Perception of Whether an Object Can Be Carried Through an Aperture Depends on Anticipated Speed

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1 J.B. Wagman & E.A. ExperimentalP Malek: Perception sychology 2007 Hogrefe and 2007; Anticipated & Vol. Huber 54(1):54 61 Publishers Speed Perception of Whether an Object Can Be Carried Through an Aperture Depends on Anticipated Speed Jeffrey B. Wagman and Eric A. Malek Department of Psychology, Illinois State University, Normal, IL, USA Abstract. We investigated whether anticipated speed of locomotion through an aperture influences perception of whether an object can be carried through that aperture. Participants reported whether they would be able to carry objects through an aperture (a) if they were to attempt to walk through the aperture and (b) if they were to attempt to run through the aperture. Furthermore, they did so when the object was held but not seen and when the object was seen but not held. In general, perception was influenced by object width and by anticipated speed but not by perceptual modality. Perceptual boundaries occurred at smaller object widths when participants anticipated running through the aperture than when they anticipated walking through the aperture. The results build on work showing that perception of affordances is influenced by kinetic potential as well as geometric properties and that perception may be supported by the detection of modality-neutral stimulation patterns. Keywords: haptic perception, visual perception, affordances, handheld objects In general, successful behavior requires successful perception. For a person to achieve a behavioral goal, the perceptual systems must provide that person with an awareness of which behaviors are possible and which are not. Possibilities for behavior for a particular person have been termed affordances (Gibson, 1979). Affordances are determined by the fit between a person s action capabilities and a particular property of the environment (Turvey, 1992). Therefore, perceiving affordances means perceiving the environment in terms of one s action capabilities. For example, perceiving whether an aperture can be passed through (without excessive shoulder rotation) means perceiving the aperture width in relation to the widest horizontal body dimension. Perception of this affordance is constrained by the shoulder width of the perceiver, and the perceptual boundary between apertures that afford passing through and those that do not occurs at a wider aperture width for perceivers with wide shoulders than for perceivers with narrow shoulders (Gordon & Rosenblum, 2004; Warren & Whang, 1987). Attachments to the Body and Action Capabilities Experimental Psychology 2007; Vol. 54(1):54 61 DOI / The challenge of perceiving environmental properties in terms of one s action capabilities is amplified by objects attached to the body such as handheld tools, equipment worn by fire fighters, and even luggage or backpacks. Attaching an object to the body creates an integrated personplus-object system (Wagman & Taylor, 2004), the action capabilities of which may be entirely different than those of the person-without-object. For example, objects attached to the body (e.g., a wheelchair) or objects carried by the person (e.g., a large box) may extend the widest horizontal body dimension and therefore change action capabilities for passing through apertures (see Higuchi, Takada, Matsuura, & Imanaka, 2004). Therefore, perceiving affordances for the person-plus-object system means perceiving properties of the environment in relation to the action capabilities of the integrated person-plus-object system (Bongers, Smitsman, & Michaels, 2003; Smitsman, 1997; Wagman & Taylor, 2005). Perception of whether an object can be carried through an aperture is constrained by the width of the person-plus-object system, and the perceptual boundary between objects that can be carried through an aperture and those that cannot occurs when the width of the person-plus-object system approximates the width of the aperture (Wagman & Taylor, 2005). Objects attached to the body or carried by the person change action capabilities for passing through apertures because they change the person s geometric properties. Importantly, changes in action capabilities can also result from changes in a person s kinetic potential (Adolph & Avolio, 2000; Bhalla & Proffitt, 1999; Oudejans, Michaels, Bakker, & Dolné, 1996; Proffitt, Stefanucci, Banton, & Epstein, 2003). For example, a gap in the support surface that might not be crossable when approached by walking might be crossable when approached by running (see Turvey, 2004). However, whereas increased speed 2007 Hogrefe & Huber Publishers

2 J.B. Wagman & E.A. Malek: Perception and Anticipated Speed 55 may enhance action capabilities for crossing gaps in a support surface, it hinders action capabilities for passing through apertures. Participants rotate their shoulders to a greater degree when walking through apertures at a fast pace than when walking through apertures at a normal pace (Warren & Whang, 1987, Experiment 1). Accordingly, increased speed toward an aperture may also hinder action capabilities for carrying an object through an aperture, particularly when the width of the carried object is approximately equal to the width of the aperture. It is not known, however, whether anticipated speed of locomotion will influence perception of whether an object can be carried through an aperture. Perception of Affordances by Different Perceptual Modalities The two perceptual modalities primarily involved in perceiving whether an object can be carried through