浙江大学文本 On-line programming of simple movement sequences_生理学

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462 MA.C.Kefelaurs et af.Human Movement Science 16(1997)46/-483 1.Introduction A commonly observed phenomenon in the production of a movement se- quence is that the time required to initiate the sequence (i.e.,reaction time) increases with the number of response elements in the sequence.This phe- nomenon has been referred to as the response complexity effect (see Christina, 1992,for a comprehensive review).Henry and Rogers(1960)were among the first to show this relationship between reaction time and response complexity. Specifically,they demonstrated that a simple key lift response was initiated more quickly than a response composed of a key lift and additional movements to specified targets.More recently,this effect has been investigated using a varicty of tasks,including typing (Sternberg ct al.,1978.1990),pronouncing word sequences (Eriksen et al.,1970:Klapp,1971:Sternberg et al..1988, 1990),writing words of different lengths (Hulstijn and Van Galen,1983; Thomassen and Van Galen,1992;Van Galen,1991).making sequential hand postures(Harrington and Haaland,1987)and executing sequences of gross arm movements (Fischman and Lim,1991;Norrie,1967:Ulrich et al.,1990). In general terms,models that account for the response complexity effect assume that the following processes take place prior to movement initiation. First,an abstract representation of the movement sequence (i.c.,motor program) is retrieved from long-term memory and,is then temporarily stored as a subprogram in a short term motor buffer.Second,before execution of each individual movement in the sequence,the corresponding subprogram is retrieved from the buffer.unpacked into its constituents and initiated.The model pro- posed by Klapp (1976.1977)attributes the response complexity effect to the difference in time needed to read the motor program from long-term memory into a short-term motor program buffer.Alternatively,Rosenbaum and associ- ates (Rosenbaum and Saltzman.1984;Rosenbaum et al,1987)believe the response complexity effect is due to the time required to edit the program while it is in the buffer.Stemberg and colleagues (Stemberg et al.,1978)offer yet another explanation for this effect by attributing the increase in reaction time to the time needed to search the butfer for the subprogram that controls the first part of the movement response.Presumably,the search time increases with the number of subprograms in the buffer.Because these models assume that movement sequences are programmed prior to their initiation (from here on termed preprogramming),they predict a direct relationship between the number of response elements in a movement sequence (i.e.,the number of subprograms of the motor program)and reaction time. Before the response complexity effect can be attributed to central processes

462 h4.A.C. Ketelaars et al. /Human Mouement Science 16 (1997) 461-483 1. Introduction A commonly observed phenomenon in the production of a movement sequence is that the time required to initiate the sequence (i.e., reaction time) increases with the number of response elements in the sequence. This phenomenon has been referred to as the response complexity effect (see Christina, 1992, for a comprehensive review). Henry and Rogers (1960) were among the first to show this relationship between reaction time and response complexity. Specifically, they demonstrated that a simple key lift response was initiated more quickly than a response composed of a key lift and additional movements to specified targets. More recently, this effect has been investigated using a variety of tasks, including typing (Sternberg et al., 1978, 19901, pronouncing word sequences (Eriksen et al., 1970; Klapp, 1971; Sternberg et al., 1988, 1990), writing words of different lengths (Hulstijn and Van Galen, 1983; Thomassen and Van Galen, 1992; Van Galen, 1991), making sequential hand postures (Harrington and Haaland, 1987) and executing sequences of gross arm movements (Fischman and Lim, 1991; Nor-tie, 1967; Ulrich et al., 1990). In general terms, models that account for the response complexity effect assume that the following processes take place prior to movement initiation. First, an abstract representation of the movement sequence (i.e., motor program) is retrieved from long-term memory and, is then temporarily stored as a subprogram in a short term motor buffer. Second, before execution of each individual movement in the sequence, the corresponding subprogram is retrieved from the buffer, unpacked into its constituents and initiated. The model proposed by Klapp (1976, 1977) attributes the response complexity effect to the difference in time needed to read the motor program from long-term memory into a short-term motor program buffer. Alternatively, Rosenbaum and associates (Rosenbaum and Saltzman, 1984; Rosenbaum et al., 1987) believe the response complexity effect is due to the time required to edit the program while it is in the buffer. Stemberg and colleagues (Sternberg et al., 1978) offer yet another explanation for this effect by attributing the increase in reaction time to the time needed to search the buffer for the subprogram that controls the first part of the movement response. Presumably, the search time increases with the number of subprograms in the buffer. Because these models assume that movement sequences are programmed prior to their initiation (from here on termed preprogramming), they predict a direct relationship between the number of response elements in a movement sequence (i.e., the number of subprograms of the motor program) and reaction time. Before the response complexity effect can be attributed to central processes

