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This article was downloaded by: [Georgia Technology Library] On: 22 December 2010 Access details: Access Details: [subscription number 788830828] Publisher Psychology Press Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37- 41 Mortimer Street, London W1T 3JH, UK The Quarterly Journal of Experimental Psychology Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t716100704 Carrying the height of the world on your ankles: Encumbering observers reduces estimates of how high an actor can jump Verónica C. Ramenzonia; Michael A. Rileya; Kevin Shockleya; Tehran Davisa a University of Cincinnati, Cincinnati, OH, USA First published on: 19 June 2008 To cite this Article Ramenzoni, Verónica C. , Riley, Michael A. , Shockley, Kevin and Davis, Tehran(2008) 'Carrying the height of the world on your ankles: Encumbering observers reduces estimates of how high an actor can jump', The Quarterly Journal of Experimental Psychology, 61: 10, 1487 — 1495, First published on: 19 June 2008 (iFirst) To link to this Article: DOI: 10.1080/17470210802100073 URL: http://dx.doi.org/10.1080/17470210802100073 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY 2008, 61 (10), 1487 –1495 Short article Carrying the height of the world on your ankles: Encumbering observers reduces estimates of how high an actor can jump ´ Veronica C. Ramenzoni, Michael A. Riley, Kevin Shockley, and Tehran Davis University of Cincinnati, Cincinnati, OH, USA Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 The authors investigated how changes in action capabilities affect estimation of affordances for another actor. Observers estimated maximum jumping-reach height for themselves and another actor. Half of the observers wore ankle weights that reduced their jumping ability. The ankle weights reduced estimates of maximum jumping-reach height that observers made for themselves and for the other actor, but only after observers had the opportunity to walk while wearing the weights. Changes in estimates closely matched changes in actual jumping-reach ability. Results conﬁrm and extend recent investigations that indicate that perception of the spatial layout of surfaces in the environment is scaled to an observer’s capacity to act, and they link that approach to another embodied cognition perspective that posits a link between one’s own action capabilities and perception of the actions of other agents. Keywords: Action understanding; Affordance perception; Embodiment. Studies that report the ability to accurately Findings such as an increase in perceived distance perceive what is afforded by objects and the when an observer is encumbered by a heavy back- layout of environmental surfaces support Gibson’s pack (Profﬁtt et al., 2003) suggest that perception (1979/1986) assertion that the world is funda- is scaled to the capacity to produce action. mentally apprehended with respect to how percei- An outstanding question is whether an obser- vers are capable of acting (see review by Fajen, ver’s capacity to produce a given action plays a Riley, & Turvey, in press). Recent ﬁndings that determining role when the observer is faced with perception of distance and geographical slant estimating whether the environment affords that vary with the degree of effort required to traverse action for someone else. Observers can visually the distance or scale the slanted surface also perceive affordances for other agents, often with support Gibson’s view (Bhalla & Profﬁtt, 1999; quite high accuracy (e.g., Mark, 2007; Profﬁtt, 2006; Profﬁtt, Stefanucci, Banton, & Ramenzoni, Riley, Davis, Shockley, & Epstein, 2003; Stefanucci, Profﬁtt, Banton, & Armstrong, in press; Ramenzoni, Riley, Epstein, 2005; Witt, Profﬁtt, & Epstein, 2004). Shockley, & Davis, 2008; Stoffregen, Gorday, ´ Correspondence should be addressed to Veronica C. Ramenzoni, Department of Psychology, University of Cincinnati, P. O. Box 210376, 429 Dyer Hall, Cincinnati, OH 45221–0376, USA. E-mail: firstname.lastname@example.org # 2008 The Experimental Psychology Society 1487 http://www.psypress.com/qjep DOI:10.1080/17470210802100073 RAMENZONI ET AL. Sheng, & Flynn, 1999). If “perception scales observer (Pepping & Li, 2000) or another actor the geometry of spatial layout to the economy (Ramenzoni et al., in press) could jump to reach of action” (Profﬁtt, 2006, p. 121) then the kinds an object. Ankle weights were attached to the of effects observed by Profﬁtt and colleagues observers (the weights were approximately 5% of should be general, and estimates of what is each observer’s mass), reducing their jumping afforded another actor should depend (at least in ability by about 6 cm, on average. No such part) on the observer’s capacity to produce the reduction to the actor’s jumping capability was action. introduced. We asked whether the kinds of Some studies on perceiving affordances for effects observed by Profﬁtt and colleagues (Bhalla other actors have indicated decreased accuracy in & Profﬁtt, 1999; Profﬁtt, 2006; Profﬁtt et al., cases where the observer and other actor possessed 