View makes a difference: Presenting human figures from the back or front affects mental spatial transformations of children and adults

Transcription

1 Spatial Cognition & Computation An Interdisciplinary Journal ISSN: (Print) (Online) Journal homepage: View makes a difference: Presenting human figures from the back or front affects mental spatial transformations of children and adults Mirjam Ebersbach & Markus Krüger To cite this article: Mirjam Ebersbach & Markus Krüger (2016): View makes a difference: Presenting human figures from the back or front affects mental spatial transformations of children and adults, Spatial Cognition & Computation, DOI: / To link to this article: Accepted author version posted online: 28 Jan Submit your article to this journal Article views: 3 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at Download by: [Universitaetsbibliothek Kassel], [Mirjam Ebersbach] Date: 01 February 2016, At: 07:14

2 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 1 View makes a difference: Presenting human figures from the back or front affects mental spatial transformations of children and adults Mirjam Ebersbach 1 and Markus Krüger 2 1 Universität Kassel, Germany; 2 Ernst-Moritz-Arndt-Universität Greifswald, Germany Correspondence concerning this article should be addressed to: Mirjam Ebersbach, Institut für Psychologie, Universität Kassel, Holländische Str , D Kassel, Germany. mirjam.ebersbach@uni-kassel.de

3 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 2 Abstract Previous research suggested that performance in spatial judgments involving rotated human figures is poorer if these figures are presented from the front than from the back. We further investigated this effect, controlling for visible facial information in front and back view by presenting figures faces as profile. Children s and adults judgments were still faster and less error prone if figures were presented from the back. Moreover, reaction times indicated that participants did not mentally rotate figures in front view. Children performed overall more poorly than adults, but there were also qualitative differences suggesting that children are more susceptible to embodiment effects than adults. This study underlines that embodiment may have differential effects in spatial transformation tasks, enhancing or impairing performance. Key words: Mental rotation, Spatial cognition, Object-based transformations, Perspective transformations, Laterality judgments, Effect of view, Embodiment, Imagery

4 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 3 Introduction Spatial imagery is an important cognitive ability allowing people, for instance, to imagine how objects appear from different perspectives, or to adopt the perspective of others. It can be investigated by means of spatial judgment tasks, in which people have to decide whether two figures that are rotated against each other are identical or not (same-different task). Alternatively, people are asked to provide laterality judgments, that is, they indicate whether a target is situated on the left or right side relative to a presented object or another person. Same-different tasks are usually solved by object-based transformations, as the observer mentally manipulates the objects to be judged by spatial imagery and brings them into alignment while he keeps his own perspective. Laterality judgments, in contrast, involve perspective transformations (Zacks & Tversky, 2005) also called viewer-based transformations (van Lier, 2003), egocentric transformations (Kaltner, Riecke, & Jansen, 2014), imagined spatial transformations of one s body (Parsons, 1987a), or own body transformations (May & Wendt, 2013). Here, the observer changes his own perspective and adopts the perspective of the object or person in order to provide a left-right decision (cf. Huttenlocher & Presson, 1973; Zacks, Mires, Tversky, & Hazeltine, 2002). A classic paradigm examining spatial imagery by means of a same-different task goes back to Shepard and Metzler (1971) who presented adults with pairs of abstract cube combinations that were rotated against each other. Asked to decide whether the cube combinations were identical or not, adults needed more time and made more errors the more the two stimuli were rotated. It was assumed that participants mentally simulated rotating one stimulus back into the position of the other one to come to a decision. Linearly increasing reaction times (RTs) with increasing angular differences between the two stimuli were taken as an indicator of mental rotation processes.

5 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 4 A vast number of studies on spatial imagery followed that addressed more recently also effects of embodiment and motor processes. A selection of these studies will be presented in the following. Performance in same-different judgment tasks involving body-like stimuli Sayeki (1981) was one of the first concerned with embodiment effects in spatial imagery using same-different judgment tasks. Adults were asked to decide whether pairs of line drawings showing simple, abstract cube combinations were identical or not. In addition, pairs of cube combinations attached with a human head were presented, suggesting body-like stimuli. Judgments were significantly faster if cube combinations were added by a human head. Sayeki assumed that the body analogy of the stimuli elicits the schema of one`s own body that facilitates the identification of body-like stimuli also in rotated perspectives. Interestingly, although these cube combinations with a human head were responded to rather quickly, they elicited almost no increase of RTs with larger angular differences. This finding raises the question whether participants used mental rotation at all when presented with bodylike stimuli in spatial judgment tasks, or if they applied other strategies (e.g., Gronholm, Flynn, Edmonts, & Gardner, 2012). However, other studies involving body-like stimuli in same-different tasks found support for mental rotation strategies. For instance, Amorim, Isableu, and Jarraya (2006) presented adults with pairs of computer-generated, body-like and abstract 3D-stimuli that were rotated in depth or in picture plane. In addition to a general advantage of body-like stimuli in terms of faster and less error prone judgments, RTs linearly increased with larger angular differences within each stimulus pair of body-like and abstract stimuli. A linear increase of RTs was also reported by Kaltner et al. (2014) who used a same-different task involving photographs of humans standing with their back or front to the observer, and by

