changing kinematics as a means of reducing vulnerability to physical attack

Changing Kinematics as a Means of Reducing Vulnerability to Physical Attack1

LUCY JOHN ST ON,^ STEPHEN M. HUDSON, MICHAEL J. RICHARDSON, REBEKAH E. GUNNS,

AND MEGAN GARNER Universily of Canterbury

Christchurch, New Zealand

Three experiments investigated whether women can change their walking style and hence reduce their vulnerability to physical attack. In Experiment I , women were videotaped walking normally and when imagining themselves in a situation of low personal safety. Women were rated as harder to attack in the low safety condition. Differences in walking style accounted for differences in ease-of-attack ratings. Experiment 2 compared walking styles and vulnerability of women before and after completing a self-defense course. No differences were seen across sessions. Experiment 3 investigated walking styles and vulnerability of women before and after completing individualized walking training pro- grams. Differences in vulnerability between sessions were revealed and could be accounted for by changes in walking-style features.

Recent research (Gunns, Johnston, & Hudson, 2001 ; Montepare & Zebrowitz- McArthur, 1988) has provided evidence for the assumed link between movement (specifically walking style) and vulnerability to physical attack (Grayson & Stein, 1981; Murzynski & Degelman, 1996). Using a point-light technique to isolate movement (Johansson, 1973), these experiments demonstrated that specific walking-style features (e.g., arm swing, hip movement) could predict ratings of ease of attack. That is, walking-style features could specify the vulnerability of walkers (both male and female). An obvious and socially important question that arises from this research is whether individuals can change their walking style and con- sequently lower their vulnerability to attack. The reported research investigates this question.

The specification of characteristics such as vulnerability from movement is consistent with the kinematic specification of dynamics (KSD) principle

'The authors thank Dean Owen for his valuable contributions to this research. This research was conducted with the financial assistance of University of Canterbury Research Committee Grant #116279.

'Correspondence concerning this article should be addressed to Lucy Johnston, Department of Psychology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. E-mail: luc [email protected]

51 4

Journal of Applied Social Psychology, 2004, 34, 3, pp. 51 4-537. Copyright 0 2004 by V. H. Winston & Son, Inc. All rights reserved.

CHANGING KINEMATICS 51 5

(Runeson & Frykholm, 1983) that states that the detailed spatio-temporal pattern of movement (the kinematics) specifies the underlying causes (the dynamics) of any event (Runeson & Frykholm, 1986). Thus, the kinematics (movement) of an event directly specify the dynamics that constrain and determine them. These &namic constraints refer to the dispositions that restrain an object’s movement, given its mechanical properties or anatomical makeup (e.g., movement limita- tions as a function of height and weight).

In the case of animate beings, these dispositions also include internal states, such as intentions and emotions (Runeson & Frykholm, 1983). According to the KSD principle, changes to kinematics are brought about through changes to the underlying dynamics of the movement. Changes to dynamics may occur as a result of either physical constraints (e.g., as a consequence of injury to a limb or through wearing restrictive clothing; Gunns et al., 2002) or changes to internal states (e.g., intentions). The present research investigates the impact of the intention to reduce vulnerability on gait and the consequent impact on vulnerability.

As any child who has attempted to fake a sprained ankle in order to avoid school can attest, it is not easy to effectively changes one’s movement style. Accurate replication of the kinematic pattern that would result from an actual sprained ankle is required. Any deviations from those kinematics, or inconsisten- cies in the kinematic pattern, are cues to the perceiver that the injury is not real and that the actor is attempting to deceive. When an individual attempts to deceive, there are two sets of dynamic constraints: one set a result of the individual’s inherent style of moving; and an additional, superimposed set a result of the individual’s attempt to deceive. Successful deception will occur only if the perceiver is not sensitive to the latter constraints and hence does not detect the actor’s deceptive intentions. The less dominant the second set of constraints, the harder it is for the perceiver to detect deceptive intention.

Experiments that isolate movement, using the point-light technique, have demonstrated the difficulty of successful deception. Perceivers were able to detect both the gender of actors who had attempted to walk as a member of the opposite gender and the true weight of boxes being lifted by actors who were attempting to convince the perceivers that the boxes were heavier than they actually were (Runeson & Frykholm, 1983). The actors’ kinematics revealed not only their true gender, or the true weight of the lifted boxes, but also their deceptive intentions. The kinematics of the actors did not sufficiently replicate those of members of the opposite gender, or of lifting heavier boxes, for perceivers to be misled.

To reduce their perceived vulnerability, individuals must adopt the walking style associated with low vulnerability. However, this new walking style must be smooth and consistent, or perceivers will be able to detect this attempt to mask a more vulnerable movement style. Work with stroke and multiple sclerosis patients has shown that specific training can lead to improved walking, suggesting a flexi- bility in walking style (Hesse et al., 1995; Lord, Wade, & Halligan, 1998).

51 6 JOHNSTON ET AL.

The present research investigates the extent to which specific training and practice result in changes to walking style, and hence vulnerability. Runeson and Frykholm’s (1 983) actors did not receive any training or advice on how to change their movement style in order to be convincing; they were simply asked to walk as if a member of the opposite gender or to lift boxes as if the boxes were heavier than they actually were. Recent research in our laboratory has demonstrated that changes to certain gait features (e.g., weight shift) are central to determining the success or failure of deceptive attempts (Richardson & Johnston, in press). Training that focuses on such critical features of walking style should increase the extent to which actors can effectively mislead perceivers.

Previous research has identified a prototypical low-vulnerability walking style (Grayson & Stein, 1981; Gunns et al., 2001). In Experiment 3, we investigate whether training that focused specifically on this walking style resulted in convincing movement changes and reduced vulnerability. The effectiveness of this approach in reducing vulnerability was compared with that of attendance at a self-defense course endorsed by the local city council (Experiment 2). One of the stated aims of this self-defense course is to reduce vulnerability to attack, although the course does not identify changing walking style as a means of achieving this. Specific advice about movement patterns in order to reduce vulnerability is not provided.

The present studies allowed participants to practice, and to become comfort- able with, their new movement style, in contrast to previous research that has given actors very little practice prior to videotaping (Richardson & Johnston, 2001; Runeson & Frykholm, 1983). Both the self-defense course and the individualized training course ran over a period of 4 weeks; the former lasting for 2 hr each week, and the latter for 1 hr. Follow-up tests were also completed 1 week and 1 month after the end of both the self-defense and the training courses to investigate the persistence of any changes in walking style.