2003; Stefanucci et al., 2005; Witt et al., 2004) different action capabilities (Rochat, 1995; Zaff, would generalize to estimates of maximum 1995), perhaps suggesting that perceiving affor- jumping-reach height for another actor. dances for another person is biased by the obser- We tested the speciﬁc hypothesis that reducing Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 ver’s action capabilities. If so, online, situated an observer’s jumping ability would result in lower manipulations of an observer’s action capabilities estimates of maximum jumping-reach height for (in contrast to intrinsic differences in an observer’s an actor who was not wearing the weights. and another actor’s action capabilities, such as Estimates were obtained from one group of par- differences in height or strength) would be ticipants (control group) who did not wear ankle expected to produce changes in estimates of affor- weights and by another group (experimental dances for another actor. However, ﬁndings by group) who did. Two sets of estimates were Ramenzoni et al. (2008) suggest the results of obtained—at the beginning of the experimental Rochat and Zaff could derive from the use of session (for the experimental group, this occurred eye-height-scaled optical information rather than immediately after donning the weights but reﬂecting a dependence on the observer’s capacity before participants had the opportunity to walk to act, per se. Eye-height-scaled optical infor- while wearing the weights) and again after obser- mation may provide a determinate (i.e., ballpark vers had walked a short distance around the room metrically accurate) source of information about (for the experimental group, walking served as an other agents’ action capabilities that also reﬂects opportunity to obtain information for recalibrating the observer’s situated relation to the environment to their altered action capabilities; cf. Mark, (i.e., the observer’s eye height, which can change as Balliet, Craver, Douglas, & Fox, 1990). The the observer moves about in the environment and effects of the weights were expected to be stronger takes up new vantage points). However, after walking with them on. Observers also pro- Ramenzoni et al. did not manipulate the observer’s vided estimates of their own maximum jumping- capacity to produce action. Thus, the extent to reach height. which an observer’s situated capacity to act (e.g., whether the actor is encumbered) inﬂuences esti- Method mates of affordances for another actor and the manner by which this may occur remain open Participants questions for the development of ecological A total of 24 participants (14 females, 10 males) (Marsh, Richardson, Baron, & Schmidt, 2006; from the University of Cincinnati gave informed Ramenzoni et al., in press) and embodied consent and participated for course credit. (Knoblich & Sebanz, 2006) accounts of social Participants were randomly assigned to either the perception –action. control or the experimental group. Control- In this study we investigated the effects of group participants ranged in age from 18 to 25 manipulating an observer’s action capabilities on years (mean ¼ 19.60 years), in weight from estimates of the maximum height to which the 43.18 to 134.09 kg (mean ¼ 74.98 kg; SD ¼ 1488 THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2008, 61 (10) SCALING THE ENVIRONMENT IN TERMS OF ACTION 26.14 kg), in height from 153 cm to 181 cm (mean their arms prior to jumping. Those deﬁnitions ¼ 167.76 cm; SD ¼ 9.43 cm), and in maximum were provided to participants prior to beginning jumping-reach height from 229 to 267 cm (mean ¼ the experiment, but participants were not 244.63 cm; SD ¼ 17.13 cm). Experimental- allowed to jump or reach for the cylinder until all group participants ranged in age from 18 to 21 trials had been completed. years (mean ¼ 19 years), in weight from 45 to Participants in the experimental (weights) and 118.18 kg (mean ¼ 67.93 kg; SD ¼ 9.21 kg), in control (no-weights) groups provided estimates of height from 158.42 cm to 181.28 cm (mean ¼ the maximum jumping-reach height for themselves 168.40 cm; SD ¼ 7.83 cm), and in maximum and for a female actor (22 years old, 175.5 cm jumping-reach height from 235.10 to 280.5 cm tall, 70 kg, maximum jumping-reach height ¼ (mean ¼ 247.51 cm; SD ¼ 14.67 cm). 246.4 cm). Estimates for the self and the other Experimental-group participants’ maximum actor each were obtained before and after walking. jumping-reach height while wearing weights The two conditions were always presented in that ranged from 224.1 to 274.5 cm (mean ¼ order in blocks of 8 trials, which included four Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 241.81 cm; SD ¼ 15.06 cm). All participants had trials of estimates for the self and four trials of esti- normal or corrected-to-normal vision. mates for the actor (self- vs. other condition was counterbalanced), for a total of 16 trials. Apparatus Estimates of maximum jumping-reach height Participants made estimates about jumping to were obtained using the method of adjustments. reach and grasp a small, white, plastic