6 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 5 Steggemann, Engbert, and Weigelt (2011) who showed photographs of human figures only in front view (Exp. 1; see also Zacks et al., 2002). Performance in laterality judgment tasks involving body-like stimuli From the findings so far, one could conclude that body-like stimuli improve people s performance in spatial judgment tasks and that this effect is largely independent of the view by which body-like stimuli are presented (i.e., front or back view). However, in tasks requiring laterality judgments that evoke the change of one s own perspective, results are less clear. Parsons (1987a, Exp. 1) presented participants with rotated line drawings of human figures shown from the front or back and asked them to decide, whether the figures stretched out their left or right arm. RTs monotonically increased with larger rotation angles indicating mental rotation processes in both the back and front view but the increase was significantly slower for figures in front view, suggesting that figures in front view are harder to mentally rotate. Jola and Mast (2005) manipulated view, amongst other variables, using a similar paradigm as Parsons (1987) with the main difference that in their study the figures faces were erased. Drawn figures presented in front view produced longer RTs and higher error rates than in back view. In contrast to Parsons, RTs and error rates for figures in front view were hardly affected by rotation angles (see also Zacks et al., 2002), which was only discernible for figures in back view. Similarly, Kaltner et al. (2014) presented participants with photographs of human figures, in which faces were visible in front view, but not in back view. They found a monotonic increase of RTs with larger rotation angles for back view only. If figures were presented from the front, RTs were overall longer and yielded a U-shaped relation with rotation angles implying a decrease of reaction times across smaller rotation angles. Steggemann et al. (2011, Exp. 2), too, reported shorter RTs if photographs of human figures were presented from the back than presented from the front and hardly any increase of RTs with larger rotation angles for figures in front view.

7 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 6 Thus, in laterality judgment tasks that involve body-like stimuli, mental rotation strategies could be assumed if these stimuli are presented in back view, while results are not fully clear if body-like stimuli are presented in front view. Potential explanations for embodiment effects in spatial judgment tasks Given that body-like stimuli enhance performance in spatial judgment tasks, embodiment processes might be responsible for this effect. Amorim et al. (2006) suggested that body-like stimuli support holistic instead of piecemeal mental rotation as the stimuli can be conceived as an entity. Moreover, the presentation of body-like stimuli allows for both motoric and spatial embodiment by enabling individuals to anatomically recapitulate the position of the stimuli and also to use spatial cues, like the head and feet, to reconstruct the position of the stimuli in space (see also Jansen, Lehmann, & Van Doren, 2012; Jola & Mast, 2005; Kessler & Thomson, 2010). The power of embodiment in mental rotation was demonstrated by Krüger, Amorim, and Ebersbach (2014). They showed that body parts added to cube combinations triggered the projections of participants body schema onto those stimuli, resulting in a better performance compared to abstract stimuli (see also Sayeki, 1981). However, when body parts were added to anatomical impossible locations (e.g., head next to feet), the participants performance dropped beyond that with abstract stimuli, indicating that a projection was attempted even as no possible anatomical position was feasible. Thus, bodylike stimuli might also evoke embodiment in situations where it is detrimental. Krüger et al. furthermore demonstrated that embodiment does not simply operate by providing additional spatial cues to the stimuli, such as top or bottom, as performance in trials including abstract stimuli that were added by abstract spatial cues, which might also be used for orientation (i.e., colored cubes), did not improve performance. Further support for the embodiment account comes from studies showing that spatial imagery of body parts is restricted by the same physical constraints as real movements.

8 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 7 Laterality judgments of drawings of rotated hands and feet, for example, took longer the more anatomically awkward the positions were (e.g., the palm of a right hand showing with the fingers down to the ground; Parsons, 1987b). In addition, motor activation is traceable in the brain when people solve spatial judgment tasks (e.g., Kosslyn, DiGirolamo, Thompson, & Alpert, 1998; Parsons et al., 1995). For instance, rotating objects by hand first led subsequently to an activation of the motor cortex when participants used mental rotation in spatial judgment tasks (Kosslyn, Thompson, Wraga, & Alpert, 2001). Moreover, first imagining the rotation of hands affected the subsequent mental rotation of abstract stimuli, which was again accompanied by activations of the motor cortex (Wraga, 2003). Interestingly, different areas of the motor cortex are involved in the mental rotation of objects and of one s own body, suggesting distinct neural mechanisms (Wraga, Shepard, Church, Inati, & Kosslyn, 2005). But how could embodiment explain differential effects of view of human body stimuli on the performance in laterality judgments? If human figures are presented in back view, the task may be solved straight forwardly by an object-based transformation: The figure has to be mentally rotated in picture plane until it matches with the projections of one s own body and a left-right judgment in alignment with the own body can be made. Alternatively, one s own perspective is mentally rotated around one axis until it is in alignment with the rotated body (Zacks & Tversky, 1995). If figures are presented in front view, in contrast, the approach is more complex and may involve multiple transformations of one s own perspective. Kaltner et al. (2014) proposed that individuals first mentally execute a 180 turn along their own vertical axis to align their own body with the target with regard to view. This perspective has to be mentally transformed further by rotating it along the horizontal axis, which might result in longer RTs and more errors. This strategy would result in larger RTs for figures in front view