We also considered the possibility of spontaneous changes to walking style, and hence vulnerability, as a function of situational cues. Some situations are safer or are perceived to be safer than others. For example, visitors to many cities are advised not to walk through narrow streets or inner-city parks alone at night. Finding oneself in such situations is likely to make one’s potential vulnerability salient. We investigate whether evoking a situation that increases the salience of safety, or lack thereof, leads walkers to spontaneously change their walking style. The impact of any changes on judgments of ease of attack is also assessed. Any change in walking style under such conditions would suggest that walkers themselves assume that there is a link between walking style and vulnerability. However, it is important to consider whether such spontaneous changes to walking style are adaptive changes; that is, changes that do indeed lead to reduced vulnerability.

CHANGING KINEMATICS 517

Experiment 1

Overview

Female participants were videotaped walking across a darkened room. They were first asked to walk normally and then to walk as if they were walking through an inner-city park alone late at night. Each walk was coded according to a number of walking-style features. Each walk was also rated by male and female perceivers according to how easy the walker would be to attack. Walkers also were categorized according to whether or not they had ever completed a self- defense course. Comparisons between those who had and had not completed a course were made on ease-of-attack ratings and on walking-style features.

Method

Part I : Mdeotaping

Participants. Seventy-nine women volunteered to participate in return for payment. The women were aged 13 to 45 years ( M = 21 years, 2 months), were between 1.54 and 1.85 meters in height ( M = 1.66 m), weighed between 44.0 and 99.5 kg ( M = 64.0 kg), and were predominantly of European origin (New Zealand European, n = 78; Asian, n = 1). The women were categorized into three groups: those who had just completed a targeted self-defense course (course; n =

20), those who had never participated in a self-defense course (none; n = 44), and those who had completed a self-defense course of at least 6 hr duration at least 6 months prior to this study (previous; n = 15).3

Apparatus. The videotaping apparatus was set up in an experimental room. Black sheeting was fixed to one wall and spread out across the floor. All windows were fully blacked out. A Panasonic video camera, WV-3085, was positioned approximately 4.5 m from the participants. The camera was fixed in position on a tripod and did not pan to follow the participants. It was located off-center, approximately 1 m from the right-hand side of the black sheeting. The camera lens was 1.5 m from the floor. A spotlight was mounted adjacent to the camera (25 cm from the camera lens) facing the walking area. The images were viewed on a Panasonic 29-in. (74-cm) television monitor.

31n additional 18 women were videotaped, but were not included in the analysis. These women had not participated in a self-defense course, but had participated in martial-arts training (kickboxing, judo, karate, zen do kai, kung fu, aikado, ninjitzu, tae kwon do) for at least I month. Since martial-arts training often involves specific movement training, it was difficult to classify these women in the none category, but equally they did not fit neatly into either of the self-defense categories. Analysis of data from this group showed a similar pattern of results to the course group. Full details of this analysis can be obtained &om the first author.

51 8 JOHNSTON ET AL.

Figure I . Still frame of a walker showing the point-lights at the toes, ankles, knees, hips, wrists, elbows, and shoulders.

The point-light technique (Johansson, 1973) was employed in filming. Indi- viduals were videotaped wearing tight-fitting black clothes. The black color of the clothing minimizes reflection, and its tight-fitting nature minimizes any vari- ations in movement as a result of clothing type. Close-fitting LycraO allows the movement of the individual’s body, rather than the independent movement of the clothes, to be viewed. Reflectors were attached to the principal joints and limb extremities of the individuals, and when the video was played back (with the contrast maximized and the brightness minimized), only a configuration of bright lights moving against a dark background was visible. Only movement is visible to the perceiver. Using this technique, movement is separated from body shape, clothing, and attractiveness. Therefore, the impact of movement alone on perception can be investigated without any possible confound.

Procedure. Female participants were recruited by advertising around the university campus and from a self-defense course that was under way at one of the university residence halls. Participants were informed that the aim of the study was to investigate links between walking style and vulnerability to attack. The women were told that they would be required to change into tight-fitting black LycraO clothing and walk across a room a number of times while being videotaped.

The women were guaranteed anonymity. It was stressed that there was no way they would be identifiable in the videotape segments; that only the moving light patches attached to their bodies would be visible, as illustrated in Figure 1.


Each participant was shown a video clip of one of the experimenters walking across the room in this manner, to demonstrate the complete inability to recog- nize individuals from the videotape.

Participants were asked their age, height, weight, ethnicity, and whether they currently or previously had participated in any self-defense courses. They changed into the clothing provided: skivvy (a tight-fitting, long-sleeved, high- neck top), leggings, socks, gloves, and a balaclava (a woolen mask covering the head, face, and neck, with small holes for the eyes, nostrils and mouth). Reflec- tive tape cut into 40-mm-diameter circles was attached to participants’ joints by the experimenter, on the outside of joints on the left-hand side of the body, and the inside of joints on the right-hand side of the body. The experimenter affixed 12 reflective tape circles to each participant’s moving joints (shoulder, elbows, hip, knees, wrists, and ankles) and limb extremities (toes).

Participants were instructed to walk as naturally as possible, back and forth across the black sheeting, four times. After a practice walk, walkers were informed that videotaping would begin. Participants were videotaped from a side view only. Both head and feet were in the camera shot at all times. Participants were then asked to repeat the task while imagining that they were walking alone late at night through Hagley Park (a large, local inner-city park). Pilot testing indicated that walkers, both male and female, thought that their vulnerability would be both increased and more salient to them when walking through the park late at night alone than when walking alone during the day. Participants were again videotaped walking across the room four times. After videotaping was completed, participants were paid and thanked for their participation.

Editing. Each walker’s first right-to-left cross in each condition and all of their left-to-right returns were edited out. As a result, the edited version showed each woman walking three times across the screen from right to left in each condition. Walker numbers and a 5-s space were edited into the tape between each set of walks. A unique walker number was given to each walker in each condition; hence, there were twice as many walker numbers as there were individuals.

Part 2: Ratings

Participants. Participants were 15 males and I 5 females who had not participated in the videotaping phase of the experiment. Participants volunteered in return for payment of $5.