M.A.C.Keteiaars et al.Human Movemend Science 16(1997)461-483 463 alternative explanations must be eliminated (see Anson,1982:Klapp,1977, 1980).Christina (1992)suggests that a "..valid way of investigating the response complexity effect could be provided by standardizing the initial movement segment among the responses being studied and manipulating com- plexity by systematically adding elements to this invariant initial segment"(p. 220).This invariance can be evidenced not only in the spatial/temporal aspects of the movement itsclf,but also at an clectrophysiological level within the musculature producing the movement.Alterations of either,or both,of these characteristics with the addition of subsequent response elements must be considered to be different movements.and any changes in RT will therefore be confounded by the alteration of the initial movement segment.Thus.our operational definition of complexity is related to the number of response elements in movement sequences that contain an invariant initial segment. Recently,several studies have indicated that there are some conditions in which increases in response complexity do not lead to increases in reaction time. Specifically,researchers have shown that reaction time increased linearly in relation to the number of response elements when movements were completed as fast as possible,but either failed to do so,or did so non-linearly when performed at a less than maximal speed (Garcia-Colera and Semjen.1987.1988: van Donkelaar and Franks,1991a.b).Rosenbaum et al.(1986)explained these findings by suggesting that in some instances,subjects do not program the entire movement sequence prior to its execution;rather,some aspect of this process carries on into the period of movement execution (from here on termed on-line programming） In two earlier studies we (Franks and Nagelkerke,1991;Franks et al.,1992) found evidence of on-line programming when subjects performed forearm extension movements and two types of extension-flexion movements.For one group of extension-flexion movements,subjects were instructed to extend and flex in a continuous movement,resulting in an acceleration profile with only one zero line crossing.For the second group,subjects were instructed to extend, pause for a short time and then flex,resulting in several zero line crossings of the acceleration profile.The main findings were that the reaction times required to initiate extension movements were significantly shorter than the reaction times required to initiate extension-flexion movements in the one zero line crossing condition.Thus,it was suggested subjects were forced to preprogram extension-flexion movements that were continuous in nature.However.the reaction times required to initiate extension movements were not significantly different from those of the extension-pause-flexion movements.On the basis of these findings subjects may have been able to program the flexion portion of the

M.A.C. Ketelaars et al./Human Movement Science 16 (1997) 461-483 463 alternative explanations must be eliminated (see Anson, 1982; Klapp, 1977, 1980). Christina (1992) suggests that a “. . . valid way of investigating the response complexity effect could be provided by standardizing the initial movement segment among the responses being studied and manipulating complexity by systematically adding elements to this invariant initial segment” (p. 220). This invariance can be evidenced not only in the spatial/temporal aspects of the movement itself, but also at an electrophysiological level within the musculature producing the movement. Alterations of either, or both, of these characteristics with the addition of subsequent response elements must be considered to be different movements, and any changes in RT will therefore be confounded by the alteration of the initial movement segment. Thus, our operational definition of complexity is related to the number of response elements in movement sequences that contain an invariant initial segment. Recently, several studies have indicated that there are some conditions in which increases in response complexity do not lead to increases in reaction time. Specifically, researchers have shown that reaction time increased linearly in relation to the number of response elements when movements were completed as fast as possible, but either failed to do so, or did so non-linearly when performed at a less than maximal speed (Garcia-Colera and Semjen, 1987, 1988; van Donkelaar and Franks, 1991a,b). Rosenbaum et al. (1986) explained these findings by suggesting that in some instances, subjects do not program the entire movement sequence prior to its execution; rather, some aspect of this process carries on into the period of movement execution (from here on termed on-line programming). In two earlier studies we (Franks and Nagelkerke, 1991; Franks et al., 1992) found evidence of on-line programming when subjects performed forearm extension movements and two types of extension-flexion movements. For one group of extension-flexion movements, subjects were instructed to extend and flex in a continuous movement, resulting in an acceleration profile with only one zero line crossing. For the second group, subjects were instructed to extend, pause for a short time and then flex, resulting in several zero line crossings of the acceleration profile. The main findings were that the reaction times required to initiate extension movements were significantly shorter than the reaction times required to initiate extension-flexion movements in the one zero line crossing condition. Thus, it was suggested subjects were forced to preprogram extension-flexion movements that were continuous in nature. However, the reaction times required to initiate extension movements were not significantly different from those of the extension-pause-flexion movements. On the basis of these findings subjects may have been able to program the flexion portion of the