cylinder Participants verbally instructed an experimenter (5 cm diameter Â 4 cm) suspended from the who, while standing out of sight behind the appar- ceiling via a pulley by a white nylon rope in front atus, either raised or lowered the object (random- of a large wooden surface (250 cm tall Â 96 cm ized by trial) by means of the rope and pulley until wide). The surface stood perpendicular to the the object was just at the estimated maximum ﬂoor and was covered in black felt (Figure 1). jumping-reach height. Participants could ﬁne- The cylinder hung 22 cm in front of the back- tune their estimates until satisﬁed. Between ground surface. One Reebok weight was attached trials, participants closed their eyes while the with Velcro about the ankle of each of the exper- experimenter reset the apparatus. Participants imental-group participants’ legs. Each weight stood barefoot at a ﬁxed location 3 m away from was adjustable between 0.91 kg and 3.63 kg in the apparatus. The actor was stationed to the left 0.91-kg increments by adding or removing of the apparatus, remaining stationary with her masses from pockets. The weights could not be arms at her sides while participants provided esti- adjusted to exactly equal 5% of the participants’ mates for her. The actor stood out of the room weight given the amount of the increment but when participants provided estimates for them- the closest possible weight was used (+ g). 10 selves. Participants never witnessed the actor jump or stand with the arms outreached and Procedure were not themselves allowed to jump or stand Procedures were approved by the University of and reach in front of the apparatus until data col- Cincinnati Institutional Review Board. For the lection was completed. At that time, each control- purposes of this investigation, maximum group participant performed three jump-with- jumping-reach height was deﬁned as a vertical reach actions that were later averaged to yield power jump, performed without taking approach the empirically determined maximum jumping- steps, that would allow for the cylinder to be reach height. Experimental-group participants grasped at the peak of the jump with the preferred performed three jumps without the weights and arm extended overhead. Participants were three with the weights, which were respectively instructed that they could bend their knees in averaged to obtain maximum jumping-reach preparation for the jump but could not swing height without and with the weights. THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2008, 61 (10) 1489 RAMENZONI ET AL. Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 Figure 1. Apparatus and depiction of experimental conditions. Participants (half in the control, no-weights, group, left, and half in the experimental, weights, group, right) estimated the maximum height to which they or the actor could jump to reach the suspended object before walking (top) and after walking (bottom). At the beginning of the experiment participants participants were allowed to move their legs or provided estimates for themselves and the actor in walk during this portion of the experiment once the before-walking condition. The ankle weights they stood in place and began making estimates were attached to experimental-group participants (although postural sway probably occurred; see by the experimenter as the participants stood in Mark et al., 1990). After providing this ﬁrst set the location at which they provided estimates. of estimates, participants then walked at a self- Neither experimental- nor control-group elected comfortable pace in an elliptical path 1490 THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2008, 61 (10) SCALING THE ENVIRONMENT IN TERMS OF ACTION around the laboratory for 5 minutes, with each lap control group was intermediate between the values around the room requiring participants to traverse obtained for the experimental group assessed with about 16 m. Experimental-group participants and without the weights and did not differ signiﬁ- walked around the room while wearing the ankle cantly from either of those values: both unpaired weights, which were not removed until the end t(22) , 1, respective p ¼ .75 and .59. A paired t of the experiment. After completing the walking test revealed that experimental-group participants task, participants resumed the position in front exhibited a signiﬁcantly lower maximum jumping- of the apparatus and again provided estimates for reach height while wearing the weights than when themselves and for the actor. On average partici- not wearing the weights, t(11) ¼ 8.43, p , .0001. pants in the two groups walked equivalent dis- Analysis of variance (ANOVA) was performed tances: weights group, mean ¼ 23.73 laps, SD ¼ on the mean estimates of maximum jumping- 3.26 laps; control group, mean ¼ 24.13 laps, SD ¼ reach height, with group (control, no-weights, 4.13 laps; t(23) ¼ 0.224, p ¼ .83. vs. experimental, weights), condition (estimates made before and after walking), and estimate Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 type (estimates for the self- or other