an aperture are the haptic system and the visual system. In a situation where the object is already in the hand(s) of the perceiver, the haptic system is primarily involved in perceiving the properties of the carried object and the visual system is primarily involved in perceiving the properties of the aperture. In a situation where the object is not yet in the hand(s) of the perceiver, the visual system is primarily responsible for perceiving properties of both the object and the aperture. From the ecological perspective on perception-action (Gibson, 1979; Turvey, 1992, 2004), there is reason to expect that perceivers will be just as successful in perceiving whether the object can be carried through the aperture regardless of which perceptual modalities are involved. From this perspective, the stimulation patterns that support perception of affordances can be found in structured ambient energy arrays (Gibson, 1979). However, structured ambient energy arrays not only support perception of affordances within a given energy array, they also seem to support perception of the same affordance across different energy arrays. For example, participants are capable of perceiving whether an aperture affords passing through regardless of whether they are viewing that aperture (Warren & Whang, 1987) or whether they are listening to sounds projected through that aperture (Gordon & Rosenblum, 2004). In addition, participants are capable of perceiving whether a surface affords upright posture regardless of whether they are viewing that surface or whether they are probing that surface with a handheld rod (while blindfolded) (Fitzpatrick, Carello, Schmidt, & Corey, 1994). Findings such as these suggest that the particulars of a given energy array may be irrelevant so long as structure in that array is sufficient to support perception of the affordance. That is, it is possible that the information for perception of affordances may be modality-neutral (Rosenblum & Gordon, 2001; see Carello, Wagman, & Turvey, 2005). With respect to perception of whether an object can be carried through an aperture, results of previous experiments have shown that participants are capable of perceiving this affordance regardless of whether the objects are perceived visually or whether the objects are perceived haptically (Wagman & Taylor, 2005). It is not known, however, whether anticipated speed of locomotion will influence perception of this affordance differently when the objects are perceived visually and when the objects are perceived haptically. Experiments 1A and 1B Experiments 1A and 1B investigated perception of whether an object can be carried through an aperture (a) when the perceiver anticipates running through the aperture and (b) when the perceiver anticipates walking through the aperture. Experiment 1A investigated perception of this affordance under these conditions when the object is held but not seen, and Experiment 1B investigated perception of this affordance under these conditions when the object is seen but not held. In order to test hypotheses about the ability to perceive this affordance when the objects are perceived haptically and when the objects are perceived visually, data from Experiments 1A and 1B were combined prior to data analysis. In this analysis, anticipated speed is treated as a within participants variable and perceptual modality is treated as a between participants variable. We expect that perception of this affordance will be influenced by the width of the object and by the anticipated speed of locomotion through the aperture. However, we do not expect that perception of this affordance will be influenced by the perceptual modality by which the objects are perceived. Specifically, we expect that in both perceptual modalities, perceivers will be more conservative in reporting that they would be able to carry objects through the aperture when they anticipate running through the aperture than when they anticipate walking through the aperture, particularly when the width of the object is approximately equal to the width of the aperture. Furthermore, we expect that perceivers will exhibit perceptual boundaries at smaller object widths when they anticipate running through the aperture than when they anticipate walking through the aperture, but we do not expect that perceptual boundaries will differ across perceptual modalities. We also expect that regardless of anticipated speed of locomotion, perceivers will be least confident in their perceptual judgments when the object width is approximately equal to the perceptual boundary. Finally, given the findings of previous research (Wagman & Taylor, 2005, see Fitzpatrick et al., 1994), we expect perceivers to be less confident in their judgments when the objects are perceived haptically than when the objects are perceived visually Hogrefe & Huber Publishers Experimental Psychology 2007; Vol. 54(1):54 61