464 M.A.C.Ketelaars et al /Haman Movement Science 16(1997)461-483 extension-pause-flexion sequence during the execution of the extension move- ment or during the pause time (the mean pause time was 247 ms,with a standard deviation of 56 ms).In a follow-up study (Franks et al.,1992)the pause time between extension and flexion was limited in one condition to only 100 ms.Results indicated that the reaction times were significantly shorter for extension movements than for extension-flexion movements with a short pause time.Therefore,an individual's ability to program subsequent movements appears to be limited by the time available at the juncture points of simple movement sequences. The experiment reported here attempted to identify the exact conditions under which subjects program sequences of forearm movements on-line (either during cxtension or during the juncturc point between cxtension and flexion)and thosc in which subjects are forced to preprogram.The simple movement sequences used in this experiment were forearm extension,continuous extension-flexion with a smooth transition at the juncture point and two types of extension-flex- ion movements for which the pause time at the juncture point was varied.That is,subjects were instructed to make either a short pause (approximately 50-100 ms),or a long pause (approximately 200 ms)at movement reversal.If our earlier hypotheses are correct then subjects will preprogram fast movement sequences unless they have sufficient time to program the subsequent movement on-line.Therefore the response complexity effect as measured by reaction time should be evident in the extend-flex conditions that are time restrained at the juncture points,but not when the pause time between movements exceeds 200 ms. 2.Method 2.1.Subjects Fourteen right-handed male and female university students,aged between 19 and 30 years,volunteered to serve as subjects in this study.All were naive as to the hypotheses under investigation and none had previous experience with the experimental task or procedures used.Subjects were paid $10 for volunteering to participate.The experment was carried out according to the ethical guidelines laid down by the University of British Columbia behavioural sciences screening committee for research and other studies involving human subjects

464 M.A.C. Ketelaars et al./Human Movement Science 16 (1997) 461-483 extension-pause-flexion sequence during the execution of the extension movement or during the pause time (the mean pause time was 247 ms, with a standard deviation of 56 ms). In a follow-up study (Franks et al., 1992) the pause time between extension and flexion was limited in one condition to only 100 ms. Results indicated that the reaction times were significantly shorter for extension movements than for extension-flexion movements with a short pause time. Therefore, an individual’s ability to program subsequent movements appears to be limited by the time available at the juncture points of simple movement sequences. The experiment reported here attempted to identify the exact conditions under which subjects program sequences of forearm movements on-line (either during extension or during the juncture point between extension and flexion) and those in which subjects are forced to preprogram. The simple movement sequences used in this experiment were forearm extension, continuous extension-flexion with a smooth transition at the juncture point and two types of extension-flexion movements for which the pause time at the juncture point was varied. That is, subjects were instructed to make either a short pause (approximately 50-100 ms), or a long pause (approximately 200 ms) at movement reversal. If our earlier hypotheses are correct then subjects will preprogram fast movement sequences unless they have sufficient time to program the subsequent movement on-line. Therefore the response complexity effect as measured by reaction time should be evident in the extend-flex conditions that are time restrained at the juncture points, but not when the pause time between movements exceeds 200 ms. 2. Method 2.1. Subjects Fourteen right-handed male and female university students, aged between 19 and 30 years, volunteered to serve as subjects in this study. All were naive as to the hypotheses under investigation and none had previous experience with the experimental task or procedures used. Subjects were paid $10 for volunteering to participate. The experiment was carried out according to the ethical guidelines laid down by the University of British Columbia behavioural sciences screening committee for research and other studies involving human subjects

M.A.C.Ketelaars et al.Human Mocement Science J6 (1997)461-483 465 2.2.Task and apparatus Subjects were required to make arm extension and extension-flexion move- ments in the horizontal plane,through a range of 45 degrees (from 67.5 degrees to 112.5 degrees where 180 degrees was defined as full extension).The right forearm was positioned on a manipulandum which consisted of a padded horizontal lever attached to a bearing-mounted vertical shaft,such that the elbow was coaxial with the axis of rotation.The right hand was supinated to grasp a vertical handle at the end of the lever and the position of the handle was adjusted to accommodate for varying forcarm lengths.Subjects were sccured in their seat with a shoulder harness in order to keep the contribution from the shoulder muscles constant within each movement condition and their arm was secured to the manipulandum with Velcro straps.In addition,the height at which the subjects were seated was adjusted so that the shoulder angle remained constant in the frontal plane across all subjects. Subjects viewed an oscilloscope screen that was positioned directly in front of them at a distance of 50 cm.Two 'target boxes'(consisting of four cursors spaced 1 cm apart)and a response cursor were displayed.These target boxes were 10 cm apart at the horizontal center line of the oscilloscope screen:5 cm to the right and left of center. An optical encoder (Dynapar E20-2500-130),attached to the shaft of the manipulandum and a custom made computer interface card (for details see Nagelkerke and Franks,1996),allowed for high speed sampling of the angular position of the manipulandum (the sampling rate was 1000 Hz). Angular acceleration data were obtained through the use of a Kistler ac. celerometer (type 8638B50,+50 G),positioned at the end of the manipulan- dum.42 cm from the center of rotation.Its signal,which was measured in volts, was filtered with an active lowpass filter (Krone-Hite,3750)set at 50 Hz and then sampled. Electrical activity from the medial head of the right Biceps muscle and the lateral head of the right Triceps muscle was monitored using Ag/AgCl surface electrodes (8 mm diameter).The electrical signal from the two sets of surface electrodes was amplified by a multichannel electromyographic (EMG)system (model 544,Therapeutics Unlimited Inc.)and raw amplified EMG signals (maximum +10 V)were sampled at a frequency of 1000 Hz and stored for subsequent analysis. All data were sampled by a 12 bit A/D converter (Teemar Labmaster Data Acquisition System)and stored on an MS-DOS 386-33 MHz personal computer for later analysis.This computer was programmed (Borland Turbo Pascal 6.0)to control the entire experiment