9 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 8 compared to back view, which would nevertheless increase monotonically with larger rotation angles. However, as in several studies no linear relationship between rotation angle and RTs for figures in front view was found (e.g., Jola & Mast, 2005; Kaltner et al., 2014; Steggemann et al., 2011; Zacks et al., 2002), individuals may have used other strategies than plain mental rotation. While upright standing figures in front view require a more complex account, as described earlier, the same figures presented upside down (i.e., inverted) allow a direct emulation of this position by mentally slipping with the feet first into the body that could be conceived as a body lying on its back, which would result in shorter RTs (and probably less errors) for the largest rotation angle. Another assumption is that inverted figures are mentally flipped into an upright position instead of being rotated (Murray, 1997). In all cases, the relationship between RTs and rotation angle would not be linear. Moreover, compatibility between the side of the stimulus to be judged (e.g., left arm ) and the location of the response key (e.g., left key press ) might contribute at least to some part to differential effects of view (May & Wendt, 2012). Stimulus-response compatibility can occur for figures presented in back view in an upright position as well as for figures presented in front view but upside down as the side to be judged corresponds to the participant s body side. Incompatibility, in contrast, results for stimuli that are presented in front view in an upright position as well as for stimuli presented from the back but upside down. Stimulus-response compatibility, however, cannot fully explain the general back-view advantage, which also emerged if figures were presented horizontally (i.e., rotated by 90 to the left or right) and body parts to be judged were located vertically to each other instead of on the left or right (May & Wendt, 2012). Thus, further processes might be involved in the effect of view.

10 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 9 Besides compatibility, another confounding factor might have contributed to the effect of view. If human figures are presented from either the front or back, not only their position differs but also the accessible information of the figure s face. In front view, the face is usually visible, which might catch attention and elicit face processing even if this is not required by the task. In turn, additional information of the face might lead to a poorer and less systematic performance of human figures presented from the front. Jola and Mast (2005) tried to diminish this effect by presenting drawings of human figures whose faces were erased and information about front or back view could only be inferred from other body characteristics. However, this stimulus material is quite artificial (i.e., figure with an empty face) and the disadvantage for the front view might have arisen from the fact that unexpected views (i.e., an empty face) catch the attention of the participants and, as a result, enhances RTs and error rates. Central aim of the present study was to replicate and extend findings concerning the effect of view in laterality judgments that involve human body stimuli. In order to investigate whether the effect of view, as reported in other studies, was an artefact of facial information that was visible in previous paradigms for figures in front view but not in back view, two conditions were designed. One condition (arm condition) was adopted from Steggemann et al. (2011) showing human figures from the front or back who lifted their left or right arm. In addition, we designed a condition in which human figures, presented from the front or back view, looked to the left or right side with both arms along their bodies (head condition). In this condition, the visibility of facial features is constant for both the front and back view as in each perspective half of the face is visible (see Figure 1). Moreover, the positions are quite natural and should not elicit particular attention due to their artificial appearance. The comparability of the front and back view should thus be higher in the head condition and provide more valid results.

11 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 10 The effect of view was examined with regard to mean RTs and mean error rates (ERs) and also with regard to the relationship between rotation angle of the figures and RTs. Previous studies using laterality judgments yielded contradicting results with regard to the question if there is a linear relationship between rotation angle an RT for figures in front view (Parsons, 1987a) or not (Jola & Mast, 2005; Kaltner et al., 2014). Furthermore, we aimed at investigating effects of stimulus-response compatibility (May & Wendt, 2012). Reactions to upright figures should be faster and less error prone if these figures are presented from the back as in this case, the side of the lifted arm / the gaze direction of the figure from the figure s standpoint corresponds to the side of the participant and the side of the key press. No such correspondence exists in front view for upright figures, which therefore should result in an impaired performance. The opposite pattern was expected for figures presented upside down: Performance should be better for figures in front view compared to figures in back view. Finally, a developmental perspective was pursued in this study by examining whether similar effects of view could be observed in children and adults. So far, there are hardly any studies assessing embodiment effects among both children and adults in spatial judgment tasks involving laterality judgments in particular no studies that were concerned with the effect of view. Frick, Daum, Walser, and Mast (2009), using abstract 2-D stimuli in figureground matching tasks that resembled same-different judgments, reported that 5- and 8-yearolds, but not 11-year-olds and adults, showed an impaired mental rotation performance if they simultaneously executed a manual rotation in a direction that was incompatible with the required mental rotation. Funk, Brugger, and Wilkening (2005) showed that 6-year-olds but not adults performed more poorly if they had to decide whether a left or right hand was presented if the posture of this hand (i.e., palm up or down) did not correspond to the posture of their own hand. This suggests that children might be more strongly or at least differently

