Human Movement Science 1 (1982) 235-249

North-Holland Pubhshmg Company

235

THE CHOICE REACTION TIMES OF SINGLE AND DUAL JOINTED ACTIONS *

Andrew BISHOP and Ann HARRISON Sheffield Unrverszty, UK

Bishop, A and A. Harrison, 1982. The chotce reaction times of single and dual Jointed actions. Human Movement Science 1, 235-249.

The choice reactlon times of dual (elbow and wnst) and smgle (elbow) Jomted movements were

measured usmg ‘mixed’ (dual and smgle) and ‘matched’ (both dual or both single) response

pmnngs. Although subjects found It more difficult to execute dual Jomted actions (as shown by

error rate), there was no concomitant prolongation of latencles for acceptable responses In the

hght of these fmdmgs, the utility of CRT as an mdex of motor programmmg complexity, and the

claim that pre-programmmg of responses IS precluded with CRT testing, were discussed

Introduction

In a recent study (Harrison and Bishop 1982), we investigated how accurately people make unsighted ‘ballistic’ movements to targets, and included a comparison of single (elbow or wrist) and dual (elbow and wrist) Jointed actions. Joint angles were measured gomometrically, and accuracy was assessed in terms of how far final elbow and wrist angles deviated from being precisely on target. In terms of total error, dual actions were less accurate, wluch offers some support for the idea that increasing the number of movmg ~omts raises movement complexity (Henry and Rogers 1960). One complication is that this poorer prect-

* The work reported m this paper forms part of the research programme supported by a grant from the Natlonal Fund for Research into Cnpphng Diseases (grant number 421700) Dr Bishop

was supported by a research studentship from the Social Science Research Council Both are

gratefully acknowledged

Requests for repnnts should be addressed to Dr A Harnson, Dept eif Commumty Medlcme and Behavioral Sciences, Faculty of Medlcme, Kuwait University, P 0 Box 24923, Kuwat

0167-9457/82/0000-0000/$02.75 0 1982 North-Holland

236 A. Bishop, A. Harmon / CRTs of srngle and dualjomted actrons

sion was largely restricted to wrist performance: as far as elbow positioning was concerned, this was just as accurate for dual as single jointed actions. No time limit was placed on beginning an action, and so angular inaccuracy may be a poor index of complexity: for per- formers could in theory compensate for additional demands by spend- ing longer programming actions and by adopting more sophisticated methods for detecting and correcting executional errors.

The question of whether incorporating more moving joints does indeed increase movement complexity and jeopardise accuracy, there- fore, remains unanswered. The present study investigated this issue by comparing the reaction times (latencies) of single and dual jointed movements: the rationale being that the more complicated an action is, the longer it should take to construct an appropriate motor program and commence movement. An essential assumption, as outlined by Henry and Rogers (1960) in their Memory-Drum theory of motor performance, is that movement does not begin until a sizeable propor- tion of the ‘assembly work’ involved in programming the action has been completed; for only if this is so, will latency reflect the complexity of the entire action. In terms of validity, latency measures of motor performance have an uneven record: sometimes confirming variables which intuitively should affect difficulty (e.g. amplitude (Klapp 1975), duration of switch closure (Klapp et al. 1974; Klapp and Wyatt 1976; Klapp 1977)), but failing to do so in other instances (e.g. movement extent (Glencross 1972, 1973; Largasse and Hayes 1973), force and reversal pattern (Glencross 1973)). Number of joints is a variable which Henry and Rogers (1960) predicted would affect movement complexity and latency, but as yet empirical confirmation is lacking.

Outline design

The present study contained two experiments. The first measured choice reactions times when a single and dual action were paired; whilst in the second, pairs of single and pairs of dual actions were set. A choice reaction time (CRT) paradigm was chosen because it has been assumed that this precludes any response preparation until the required action is identified, and so offers a better index of programming time than simple reaction time (Klapp et al. 1974).

The actions chosen were dual (elbow and wrist) and single (elbow)

A Bishop, A. Harrison / CRTs of single and dualjornted actlow 237

movements of the right arm, executed to the left and right. An initial problem was to find appropriate dual pairings (see fig. 1). If, for instance, flexions of the wrist and elbow are executed in a horizontal

elb’w joint

Fig. 1. Possible pairmgs of dual jointed actions.

plane (A), what is the appropriate partner? B is the mirror image of A but involves extension of both joints, C preserves wrist flexion but is topographically inconsistent. The problem was solved by rotating the wrist so that movement occurred in the vertical plane. The left dual action required flexion of the elbow and simultaneous straightening of the wrist (fig. 2), and the right dual action simultaneous extension of the elbow and straightening of the wrist. This solution has the added advantage that it minimises interference between joint movements, but

padded arm support

Fig. 2. Expenmental arrangement.