M.A.C. Ketelaars et al./Human Movement Science 16 (1997) 461-483 465 2.2. Task and apparatus Subjects were required to make arm extension and extension-flexion movements in the horizontal plane, through a range of 45 degrees (from 67.5 degrees to 112.5 degrees - where 180 degrees was defined as full extension). The right forearm was positioned on a manipulandum which consisted of a padded horizontal lever attached to a bearing-mounted vertical shaft, such that the elbow was coaxial with the axis of rotation. The right hand was supinated to grasp a vertical handle at the end of the lever and the position of the handle was adjusted to accommodate for varying forearm lengths. Subjects were secured in their seat with a shoulder harness in order to keep the contribution from the shoulder muscles constant within each movement condition and their arm was secured to the manipulandum with Velcro straps. In addition, the height at which the subjects were seated was adjusted so that the shoulder angle remained constant in the frontal plane across all subjects. Subjects viewed an oscilloscope screen that was positioned directly in front of them at a distance of 50 cm. Two ‘target boxes’ (consisting of four cursors spaced 1 cm apart) and a response cursor were displayed. These target boxes were 10 cm apart at the horizontal center line of the oscilloscope screen: 5 cm to the right and left of center. An optical encoder (Dynapar E20-2500-130), attached to the shaft of the manipulandum and a custom made computer interface card (for details see Nagelkerke and Franks, 1996), allowed for high speed sampling of the angular position of the manipulandum (the sampling rate was 1000 Hz). Angular acceleration data were obtained through the use of a Kistler accelerometer (type 8638B50, +50 G), positioned at the end of the manipulandum, 42 cm from the center of rotation. Its signal, which was measured in volts, was filtered with an active lowpass filter &one-Hite, # 3750) set at 50 Hz and then sampled. Electrical activity from the medial head of the right Biceps muscle and the lateral head of the right Triceps muscle was monitored using Ag/AgCl surface electrodes (8 mm diameter). The electrical signal from the two sets of surface electrodes was amplified by a multichannel electromyographic (EMG) system (model 544, Therapeutics Unlimited Inc.) and raw amplified EMG signals (maximum k 10 V) were sampled at a frequency of 1000 Hz and stored for subsequent analysis. All data were sampled by a 12 bit A/D converter (Tecmar Labmaster Data Acquisition System) and stored on an MS-DOS 386-33 MHz personal computer for later analysis. This computer was programmed (Borland Turbo Pascal 6.0) to control the entire experiment

466 M.A.C.Ketelaars et al./Hwman Movement Science 16(1997)461-483 2.3.Independent variable One variable,the complexity of the movement response,was manipulated in this experiment.The subjects completed extension (E),extension-flexion con- tinuous (EFC)and two types of extension-flexion movements for which the time between subsequent extension and flexion movements (i.e.,pause time) was manipulated.For one group of extension-flexion movements the pause time at reversal was between 50-100 ms (i.e.,extension-flexion short pause (EFS)). For the second group,this time was 200 ms (i.e.,extension-flexion long pause (EFL)).The pause time was calculated from the angular acceleration profiles and was defined as the time interval between the second zero line crossing of the acceleration profile (at the end of extension)and third zero line crossing (at the beginning of flexion). 2.4.Experimental procedure and design The experiment was comprised of one session,lasting approximately I hour. At the beginning of the session.the experiment and task were described to the subjects and informed consent was obtained. EMG electrodes were attached to the skin,foilowing standard EMG proce- dures (Basmajian,1974:O'Connell and Gardner.1963).First.the electrode placement area was shaved to remove hair from the electrode site;second,the site was rubbed with an abrasive pad to remove the dead surface layer of skin; and third,the site was cleaned with a solution of 91%isopropyl alcohol. Electrode gel was rubbed into the skin at each electrode site to diminish skin impedances.Each pair of electrodes was filled with electrode gel (Parker Laboratories,Inc..Signa Creme)and affixed to the surface of the skin by double sided adhesive tapes (Converters,Inc..#AET-250).The electrodes were aligned longitudinal to the direction of the muscle fibers and the wires were taped to the skin to prevent movement artifacts.A ground electrode was attached to the left wrist. The subjects were first required to complete as many practice trials as needed to perform the movements accurately.The subjects then performed one block of five to ten acceptable trials for each of the four movement conditions (E.EFC. EFS,EFL).The order of presentation of each movement condition was counter- balanced across subjects to control for any order effects.Each subject was randomly assigned to a predetermined order of movement conditions.In order to discourage subjects from anticipating the onset of the imperative stimulus and responding prematurely.20%of trials were catch trials