12 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 11 affected by embodiment effects compared to adults (cf. Krüger & Krist, 2009). To investigate the developmental aspect, 9-year-olds were tested. The performance in this age group might differ more strongly from that of adults than the performance of older children but 9-year-olds are already old enough to complete the same paradigm with the same number of trials as adults (cf. Heil & Jansen-Osmann, 2008; Karádi, Szabó, & Szepesi, 1999). We expected to replicate the advantage of back view in spatial judgment tasks: Figures in back view should yield shorter RTs and smaller ERs than figures in front view perspective. If this effect emerges in the arm and in the head condition, one could assume that it is not only due to the visibility of facial information that differs in the arm condition between front and back view. Moreover, linearly increasing RTs with larger rotation angles were expected mainly in the back view perspective indicating mental rotation while this effect should be smaller or remain absent for figures in front view (e.g., Jola & Mast, 2005). In addition, a stimulus-response compatibility effect was expected (see May & Wendt, 2012): ERs and RTs should be smaller if the target location corresponds with the response location, that is, for upright figures in back view and inverted figures in front view. Finally, children s performance in the laterality judgments should also and potentially, even more strongly than that of adults be affected by the different views and compatibility effects. Participants Method Nineteen adults (11 women, 8 men, mean age: 23;1 years, range: 18;11 to 35;11 years) and 30 children (17 girls, 13 boys, mean age: 9;9 years, range: 8;8 to 10;8 years) participated. Adults were psychology students of the local department who received credit points for their course of studies. Children were recruited from two different after school centers of the same medium-sized town as the adults. They received a sticker as a reward after they had completed the experiment. The majority of the sample was right-handed with the exception of

13 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 12 two left-handers and one bi-manual among each age group. The research has been conducted in line with the ethical standards of the partaking institutions, the participation was voluntary, and all participants gave informed consent or consent was given by their respective parents to partake in this study. Materials and Procedure Stimuli consisted of photographs ( pixel jpg-files) of an upright standing male or female plastic doll being rotated in the picture plane in nine different angles (0, 45, 90, 135, 175, 185, 225, 270, and 315 ). The doll was shown either from the front or back view (see Fig. 1). There were two conditions that were blocked. In the arm condition, the doll lifted her left or right arm, while in the head condition it looked either to the left or right side, resulting in 2 (gender of the doll: male, female) x 9 (rotation angle: 0 to 315 ) x 2 (view: front, back) x 2 (orientation: left, right) = 72 trials per block. Both blocks were presented twice resulting in a total of 288 trials. Gender of the doll and orientation were manipulated to allow for more general conclusions due to a more variable stimulus material. However, no hypotheses were formulated with regard to these variables. Stimuli were presented on a DELL laptop computer (17 ) by means of E-Prime software. Participants had to press a right, blue key ( l ) with their right index finger if the doll lifted her right arm (or looked to the right from its point of view) and a left, yellow key ( f ) had to be pressed with their left index finger if the doll lifted its left arm (or looked to the left), yielding stimulusresponse compatibility for upright standing figures in back view and figures presented upside down in front view. Procedure. Participants were tested individually in a quiet room at their institution. They were seated in front of the computer screen in a distance of about 50 cm. Each stimulus was presented separately and in a random order within each block. Each condition (arm and head) was presented once in the first two blocks and once in the last two blocks, while the

14 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 13 order of the conditions within the first two and second two blocks was randomized. Each block started with a short instruction explaining the task that was printed on the screen and additionally read for the children. No practice trials were given. Between each block there was a short break that could be finished by the participants by pressing the Enter key. All trials started with a fixation cross in the middle of the screen for 1s, followed by the presentation of the respective stimuli. Stimuli presentation lasted until participants pressed either the blue or yellow key. A visual (smiling or frowning schematic face) and auditory (positive jingle vs. negative toot) feedback was given lasting 800 ms. The next trial started immediately after the feedback with the fixations cross. Data preparation and analyses. Only correct responses were considered in the analysis of RTs. Trials with RTs smaller than 300 ms (Schmidt & Lee, 2011) or larger than three standard deviations above the mean were excluded (i.e., 2.1% of correct trials in adults, 2.4% in children). Mean RTs and ERs (ERs = number of incorrect trials / total number of valid trials) were computed by aggregating across those trials, for which the shortest rotation path between stimulus and target was the same (e.g., 45 and 315 ) as it can be assumed that participants use the shortest path (cf. Sayeki, 1981), resulting in five rotation angles (0, 45, 90, 135, 175 ). Furthermore, dependent measures were aggregated across both orientations (left and right arm or head direction of the figure) and both figures (male and female). Three children with more than 10% missing values in the RTs were excluded from the analyses. For the sake of clarity, analyses were computed separately for each condition as our hypotheses addressed only qualitative but not quantitative differences between the two conditions. Results Arm condition: Reaction times (RTs) Mean RTs are shown in Figure 2 separately for each condition, view, age group, and rotation angle. The general pattern seems to be quite similar between both conditions and