Procedure. Participants were tested individually or in pairs of the same gender. The participants sat at a small table in the laboratory, approximately 2.5 m from a 29-in. (74-cm) Panasonic television monitor, All participants read an information sheet that explained that the current study was investigating links between walking style and vulnerability to attack. They were informed that they would be required to watch a videotape of clips of female walkers and rate each

520 JOHNSTON ET AL.

according to how easy or difficult they thought she would be to physically attack on a 10-point scale ranging from 1 (very easy) to 10 (very difficutt). It was emphasized that the study was concerned with how easy these women would be to attack, and not the likelihood that participants would actually attack any of them.

Participants were informed that there were no right or wrong answers, and that all judgments were equally valid. They were asked to make instinctive and immediate judgments as much as possible. The raters were not told that each walker appeared twice on the videotape or that there were two conditions (normal, park) under which the walkers were videotaped.

Once participants felt familiar with the scale, the lights were turned off and the videotape was played with the contrast turned up and the brightness turned down, so that only the point-lights were visible on the display. After completion of the ratings, participants were fully debriefed, paid, and thanked for their participation.

Results and Discussion

For ease of comprehension, the ease-of-attack ratings were reversed so that higher scores represent greater ease of attack. The focus of this study is on whether walking-style or ease-of-attack ratings differ as a function of situation (normal vs. park) or walker type (course, none, previous). Prior to conducting that analysis, preliminary analyses were conducted on the ability of walking-style features to predict ease-of-attack ratings, to ensure comparability with previous research in this domain.

Preliminary Analyses: Predicting Ease of Attach?

Each of the walking clips was coded on eight kinematic features of walking style (Laban, 1972; Laban & Lawrence, 1967): weight shift (primarily lateral, side-to-side motion; three-dimensional, smooth motion involving the whole body centered around the hips; primarily up-and-down motion; or primarily forward- and-back motion); type of walk (postural motion activating the whole body or gestural motion activating only a part of the body); use of the whole body; foot movement, which was rated on a 5-point scale ranging from 1 (swung, heel- to-toe motion) to 5 (lifted, the whole foot being raised and lowered as a unit); stride length relative to height, which was rated on a 5-point scale ranging from

4Full details of the preliminary analyses and of the separate analyses for each experimental condition can be obtained from the first author. Some caution should be exercised when considering the regression analyses for individual conditions in each experiment as participant numbers are low such that the independent variabkdependent variable ratio in the regression analyses is lower than desir- able.


1 (short) to 5 (long); arm swing, which was rated on a 5-point scale ranging from 1 (none) to 5 (very much); energy, which was rated on a 5-point scale ranging from 1 (none) to 5 (very much); and constraint, which was rated on a 5-point scale ranging from 1 (none) to 5 (very much). These walking-style features were then entered as predictor variables into a regression analysis, with ease-of-attack ratings as the dependent variable. The regression was significant, F(7, 143) =

78.73, p < .00001, and accounted for 78.4% of the variance in ease-of-attack ratings. Five features-stride length (p = -.20), (143) = - 4 . 1 8 , ~ < .0001; type of walk (p = -.09), (143) = - 2 . 2 2 , ~ < .05; use of the whole body (a = -.17), t(143) =

- 4 . 1 3 , ~ < .0001; energy (p = -.63), t(143) = -14 .06 ,~ < .0001; and constraint (p =

.lo), t(143) = 2.09, p < .05-predicted ratings of ease of attack. Shorter stride lengths, less energy, greater constraint, a gestural walk, and the non-use of the whole body resulted in higher ratings of ease of attack. Separate regression analyses conducted for each experimental condition were significant and accounted for between 67% and 83% of the variance in ease-of-attack ratings. Energy was the only feature that predicted ease-of-attack ratings in each condition.

Consistent with predictions and with previous research, differences in walking style explained a large amount of the variance in ease-of-attack ratings. Spe- cific features of walking style were related to ease-of-attack ratings. The pattern of relationships between walking-style features and ease-of-attack ratings was similar to that reported in previous research (Grayson & Stein, 1981; Gums et al., 2002).

Impact of Condition and p p e of Walker

A 3 x 2 (Walker: CourseDIonePrevious x Condition: NormalPark) ANOVA with repeated measures on the second factor on participants’ ratings of ease of attack reveals a main effect of condition, F(1, 76) = 42.14, p < .0001 (R2 = .35), that was qualified by a significant interaction between walker and condition, F(2, 76) = 3.67, p < .05 (R2 = .09). Post hoc analysis (Tukey, p < .05) reveals that walkers who had never completed a self-defense course (or who had completed one at least 6 months previously) were each rated as easier to attack in the normal condition than in the park condition (none, M= 5.99 vs. 5.25; previous, M = 6.19 vs. 5.08), but walkers who had just completed the targeted self-defense course were rated as equally difficult to attack in the normal and park conditions (A4 = 5.53 vs. 5.23). For the normal walk, the course walkers were rated as harder to attack than either the none or previous walkers ( M = 5.53 vs. 5.99 and 6.19). For the park walk, there was no difference between walkers in the ratings of ease of attack (M= 5.23, 5.25, and 5.08).

Both situational factors and the completion of self-defense courses affected ratings of ease of attack. Under normal walking conditions, those walkers who had recently completed a self-defense course were rated as harder to attack than

522 JOHNSTON ET AL.

walkers who had never completed a self-defense course or who had done so at some previous time. For those walkers who had attended a recent course, there was also no difference between ratings of ease of attack in the normal and park conditions. Attendance at the self-defense course did, then, result in lower vulnerability, but only under the normal walking condition.

There was no impact of self-defense course attendance in the park condition; all the walkers were rated as equally difficult to attack in this condition. Walkers who had never completed a self-defense course or who had done so at some time previously were rated as harder to attack in this condition than in the normal walk condition. A Spearman rank correlation between the normal and park conditions for ease-of-attack ratings was significant, indicating that those walkers who were rated as easiest to attack in the normal walking condition were also rated as easiest to attack in the park condition (overall, r = .58,p < .001; none, r =

.62,p < .01; previous, r = S 3 , p < .05; course, r = .54,p < .Ol ) . Changing situational factors reduced the vulnerability of the walkers, but had

little impact on the relative vulnerability within the group of walkers, an effect similar to changing the constraints on gait through clothing and footwear varia- tions (Gunns et al., 2002). Since the perceivers were not aware that there were two walking conditions and that each walker appeared twice on the videotape, the difference in ratings between the normal and park conditions is unlikely to be a result of perceivers differentiating between conditions for each walker. The analysis in this article investigates whether this reduction in vulnerability in the park situation was a function of changes to walking-style features.

