deceleration time, and placing time, and a decrease in placing peak velocity (Table 1 and Fig. 2). Variabilty of placing end point on receiver’s coronal plane was not affected by task (YSD F(1,11) = 0.16, n.s., ZSD F(1,11) = 0.19, n.s.). The slowing down of the final phase of reach, and of the whole placing, observed in the conspecific feeding task indicates an increasing accuracy in the control of all the sequence, due to an interaction with the entire receiver’s body, rather than in the control of the final placing phase, due to an interaction with the receiver’s mouth only (see the results concerning variability of placing end point). A first hypothesis explaining these results is that they are due to a social affordance implicitly demanding greater visual control of sequence execution. The social affordance could be activated by the social request to be fed (remember that the conspecific’s mouth was opened before and during sequence execution). A second consistent hypothesis is that the hand trajectory was close to the conspecific’s body (i.e. inside the peripersonal space, [14]); this could require greater accuracy in trajectory control in order to avoid touching the conspecific’s (receiver’s) body. These two hypotheses were tested in experiments 2 and 4 (first hypothesis) and 3 (second hypothesis). Experiment 2 In experiment 2 we dissociated the social request to be fed from the final intention of the sequence of reaching-grasping and placing; specifically, the action sequence was directed to a mouth-like aperture in a support placed either beside the conspecific’s face (close-to-conspecific placing task) or the ‘‘face’’ of the body shape (close-to-body-shape placing task, Fig. 1). Before and during the conspecific placing task the conspecific’s mouth was opened as in experiment 1. If the social request (i.e. the opened mouth) is responsible for increasing accuracy in sequence control because a social affordance is activated, we could find an effect on sequences directed to the conspecific even when they were unrelated to feeding. Methods Participants. A new sample of twelve right-handed [18], naive volunteers (6 females and 6 males, age 20–23 yrs.) participated in the experiment. Social Request and Social Affordance Apparatus, stimuli and procedure. The same apparatus and stimuli as in experiment 1 were used, except that the final target of the sequence of actions was an ellipse-shaped slit resembling a human mouth (mouth-like aperture) whose size was approximately the same as that of the human receiver’s mouth (when it was opened). The support of the mouth-like aperture was placed either beside the conspecific’s right cheek or the corresponding position of the human body shape used in experi- ment 1 (Fig. 1). The participants were required to reach-grasp and place the sugar lump into the mouth-like aperture next the right conspecific’s cheek (close-to-conspecific placing task) or the corresponding position of the human body-shape’s (close-to-body- shape placing task). The conspecific’s mouth was opened as in experiment 1. The remaining procedure was the same as in experiment 1. Movement recording and data analysis. Movement recording and data analysis were the same as in experiment 1 except that two markers were attached to the upper and lower edges of the mouth-like aperture beside the conspecific’s right cheek or the corresponding position of the human body shape. In the ANOVAs the within-subjects factor was task (close-to- conspecific placing task vs close-to-body-shape placing task). Results Reach peak deceleration and placing peak velocity decreased in the close-to-conspecific placing task as compared to the close-to- body-shape placing task (Table 1 and Fig. 2). In sum, both the final reach and the placing were slowed down in the close-to-conspecific placing task. Experiment 3 In experiment 3 the participants executed the same two tasks (i.e. close-to-conspecific placing and close-to-body-shape placing); however, the position of the sugar lump was closer to the conspecific’s body as compared to experiments 1 and 2. Differently from experiment 2, the conspecific’s mouth was closed. If the peripersonal space is responsible for increasing accuracy during reaching and placing, we should find greater effect for hand trajectories closer to the conspecific’s body. Table 1. Results of the ANOVAs performed on the kinematic parameters collected in experiments 1–6. FACTOR TASK Experiment 1 Experiment 2 Experiment 3 Experiment 4 Experiment 5 Experiment 6 Peak Velocity of Finger Opening (mm/s) Maximal Finger Aperture (mm) F(1,11) = 3.6 p = 0.08 F(1,11) = 0.02, n.s. F(1,11) = 6, p = 0.032; F(1,11) = 1.6, n.s. g2p = 0.4 F(1,11) = 0.3, n.s. F(1,11) = 0.4, n.s. F(1,11) = 0.5, n.s. F(1,11) = 0.15, n.s. F(1,11) = 0.01, n.s. F(1,11) = 0.58, n.s. F(1,11) = 7.1, p = 0.022, g2p = 0.4 F(1,11) = 0.12, n.s. F(1,11) = 0.15, n.s. F(1,11) = 0.10, n.s. F(1,11) = 0.02, n.s. GRASPING F(1,11) = 0.8, n.s. F(1,11) = 0.5, n.s. F(1,11) = 0.7, n.s. REACHING Reach Peak Velocity (mm/s) PLACING Placing Time (ms) g2p: partial eta squared. doi:10.1371/journal.pone.0015855.t001 Percentage of Reach F(1,11) = 6.7, Deceleration Time (%) p = 0.025; g2p = 0.4 Reach Peak Deceleration (mm/s2) F(1,11) = 0.9, n.s. F(1,11) = 12.1, p = 0.005; g2p = 0.5 F(1,11) = 1.1, n.s. F(1,11) = 0.02, n.s. F(1,11) = 4, p = 0.07 F(1,11) = 1.35, n.s. F(1,11) = 0.26, n.s. F(1,11) = 7.2, p = 0.021; g2p = 0.4 F(1,11) = 0.1, n.s. F(1,11) = 1.5, n.s F(1,11) = 0.12, n.s. F(1,11) = 7.1, p = 0.021; g2p = 0.4 F(1,11) = 4.3, p = 0.06 F(1,11) = 0.09, n.s. F(1,11) = 0.01, n.s. F(1,11) = 0.18, n.s. F(1,11) = 1.97, n.s. Placing Peak Velocity (mm/s) F(1,11) = 33, F(1,11) = 5.8, F(1,11) = 39.2, F(1,11) = 25, F(1,11) = 9.1, F(1,11) = 52.1, p,0.001; g2p = 0.7 p = 0.034; g2p = 0.4 p,0.001; g2p = 0 .8 p,0.001; g2p = 0.7 p = 0.01; g2p = 0.5 p,0.001; g2p = 0.8 PLoS ONE | www.plosone.org 4 January 2011 | Volume 6 | Issue 1 | e15855