15 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 14 between adults and children: RTs appear to be shorter at least for smaller rotation angles and to increase with rotation angles only for figures presented in back view but not for figures in front view. An ANOVA with repeated measurements on RTs in the arm condition revealed a significant effect of age group, F(1, 44) = 57.86, p <.001, ƞ 2 = Planned contrasts showed that RTs were significantly larger among children (M = 2277 ms, SD = 733 ms) than among adults (M = 970 ms, SD = 169 ms), t(29.82) = 8.93, p <.001, d = In addition, there was a significant effect of view, F(1, 44) = 17.24, p <.001, ƞ 2 =.08, with shorter RTs for figures presented in back view than in front view, which was confirmed for children (M = 2050 ms, SD = 607 ms vs. M = 2505 ms, SD = 944 ms), t(26) = 3.90, p =.001, d = 0.57, and adults (M = 902 ms, SD = 186 ms vs. M = 1039 ms, SD = 184 ms), t(18) = 3.92, p =.001, d = Finally, there was a significant effect of rotation angle, F(2.28, ) 2 = 29.09, p <.001, ƞ 2 =.16, as well as significant two-way interactions of age group view, F(1, 44) = 5.00, p =.030, ƞ 2 =.02, age group rotation angle, F(2.28, ) = 5.96, p =.002, ƞ 2 =.03, view angle, F(2.77, ) = 12.88, p <.001, ƞ 2 =.05, and a three-way interaction of age group view angle, F(2.77, ) = 2.95, p =.039, ƞ 2 =.01. To further examine the effect of rotation angle and to account for the three-way interaction in the arm condition, separate post-hoc analyses were conducted for each age group and view (Bonferroni corrected). For figures in back view, rotation angle yielded a significant effect in children, F(2.36, 61.46) = 44.97, p =.004, ƞ 2 =.63, and adults, F(1.81, 32.49) = 81.53, p =.004, ƞ 2 = 1 Eta squared values were computed (rather than partial eta squared values) as η² = SSeffect/SStotal so that the sum of eta squared values would not be greater than 100% of the explained variance, which might be the case with partial eta squared values (e.g., Levine & Hullett, 2002). 2 Greenhouse-Geisser is reported if sphericity could not be assumed.

16 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES Repeated contrasts revealed for children increasing RTs in the arm condition for rotation angles larger than 45, ps <.028, while this effect was present among adults for all increasing rotation angles, ps <.020. In contrast, if figures were presented in front view, no effect of rotation angle emerged among children, p =.28, or adults, p =.17. In order to test for an effect of stimulus-response compatibility between side of the target and response location as it is suggested by the interaction of rotation angle and view in the arm condition (see also Fig. 2) RTs were merged across the two smallest (i.e., 0-45 ) and the two largest rotation angles (i.e., ) and compared for figures in back versus front view. RTs should be smaller for upright figures in back view compared to front view and for inverted figures in front view compared to back view. In fact, children and adults reacted faster to upright figures that were presented from the back compared to upright figures presented from the front, children: t(26) = 4.64, p =.006, d = 0.97, adults: t(18) = 4.58, p =.006, d = 1.46 (Bonferroni). However, this difference was absent for inverted figures in both age groups, ps >.37. To examine whether the relationship between rotation angle and RTs was linear what could indicate mental rotation linear regression analyses were computed separately for each age group and view to account for the unequal graduation of rotation angles (i.e., 45 for the first three rotation steps and 40 for the last). These analyses confirmed and refined the results of the ANOVAs. As shown in Table 1, a linear model yielded significance in the arm condition in adults for both views and in children only for figures presented in back view. However, the regression model of adults for figures in front view explained only minimal variance and is no longer significant after Bonferroni correction. Head condition: Reaction times (RTs) The same analyses as for the arm condition were conducted for the head condition. An ANOVA with repeated measures yielded a significant main effect of age group, F(1, 42) =