Walking Style as a Function of Condition

Walking-style features were compared across the normal and park conditions, and whether differences in walking-style features could explain differences in ease-of-attack ratings across those conditions was investigated. For each of the walking-style features that were rated on a 5-point scale (stride length, foot movement, arm swing, energy, constraint), single-factor ANOVAs (condition: normal/park) were computed. There were significant effects of condition for arm swing,F(1,76)=78.17,~< .01 (R2= .51; M=2.74vs. 3.02fornormalandpark conditions, respectively), and for energy, F( 1,76) = 6 0 . 6 0 , ~ < .01 (R2 = .44 ; M = 2.74 vs. 3.37), and a marginally significant effect of stride length, F( 1, 76) = 2 . 2 1 , ~ = .14 (R* = .03; M = 2.99 vs. 3.07). These findings indicate that, as predicted, there were some differences in walking style across conditions. In the park conditions, the women walked with more energy, greater arm swing, and longer stride lengths than in the normal condition.

Difference scores between the normal and the park conditions were calculated for each walker for each walking-style feature and for the ease-of-attack ratings. A multiple regression analysis was conducted in order to determine


whether differences in walking-style features predicted differences in ease- of-attack ratings. Regressions were conducted across all the walkers and sepa- rateIy for each type of walker. The overall regression analysis was significant, F(5, 73) = 34.23, p < .0001, and accounted for 68.05% of the variance in the ease-of-attack difference scores. Four features-differences in stride length (J3 =

-.28), 473) = 3 . 9 3 , ~ < .0001; differences in arm swing (p = -.28), 473) = 3.72, p < .0001; differences in energy (J3 = -.SO), t(73) = 7 . 1 8 , ~ < .0001; and differences in constraint (p = . l s), t(73) = -2.07, p < .0S-predicted differences in ratings of ease of attack across conditions. The more walkers lengthened their stride, increased their arm swing, increased their energy levels, and reduced their constraint in the park walk compared to the normal walk, the more difficult to attack they were rated in the park compared to the normal condition. The separate regression analyses conducted for each walker type were all significant and accounted for between 55% and 93% of the variance in differences in ease-of- attack ratings. A difference in energy level was independently predictive of ease of attack in all conditions.

The results of Experiment 1 indicate that vulnerability and walking style varied as a function of experimental situation and completion of a self-defense course. Walkers were rated as harder to attack in the park than in the normal walking condition, unless they had just completed a self-defense course, and this difference in ease-of-attack ratings could be explained largely by differences in walking-style features between these conditions. This suggests that walkers are aware of an association between walking style and vulnerability, and hence when vulnerability is made salient through environmental cues, walking style is adjusted. Furthermore, the changes made to walking style were adaptive; the walkers adopted walking-style features associated with low vulnerability. In turn, walkers in these conditions were rated as relatively harder to attack. It appears that when vulnerability is salient, walkers can successfully adapt their walking style in order to appear less vulnerable. However, these changes in walking style were not necessarily conscious. Previous research has shown individuals to be unable to name movement features indicative of high or low vulnerability to attack (Grayson & Stein, 2000; Gunns, 1998). This study offers encouragement for attempts to reduce vulnerability to attack. It is possible that walkers do not necessarily have to be taught completely new walking styles. Rather, they have to be encouraged to adopt already available low-vulnerability walking styles,

Recent completion of a self-defense course resulted in lower vulnerability ratings under normal walking conditions, compared to walkers who had never completed a self-defense course or who had done so some time in the past. There was also no difference in ease-of-attack ratings for these walkers between the normal and park walking conditions. Before concluding that self-defense courses are successful in reducing vulnerability to attack, two caveats to the present findings should be noted. First, the walker groups in this experiment were self-selected. It

524 JOHNSTON ET AL.

is possible that attendance at a self-defense course was not the only difference between the groups, such that differences in vulnerability may not be attributed solely to attendance or not at the self-defense course. Second, attendance at a self-defense course did not appear to be an effective long-term strategy for reducing vulnerability under normal walking conditions. Walkers who had completed a self-defense course at least 6 months previously were rated, under normal walking conditions, as equally easy to attack as those walkers who had never completed such a course, and as easier to attack than those who had just completed the self-defense course. However, the targeted course and those courses attended by the walkers in the previous condition also may have differed in focus and approach, which could explain differences in their impact on vulnerability. Experiment 2 investigates further the impact of attendance at a self-defense course on both walking style and vulnerability.

Experiment 2

Overview

In Experiment 2, we paid for women who had never attended a self-defense course to attend a course of the same duration, run by the same instructor, as participants in the course condition in Experiment 1. These women were videotaped immediately before the first self-defense session and immediately after the final session, and comparisons between walking-style features and ratings of ease of attack were made. The ability of any changes in walking style to predict changes in ratings of ease of attack was investigated. In addition, to investigate persistence effects, each walker was videotaped 1 week and 1 month after the final session.

Method

Purt 1: yideotuping

Participants. Two attempts were needed to recruit participants for this study. Initially, women in the none condition of Experiment 1 who had high ratings for ease of attack in the normal walking condition were approached and asked to participate. Only 2 women of the 6 who agreed to participate completed three or more of the four sessions in the self-defense course. Neither of these women returned for the follow-up videotaping.

The second recruitment involved approaching women who had signed up for the self-defense course being run at the University Recreation Centre. Of the 9 women attending the course, 7 agreed to participate in the experiment (and hence had their course fees refunded). Of these 7 women, 5 completed all four of the self-defense sessions and returned for each of the follow-up videotaping sessions. Data are presented only from these 5 women. The women were aged 18 to 25


years ( M = 21 years), were between 1.65 and 1.73 m in height ( M = 1.69 m), weighed between 56.5 and 68.5 kg ( M = 62.1 kg), and were all of European origin.

Apparatus. The videotaping set-up was the same as for Experiment 1. Procedure. The procedure for videotaping followed that for Experiment 1.

Each woman completed four separate videotaping sessions (before course, after course, 1 week later, 1 month later). As the number of walkers involved in Exper- iments 2 was small, a single videotape containing all the walkers from Experi- ments 2 and 3, along with some fillers, was used for coding walking-style features and ratings of ease of attack. For ease of comprehension, however, the impact of the self-defense course (Experiment 2) and the individualized training (Experiment 3) are presented as two separate experiments. Direct comparisons are made between the two types of training after the results of Experiment 3 are reported.