3 56 J.B. Wagman & E.A. Malek: Perception and Anticipated Speed Figure 1. (a) The experimental paradigm for Experiment 1A. Participants held occluded objects of different widths and reported whether they would be able to carry the object through the aperture when they anticipated running through the aperture and when they anticipated walking through the aperture. (b) Perceivers were more conservative and exhibited perceptual boundaries at smaller object widths when they anticipated running through the aperture than when they anticipated walking through the aperture. Bars indicate standard error. (c) Perceivers were least confident in their perceptual reports when the width of the object was approximately equal to the perceptual boundary. Method Participants Twenty-five undergraduate students (22 women and 3 men) from Illinois State University participated in Experiment 1A. Nineteen undergraduate students (12 women and 7 men) from Illinois State University participated in Experiment 1B. All participants received extra credit in their psychology courses in exchange for their participation. One participant in Experiment 1A was excluded from data analysis due to failure to follow instructions. Materials and Apparatus Experimental Psychology 2007; Vol. 54(1):54 61 The stimuli used in Experiments 1A and 1B consisted of ten T-shaped objects constructed from (hollow) PVC pipe (1 cm inner radius, 1.35 cm outer radius). Each object consisted of a stem (15 cm in length and 50 g in mass) and two branches of equal length. The three pieces were connected by means of a standard three-way connector for PVC of this diameter (37 g) to create a T. The ten objects ranged in width (from branch tip to branch tip including three-way connector) from 50 cm to 140 cm in 10 cm increments (cf. Wagman & Taylor, 2005). For such objects, the frontal dimension that constrains whether the aperture can be passed through is the width of the carried object (see Figure 1a and Figure 2a). The aperture used in Experiments 1A and 1B was also constructed from PVC pipe (1.25 cm inner radius, 1.65 cm outer radius). The aperture was 90 cm wide and 218 cm tall. Black curtain was hung behind the aperture so that no other information about size was available to the participant. In Experiment 1A, participants wore modified plastic safety goggles with a horizontal cardboard occlusion screen (75 cm wide by 25 cm deep) attached to the bottom 2007 Hogrefe & Huber Publishers

4 J.B. Wagman & E.A. Malek: Perception and Anticipated Speed 57 Figure 2. (a) The experimental paradigm for Experiment 1B. Participants viewed objects of different widths and reported whether they would be able to carry the object through the aperture when they anticipated running through the aperture than when they anticipated walking through the aperture. (b) Perceivers were more conservative and exhibited perceptual boundaries at smaller object widths when they anticipated running through the aperture than when they anticipated walking through the aperture. Bars indicate standard error. (c) Perceivers were least confident in their perceptual reports when the width of the object was approximately equal to the perceptual boundary. Figure 1a and Figure 2a adapted from Wagman, J.B., & Taylor, K.R. (2005). Perceiving affordances for aperture crossing for the person-plus-object system. Ecological Psychology, 17, rims so that they were unable to see the T-shaped objects but were still able to see the aperture (cf. Wagman & Taylor, 2005) (see Figure 1a). In Experiment 1B, a box (95 cm tall 45 cm wide 45 cm deep) was used to support the objects (see Figure 2a). A box of this height was chosen because it approximated the waist height of an average participant. The box was placed 20 cm from the participant and was centered with the aperture. Procedure for Experiment 1A The participant stood 350 cm from the aperture in a designated area (90 cm wide 40 cm deep). The outer edges of this area were parallel with the aperture. The participant was handed one of objects such that their right hand was flush with the bottom of the stem and the object was roughly horizontal (i.e., so that the branches extended to each side). The participant grasped the object firmly and held it at the center of his or her waist (see Figure 1a). The task of the participant was to determine whether they would be able to carry each T-shaped object through the aperture if they were to hold the object horizontally at their waist and approach the aperture without turning their shoulders (cf. Wagman & Taylor, 2005; Warren & Whang, 1987). Participants provided two reports. The first was a yes or no judgment as to whether they would be able to carry the object through the aperture under these conditions, and the second was their confidence in that judgment on a scale of 1 to 7 (1 being very uncertain/not at all confident and 7 being absolutely certain/very confident). When the partic Hogrefe & Huber Publishers Experimental Psychology 2007; Vol. 54(1):54 61

5 58 J.B. Wagman & E.A. Malek: Perception and Anticipated Speed ipant provided both reports, the experimenter handed the participant the next object. Participants were allowed to wield the object for as long as necessary to provide both reports. Wielding was restricted to the wrist positioned at the center of the waist, and participants were asked not to wield the object in any way such that it would come into contact with anything (such as the floor or the goggles). At no point did the participant see the object. Participants performed this task under two conditions. In the walk condition, participants reported whether they would be able to carry the object through the aperture if they were to attempt to walk through the aperture. In the run condition, participants reported whether they would be able to carry the object through the aperture if they were to attempt to run through the aperture. All participants completed both conditions in blocked fashion, and the order of conditions was counterbalanced across participants. Within a given condition, objects were presented three times each, and order of presentation of objects was randomized. Procedure for Experiment 1B The participant stood in the designated area described above and viewed an object that had been placed on the box such that the bottom of the object was flush with the edge closest to the participant