238 A Bishop, A Harmon / CRTs of s&e and dualyornted actrons

admttedly the resultant actions are somewhat artificial. The smgle actions consisted of flexions and extensions of the elbow executed with the wrist held rigid.

Reaction time measurement

Latency measurements were controlled on-line by a Nova 840 com- puter, using a specially written program running under RDOS. When the subject had adjusted his arm to the required starting posture (fig. 2), had fixated his gaze and was ready for testing, he pressed the start button. A variable foreperiod followed, consisting of one of five delays (800, 1200, 1600, 2400 or 3000 msecs) selected at random. Wrist and elbow angles were monitored throughout the foreperiod, and if move- ment (an angular shift greater than 1”) was detected, a ‘false start’ error was registered on the light box and the trial was restarted At the end of the foreperiod, wrist and elbow angles were measured. The light identi- fying the required action was then ht and latency measurement started using a milhsecond timer located within the computer. Joint angles were sampled 500 times per second, and movement was operationally defined as beginmng as soon as a 1” shift was detected; latency was computed on this basis. The same criteria were applied independently to both Joints in a dual action, and a separate RT for each was derived. Monitoring of Joint movements continued until a shift of 35” had been completed, and then checks followed to ensure that the action executed was appropriate. It was checked that movements were m the proper direction and that the correct Joints had been used. Further, for a smgle elbow action to be accepted, the wrist had to be held stationary (the criterion adopted, on the basis of observmg skilled performers, was an angular shift no greater than loo) For a dual movement to be accepted, the difference between wrist and elbow CRT had to be less than 50 msecs, and movements had to be completed within 130 msecs of each other. These last criteria were imposed m an attempt to exclude cases where simultaneous ~omt action was not planned: where wrist move- ment was added as an afterthought, or was a ‘passive’ consequence of elbow momentum. When invalid movements were detected, error feed- back was given using the display, and the trial was aborted. Testing was self-paced in that a subject took whatever time he needed to reposition his arm and prepare for the next trial.

A Bishop, A Harmon / CRTs of srngle and dualjointed actions 239

Apparatus

Joint movements were monitored goniometncally. Bourne 7335EA 2K5L wrrewound potentrometers (linear f 1”) fitted with one fixed and one movable shaft were placed so as to record faithfully changes in wrist and elbow posture, and then securely attached The voltage outputs from these goniometers were sampled every 2 msecs and drgttahsed using an A-D converter. Selected data were stored on a Nova 840 computer. Joint angles were measured to an accuracy of about l/3”. The arm was positioned (fig. 2) with the upper arm supported in a padded section of plastic guttering, with the elbow subtending an angle of about loo”, allowing roughly 70” of movement m either dn-ectron (flexion and extension). The wooden finger block was positioned so that the wrist was almost fully flexed and prone, and the forearm horizontal. The light display box was placed 1 metre in front of the subject, with the right bank of lights in hrs direct line of gaze The centre one of these provided a fixation pomt, and the lights above and below were used to rdentrfy which category of movement was required. The left bank of hghts provrded error feedback, drfferentratmg (I) false starts, (ii) movements m the wrong dnectron, and (m) movements with an incorrect time pattern.

Experiment 1: The reaction times of single and dual jointed actions tested in ‘mixed’ pairings

For each SubJect, the latencres of four types of action were measured: dual wrist and elbow movements to the left (DL) and nght (DR), and single elbow movements left (SL) and right (SR). All actions were executed with the right arm. Actions were presented m ‘mixed’ dual and single 2-CRT pan-mgs i.e. SL : DR and SR : DL

Method

Subjects The group comprised twelve right-handed subjects drawn from

amongst the staff and students of the Psychology Department, age range 19 to 38 years (median = 21 years).

240 A. Bishop, A. Harmon / CRTs of single and dualJouzted actrons

Procedure

1 A of the of recorded experiment 1.

Total number of (N =

Smgle-Jointed movements

Left fight Total

Dual-Janted movements

Left R&t Total

Dzrectzon errors First half of testing a) 1 8 9 3 6 9 Second half of testing b, 6 5 11 6 3 9

Total 7 13 20 9 9 18

Other errors First half of testing 24 30 54 40 29 69 Second half of testing 23 25 48 18 28 46

Total 41 55 102 58 57 115

s) Refers to the period during which the first 18 satisfactory reactron trmes were regtstered. b, Refers to the period durmg which the second 18 sattsfactory reactton ttmes were registered.