Editing. As in Experiment 1, each walker’s first right-to-left cross in front of the camera in each condition and all of the walkers’ left-to-right returns were edited out. The edited version showed each woman walking three times across the screen from right to left in each of the experimental conditions. Walker numbers and a 5-s space were edited into the tape between each set of walks.

A videotape was made, comprised of 40 video clips from this experiment (each walker in the normal and park conditions in each of the four videotaping sessions), 40 video clips from Experiment 3 (each walker in the normal and park conditions in each of the four videotaping sessions), and 10 fillers from the none condition of Experiment 1 ( 5 walkers each walking under normal and park conditions). Four versions of the videotape were made, with the order of the video clips randomly assigned in each version to avoid order effects.

Part 2: Ratings

Participants. Twenty-five male and 26 female participants who had not participated in any other stage of this research volunteered to participate in return for payment of $5.

Procedure. The procedure followed that of Experiment 1. The raters were not told that each walker appeared more than once on the videotape.


For ease of comprehension, the ease-of-attack ratings were again reversed so that higher scores represent greater ease of attack.

Preliminary Analyses: Predicting Ease of Attack

Each of the walking clips was coded on the same eight kinematic features of walking style as in Experiment 1. These walking-style features were then entered

526 JOHNSTON ET AL.

as predictor variables into a regression analysis with ease-of-attack ratings as the dependent variable. The overall regression analysis was significant, F(3, 36) =

22.81, p < .0001, and accounted for 62.7% of the variance in ease-of-attack ratings. Arm swing (p = -.41), t(36) = -4.03, p < .001, and energy (p = -.59), (36) =

- 5 . 8 7 , ~ < .0001, predicted ratings of ease of attack. The less walkers swung their arms and the less energy in their walk, the easier to attack they were considered to be. Consistent with our previous research, the results from Experiment 2 show a relationship between walking-style features and vulnerability.

Impact of Self-Defense Training

A 4 x 2 (Session: Before/After/l WeeWl Month x Condition: NormaUPark) within-subjects ANOVA was conducted on ratings of ease of attack. Surprisingly, there were no significant effects of either session or condition. Unlike in Experi- ment 1, walkers were not judged to be significantly harder to attack in the park than in the normal walking condition, although means were in the predicted direction ( M = 5.48 vs. 5.75). In Experiment 1, walkers who had completed the self-defense course were rated as harder to attack in the normal walking condition than walkers who had not completed the course. The results of Experiment 2 suggest that this difference was not solely a function of completing the self- defense course since ease-of-attack ratings did not differ before and after the course for these walkers. A planned comparison between the pre- and post- course ratings in the normal walk condition was also not significant. Closer inspection of the mean ease-of-attack ratings did reveal that for 3 of the 5 walkers, ease-of-attack ratings under normal walking conditions were higher immediately after completion of the course than prior to beginning the course. We investigated whether these small differences in vulnerability were a function of differences in walking style across session and condition.

Walking Style as a Function of Session and Condition

For each of the walking-style features that were rated on a 5-point scale (stride length, foot movement, arm swing, energy, constraint), a 4 x 2 (Session: Before/ After/l WeeW1 Month x Condition: NormaUPark) within-subjects ANOVA was computed. The means are presented in Table 1. There were no significant effects for any of the walking-style features. A number of means were in the predicted direction, but the differences between conditions were very small. Similarly, for the categorical walking-style features (weight shift, type of walk, whole body), there were no differences in the frequency of walkers in each category as a function of condition or type of walker. The lack of difference in walking style and ease-of-attack ratings across conditions meant that it was not possible to compute the planned analyses of whether differences in walking style predicted differences in vulnerability as a function of session.

Tabl

e I

Mea

n Sc

ores

for

Wal

king

-Sty

le F

eatu

res

as a

Fun

ctio

n of

sess

ion

and

Con

ditio

n: E

xper

imen

ts 2

and

3

Sess

ion

Bef

ore

Afte

r 1

Wee

k 1 M

onth

Con

ditio

n N

orm

al

Park

N

orm

al

Park

N

orm

al

Park

N

orm

al

Park

Strid

e le

ngth

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528 JOHNSTON ET AL.

The results of Experiment 1 led us to predict that attendance at a self-defense course would lead to lower ratings of ease of attack, at least under normal walking conditions. The results of Experiment 2 did not, however, support this prediction. There were no differences in ratings of ease of attack before and after attendance at the self-defense course, although the means were in the predicted direction. Similarly, there were no differences in the coded walking-style features before and after completion of the self-defense course. It is unclear why participants in Experiments 1 and 2 showed a different pattern of results. As in Experiment 1, participants in the self-defense course were self-selected. Their pre-course ratings of ease of attack were already relatively low ( M = 5.79), leaving little room for reduction as a result of the course. It is possible that the impact of a self-defense course may be greater for those with initially high ease-of-attack ratings.

Experiment 3

Ovewiew

In Experiment 3, women received individual training sessions that focused on specific walking-style features. Changes in walking-style features and in ratings of ease of attack as a function of this training and persistence across time were again considered.

Method

Part I : Edeotaping

Participants. Five women were approached to participate in return for payment of $32. These women were selected from the none condition of Experiment 1 on the basis of their relatively high mean ease-of-attack ratings under normal walking conditions. Those approached had high ease-of-attack ratings in the none condition ( M = 7. I2), indicating that they were among the easiest watkers to attack. The women were aged 18 to 22 years ( M = 20 years), were between 1.54 and 1.79 m in height (A4 = 1.65 m), weighed between 58 and 99.5 kg (A4 =

70.4 kg), and were all of European origin. The women attended an hour-long individual training session each week with one of the researchers5 for 4 consecu- tive weeks.

Apparatus. The videotaping setup was the same as for Experiments 1 and 2. Procedure. The procedure for videotaping followed that for Experiments 1

and 2. Since the women had already been videotaped as part of Experiment 1, they were not videotaped prior to the first training session. They were videotaped immediately after the final training session, 1 week and 1 month later.

5Megan Gamer.


The training sessions with each walker followed a standard format, although the specific walking-style features on which the training focused were different for each walker. Training involved a combination of observational learning and guided practice. The first session was primarily a video-based session in which features of the walker’s present walking style were identified. The experimenter demonstrated to the walker each of the walking-style features that had been coded and explained the score they had received for each feature. In doing so, the experimenter showed the walkers video clips of walkers who were rated as especially hard to attack and differences between the walking styles of these women and their own walks were illustrated.