17 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES , p <.001, ƞ 2 =.55. Planned contrasts revealed that mean RTs were larger among children (M = 2985 ms, SD = 967 ms) than among adults (M = 1330 ms, SD = 261 ms), t(31.16) = 8.46, p <.001, d = Furthermore, there was a significant effect of view, F(1, 42) = 8.90, p =.005, ƞ 2 =.06. RTs for figures presented in back view were shorter than when presented in front view, M = 2471 ms, SD = 1354 ms vs. M = 2131 ms, SD = 960 ms, t(45) = 3.20, p =.003, d = Finally, there was a significant effect of rotation angle, F(3.03, ) = 26.09, p <.001, ƞ 2 =.11, as well as significant two-way interactions of rotation angle age group, F(3.03, ) = 5.65, p =.001, ƞ 2 =.02, and rotation angle view, F(2.23, 93.49) = 10.73, p <.001, ƞ 2 =.07. The effect of rotation angle, analyzed separately for each age group and view to account for the two-way interactions, revealed for figures in back view increasing RTs with larger rotation angles for children, F(1.81, 74.03) = 29.59, p =.004, ƞ 2 =.53, and adults, F(2.10, 37.79) = 34.20, p =.004, ƞ 2 =.66 (Bonferroni). Repeated contrasts confirmed this effect in both age groups for all angles, ps <.039. In contrast, if figures were presented in front view, RTs remained rather constant across rotation angles in both children, p =.65, and adults, p =.46. To check for a compatibility effect, RTs for upright figures were compared with RTs for inverted figures under each view. As in the arm condition, children and adults in the head condition reacted faster to upright figures if they were presented from the back than from the front, children: t(26) = 3.74, p =.006, d = 1.04, adults: t(18) = 4.12, p =.008, d = 1.40 (Bonferroni), while this effect emerged neither among children nor among adults for inverted figures, ps >.21. Linear regression analyses (see Table 1) yielded in both age groups a significant model fit if figures in the head condition were presented in back view but not if they were presented in front view.

18 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 17 To sum up, RTs in both the arm and head condition were larger for figures in front view than in back view and also larger for children than for adults. Compatibility effects appeared only for figures in an upright position in both age groups but not for figures presented upside down. A linear relationship between RTs and rotation angles emerged only for figures in back view but not for figures in front view in both age groups. Arm condition: Error rates (ERs) Mean ERs per condition, view, age group, and rotation angle are shown in Figure 3. The pattern is less clear than for RTs, even if some general effects seem to apply to ERs, too: Figures in back view elicit smaller ERs at least for smaller rotation angles than figures in front view and children seem to perform more poorly than adults. For mean ERs in the arm condition, an ANOVA with repeated measures yielded a significant effect of age group, F(1, 44) = 8.05, p =.007, ƞ 2 =.15. Planned contrasts revealed larger ERs among children (M =.11, SD =.07) than among adults (M =.06, SD =.05), t(44) = 2.84, p =.007, d = In addition, there was a significant effect of view, F(1, 44) = 12.51, p =.001, ƞ 2 =.05, with larger ERs for figures presented in front view (M =.11, SD =.09) than in back view (M =.06, SD =.06), t(45) = 3.80, p <.001, d = Finally, there was a significant effect of rotation angle, F(2.88, ) = 9.46, p <.001, ƞ 2 =.07, as well as significant two-way interactions of rotation angle age group, F(2.88, ) = 5.83, p =.001, ƞ 2 =.04, and rotation angle view, F(2.28, ) = 5.83, p =.003, ƞ 2 =.04. To unravel the interactions, effects of rotation angle were tested separately for each age group and view. For figures presented in back view, rotation angle yielded a significant effect among children, F(2.02, 52.82) = 28.87, p =.004, ƞ 2 =.52, but not among adults, p =.36 (Bonferroni). For children, repeated contrasts revealed that ERs increased for rotation angles larger than 45, ps <.016. If figures were presented in front view, ERs remained stable across rotation angles among children and adults, ps >.28.

19 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 18 To check for a stimulus-response compatibility effect on ERs in the arm condition, ERs of both views of upright and inverted figures were compared. Among adults, ERs did not differ between back and front view neither for upright and nor for inverted figures, ps >.16. However, children made significantly less errors if upright figures were presented from the back than from the front, t(26) = 4.86, p =.006, d = 0.55 (Bonferroni), while no such effect appeared among children for inverted figures, p =.64. Head condition: Error rates (ERs) For mean ERs in the head condition, there was a significant effect of age group, F(1, 44) = 11.15, p =.002, ƞ 2 =.20. Planned contrasts revealed larger ERs among children (M =.22, SD =.13) than among adults (M =.11, SD =.09), t(44) = 3.34, p =.002, d = In addition, there were significant effects of view, F(1, 44) = 24.19, p <.001, ƞ 2 =.05, and rotation angle, F(2.97, ) = 6.51, p <.001, ƞ 2 =.03, as well as two-way interactions of age group view, F(1, 44) = 13.22, p =.001, ƞ 2 =.03, and rotation angle view, F(1.84, 80.84) = 16.93, p <.001, ƞ 2 =.15. The effect of view was significant only among children, t(26) = 6.38, p <.001, d = 0.83, in terms of larger ERs for figures in front view (M =.28, SD =.17) than in back view (M =.16, SD =.11), but not among adults, p =.38. As there was neither an interaction of rotation angle and age group nor an interaction of view, rotation angle, and age group, ERs were analyzed separately for each view but across both age groups. An effect of rotation angle was confirmed for figures in back view, F(2.52, ) = 27.28, p =.001, ƞ 2 =.38, and in front view, F(2.31, ) = 6.90, p =.002, ƞ 2 =.13 (Bonferroni). However, while repeated contrasts revealed that ERs in the head condition increased from rotation angles of 90 on for figures in back view, ps <.001, ERs for figures in front view were rather constant between 0 and 90, significantly decreased between 90 and 135, and significantly increased between 135 and 175, suggesting a U-shaped relationship, ps <.004.

