the color shade. On the trials where the ball did not change color, participants estimated the point of intersection. In this dual attention condition, we expected males to experience a degree of interference at the start of each trial because they are holding opposing strategies that depend upon whether it will be a targeting or color recognition tasks. The interference would derive from their bias toward bottom up-processing for targeting, which goes against the required top- down strategy for object recognition. Therefore, we expected male targeting performance to be relatively impaired in this condition compared to performance observed when only targeting was required. In contrast, we reasoned that a top-down strategy for targeting in females should present little interference and their performance should be similar to targeting alone. Support for these hypotheses is provided in the results of the studies described below. Results Targeting and Reaction Time (Experiment 1) Preliminary analyses of the accuracy results of Experiment 1 revealed no left/right error bias, so this factor was included in subsequent analyses. Accuracy across the four conditions was analyzed using a 2 (Gender)63 (Ball Speed)64 (Ball Perspective) ANOVA with repeated measures over Speed and Ball Orienta- tion. Main effects were observed for Gender (F[1,33] = 9.17; p,0.01), and Ball Orientation (F[3,99] = 88.02; p,0.0001). There was also a significant Gender X Ball Orientation interaction (F[3,99] = 7.81; p,0.001). As shown in Fig. 2, males were significantly more accurate than females in both allocentric conditions, as well as Ego-2. Effect sizes for accuracy in the Allo-1 and Allo-2 conditions ranged from 0.91 to 1.1 (Cohen’s d). Reaction time showed little relationship to ball perspective, but a strong inverse relationship to ball speed was observed. Analyses revealed a main effect of Speed (F[2.66] = 57.39; p,0.0001) and a Speed X Ball Perspective interaction (F[6,198] = 2.26; p,0.05). Figure 2 shows that reaction time in both sexes decreased as ball speed increased, with a steeper change across speeds in the more difficult allocentric perspectives. Covariate analysis of error and reaction times revealed no significant relationship between the two variables across ball speed or perspective. Color Shade Detection and Reaction time (Experiment 2) Accuracy in discriminating the color shade was analyzed using a 2 (Gender)62 (Ball Speed)62 (Ball Orientation) ANOVA with repeated measures over Speed and Ball Orientation. A similar analysis was employed to analyze reaction time. The analysis of color discrimination accuracy revealed significant main effects for Ball Orientation (Ego-2 vs Allo-1: F[1,26] = 4.44; p,0.05) and ball speed (F[1,26] = 5.12; p,0.05), as well as a significant interaction between condition and speed (F[1,26] = 7.67; p,0.02). No sex effects were observed. As shown in the upper panel of Figure 3, accuracy in both sexes was similar in both conditions at the slow speed, whereas there was a significant drop in accuracy in the Allo- 1 condition at the fast speed. The analysis of reaction time revealed significant main effects for Ball Orientation (F[1,26] = 7.38; p,0.02) and Ball Speed (F[1,26] = 24.75; p,0.0001). The bottom panel of Figure 3 shows that reaction time to make a choice was faster when the balls travelled at 8 cm/sec compared to 4 cm/sec. Reaction times at both speeds were slower for the Ego-2 condition compared to the Allo-1 condition. Dual Attention Results. Target accuracy and reaction time were each analyzed using a 2 (Gender)62 (Ball Speed)62 (Ball Perspective) Sex Differences in Processing Movement vs Objects ANOVA, with repeated measures over Ball Speed and Ball Perspective. The analysis of target accuracy revealed only a main effect of Ball Perspective (F[1,44] = 88.35; p,0.0001). As shown in Figure 4, error rates were significantly higher at both speeds in the Allo-2 condition, compared to the Ego-2 condition. Males and females did not show any significant differences in targeting accuracy in this task. The analysis of color accuracy revealed a significant interaction between Ball Perspective and Gender (F[1,44] = 4.85; p,0.05). Figure 4 shows that female color accuracy was significantly better than male accuracy in the Ego- 2 perspective at 4 cm/sec (p,0.05). Main effects for Ball Speed were observed in the analysis of the target response reaction time, (F[1,44] = 7.37; p,0.01) and the analysis of the response time to make a color choice (F[1,44] = 24.27; p,0.0001). Figure 5 shows that the reaction time in males and females decreased when ball speed was increased from 4 cm/sec to 8 cm/sec. No significant sex differences were observed in reaction time. Dual Attention: Within Subject Comparison across Conditions Data were analyzed using a 2 (Gender)62 (Color and Target Accuracy in the single condition)62 (Color and Target Accuracy in the dual condition) ANOVA with repeated measures over the last two factors. The analysis yielded main effects for Gender (F[1,31] = 15.61; p,0.0004, Single Condition (F[1,31] = 6.36; p,0.02, and Dual Condition (F[1,31] = 199.8; p,0.0001), as well as interactions between Gender and Dual Condition (F[1,31] = 12.16; p,0.01), and Single Condition and Dual Condition (F[1,31] = 8.18; p,0.01). Overall, the analysis revealed that target accuracy was better in males under both conditions compared to females. However, males and females showed a differential response pattern under dual attention conditions compared to single testing of color and target accuracy. These effects were examined in subsequent analyses, where target and color accuracy were separately analyzed using a 2 (Gender)62 (Condition: Dual vs Single) with repeated measures over Condition. The analysis of target accuracy yielded main effects of Gender (F[1,30] = 12.42; p,0.01) and Condition (F[1,30] = 10.63; p.0.001). Subsequent analyses revealed that male, but not female, accuracy was significantly poorer under the Dual Attention condition (F[1,14] = 7.5; p,0.02). Male color accuracy was also found to be significantly poorer under the dual attention condition as reveled by a Gender X Condition interaction (F[1,30] = 4.77; p,0.04). These results are depicted in Figure 6. Discussion These studies show a large and consistent male advantage for accurately estimating the vector of a moving ball. The sex difference is present whether the ball movement has an egocentric or allocentric orientation and is not influenced significantly by slow or fast ball speeds. In Experiment 1, the size effect of the sex difference approached 1.0 in the allocentric conditions, which is in the range reported for sex differences in targeting tasks that involve physical responses such as catching or throwing [14]. These findings support the assumption that perceptual factors unrelated to motor coordination play an essential role in the sex difference in targeting performance [12,14]. Support for the hypothesis that males are biased for processing movement over objects was found in the results from the dual attention experiments. The large sex difference in targeting performance that we observed in Experiment 1 was absent in the dual attention condition in Experiment 3. In this experiment, PLoS ONE | www.plosone.org 4 March 2012 | Volume 7 | Issue 3 | e32238