466 M.A.C. Ketelaars et aL/Human Movement Science 16 (1997) 461-483 2.3. Independent variable One variable, the complexity of the movement response, was manipulated in this experiment. The subjects completed extension (E), extension-flexion continuous (EFC) and two types of extension-flexion movements for which the time between subsequent extension and flexion movements (i.e., pause time) was manipulated. For one group of extension-flexion movements the pause time at reversal was between 50-100 ms (i.e., extension-flexion short pause (EFS)). For the second group, this time was 200 ms (i.e., extension-flexion long pause (EFL)). The pause time was calculated from the angular acceleration profiles and was defined as the time interval between the second zero line crossing of the acceleration profile (at the end of extension) and third zero line crossing (at the beginning of flexion). 2.4. Experimental procedure and design The experiment was comprised of one session, lasting approximately 1 hour. At the beginning of the session, the experiment and task were described to the subjects and informed consent was obtained. EMG electrodes were attached to the skin, following standard EMG procedures (Basmajian, 1974; O’Connell and Gardner, 1963). First, the electrode placement area was shaved to remove hair from the electrode site; second, the site was rubbed with an abrasive pad to remove the dead surface layer of skin; and third, the site was cleaned with a solution of 91% isopropyl alcohol. Electrode gel was rubbed into the skin at each electrode site to diminish skin impedances. Each pair of electrodes was filled with electrode gel (Parker Laboratories, Inc., Signa Creme) and affixed to the surface of the skin by double sided adhesive tapes (Converters, Inc., # AET-250). The electrodes were aligned longitudinal to the direction of the muscle fibers and the wires were taped to the skin to prevent movement artifacts. A ground electrode was attached to the left wrist. The subjects were first required to complete as many practice trials as needed to perform the movements accurately. The subjects then performed one block of five to ten acceptable trials for each of the four movement conditions (E, EFC, EFS, EFL). The order of presentation of each movement condition was counterbalanced across subjects to control for any order effects. Each subject was randomly assigned to a predetermined order of movement conditions. In order to discourage subjects from anticipating the onset of the imperative stimulus and responding prematurely, 20% of trials were catch trials

M.A.C.Ketelaars et al.Human Mocemeent Science 16 (1997)461-483 467 The procedure for each trial was as follows.At the start of a trial the target boxes and response cursor were visible on the oscilloscope screen.Subjects positioned the manipulandum such that the response cursor was centered inside the left target box (designated as -22.5 degrees)and then reported 'ready', indicating to the experimenter that the trial sequence should begin.Two seconds after the subjects had reported 'ready',the target boxes were removed from the oseilloseope sereen for 250 ms.The target boxes then reuppeared,signaling the start of the trial.After a variable foreperiod (1500-2500 ms),the two target boxes and response cursor were removed from the oscilloscope screen.This served as the imperative stimulus.In the extension movement condition,sub- jects were then required to move the response cursor to the right target (dcsignatcd as +22.5 degrces).This movement was therefore an extension of 45 degrees.In the extension-flexion movement conditions,subjects were required to perform an extension movement to the right target and then a flexion movement back to the start position. Once the subjects had completed the required movement(s),the target boxes and response cursor reappeared on the oscilloscope screen for 500 ms,marking the end of the trial. Immediately following each trial the kinematics of the subject's response and the stimulus were displayed on a colour graphics video monitor (Zenith 'Flat Screen'ZCM1490)which was positioned directly underneath the oscilloscope. The first display consisted of the subject's displacement during the trial.Two sets of vertical lines on each side of the monitor screen represented the two target boxes and the subject's displacement data were displayed with the X axis representing displacement and Y axis representing time.The second display consisted of the subject's acceleration profile,reaction time and first movement target error (signed constant error in degrees). The subject's attention was directed to the first feedback display for accuracy and then the acceleration profile display for trial acceptability as per the required movements and reaction time.The subjects were then told that any trials with an error score greater than +1.125 degrees,or a reaction time less than 100 ms (indicating anticipation)or greater than 500 ms (indicating a lack of attention) were discarded from further analysis.In addition.trials in which the subjects failed to complete the entire movement sequence during the sampling period were also discarded.These criteria were not difficult to achieve and were merely meant to insure that the subjects were performing the forearm movements in the required manner.Additional trials were administered until the subjects had performed between five and ten acceptable trials for each movement condition. During a catch trial,the variable foreperiod was extended and the target