actor) as Results factors. There was a signiﬁcant Group Â Results are summarized in Table 1, which presents Condition interaction, F(1, 22) ¼ 10.98, p , each group’s mean actual jumping performance, .05, h2 ¼ .33. Follow-up tests involving separate p mean estimates, and mean estimate error (actual analyses for the before-walking and after-walking performance – mean estimate) for self- and conditions showed no signiﬁcant group effect other estimates obtained before and after (p ..05). Follow-up tests involving separate walking. The amount and direction (underestima- analyses for each group showed no signiﬁcant tion) of error exhibited by control group closely effect of before versus after walking for the no- matched the amount of error seen in similar con- weights group, but showed a signiﬁcant decrease ditions by Ramenzoni et al. (in press). in estimates for the weights group after walking We ﬁrst analysed actual jumping performance. compared to before walking, F(1, 11) ¼ 9.50, The mean maximum jumping-reach height for the p , .05, h2 ¼ .46. p Table 1. Actual and estimated maximum jumping-reach height provided by observers for themselves and the other actor in the before-walking and after-walking conditions Maximum jumping-reach height Group Actual Mean estimated Errora No-weights Before walking Self 244.63 231.41 (17.01) 14.36 Actor 244.40 230.89 (12.51) 13.05 After walking Self 244.63 236.46 (21.30) 12.89 Actor 244.40 230.30 (16.13) 10.07 Weights Before walking Self 247.51 231.48 (16.14) 14.43 Actor 244.40 231.90 (11.11) 11.76 After walking Self 241.80 224.95 (17.22) 16.20 Actor 244.40 227.70 (10.45) 17.14 Note: All measurements in cm. Standard deviations in parentheses. Estimated error (actual – estimated maximum jumping-reach height) is also presented for each condition. For the observers (self condition), actual jumping-reach height varied in the before- walking condition relative to the after-walking condition because of the added weights. Since the other actor never wore the weights actual jumping-reach height was constant across other-actor conditions. a Error ¼ Actual – mean estimated maximum jumping-reach height. THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2008, 61 (10) 1491 RAMENZONI ET AL. The lack of any effect of estimate type (self- vs. relation—to determine how estimates were cali- other-actor estimate) in the primary ANOVA on brated relative to actual jumping ability. First, we the mean estimates indicates that the weight and computed the difference between estimates pro- walking manipulations had equivalent effects on vided before walking and actual jumping ability judgements for the self and the other actor. measured without weights. This quantity However, a stronger claim for equivalent effects expressed how initial estimates obtained before on self- and other-actor estimates would be participants had an opportunity to feel how the possible if the same Group Â Condition effect weights affected them were calibrated to their was found for each estimate type. Group Â unaltered jumping capability. We then computed Condition ANOVAs for self- and other-actor the difference between estimates provided after estimates revealed signiﬁcant interactions in both walking and their actual jumping ability measured cases, F(1, 22) ¼ 12.79, p , .05, h2 ¼ .37, and p with weights, which expressed how their post- F(1, 22) ¼ 6.77, p , .05, h2 ¼ .23, respectively, p walking estimates related to their altered jumping with post hoc tests indicating a signiﬁcant capability. Those two quantities did not differ sig- Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 decline in experimental-group estimates obtained niﬁcantly from one another, t(11) ¼ – 0.39, p ¼ after walking (compared to before walking) in .70, indicating that participants exhibited the both cases, t(11) ¼ 3.00 and t(11) ¼ 2.25, both same degree of calibration to their altered jumping p , .05. That is, after walking, experimental- ability after walking and feeling the effects of their group participants provided lower estimates of weights as they exhibited to their unaltered maximum jumping-reach height both for them- jumping ability before walking. We then com- selves and for the other actor. puted the difference between before-walking ANOVA on the error data revealed a signiﬁ- estimates and their actual jumping capability cant interaction between condition, estimate measured with the weights, which expressed how type, and group, F(1, 22) ¼ 5.77, p , .05, h2 ¼ p estimates made before walking related to altered .19. Separate analysis of the self- and other-actor jumping ability, and compared that to the second estimates revealed no signiﬁcant condition effect quantity described above (the measure of post- (p ¼ .93, h2 ¼ .01) or group (p ¼ .36, h2 ¼ .01) p p walking calibration to altered jumping capability). on errors for self-estimates but a signiﬁcant The latter was signiﬁcantly lower than the former, Condition Â Group interaction on errors for t(11) ¼ 3.00, p ¼ .01, indicating that walking other-actor estimates, F(1, 22) ¼ 5.18, p , .05, served to calibrate