A. Btshop, A Harmon / CRTs of single and dualJornted actlons 241

Table 2 Total numbers of errors recorded for single and dual jointed actions, during the first and second halves of testing (expenment 1)

Total number of eriprs (N = 12 subjects)

Single-jointed actton Dual-jomted actron

1st half testing 63 78 2nd half testmg 59 55

Total 122 133

to produce of movement not meeting the criteria simultaneous movement of and wrist, or to lock the wrist The worry is dual and single actions are found to be differentially affected, for interpretation of is then problematic, of errors. the procedure used, periods were not necessarily xon matched pairs signed to the error scores

each subject. for single and did not differ significantly ( p > 0.05) either overall or when the 1st and 2nd halves were analysed separately; and so a latency comparison is valid.

Reaction terms Histograms of reaction times were negatively skewed, and so median

scores were computed for each subject. Latencies for the wrist and elbow components of dual actions were measured separately, and so a decision had to be made concerning how best to represent dual latency. Using the fastest in each case would bias the results, for the resultant

Table 3 Group choice reaction trmes (mean of medtans) for smgle and dual jointed actrons, recorded during the first and second halves of testing (experiment 1)

Choice reaction time (msec)

Single-jointed action Dual-jointed action

1st half testing 477 444 2nd half testing 460 453

242 A Bzshop, A Harmon / CRTs of srngle and dual]ornted actions

distribution of RT’s would have a lower mean than either the parent wrist or elbow distribution; even if smgle elbow, dual elbow and dual wrist had identical RT distributions, dual trials would emerge as bemg faster. To maxim&e comparability, it was decided to use the component common to all conditions i.e. elbow RT (table 3). Dual elbow latencies were 33 msecs shorter than single durmg the first half of testing, but this difference fell to 7 msecs in the second half. A 4-way analysis of variance was applied to the reaction time data. Condition order, direc- tion (left or right), movement type (smgle or duallomted), and stage of testing (1st and 2nd halves) were the mam factors declared. The only factor to reach significance was movement type (F (1, 10) = 6.613, p < 0.05); all interactions were non-significant (p > 0.05). The 1st and 2nd halves of testing were then analysed separately. During the first half, dual Jointed actions were significantly faster (F (1.10) = 9.865, p < 0.05); but not so m the second half (p > 0.05).

Dmxsslon

It is evident from the very high error rates that subjects found the criteria for acceptable dual and single actions very demanding. In the first half of testing, dual Jointed actions tended to be more prone to error, and it was at this stage that their CRT’s were significantly shorter than those of single actions. With the system of top-up trials used, the first halves of testing were not necessarily contemporaneous for the two movements; and so it could be argued that these shorter reaction times were the result of extra practrce. Such an explgnatron is not very convincing, however, for most subjects required less than 25 top-up trials, making the lag between the endings of the two first halves short. A more credible alternative is that subjects found the dual actions more difficult to execute initially, and so invested more attention in perform- ing them, hence their shorter latencies. In the second half, when single and dual actions error rates were equivalent, reaction time differences disappeared. Whatever the true explanation for the pattern of results seen, they offer no support for the prediction (Henry and that practised performers will take longer to mitiate actions because of their greater movement complexity.

Rogers 1960) dual Jointed

A Bzshop, A Harmon / CRTs of mgle and dual/ornted actions 243

Experiment 2: The reaction times of single and dual jointed actions tested in ‘matched’ pairings

Some msecunty m the interpretation of experrment 1 was felt because of the imbalance in error scores for dual and single actions. The present experiment sought to overcome this problem by presenting pairs of dual Jointed (DL : DR) and single Jointed (SL : SR) actions, so prevent- ing any trade-off m attention and preparation between single and dual actions.

Method

Subjects Twelve subjects were recruited, matched as far as possrble m terms of

age and sex to the group participatmg m experrment 1.

Procedure The procedure was identical to experiment 1, except for the move-

ment pairs used.