To ensure the anonymity of the low-vulnerability walkers, the videotapes were shown in point-light. This may have assisted our participants’ learning. Recent research has shown that unfamiliar dance movements are more accurately replicated after being viewed in point-light than under normal viewing conditions (Scully & Carnegie, 1998).

For 3 of the 5 walkers involved in the training, their park walks in Experiment 1 received lower mean ratings for ease of attack than did their normal walks. For these women, comparisons were made between walking-style features in the normal and park walks, and positive changes in walking styles associated with lower vulnerability were highlighted. Each walker was given a prepared training sheet that, for each of the coded walking-style features, detailed their current movement type, the ideal movement type for this feature, and the method of training to be used. The second training session involved guided training and practice in each of the individual walking-style features. The third and fourth sessions involved a revision of each individual movement feature, followed by guided training and practice combining all the movement features into a fluid walking style. An overview of the training schedule is in the Appendix. Participants were videotaped at the end of the fourth training session, 1 week and 1 month after that session.

Part 2: Ratings

The video clips were rated by the same participants, in the same experimental session as in Experiment 2 .


For ease of comprehension, the ease-of-attack ratings were again reversed so that higher scores represent greater ease of attack.

Preliminary Analyses: Predicting Ease of Attack

Each walking clip was coded on eight kinematic features of walking style as detailed in Experiment 2. These walking-style features were entered as predictor variables into a regression analysis with ease-of-attack ratings as the dependent

530 JOHNSTON ET AL.

-+- Walker 1 - Walker2

--C Walker 3

* Walker4

+ Walker5

34 1 T -1.- -- I

Before After 1 Week 1 Month Session

Figure 2. Ease-of-attack ratings as a function of session, condition, and walker (Experiment 3).

variable. The overall regression analysis was significant, F(6, 42) = 33.47, p < .000 I , and accounted for 80.23% of the variance in ease-of-attack ratings. Three features-type of walk (p = -.31), t(42) = -3.47, p < .001; use of whole body (p = -.24), t(42) = -2.26, p < .05; and energy (p = -.43), t(42) = -3.59, p < .001- predicted ratings of ease of attack. Walkers with a gestural walk, who did not use their whole body when walking and who had little energy in their walk, were rated as easier to attack.

Impact of Movement Training

A 4 x 2 (Session: Before/After/l WeeWl Month x Condition: Normal/Park) repeated-measures ANOVA was conducted on participants’ ratings of ease of attack. There was a main effect of session, F(3, 12) = 2 9 . 0 6 , ~ < .0001 (R2 = 38). Post hoc analysis (Tukey, p < .05) reveals that walkers were rated as easier to attack before training than in each of the other sessions, which did not differ from one another ( M = 7.38 vs. 4.73,4.96, and 4.87). This effect is shown in Figure 2, for each individual walker. The same pattern of results was seen for each walker. There was also a significant effect of condition, F( 1,4) = 9.65, p < .05 (R2 = .7 I). Walkers were rated as easier to attack in the normal condition than in the park condition ( M = 5.73 vs. 5.25).

Ease-of-attack ratings varied as a function of session and experimental condition. Ratings were lower after training than before training, and this lower vulnerability rating persisted until the videotaping session 1 month after completion of the training. Overall, walkers were rated as harder to attack in the park condition than in the normal walking conditions, as in Experiment 1.


Walking Style as a Function of Condition andsession

For each of the walking-style features that were rated on a 5-point scale (stride length, foot movement, arm swing, energy, constraint), a 4 x 2 (Session: Before/After/l Week/] Month x Condition: Normal/Park) within-subjects ANOVA was computed. The means are presented in Table 1.

There was a significant effect of session for four of the walking-style features: stride, F(3, 12) = 9.32, p < .0001 (R2 = .70); arm swing, F(3, 12) = 32.19, p < .0001 (R2 = 39); energy, F(3, 12) = 2 3 . 8 5 , ~ < .0001 (R2 = 36); and constraint, F(3, 12) = 7 . 2 4 , ~ < .01 (@ = .64). For each of these four walking-style features, post hoc tests (Tukey, p < .05) reveal that scores in the before session were significantly different from those in the other three sessions, which did not differ from one another (stride: M = 2.33 vs. 3.47,3.07, and 3.13; arm swing: M = 1.87 vs. 3.53, 3.27, and 3.43; energy: M = 2.23 vs. 3.50, 3.23, and 3.37; constraint: M = 3.57 vs. 3.13, 3.10, and 2.87). Walkers had longer stride lengths, more arm swing, more energy, and less constraint in their walking style after training than beforehand.

Small numbers of walkers in each cell prevented meaningful analyses being conducted on the categorical walking-style features. It is worth noting, however, that for whole body movement before training, 9 of the 10 walks (2 for each walker: 1 normal walk and 1 park walk) involved mostly lower body movement, but after training (immediately, 1 week, and 1 month after training), all of the walks involved moving the body as one, the style previously associated with the lowest vulnerability.

These findings indicate that there were differences in the walking styles adopted across sessions. Difference scores were calculated for each walker for each walking-style feature and for ease-of-attack ratings to investigate whether these differences in walking style influenced ratings of ease of attack. For each walker, six sets of difference scores were calculated: between the before and after training scores, between the before and 1 week scores, and between the before and 1 month scores for both the normal and the park walks. As there were no differences between the after, 1 week, and 1 month sessions on ratings of any of the walking-style features or ease of attack, difference scores were not calculated between these sessions. Since walker numbers (n = 5) were small, the analyses were conducted across all six sets of comparisons (n = 30), rather than separately as a function of session and condition.

Pearson product-moment correlations reveal that differences in each of the walking-style features, except constraint, were significantly correlated (p < .O 1) with differences in ease-of-attack ratings (stride, r = .64; foot swing, r = -.42; arm swing, r = .72; energy, r = 33). A multiple regression analysis was conducted in order to determine whether differences in walking-style features before and after training predicted differences in ease-of-attack ratings between these sessions.