and the branches extended to each side of the box (see Figure 2a). As in Experiment 1A, participants provided two reports. The first was a yes or no judgment as to whether they would be able to carry the object through the aperture if they were to pick the object up, hold it at the center of their waist so that the branches extended to each side, and carry it toward the aperture without turning their shoulders. The second was their confidence in that judgment on a scale of 1 to 7 (see above). When the participant provided both reports, they closed their eyes while the experimenter replaced the object. Participants were allowed to view the object for as long as necessary to provide both reports. At no point did the participant touch or pick up the object. As in Experiment 1A, participants performed this task under two conditions. In the walk condition, participants reported whether they would be able to carry the object through the aperture if they were to attempt to walk through the aperture. In the run condition, participants reported whether they would be able to carry the object through the aperture if they were to attempt to run through the aperture. All participants completed both conditions in blocked fashion, and the order of conditions was counterbalanced across participants. Within a given condition, objects were presented three times each, and order of presentation of objects was randomized. Results and Discussion As described above, the data from Experiments 1A and 1B were combined prior to data analysis. In this analysis, anticipated speed is treated as a within participants variable and perceptual modality is treated as a between participants variable. First, we compared the mean percentage of yes responses for each object in each condition. A 2 (anticipated speed: walk vs. run) 2 (perceptual modality: haptics vs. vision) 10 (object width) analysis of variance (ANOVA) revealed that the percentage of yes responses (i.e., responses of crossable ) decreased with increasing object width, F(9, 378) = , MSE = , p <.01, and that the percentage of yes responses was greater in the walk condition (59.8%) than in the run condition (53.1%), F(1, 42) = 25.75, MSE = , p <.01. A significant interaction of anticipated speed and object width indicated that in each perceptual modality the difference in percentage of yes responses between the run condition and the walk condition was most pronounced for objects between 90 cm and 110 cm, F(9, 378) = 6.74, MSE = , p <.01 (see Figures 1b and 2b). An interaction of object width and perceptual modality suggested that percentage of yes responses was greater in the vision condition than in the haptics condition for objects that were larger than 100 cm. There were no other significant effects (all F values < 1). 1 As expected, perception of whether the object could be carried through the aperture was influenced by the width of the object and the anticipated speed of locomotion through the aperture. Regardless of whether the objects were perceived haptically or visually, perceivers were more conservative in reporting that they would be able to carry objects through the aperture when they anticipated running through the aperture than when they anticipated walking through the aperture, particularly when the width of the object was approximately equal to the width of the aperture. Participants were more conservative in reporting that they would be able to carry objects through the aperture when objects were perceived visually than when they were perceived haptically but only for objects that were wider than the aperture (see Wagman & Taylor, 2005). Second, in order to determine if the differences in percentage of yes responses would lead to differences in perceptual boundaries, we compared perceptual boundaries derived in each of the conditions both at the level of the aggregate data and at the level of the individual participants. At the level of the aggregate data, probit analysis (Finney, 1971) was used to determine the object width that would result in a response of yes fifty percent of the time in each condition. This width is the boundary between those objects that are perceived to afford carrying through the aperture and those objects that are not (see Burton, 1992; Fitzpatrick et al., 1994). Regardless of perceptual modality, the perceptual boundary occurred at a 1 The results of this ANOVA were verified with nonparametric analyses. There were no differences between the results of the ANOVA and the results of the nonparametric analyses. Experimental Psychology 2007; Vol. 54(1): Hogrefe & Huber Publishers

6 J.B. Wagman & E.A. Malek: Perception and Anticipated Speed 59 smaller object width in the run condition than in the walk condition (p values <.05). In the haptic condition, the perceptual boundary occurred at an object width of 99.1 cm in the run condition (with lower and upper fiducial limits of 94.3 cm and cm, respectively) and at an object width of cm in the walk condition (with lower and upper fiducial limits of cm and cm, respectively) (see Figure 1b). In the vision condition, the perceptual boundary occurred at an object width of 98.1 cm in the run condition (with lower and upper fiducial limits of 96.1 cm and cm, respectively) and at an object width of cm in the walk condition (with lower and upper fiducial limits of cm and cm, respectively) (see Figure 2b). The fiducial limits overlap only in the two cases when anticipated speed is the same and perceptual modality differs, suggesting that the perceptual boundaries differ as a function of anticipated speed (p <.05) but not as a function of perceptual modality (Finney, 