial: a double blind-cross-over of tests for evaluating steadiness in clinical trials. study. Technical Report, VA Wadsworth Hospital Med. & Biol. Eng. 13, 914-922. Center. POTVIN, A. R., TOURTELLOTTE,W. W., SNYDER,D. N., WALKER, J. E., POTVIN, A. R., TOURTELLOTTE, W. W., HENDERSON, W. G., and ALBERS, J. W., (1975b). ALBERS, S. W., REPA, B. S., HENDERSON,W. G. and Validity of quantitative tests measuring tremour. SNYDER, D. N. (1972) Amantadine and levo-dopa in Am. J. Phys. Med. 54, 243-252. the treatment of Parkinson's disease. Clin. Pharm. POTVIN, A. R., SALAMY,J. G., CROSIER, W. G., JONES, Therap. 13, 28-36. K. W., and DOER_R, J. A. (1975c). Effects of seco- YOUNG, L. R., and STARK,L. (1975) Biological control barbitol on performance upon arousal from stage 4 systems--a critical review and evaluation: developsleep. AppL Neurophysiol. 38, 240-250. ments in manual control. National Aeronautics & POTVIN, A. R., CROSIER, W. G., and TOURTELLOTTE, Space Administration Report CR-190.
Appariel portable de d6pistage en clinique Sommaire---I1 est bien connu que le d6pistage peut servir /l d6tecter les variations faibles, bien que significatives, des fonctions neurologiques. Toutefois, la taille, le coot et la complexit6 des 6quipements ont, jusqu'ici, emp~ch6 leur application g6n6ralis6e pour l'6valuation des tests cliniques. Neuf ans de travaux de mise au point ont abouti b. l'6tude et l'6valuation d'une batterie de d6pistage et de d6tection de tremblements. Elle est portable, et facile h utiliser. Elle 6value les fonctions neurologiques correspondant ~t la r6gularit6, le temps de r6action, la vitesse et la coordination des extr6mit6s sup6rieures du corps. Les appareils de mesure comprennent un groupe 61ectronique central avec unit6 d'alimentation et minuteries de test, un affichage de donn6es num6riques un tube cathodique de visualisation, un enregistreur ~t bande, ainsi que des transducteurs de position, de force et d'acc616rom~tres. Les tests pr6vus comportent, entre autres, la r6gularit6 de la force, le tremblement au repos et en sustentation, ainsi que le d6pistage al6atoire, sinusoidale, pas-h-pas et critique en modes de poursuite et de compensation. L'analyse des donn6es peut se faire en mode direct ou autonome.
Ein tragbares, klinisches Eingrenzungsinstrument Zusammenfassung--Es ist bekannt, dab Eingrenzungsaufgaben ftir das Auffinden geringfiigiger, jedoch bedeutsamer .~nderungen in der neurologischen Funktion ntitzlich sein k6nnen. Gr613e, Kosten und Kompliziertheit der Ausriistung haben ihre weitgehende Anwendung zur Auswertung klinischer Versuche jedoch bisher verhindert. In neunj~ihriger Entwicklungsarbeit ist nunmehr eine Zitterund Spureneingrenzungsbatterie entwickelt und ausgewertet worden. Sie ist tragbar und leicht zu benutzen. Sie wertet neurologische Funktionen in Verbindung mit Bestandigkeit, Reaktionszeit, Geschwindigkeit mad Koordinierung der oberen Extremitaten aus. Die Instrumentenausstattung schlieBt ein zentrales Elektronik-Paket mit Netzteil und Prtifzeitschaltern, eine digitale Datenauslesung, eine Fernsehanzeige, einen Streifenblattschreiber sowie Positions-, Kraft- und Beschleunigungsmesser-Wandler ein. Die verfiigbaren Tests umfassen Kraftbest~ndigkeit, Ruhe- und Aushaltezittern mad wahllose-, sinus~ihnliche-, stufenartige- und kritische Spureneingrenzung in Verfolgungs- und Ausgleichs~ Die Datenanalyse kann systemabh~ingig oder systemunabh~ngig erfolgen.
Medical and Biological Engineering & Computing
July 1977
397