M.A.C. Ketelaars et al./Human Movement Science 16 (1997) 461-483 461 The procedure for each trial was as follows. At the start of a trial the target boxes and response cursor were visible on the oscilloscope screen. Subjects positioned the manipulandum such that the response cursor was centered inside the left target box (designated as -22.5 degrees) and then reported ‘ready’, indicating to the experimenter that the trial sequence should begin. Two seconds after the subjects had reported ‘ready’, the target boxes were removed from the oscilloscope screen for 250 ms. The target boxes then reappeared, signaling the start of the trial. After a variable foreperiod (1500-2500 ms), the two target boxes and response cursor were removed from the oscilloscope screen. This served as the imperative stimulus. In the extension movement condition, subjects were then required to move the response cursor to the right target (designated as + 22.5 degrees). This movement was therefore an extension of 45 degrees. In the extension-flexion movement conditions, subjects were required to perform an extension movement to the right target and then a flexion movement back to the start position. Once the subjects had completed the required movement(s), the target boxes and response cursor reappeared on the oscilloscope screen for 500 ms, marking the end of the trial. Immediately following each trial the kinematics of the subject’s response and the stimulus were displayed on a colour graphics video monitor (Zenith ‘Flat Screen’ ZCM1490) which was positioned directly underneath the oscilloscope. The first display consisted of the subject’s displacement during the trial. Two sets of vertical lines on each side of the monitor screen represented the two target boxes and the subject’s displacement data were displayed with the X axis representing displacement and Y axis representing time. The second display consisted of the subject’s acceleration profile, reaction time and first movement target error (signed constant error in degrees). The subject’s attention was directed to the first feedback display for accuracy and then the acceleration profile display for trial acceptability as per the required movements and reaction time. The subjects were then told that any trials with an error score greater than + 1.125 degrees, or a reaction time less than 100 ms (indicating anticipation) or greater than 500 ms (indicating a lack of attention) were discarded from further analysis. In addition, trials in which the subjects failed to complete the entire movement sequence during the sampling period were also discarded. These criteria were not difficult to achieve and were merely meant to insure that the subjects were performing the forearm movements in the required manner. Additional trials were administered until the subjects had performed between five and ten acceptable trials for each movement condition. During a catch trial, the variable foreperiod was extended and the target

468 M.A.C.Kelelars ef al /Homan Movemend Science 16(1997)461-483 boxes were not removed from the oscilloscope screen.After five seconds the experimenter reported the catch trial to the subjects and recorded any movement as error. 2.5.EMG analysis Among the many methods used in current motor control research literature for defining the onset and offset times of EMG activity,visual inspection of the raw,or the raw rectified EMG is by far the most widely used (e.g.,Anson,1982, 1989;Carlton et al.,1985;Christina and Rose,1985;Fischman,1984).A second method is to design computer programs that determine the onset time of musclc activation by calculating when the level of activity has reached a valuc determined by either the product of baseline activity and a constant,e.g.,t25 micro volts(Sidaway,1988).or by a certain percentage of the peak amplitude of activity observed for a particular experimental condition.e.g..10%of the peak amplitude of the subject's averaged rectified EMG profile (Schmidt et al..1988). Recently,we (Ketelaars et al.,1993)compared various methods for defining the onset and offset times of EMG activity.It was concluded that when computer algorithms were used,the calculated onset times were overestimated and the offset times underestimated compared to the results of visually inspect- ing the raw and rectified EMG signal.The method of visual inspection of the raw and rectified EMG,however,did not provide reliable inter-and intra-ob- server results.In order to improve the method of visual inspection,the following procedure was used.The raw EMG signals were first full-wave rectified and then low pass filtered using a fourth-order zero-phase-shift Butterworth filter with a cut-off frequency set at 30 Hz.Following this procedure,the experi- menter was presented with a raw,rectified EMG signal (inverted)and a raw, rectified and filtered EMG signal on the computer screen.The experimenter placed a cursor at the first indication of heightened EMG activity ahove the baseline for each raw,rectified and filtered EMG signal and compared the placement of the cursor to the raw,rectified profilc.This method provided reliable inter-and intra-observer results (the inter-observer reliability coefficient was 0.87;the intra-observer reliability coefficient was 0.89)and therefore this methnd was used to detect the onset times of muscle activation. 2.6.Dependent variables Angular displacement,angular acceleration and two EMG profiles (Biceps and Triceps muscle)were recorded for each trial.Angular displacement was