estimates to actual jumping h2 ¼ .19. Paired t tests subsequent to that inter- p ability. action revealed a signiﬁcant increase in error for other-actor estimates provided by participants Discussion in the weights group in the after-walking con- dition compared to the before-walking condition, Interpretation of the reduced estimates of t(11) ¼ –2.65, p , .05. Control participants maximum jumping-reach height for the other made equivalent errors for self- and other-actor actor observed for the experimental group hinges estimates before and after walking. Experimental- on the pattern of self-estimate data and the group participants made equivalent errors for self- relation of those estimates to actual jumping per- estimates before and after walking, indicating formance. The only signiﬁcant difference in they were sensitive to their signiﬁcantly reduced jumping performance (a reduction in jumping jumping capability, but after walking they made height for experimental participants when wearing signiﬁcantly larger errors for other-actor estimates. the weights compared to when not wearing the We conducted additional analyses of the exper- weights) was paralleled by the identiﬁcation of imental-group’s data to further determine how only one signiﬁcant difference in self-judgements: their self-estimates related to their actual Experimental (weights) group participants pro- jumping ability and how walking affected that vided signiﬁcantly lower estimates of maximum 1492 THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2008, 61 (10) SCALING THE ENVIRONMENT IN TERMS OF ACTION jumping-reach height after walking than before the observers to explore their new action capabilities walking. No other differences in jumping perform- resulting from donning the weights. In Mark et al. ance or in self-estimates were identiﬁed. Analyses (1990), participants’ action capabilities were modi- of actual jumping performance thus predicted the ﬁed by attaching 10-cm-tall blocks to the feet. pattern of self-estimates. Furthermore, the com- Participants were able to calibrate to their new abil- parisons of self-estimates to jumping performance ities even when not allowed to walk while wearing indicate that experimental-group participants the blocks, provided that normal postural sway initially exhibited calibration to their normal (i.e., was present. Thus other forms of exploratory nonweighted) jumping ability but after walking activity might have been sufﬁcient to produce the with the weights exhibited calibration to their changes we observed after experimental-group par- altered jumping ability. These ﬁndings suggest ticipants walked while wearing the weights. that the pattern of self-estimate data accurately An alternative interpretation of the results is reﬂected participants’ actual jumping abilities, that walking with the weights induced fatigue, although as shown in Table 1 there was an overall and it was fatigue, rather than the reduction in Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 tendency to underestimate maximum jumping- jumping height caused by adding the weights, reach height (see also Ramenzoni et al., in press). that drove the change in estimates (cf. Bhalla & The novel ﬁnding was that after walking with Profﬁtt, 1999). That is, as the observers’ action the weights experimental-group participants not capabilities were altered by fatigue, their estimates only provided lower maximum jumping-reach of their own and the other actor’s maximum height estimates for themselves but did so also jumping-reach height changed accordingly. for the other actor—altering the observers’ However, it is unlikely that the brief period of action capabilities affected estimates of walking with the weights induced fatigue in our maximum jumping-reach height for another observers, and none reported fatigue to the exper- actor who was not encumbered by the weights. imenter. Still, even if fatigue was responsible for This suggests that the kinds of effect observed the change in estimates, the central argument by Profﬁtt and colleagues (e.g., Bhalla & remains the same—observers apprehend the Profﬁtt, 1999; Profﬁtt et al., 2003; Stefanucci actions afforded themselves and another actor by et al., 2005; Witt et al., 2004) generalize to the the layout of environmental surfaces with regard case of estimating the maximum range of to their own capacity to produce action. We another person’s action capabilities. Interpreted would predict exactly the same pattern of results in terms of the effort hypothesis (Profﬁtt, observed in the present study if a fatigue manipu- 2006), the data suggest that because the observers lation replaced the weight manipulation. wore the ankle weights, which increased the An important implication of these results is that effort associated with jumping, they estimated perceiving affordances for another person may the height of the target as greater. As a result, not be independent of the observer’s situated they adjusted the target to a lower position to relation to the environment (i.e., to the observer’s make it appear reachable via