The Quarterly Journal of Experimental Psychology Carrying the by wuzhenguang


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                             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
                               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

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                                                                         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
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                                                                                 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:

                                                                                                               # 2008 The Experimental Psychology Society                                    1487
                                                                         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
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                                                                         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-
                                                                         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

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                                                                         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
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                                                                         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  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  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.

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                                                                         RAMENZONI ET AL.
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                                                                         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

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                                                                                                                                                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
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                                                                                                                                              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
                                                                         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.

                                                                         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
                                                                                                                                                     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.
                                                                          Error ¼ Actual – mean estimated maximum jumping-reach height.

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                                                                         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  Condition effect            weights affected them were calibrated to their
                                                                         was found for each estimate type. Group                 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-
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                                                                         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  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
                                                                         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

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                                                                         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
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                                                                         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

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                                                                         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-
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                                                                         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
                                                                         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. Journal of
                                                                         proprioceptive feedback. Our approach differs with         Experimental Psychology: Human Perception and
                                                                         regard to the possible mechanisms underlying               Performance, 25, 1076– 1096.
                                                                         these abilities, however. We propose the develop-       Bosbach, S., Cole, J., Prinz, W., & Knoblich, G. (2005).
                                                                         ment of an information-based approach consistent           Understanding another’s expectation from action:

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                                                                                                                                         SCALING THE ENVIRONMENT IN TERMS OF ACTION

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