Table 4 A breakdown of the types of errors recorded m expenment 2

Total number of errors (N = 12 subjects)

Smgle-Jointed movements

Left R&t Total

Dual-Jomted movements

Left fight Total

Dtrectron errors

First half of a) testing 8 28 36 9 11 20

Second half of testmg b, 8 11 19 6 5 11

Total ‘16 39 45 15 16 31

Other errors

First half of testmg 22 13 35 31 64 95

Second half of testmg 12 2 14 28 48 76

Total 34 15 49 59 112 171

a) Refers to the penod dunng which the first 18 satisfactory reactlon times were regstered b, Refers to the penod dunng whxh the second 18 satisfactory reaction times were regstered

244 A. Bishop, A. Harmon / CRTs of srngle and dualjomted a&Ions

Table 5 Total numbers of errors recorded for single and dual Joined acttons, during the first and second halves of testing (expenment 2)

Total number of errors (N = 12 subJects)

Single-jointed action Dual-Jointed actton

1st half testing 11 115 2nd half testing 33 87

Total 104 202

Results

Errors The overall error rate at 15% was a little higher than in experiment 1.

28% of errors were directional, a higher proportion than before; whilst 72% involved movement pattern errors (table 4). As anticipated, the error rates for single jointed actions were lower than for dual (table 5); and Wilcoxon matched pairs signed ranks tests revealed a significant difference for the second half of testing (t = 7.5, n = 12, p < 0.05), but not for the first (p > 0.05). When the 1st and 2nd halves of testing were compared, a significant drop in error rate was found for single jointed actions (t = 3.0, n = 12, p < 0.05), but not for dual.

Reaction times The differences in latencies (table 6) were small compared with those

of experiment 1. In the first half of testing, dual jointed actions were 2 msecs slower, and in the second half 7 msecs faster. Analyses of variance were applied as in experiment 1; but no main factors or

Table 6 Group choice reactron trmes (mean of medians) for smgle and dual Jomted actrons, recorded during the first and second halves of testmg (expertment 2).

Choice reactron time (msec)

Smgle-Joined action Dual-Jointed actton

1st half testing 440 442 2nd half testing 435 428

A Bishop, A Harmon / CRTs of single and dual JoInted acttons 245

interactions reached significance. Despite a significant drop in error rate for single actions from the first to the second half of testing, there was no concomitant decrease in reaction time. It, therefore, seems reasonable to ignore error rate differences when comparing dual and single action latencies.

Dzscussion

Using ‘matched’ pairs did not eliminate error rate differences; but for the reasons outlined above, there seems little reason to worry that reaction times for single and dual actions were differentially affected. The present study clearly shows that practised performers can initiate dual jointed actions just as quickly as single jointed ones. Arguing on the basis of error scores, which were consistently higher for dual actions (though statistically significantly so only in the 2nd half of testing), there is some support for the notion that dual actions involve greater movement complexity. An important finding is that reaction time does not provide a reliable index of this complexity, which is what was also found in experiment 1.

A comparison of ‘mixed’ and ‘matched’ pair CRT’s

The mean reaction time for ‘mixed’ pairs was 459 msecs, whilst for ‘matched’ pairs it was 23 msecs faster (436 msecs). This suggests that when similar responses are paired, the initiation of a response is facilitated; an independent groups t-test, however, proved non-signifi- cant (t = 0.988, df = 22, p > 0.05).

Discussion

The above studies provide absolutely no support for the prediction (Henry and Rogers 1960) that dual jointed actions will have longer latencies than single actions because they are more complex and so take longer to programme. It is only proper to ask whether the movements selected offer a fair test of the hypothesis. Clearly in terms of overt movement, single actions are simpler, because they involve displace- ment of only one joint; however, in the present study both the elbow and wrist had to be controlled in order to satisfy the criteria set, and so

246 A Btshop, A Harmon / CRTs of srngle and dualjornted actrons

single Jointed actions were not necessarily any less demanding than dual ones. This constitutes a criticism of the original formulation which takes into account only the number of Joints moved, and ignores the fact that ehmmatmg unwanted activity and stabilismg relevant Joints are sometimes essential if the prime action is to be executed successfully and that these also consume processing capacity. If such factors are properly thought of as contributing to movement complexity, then the action with the largest number of moving Joints will not always be the more complex. Henry and Rogers state that as movement complexity increases “a larger amount of stored information will be needed and thus the neural impulses will require more time for co-ordmation and direction to the eventual motor neurons and muscles” (1960: 450). The modifications suggested are compatible with this statement, for factors such as inhibiting unwanted muscular activity, setting up appropriate antagonist breaking, and stabilismg Joint posture all involve neural activity.