1971; Payton, Greenstone, & Schenker, 2003). At the level of the individual participants, the largest object for which at least two of the three responses were yes was taken to be the perceptual boundary for that participant in that condition (see Burton, 1992). A 2 (anticipated speed) 2 (perceptual modality) ANOVA revealed that the perceptual boundary occurred at a smaller object width in the run condition (96.4 cm) than in the walk condition (103.4 cm), F(1, 42) = 11.34, MSE = 96.53, p <.01. There were no other significant effects (F values < 1). Thus, as expected, both at the level of the aggregate data and at the level of the individual participant data, the perceptual boundary occurred at a smaller object width when participants anticipated running through the aperture than when they anticipated walking through the aperture (see Figure 1b and Figure 2b). Also as expected, there was no difference in perceptual boundaries when objects were perceived visually and when objects were perceived haptically. Third, we compared the mean confidence judgments on each object in each condition. A 2 (anticipated speed: walk vs. run) 2 (perceptual modality: haptics vs. vision) 10 (object width) ANOVA revealed that participants were more confident in their judgments when objects were perceived visually (5.94) than when objects were perceived haptically (5.31), F(1, 42) = 12.73, MSE = 6.88, p <.01. Furthermore, confidence varied as a function of object width, F(9, 378) = 51.30, MSE = 1.13, p <.01. Inspection of Figure 1c and Figure 2c suggests that participants were least confident when object width was approximately 100 cm. The main effect of anticipated speed was nonsignificant, F < 1, suggesting that perceivers were as confident in their perceptual judgments when they anticipated running through the aperture as when they anticipated walking through the aperture. However, an interaction of anticipated speed and object width suggests that participants were more confident in their perceptual judgments on smaller objects (objects less than 100 cm wide) in the walk condition but were more confident in their perceptual judgments on larger objects (objects greater than 100 cm wide) in the run condition, F(9, 378) = 3.73, MSE = 0.567, p <.01 (see Figure 1c and Figure 2c). Given the perceptual boundaries reported above, this interaction reveals that participants were more confident in reporting that they would be able to carry smaller objects through the aperture in the walk condition but were more confident in reporting that they would not be able to carry larger objects through the aperture in the run condition. The interaction of width and perceptual modality was marginally significant, F(9, 378) = 1.78, MSE = 1.13, p =.07. There were no other significant effects, all F values < 1. Thus, as expected, perceivers were more confident in their judgments when the objects were perceived visually than when the objects were perceived haptically, and perceivers were least confident in their judgments when the width of the object was approximately equal to the perceptual boundary (see Fitzpatrick et al., 1994; Wagman & Taylor, 2005). General Discussion Previous research has shown that perception of whether an object can be carried through an aperture is influenced by a geometric property the width of the person-plus-objectsystem (Wagman & Taylor, 2005). The results of the current experiments suggest that perception of this affordance is also influenced by (anticipated) kinetic potential the anticipated speed of locomotion through the aperture. Consistent with our hypotheses: (1) perceivers were more conservative in reporting that they would be able to carry objects through the aperture when they anticipated running through the aperture than when they anticipated walking through the aperture, particularly when the width of the object was approximately equal to the width of the aperture, (2) perceivers exhibited perceptual boundaries at smaller object widths when they anticipated running through the aperture than when they anticipated walking through the aperture, and (3) perceptual boundaries were not different when objects were perceived haptically and when objects were perceived visually. Also consistent with our hypotheses, (4) perceivers were least confident in their perceptual judgments when object width was approximately equal to the perceptual boundary, and (5) perceivers were less confident in their perceptual judgments when the objects were perceived haptically than when the objects were perceived visually. Interestingly, perceivers were equally confident in their perceptual judgments when they anticipated running through the aperture and when they anticipated walking through the aperture. A number of studies have shown that perception of affordances is influenced by changes in the perceiver s geometric properties. For example, perceivers are more conservative in reporting that they can maneuver a wheelchair through an aperture than in reporting that they can walk through an aperture (Higuchi et al., 2004). Additionally, a number of studies have shown that perception of affordances is influenced by changes in the perceiver s kinetic 2007 Hogrefe & Huber Publishers Experimental Psychology 2007; Vol. 54(1):54 61