532 JOHNSTON ET AL.

Table 2

Mean Ease-of-Attack Ratings as a Function of Training Type and Session: Experiments 2 and 3

Session Before After 1 Week 1 Month

Self-defense 5.79 5.60 5.59 5.44 Training 7.38 4.73 4.90 4.87

The overall regression analysis was significant, F(5, 24) = 14.02, p < .0001, and accounted for 69.2% of the variance in ease-of-attack difference scores. Four features-differences in stride length (p = -.41), t(24) = -2.42, p .05; differences in foot swing (p = -.32), t(24) = - 2 . 9 4 , ~ < .01; differences in arm swing (p = -.81), t(24j = 4.59, p < .0001; and differences in constraint (p = .25), t(24) = - 2 . 0 1 , ~ < .06-predicted differences in ratings of ease of attack across conditions. The more walkers lengthened their strides, increased their foot and arm swings, and reduced their constraint after training, the harder to attack they were rated.

The results of Experiment 3 indicate that individual training can result in changes in walking-style features, which, in turn, predict changes in ease- of-attack ratings. In addition, these changes were shown to persist over at least a 1 -month period, although this persistence may have been enhanced by situational factors, as the walkers returned to the same situation for the follow-up videotaping, conducted by the same researcher.

Comparisons Between Types of Training: Experiments 2 and 3

Ease-of-attack ratings and walking-style features were compared across types of training, using 2 x 4 x 2 (Training: Self-Defense/Walking Training x Session: Before/After/l Week/l Month x Walk: NorrnaUPark) ANOVAs, with repeated measures on the second and third factors.

For ease-of-attack ratings, there was a significant training by session interaction, F(2,24j = 1 4 . 7 2 , ~ < .0001, R2 = .55, shown in Table 2. Post hoc analyses reveal that participants in the walking training condition were rated as easier to attack than those in the self-defense condition prior to training (A4 = 7.38 vs. 5.79), but as harder to attack immediately after training ( M = 4.73 vs. 5.60) and 1 month after training ( M = 4.87 vs. 5.44, p = .06). There was no significant difference between ratings 1 week after completion of training.

For walking-style features, there was a significant Training x Session interaction for stride length, F(3,24) = 6.54, p < .01 (R2 = .45); arm swing, F(2,24) =

6.46, p .05 (R2 = .45); energy, F(3, 24) = 23.85, p < ,0001 (R2 = .74); and constraint, F(3,24) = 4.32, p < .01 (R2 = .35). For each of these features, there was a


difference between conditions before training that was reversed after training. For stride length, those in the self-defense condition had a longer stride length than did those in the walking training condition before training ( M = 3.03 vs. 2.33), but a shorter stride length after training (post, M = 3.00 vs. 3.47; 1 week, M = 2.95 vs. 3.07; 1 month, M = 2.90 vs. 3.13). For arm swing, those in the self-defense condition had greater arm swing than did those in the walking training condition before training ( M = 2.20 vs. 1.87), but less arm swing after training (post, M = 2.55 vs. 3.53; 1 week, M = 2.55 vs. 3.27; 1 month, M = 2.45 vs.

Walkers in the self-defense condition had more energy in their walk before training than did walkers in the walking training condition ( M = 3.10 vs. 2.23), but less energy after training (post, M = 2.85 vs. 3.50; I week, M = 3.05 vs. 3.23; 1 month, M = 2.90 vs. 3.37). Walkers in the self-defense condition had less constraint in their walk before training than did walkers in the walking training condition ( M = 3.15 vs. 2.43), but more constraint after training (post, M = 3.35 vs. 2.86; 1 week, M = 2.80 vs. 2.90; 1 month, M = 3.15 vs. 3.13). Note that the changes in walking-style features across sessions were made largely by those participants in the individualized training condition.

Taken together, these results indicate that before training, walkers in the self- defense condition walked in a manner more consistent with the prototypical low- vulnerability walker (relatively long stride, high arm swing, high energy, low constraint) than did walkers in the walking training condition. This may reflect the differential recruitment of these two groups. Walkers in the walking training group were recruited on the basis of their relatively high vulnerability ratings in Experiment 1, while the self-defense group was recruited from the general student population. After training, however, the walking training group walked in a manner closer to the low-vulnerability prototype than did walkers in the self- defense condition. These differences mirror the differences in ease-of-attack ratings between the two groups across sessions. The post-training ease-of-attack ratings for walkers in the walking training condition were lower than those in the self-defense condition, which suggests that ease-of-attack ratings in the self- defense condition were not simply already at baseline level, such that vulnerability could not be improved by training.

3.43).

General Discussion

The aim of the reported research was to investigate whether individuals could change their walking styles and whether this would reduce their vulnerability to attack. Our results indicate that such change is indeed possible. Creating an experimental condition that increased the salience of personal safety resulted in spontaneous changes to walking style (Experiment 1). The walking styles of women in the less safe (park) condition more closely resembled that of the

534 JOHNSTON ET AL.

prototypical low-vulnerability walker (Grayson & Stein, 198 I ; Gunns et al., 2002; Murzynski & Degelman, 1996) than did those of the same walkers in the normal walking condition. This change in walking style is indicative of an assumed link between walking style and vulnerability, although whether this link (and the resulting adaptations to walking style) is consciously acknowledged is not clear from the present research. Importantly, however, the spontaneous changes made to walking style were adaptive changes. Women were rated as more difficult to attack in the park condition than in the normal condition. More- over, changes to walking style predicted changes in ease-of-attack ratings across situations, suggesting that this was the mechanism by which the changes in ratings were mediated.

The impact of both generic self-defense training (Experiments 1 and 2) and specific movement training (Experiment 3 ) on walking style and vulnerability was also investigated. The results regarding the impact of a self-defense course were mixed. In Experiment I , walkers who had just completed a self-defense course were rated as harder to attack, under normal walking conditions, than were those walkers who had not completed such a course or who had completed a self-defense course at least 6 months previously. In Experiment 2, however, attendance at the same self-defense course did not result in significant changes to either walking style or ease-of-attack ratings. The major focus of the self-defense course was on the ability of individuals to defend themselves against attackers, both verbally and physically, rather than on avoiding attack (reducing one’s vulnerability). As such, it is impressive that the self-defense training had any effect on perceived vulnerability of walkers. The mechanism by which this occurred for those in Experiment I , but not Experiment 2, warrants further research. The impact of the individual walking training on walking styles and vulnerability was much stronger (Experiment 3 ) , despite small numbers of participants. For each participant, there were marked changes in walking style and vulnerability as a consequence of the training. The women integrated into their walking style the targeted walking-style features previously shown to be associated with low vulnerability. This change in walking style across training sessions predicted the reduction in ease-of-attack ratings seen for each of the women. These changes to walking style and reductions in vulnerability also persisted to at least 1 month after completion of the training course.