20 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 19 No compatibility effect emerged among adults in the head condition, ps >.34 (Bonferroni), but children made significantly less errors if upright figures were presented from the back than from the front, t(26) = 6.46, p =.006, d = 1.40 (Bonferroni), while the effect was absent for inverted figures, p =.097. To sum up, in both the head and arm condition children made more errors than adults, while figures presented in front view elicited only in children more errors than figures in back view. Performance got worse with larger rotation angles for figures presented in back view, while the effect was less clear for figures in front view, including in- and decreasing ERs. Indicators of a compatibility effect emerged only among children but not among adults. Relationship between ERs and RTs To check for a potential speed-accuracy tradeoff (Parsons, 1987a), correlations between ERs and RTs were computed separately for each age group, condition, and view. Significant but positive correlations emerged only among adults if they were presented with figures from the back in both the arm condition, r =.51, p =.027, and head condition, r =.59, p =.008. Adults with longer RTs in these tasks made more errors, which contradicts the assumption of a speed-accuracy tradeoff. Discussion The aim of the present study was to further investigate the effect of view in spatial judgment tasks that involve rotated human body stimuli. To ensure that stimuli in front and back view differed only with regard to their view and not concerning their visibility of facial features, a head condition with constant facial information was implemented for the first time in addition to an arm condition, in which the visibility of facial features differed between front and back view (e.g., Steggemann et al., 2011). The general advantage of back view of human figures could be replicated: RTs were shorter and ERs smaller compared to figures presented in front view. This advantage became

21 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 20 apparent not only in the arm condition but also in the head condition, in which facial information was held constant in both views. In addition, it emerged in adults and in children with one exception: In the head condition, only children but not adults yielded smaller ERs for figures presented from the back. A linear relationship between rotation angles and RTs was observed only for figures presented in back view. This was true for both age groups and both tasks, suggesting that participants applied a mental rotation strategy only in these cases but not if they were presented with figures in front view, no matter of whether facial information was held constant between front and back view (i.e., head condition) or not (i.e., arm condition). The effect of rotation angle on ERs was less clear. It emerged for figures presented in back view in the arm condition only among children but not among adults. Potentially, adults used quite efficient strategies that resulted in an almost error-free performance across all rotation angles (see Fig. 3), and the corresponding effect emerged only in RTs (i.e., speedaccuracy tradeoff). In the more demanding head condition, the effect of rotation angle on ERs was significant across both age groups. The effect of rotation angle for figures in back view was in line with what could have been expected, that is, some, but not all ERs became larger for larger rotation angles. For figures in front view, in contrast, rotation angle yielded an effect on ERs in the head condition, too. However, this relationship was rather U-shaped than showing a monotonic increase. Furthermore, there were indicators for a compatibility effect of stimulus orientation and response location that became apparent only for upright standing figures: Children and adults reacted in both conditions faster if upright figures were presented from the back. However, the opposite effect faster RTs for inverted figures presented from the front did not emerge. Concerning ERs, a compatibility effect was revealed only for children in both