468 M.A.C. Ketelaars et al. /Human Mouement Science 16 (1997) 461-483 boxes were not removed from the oscilloscope screen. After five seconds the experimenter reported the catch trial to the subjects and recorded any movement as error. 2.5. EMG analysis Among the many methods used in current motor control research literature for defining the onset and offset times of EMG activity, visual inspection of the raw, or the raw rectified EMG is by far the most widely used (e.g., Anson, 1982, 1989; Carlton et al., 1985; Christina and Rose, 1985; Fischman, 1984). A second method is to design computer programs that determine the onset time of muscle activation by calculating when the level of activity has reached a value determined by either the product of baseline activity and a constant, e.g., f 25 micro volts (Sidaway, 1988), or by a certain percentage of the peak amplitude of activity observed for a particular experimental condition, e.g., 10% of the peak amplitude of the subject’s averaged rectified EMG profile (Schmidt et al., 1988). Recently, we (Ketelaars et al., 1993) compared various methods for defining the onset and offset times of EMG activity. It was concluded that when computer algorithms were used, the calculated onset times were overestimated and the offset times underestimated compared to the results of visually inspecting the raw and rectified EMG signal. The method of visual inspection of the raw and rectified EMG, however, did not provide reliable inter- and intra-observer results. In order to improve the method of visual inspection, the following procedure was used. The raw EMG signals were first full-wave rectified and then low pass filtered using a fourth-order zero-phase-shift Butterworth filter with a cut-off frequency set at 30 Hz. Following this procedure, the experimenter was presented with a raw, rectified EMG signal (inverted) and a raw, rectified and filtered EMG signal on the computer screen. The experimenter placed a cursor at the first indication of heightened EMG activity above the baseline for each raw, rectified and filtered EMG signal and compared the placement of the cursor to the raw, rectified profile. This method provided reliable inter- and intra-observer results (the inter-observer reliability coefficient was 0.87; the intra-observer reliability coefficient was 0.89) and therefore this method was used to detect the onset times of muscle activation. 2.6. Dependent variables Angular displacement, angular acceleration and two EMG profiles (Biceps and Triceps muscle) were recorded for each trial. Angular displacement was

M.A.C.Keteiaors et aL Hwmon Movement Science 16(1997)461-483 46的 used to determine displacement reaction time,first movement time (for the forearm extension),movement accuracy to the first target and total movement time. Displacement reaction time was measured as the time from the imperative stimulus to the start of angular displacement about the elbow joint.First movement time (for the forearm extension)was calculated as the time interval bctwcen the start of angular displaccment and the largest positive value of the angular displacement (the range of the extension movement was from -22.5 degrees to +22.5 degrees).Also,the angular position (measured in degrees)of the largest positive value was used to determine the accuracy of the movement to the first target.The constant error was calculated for each target.Subjects over-shooting the target received their positional information as the positive difference between the target position and the response cursor,while under-shoots were reported as a negative difference.Total movement time (for the forearm extension-flexion movements)was calculated as the time interval between the start of angular displacement and largest negative value of the angular displace- ment profile (the range of the flexion movement was from +22.5 degrees to -22.5 degrees). Through the use of EMG recordings.the premotor and motor components of the reaction time period were determined.Premotor reaction time was calculated by measuring the time interval between the onset of the imperative stimulus and the first sign of heightened electromyographic activity of the triceps above baseline.Motor reaction time was calculated by measuring the time interval hetween the first sign of heightened EMG activity and the initiation of overt movement (as measured by displacement values of the optical encoder). The angular acceleration profile was used to calculate peak acceleration,peak velocity.time to peak acceleration and time to peak velocity.Peak acceleration was detined as the absolute largest value of the acceleration profile.Time to peak acceleration was calculated as the time interval between the start of angular acceleration and the point of peak acceleration.Peak velocity was defined as the point where the acceleration profile crossed the zero line for the first time.Time to peak velocity was calculated as the time interval between the start of angular acceleration and the point of peak velocity 2.7.Staristical analysis A multivariate mixed model MANOVA was conducted on selected groupings of dependent variables that were theoretically related.All reaction times were grouped together (displacement,acceleration,premotor and motor reaction

M.A.C. Ketelaars et al./Humun Movement Science 16 (1997) 461-483 469 used to determine displacement reaction time, first movement time (for the forearm extension), movement accuracy to the first target and total movement time. Displacement reaction time was measured as the time from the imperative stimulus to the start of angular displacement about the elbow joint. First movement time (for the forearm extension) was calculated as the time interval between the start of angular displacement and the largest positive value of the angular displacement (the range of the extension movement was from -22.5 degrees to + 22.5 degrees). Also, the angular position (measured in degrees) of the largest positive value was used to determine the accuracy of the movement to the first target. The constant error was calculated for each target. Subjects over-shooting the target received their positional information as the positive difference between the target position and the response cursor, while under-shoots were reported as a negative difference. Total movement time (for the forearm extension-flexion movements) was calculated as the time interval between the start of angular displacement and largest negative value of the angular displacement profile (the range of the flexion movement was from +22.5 degrees to - 22.5 degrees). Through the use of EMG recordings, the premotor and motor components of the reaction time period were determined. Premotor reaction time was calculated by measuring the time interval between the onset of the imperative stimulus and the first sign of heightened electromyographic activity of the triceps above baseline. Motor reaction time was calculated by measuring the time interval between the first sign of heightened EMG activity and the initiation of overt movement (as measured by displacement values of the optical encoder). The angular acceleration profile was used to calculate peak acceleration, peak velocity, time to peak acceleration and time to peak velocity. Peak acceleration was defined as the absolute largest value of the acceleration profile. Time to peak acceleration was calculated as the time interval between the start of angular acceleration and the point of peak acceleration. Peak velocity was defined as the point where the acceleration profile crossed the zero line for the first time. Time to peak velocity was calculated as the time interval between the start of angular acceleration and the point of peak velocity. 2.7. Statistical analysis A multivariate mixed model MANOVA was conducted on selected groupings of dependent variables that were theoretically related. All reaction times were grouped together (displacement, acceleration, premotor and motor reaction