There are a number of differences between the walking training and the self- defense course that may explain the differences in impact of each on walking style and vulnerability. As mentioned earlier, the walkers in Experiment 2 were recruited from the general student population and did not have especially high vulnerability ratings or walking styles prior to completing the self-defense course. In contrast, the walkers in Experiment 3 were recruited for the training course specifically because of their high ease-of-attack ratings in Experiment 1 . Training may have a greater effect when there is more room for improvement.


However, comparisons between the participants in Experiments 2 and 3 after training reveal that those who had completed the training course received significantly lower vulnerability ratings than did those who had completed the self-defense course. Clearly, then, the vulnerability level of the participants in Experiment 2 does not represent a floor level beyond which no improvement can be made.

The walking training was adapted for each individual and was conducted on a one-to-one basis with an experimenter, while the self-defense course was group- based. Whether the introduction of a short section focusing on walking style into a group-based self-defense course is sufficient to produce the positive changes seen in Experiment 3 is worth investigating.

Our findings are consistent with the KSD principle. Changes to the dynamics underlying gait, as a function of situation (Experiment 1 ) and intention (Experi- ment 3), led to changes in the kinematics, and hence in perceived vulnerability. The walkers’ vulnerability was differentially rated before and after training. Walkers in the training condition could convincingly adopt the kinematics associated with lower levels of vulnerability. This convincing adoption of new movement styles may have been a result of the specific training and extended practice given to our participants (Richardson & Johnston, in press). Before concluding that walkers can adopt less vulnerable walking styles, however, the sensitivity of the perceivers as well as the movement of the actors must be considered. It is important to consider whether the changes to walking style are sufficient to alter the perceptions of observers most sensitive to the relevant information. The raters in each of our studies were from a university sample. It is important to replicate this research using a more relevant sample (e.g., convicted attackers) to ensure that changes in walking style also influence the judgments of vulnerability of those who are mostly likely to translate the perception into action (attack).

This research used a point-light methodology that intentionally involves a stimulus array impoverished on all dimensions except movement. Only by using such a display can the unique contribution of kinematic information to perception be considered. Accordingly, the reported research shows that kinematics can specify vulnerability and that changes to kinematics specify changes in vulnerability. The impact of additional information (e.g., clothing style) still needs to be considered, however, in order to gain a fuller picture of the extent to which this kinematic specification of vulnerability influences everyday perception. Training individuals to reduce their vulnerability must take into account factors additional to movement that influence both walking style and vulnerability.

In conclusion, the reported research demonstrates the ability of walkers to convincingly adapt their walking styles, which had a positive consequent effect on vulnerability. Further documentation of the efficacy of such training and the impact of additional information (e.g., clothing) deserves additional research attention.

536 JOHNSTON ET AL.

References

Grayson, B., & Stein, M. I. (1981). Attracting assault: Victims’ nonverbal cues. Journal of Communication, 31,68-75.

Gunns, R. E. (1998). Ectim selection and kinematics: A dynamic point-light assessment of perceived vulnerability to attack. Unpublished master’s thesis, University of Canterbury, Canterbury, UK.

Gunns, R. E., Johnston, L., & Hudson, S. M. (2002). Victim selection and kinematics: A point-light assessment of vulnerability. Journal of Nonverbal Behavior, 26, 129-158.

Hesse, S., Bertelt, C., Jahnke, M. Y., Schaffrin, A., Baake, P., Malezic, M., & Mauritz, K. H. (1995). Treadmill training with partial body weight support compared with physiotherapy in nonambulatory hemiparetic patients. Stroke,

Johansson, G. (1973). Visual perception of biological motion and a model for its

Laban, R. (1972). The mastery of movement. Boston, MA: Plays. Laban, R., & Lawrence, F. C. (1967). Effort: Economy of body movement.

London, UK: McDonald and Evans. Lord, S. E., Wade, D. T., & Halligan, P. W. ( 1 998). A comparison of two physio-

therapy treatment approaches to improve walking in multiple sclerosis: A pilot randomized controlled study. Clinical Rehabilitation, 12,477-486.

Montepare, J. M., & Zebrowitz-McArthur, L. A. (1 988). Impressions of people created by age-related qualities of their gaits. Journal of Personality and Social Psychology, 55, 547-556.

Murzynski, J., & Degelman, D. (1996). Body language of women and judgments of vulnerability to sexual assault. Journal of Applied Social Psychology, 26,

Richardson, M. J., & Johnston, L. (in press). Person recognition and dynamic events: The kinematic specification of personal identity in walking style. Journal of Nonverbal Behavior,

Runeson, S., & Frykholm, G. (1 983). Kinematic specification of dynamics as an informational basis for person-and-action perception: Expectation, gender recognition, and deceptive intention. Journal of Experimental Psychology: General, 112, 585-615.

Runeson, S., & Frykholm, G. (1986). Kinematic specification of gender and gender expression. In V. McCabe & G. J. Balzano (Eds.), Event cognition: An ecological perspective (pp. 259-273). Hillsdale, NJ: Lawrence Erlbaum.

Scully, D., & Carnegie, E. (1998). Observational learning in motor skill acquisi- tion: A look at demonstrations. Irish Journal OfPsychology, 19,472-485.

26,976-98 I .

analysis. Perception and Psychophysics, 14,201-21 1.

161 7-1 626.


Appendix

Trainirig Schedule: Experiment 3

Description

Video session Identification of your present walking-style features Comparison of normal walking style to that displayed in the Hagley Park condition Comparison of normal walking style to other walking styles rated as nonvulnerable Identification of the features in your walking style that need to be improved, and how these can be altered in order to achieve a less vulnerable walking style

Feature alteration and training Video A breakdown of each featured identified in Session 1 that needs to be addressed Guided training and practice on each individual feature separately

Feature alteration and training Video Guided training and practice on each individual feature separately Guided training and practice combining all features together

Feature training and videotaping 9 Video

A quick run-through of each individual feature previously trained Guided training and practice combining all features together Videotaping of “The New You”

Videotaping session One week after final training session Five-minute videotaping session of trained walk No training or practice

*Videotaping session One month after final training session Five-minute videotaping session of trained walk No training or practice

Session

1

2

changing kinematics as a means of reducing vulnerability to physical attack

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