22 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 21 conditions, but not for adults: Children presented with upright figures in back view made less errors in both the arm and head condition compared to upright figures in front view. Finally, children performed overall more poorly than adults with regard to RTs as well as ERs. Besides that, similar patterns were observed for children and adults, implying that the effect of view in spatial judgments that involve human body stimuli is already present in 9- year-olds. However, children also differed from adults in some aspects: Children s ERs but not adults in the head condition were affected by the view of the figures. Furthermore, only children but not adults showed indications for a compatibility effect with regard to their ERs in both conditions, and in the arm condition, there was a significant effect of rotation angle on children s but not on adults ERs. Our results in the head condition suggest that effects elicited by front and back view on human figures cannot solely be assigned to differences of figures facial information. Instead, there are quantitative and qualitative differences between both views that point to the use of different strategies. Figures in back view seem to elicit a mental rotation strategy that often leads to faster and less error prone reactions. In contrast, figures in front view appear to impair participants performance and rather constant RTs suggest that this performance does not depend on rotation angle but that participants use other strategies (cf. Murray, 1997; Steggemann et al., 2011). The findings concerning the effect of view are in line with previous studies involving laterality judgments, in which participants were presented with photographs in which face information was not held constant across both views (e.g., Kaltner et al., 2014; Steggemann et al., 2011; Zacks et al., 2002). An exception is the study of Parsons (1987a, Exp. 1) who used line drawings of humans and reported increasing RTs with larger rotation angles also for figures in front view. However, a closer view on the data shows that only ten adults were tested and RTs for figures in front view varied only in a range of about 120 ms across rotation angles, while the range of RTs for figures in back view was about 390 ms.

23 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 22 Moreover, in Exp. 2 of Parsons study, in which participants had to indicate the target side verbally instead of pressing a key, RTs for figures presented in front view did not increase if they were shown without any context. An increase with larger angles for figures in front view occurred only if they were embedded in a spatial context (i.e., a picture of a room). Thus, the finding of increasing RTs with larger rotation angles for figures in front view might not be as reliable as for figures presented in back view probably, as two different processes take place, that is, straight forward object-based transformations for figures in back view versus more complex perspective transformations for figures in front view (Zacks & Tversky, 2005). In contrast to previous studies (May & Wendt, 2012; Parsons, 1987a), the effect of stimulus-response compatibility was not as clear as expected. It emerged only for upright figures but not for inverted figures. Potentially, the effect of view is stronger and overwrites the compatibility effect. In other words, figures presented in front view are hard to judge anyway, irrespectively of their orientation so that a stimulus-response compatibility for inverted figures presented in front view cannot outrun the main effect of view. However, one has to keep in mind that May and Wendt (2012) and Parsons (1987a), who found a compatibility effect, used line drawings and not photographs, as we did in our study. Moreover, May and Wendt (2012) explicitly manipulated stimulus-response compatibility by varying the assignment of the keys used to indicate a left or right response, which was not the case in the present study. Thus, further research is necessary to examine compatibility effects under different conditions. Interestingly, children were more strongly affected by the effect of view as indicated by larger ERs in the head condition if figures were presented in front view compared to back view than adults, for whom this effect was not significant. In the head condition, children yielded the largest ERs for upright, frontal figures. Potentially, children could not suppress to follow the gaze of the figure, which opposes the response location for frontal figures rotated

24 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 23 by small angles. This effect might also account for decreasing ERs between 90 and 135 for figures in front view in the head condition, as at 135 but not at 90 gaze direction and response location correspond with each other. In addition, compatibility effects between stimulus location and response location on ERs emerged only among children but not among adults. These findings could be taken as indicators that embodiment has larger effects in children than in adults, potentially as children s ability to suppress predominant actions (or imaginations) that are activated by particular stimuli has not fully developed yet (cf. Diamond, 2013). This finding is also in line with Funk et al. (2005) and Frick et al. (2009) showing that children s spatial imagery is susceptible to motoric interferences. Finally, taking a closer look at the two tasks, the results suggest that the head task was harder to solve than the arm task, for children in particular (see Fig. 2 and 3). This might be due to stimulus features: Front and back are visually more salient in the arm task, where facial information can be used, than in the head task, where facial information is constant in both views. Potentially, children rely more strongly than adults on such salient features like the face to discriminate front from back. RTs of adults in the arm and head task seemed to be comparable, but their ERs for rotation angles larger than 90 appeared to be larger, too, in the head than in the arm task. To conclude, our results confirm the assumption that people use different strategies when making laterality judgments that involve rotated human figures: If these figures are presented from the back, they mentally rotate the presented figure (or their own perspective) to align projections of their own body with that of the figure and to make a left-right judgment. If these figures are presented from the front, more complex perspective transformations take place that yield no linear relationship between rotation angle of the figure and RTs. Importantly, the effect of view emerges independently of facial information

25 SPATIAL TRANSFORMATIONS OF HUMAN FIGURES 24 and in a similar manner in children and adults. Nevertheless, children s performance appears to be more strongly affected by embodiment effects than that of adults..

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30 MENTAL ROTATION OF HUMAN BODY 29 Table 1 Linear regression analyses including rotation angle as predictor and RTs as criterion Condition Age group View ß F df p adj. R 2 Arm Adults back , 93 < front , Children back , 133 < front , Head Adults back , 93 < front , Children back , 133 < Note. Bold: significant model fit (Bonferroni corrected). front ,

31 MENTAL ROTATION OF HUMAN BODY 30 Figure 1. Example of stimuli (left: male figure, front view in head condition, rotated by 135 ; right: female figure, back view in arm condition, rotated by 45 ), presented in color in the study.