The definition provided by Henry and Rogers is too vague to indicate precisely which factors should be considered when computing movement complexity, and what weightmg each should receive. In the past, when action parameters have been shown not to affect action latency, the tendency has been to dismiss them as factors in movement complexity. This assumes that an increase in movement complexity will inevitably lead to an increase m latency, which has yet to be proven. The present studies highlight tlns dilemma: in terms of errors, dual Jointed actions were the more complex, but then latencies were not sigmficantly prolonged. To adopt the position that other factors (such as those suggested above) must have been operating to equalise the complexity of the dual and single actions selected is to put greater credence on latency as an index of movement complexrty than on error; and yet there is no obvious Justification for doing so. One way of avoiding the circularity of a definition of movement complexity based on latency is to measure information content. Fitts adopted the follow- ing definition: “the minimum amount of information required to produce a movement having a particular average amplitude, plus or minus a specified tolerance (variable error) is proportional to the logarithm of the ratio of the tolerance to the possible amplitude range” (1954: 390). To use this approach, the required pattern of movement must be precisely defined, which can be very artificial; for some tasks can be perfectly adequately performed using a variety of different

A Bwhop, / CRTs of angle and dualJoInted actmns 241

movement patterns. Langolf et al. (1976) found that information processing rate fell as more joints were mcorporated into an aimed tapping task; unfortunately the correlation was with total movement time, not RT. Factors besides joint number can have an effect. Klapp (1975) showed that for actions requiring a fair degree of precision m the first few inches of movement, response complexity (m mformation terms) was predictive of latency; but when precision was not critical until later in the movement sequence, RT was independent of complex- ity. The explanation offered for the latter is that subjects initiate an action and only later set-up a mechanism for ensuring its accuracy. This suggests that Henry and Roger’s assumption that latency reflects the total quantity of programmmg to be done is too simplistic; for it is not only the number and types of events to be programmed which are important, but also their sequencing and time constraints.

The greatest success m linking action parameters and latency has come with simple RT paradigms, using relatively unpractised per- formers (Klapp et al. 1974). Norrie (1967) and Largasse and Hayes (1973) report instances where significant associations were found early m testing which disappeared once subjects became highly practised. This may indicate that as subjects become more slulful they radically alter their performance strategy or way of programmmg. They may, for example, switch to termmal correction of actions, rather than trying to keep movements on target from the begmnmg, which should reduce latency. Or they may lessen the work mvolved in constructmg motor programs by using larger units such as ‘subroutines’ (Bruner 1970; Connolly 1970) or efficient ‘co-ordinative structures’ (Turvey et al. 1978), and so shorten reaction time by effectively reducing program- ming complexity. This would be consistent with the findings of an earlier study (Harrison and Bishop 1982); the implication being that movement complexity for a given pattern of movement is not mvaria- ble.

The present study compared reaction times for ‘mixed’ and ‘matched response pairings. Though not significant, the trend was for latencies to be shorter for ‘matched’ responses. Further research is indicated, for if this difference can be substantiated, Klapp et al. (1974) are probably wrong in their belief that the use of a CRT paradigm prevents any motor programming before the required response is identified. It could well be that when alternative actions have suitable programming ele- ments m common, that these can be completed in advance, so reducmg

248 A. Bnhop, A Harmon / CRTs of single and dual Joanted acttons

the time needed to finish preparations and begin movement. Throughout this discussion, problems of interpretation have arisen

because of very basic ignorances concerning the nature of motor programs, how they are generated, and what stages are involved in translating a program into overt movement. What types of instructions do motor programs contain, and do elements comparable to computer program sub-routines exist? Can a person store, a complete motor program? Is there any procedure akin to normal compilation, when the high-level language computer program is translated into machine-code, and errors looked for? If there is, then it is reasonable to think that even when complete programs are called from store, that complex actions will be associated with longer latencies than simpler ones; but if there is no ‘compilation’ stage, reaction-time could be independent of complexity when stored programs are used.

In the present tasks, subjects were called upon to execute actions properly and minimise latency. There were no doubt many ways in which any one action could be performed and still meet the criteria set: and so part of the taskmanship for subjects was to experiment with different programming regimes, accuracy tolerances and correction strategies, and establish their impact on latency. If performers do indeed have the option of preparing common portions of alternative programs in advance, some may opt to minimise mean CRT for the task, rather than minimise CRT for each action independently.

For the many reasons detailed above, it is difficult to interpret confidently the data obtained, or be certain that the movements chosen should a priori differ in complexity. The results clearly show, however, that whilst the dual jointed movements set were more difficult to execute (in the sense that they were more prone to error), when people succeeded in meeting the performance criteria set, these movements took no longer to initiate than single jointed actions; which casts doubt on the utility of CRT as an index of movement complexity.

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