7 60 J.B. Wagman & E.A. Malek: Perception and Anticipated Speed Experimental Psychology 2007; Vol. 54(1):54 61 potential. For example, participants rotate their shoulders more when walking through apertures at a fast pace than when walking through apertures at a normal pace (Warren & Whang, 1987; see also Adolph & Avolio, 2000; Bhalla & Proffitt, 1999; Proffitt et al., 2003). Our results extend such findings by showing that perception of affordances is influenced by anticipated changes in the perceiver s kinetic potential. Perceivers were more conservative in reporting that they would be able to carry an object through an aperture when they anticipated running through the aperture than when they anticipated walking through the aperture (i.e., without actually approaching the aperture and without actually experiencing the changes in kinetic potential associated with either walking or running). The fact that participants made perceptual judgments before actually approaching the aperture was essential to show that perception of affordances is influenced by anticipated changes in kinetic potential. However, such a manipulation also provides an important limitation. Participants in both of the current experiments tended to overestimate their ability to carry objects through the aperture (although this tendency was reduced when perceivers anticipated running through the aperture). Overestimation of this ability is consistent with previous research, particularly when participants have little or no exposure to how an object attached to the body changes their action capabilities (Higuchi et al., 2004; Wagman & Taylor, 2005; see Mark, 1987). Research has shown that it may take some repeated exposure to a particular attachment to the body for a perceiver to become accustomed to how the geometric changes influence the action capabilities of the person-plus-object system (see Hirose & Nishio, 2001; Mark, 1987). In the same way, it may take some exposure to kinetic changes for the perceiver to become accustomed to how those changes influence their action capabilities (Bhalla & Proffitt, 1999; Oudejans, et al., 1996; Proffitt et al., 2003; but see Warren & Whang, 1987, Experiment 2). The fact that perceivers in the current experiments were not given the opportunity to experience how the kinetic changes associated with walking or running influence their action capabilities likely contributed to their overestimation of their abilities. Future research may investigate if the tendency to overestimate the ability to carry an object through an aperture will be further reduced if participants are exposed to their kinetic potential (by actually walking or running toward the aperture). Alternatively, participants may have overestimated their ability to carry objects through the aperture because of the instructions they were given to report whether they would be able to pass through the aperture without turning their shoulders. Ordinarily, people are not restricted in this way when walking through apertures. Shoulder turning is a natural adjustment when passing through apertures, particularly when the aperture is approximately equal to the shoulder width (Warren & Whang, 1987). It is a behavior that allows perceivers to fine tune their perceptually-guided behaviors as they unfold over time. Participants in the current experiment may have made their judgments assuming that they would be able to fine-tune the behavior by turning their shoulders despite the instructions provided by the experimenter. This, in turn, may have led to overestimations of whether the object could be carried through the aperture (for a similar account of overestimation in perception of whether an object is within reach, see Rochat & Wraga, 1997). The finding that the perceptual boundaries on carrying an object through an aperture did not differ when the objects were perceived haptically and when the objects were perceived visually is consistent with previous results (Wagman & Taylor, 2005). The current results build on this work by showing that anticipated speed of locomotion influences perceptual boundaries in the same way regardless of the perceptual modality by which the objects are perceived. Together, the findings add to a growing body of research suggesting that structured ambient energy arrays support perception of the same affordance across different energy arrays (see Carello et al., 2005). Overall, the results suggest that perception of whether an object can be carried through an aperture is influenced by the width of the carried object and the anticipated speed of locomotion through the aperture but not by the modality by which the objects are perceived. Such results highlight (a) that perception of affordances is constrained by the action capabilities of the perceiver (Gibson, 1979; Turvey, 1992), (b) that action capabilities of the perceiver are a function of both geometric properties and kinetic potential (Konczak, Meeuwsen, & Cress, 1992; Warren & Whang, 1987), and (c) information for perception of affordances may be modality-neutral (see Gordon & Rosenblum, 2001). Furthermore, the results may have implications for the design of objects attached to the body or for the training of people who use such objects. Acknowledgments We thank Dawn McBride for help with statistical analysis and for helpful discussion. We also thank two anonymous reviewers for their comments on a previous draft of this manuscript. References Adolph, K.E., & Avolio, A.M. (2000). Walking infants adapt to changing body dimensions. Journal of Experimental Psychology: Human Perception and Performance, 26, Bhalla, M., & Proffitt, D.R. (1999). Visual-motor recalibration in geographical slant perception. Journal of Experimental Psychology: Human Perception and Performance, 25, Bongers, R.M., Smitsman, A.W., & Michaels, C.F. (2003). Geometrics and dynamics of a rod determine how it is used for reaching. Journal of Motor Behavior, 35, Hogrefe & Huber Publishers

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