jumping. capacity to act in the environment at a given Walking, per se, did not inﬂuence estimates, moment). Ramenzoni et al. (2008) demonstrated since there was no difference between before- a similar kind of “observer-dependent” effect that walking and after-walking estimates for the no- was explainable in terms of sensitivity to eye- weights group. Furthermore, participants in the height-scaled optical information. Eye-height- two groups walked the same distance, on average, scaled optical information depends on the instan- so differences in before- and after-walking esti- taneous relation between the observer’s vantage mates seem to reﬂect sensitivity to the alteration point and the layout of environment. In their of jumping ability induced by the weights. study, there was an informational basis for the However, it cannot be concluded that walking observer-dependent effect, so explaining the effect with the weights was the only sufﬁcient means for did not require an appeal to covert cognitive THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2008, 61 (10) 1493 RAMENZONI ET AL. mechanisms or representations. The present results with Gibson’s (1979/1986) ecological theory suggest a somewhat different and perhaps stronger (Ramenzoni et al., 2008)—an approach that sense of observer-dependent effects. However, the emphasizes the embodied, embedded, and online effects observed in the present study may also perceptual-motor basis of these abilities over rep- reﬂect an online, situated sensitivity to infor- resentational processes. mation—multimodal information spanning vision A further implication of an information-based and proprioception, in the present case—about approach is that, consistent with the previously possible actions. This possibility is supported by described results of Mark et al. (1990), continued the fact that changes in estimates were observed opportunities for the observers to explore the only after participants walked while wearing the effects of the weights and learn about their weights, thereby experiencing the effects of the altered action capabilities might result in further weights on their capacity to act (albeit on their changes in estimates. That is, the effects we capacity to produce a different action from found might be temporary, and with practice an jumping). If the results reﬂected some sort of cog- observer could reattune to information that speci- Downloaded By: [Georgia Technology Library] At: 22:40 22 December 2010 nitive bias (such as a response bias induced by the ﬁes the actor’s maximum jumping-reach height demand characteristics of the experiment) then it independent of his or her own. Furthermore, it is is likely that perceivers in the experimental group possible that the opportunity to observe the unen- would have produced lower estimates even before cumbered actor walk might have revealed infor- walking while wearing the weights. mation about the actor’s unaltered jumping-reach Work by Knoblich and colleagues (e.g., Knoblich height, and this could have inﬂuenced the obser- & Jordan, 2002; Knoblich & Sebanz, 2006), follow- vers’ estimates more strongly than the ankle ing from neuroscientiﬁc research on mirror neurons weight manipulation. This raises questions about ` and motor resonance (e.g., Decety & Grezes, 1999; the relative strength of manipulating the action Rizzolatti & Craighero, 2004), similarly suggests capabilities of the observer compared to manipu- that an observer’s own action capabilities underlie lating those of the actor. Ramenzoni et al. (in the capacity to understand and predict another press) documented that observers are sensitive to person’s actions. According to this view, one’s own differences in two actors’ maximum standing- action capabilities serve as an initial model of reach and jumping-reach heights as well as to another actor’s action capabilities. Proprioceptive reductions in an actor’s action capabilities resulting feedback could provide the basis for such a model from attaching ankle weights to the actor. The (Bosbach, Cole, Prinz, & Knoblich, 2005). To the relative impact of manipulating the action capa- extent that action capabilities are mutable by bilities of the actor versus the observer poses an means of temporary manipulations such as encum- interesting question for future research. brance with a backpack or ankle weights, and pro- vided information about the effects of such Original manuscript received 10 August 2007 manipulations on the observer’s capacity to act is Accepted revision received 31 October 2007 available, the embodied motor-resonance approach First published online 19 June 2008 of Knoblich and colleagues (in accordance with the approach of Profﬁtt and colleagues) predicts that affordance estimates for another actor will REFERENCES be affected by the observer’s capacity to produce action. The present data are largely compatible Bhalla, M., & Profﬁtt, D. R. (1999). Visual-motor reca- with this view, especially with regard to the role of libration in geographical slant perception. 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