470 M.A.C.Keteloars et al /Haman Mocement Science 16 (1997)461-483 time);time to peak velocity,time to peak acceleration and time to complete the first extension movement (first movement time)were grouped;finally peak acceleration and peak velocity were also grouped.Individual univariate analyses were conducted on the dependent variables total movement time and first target accuracy.A univariate ANOVA followed by a Tukey's HSD post-hoc analysis was used to detect differences between the movement conditions if the Wilk's Likelihood Ratio was significant.The alpha level for the entire experiment was set at 0.05 and the Huynh-Feldt Epsilon factor was used to adjust the degrees of freedom for violation of the sphericity assumption. 2.8.EMG profiles Because the kinematic features of a movement are largely determined by the nct muscle activity of the muscles involved in thut spccific movement,resultant EMG activity was calculated and correlated with the acceleration profiles that were produced by all subjects in the four movement conditions.First.the Triceps and Biceps EMG profiles were rectified,filtered and combined,giving an 'acceleration-like'profile.Because the area under the Biceps and Triceps curves had to have an equivalent arca in order to sum to zero,much like the acceleration profile does at the end of the movement,the Biceps EMG profile was scaled before being combined with the Triceps EMG profile.Secondly,the combined EMG and acceleration profiles were compared using a cross correla- tion method to find the highest correlation and phase-shift values.The highest correlation (range 0.75-0.85)between the combined EMG profile and the acceleration profile was found when the EMG profile was shifted 50 ms forward in time.This indicated that the EMG pattern occurred approximately 50 ms before the resulting acceleration profile,a time frame that is comparable to motor reaction time.Therefore EMG activity appears to be reflective of the acceleration profile it produces.Pancls a-d of Fig.1 provide examples of the muscle activation patterns and acceleration traces that underlie the E.EFC,EFS and EFL movements. 2.8.1.The E movement condition The muscle activation pattern of the extension movement can be described as follows:The initial activity of the Triceps muscle is followed by a silent period. Fig 1.EMG profiies,displacement and acceleration traces for (a)the E movement condition,(b)the EFC movemest condition.(e)the EFS movemunt condition,and (d)the BPl movement oondition

470 M.A.C. Ketelaars et al. /Human Movement Science I6 (1997) 461-483 time); time to peak velocity, time to peak acceleration and time to complete the first extension movement (first movement time) were grouped; finally peak acceleration and peak velocity were also grouped. Individual univariate analyses were conducted on the dependent variables total movement time and first target accuracy. A univariate ANOVA followed by a Tukey’s HSD post-hoc analysis was used to detect differences between the movement conditions if the Wilk’s Likelihood Ratio was significant. The alpha level for the entire experiment was set at 0.05 and the Huynh-Feldt Epsilon factor was used to adjust the degrees of freedom for violation of the sphericity assumption. 2.8. EMG profiles Because the kinematic features of a movement are largely determined by the net muscle activity of the muscles involved in that specific movement, resultant EMG activity was calculated and correlated with the acceleration profiles that were produced by all subjects in the four movement conditions. First, the Triceps and Biceps EMG profiles were rectified, filtered and combined, giving an ‘acceleration-like’ profile. Because the area under the Biceps and Triceps curves had to have an equivalent area in order to sum to zero, much like the acceleration profile does at the end of the movement, the Biceps EMG profile was scaled before being combined with the Triceps EMG profile. Secondly, the combined EMG and acceleration profiles were compared using a cross correlation method to find the highest correlation and phase-shift values. The highest correlation (range 0.75-0.85) between the combined EMG profile and the acceleration profile was found when the EMG profile was shifted 50 ms forward in time. This indicated that the EMG pattern occurred approximately 50 ms before the resulting acceleration profile, a time frame that is comparable to motor reaction time. Therefore EMG activity appears to be reflective of the acceleration profile it produces. Panels a-d of Fig. 1 provide examples of the muscle activation patterns and acceleration traces that underlie the E, EFC, EFS and EFL movements. 2.8. I. The E movement condition The muscle activation pattern of the extension movement can be described as follows: The initial activity of the Triceps muscle is followed by a silent period, Fig. 1. EMG profiles, displacement and acceleration traces for (a) the E movement condition, (b) the EFC movement condition, (c) the EFS movement condition, and (d) the EFL movement condition

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浙江大学文本 On-line programming of simple movement sequences_生理学

浙江大学 文本 On-line programming of simple movement sequences_生理学

浙江大学文本 On-line programming of simple movement sequences_生理学