Presence of a human catcher affects performance in a ball-throwing task.

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Learn more: PMC Disclaimer | PMC Copyright Notice Exp Brain Res . 2026 Apr 9;244(5):84. doi: 10.1007/s00221-026-07284-z Search in PMC Search in PubMed View in NLM Catalog Add to search Presence of a human catcher affects performance in a ball-throwing task Ayane Kusafuka Ayane Kusafuka 1 Department of Intermedia Art and Science, Faculty of Science and Engineering, Waseda University, Tokyo, Japan Find articles by Ayane Kusafuka 1, ✉ , Daiki Yamasaki Daiki Yamasaki 2 Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan Find articles by Daiki Yamasaki 2 , Yuto Sakakibara Yuto Sakakibara 2 Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan Find articles by Yuto Sakakibara 2 , Taishi Okegawa Taishi Okegawa 2 Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan Find articles by Taishi Okegawa 2 , Takuya Murakami Takuya Murakami 2 Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan Find articles by Takuya Murakami 2 , Saki Takao Saki Takao 3 Waseda Institute for Advanced Study, Waseda University, Tokyo, Japan Find articles by Saki Takao 3 , Katsumi Watanabe Katsumi Watanabe 1 Department of Intermedia Art and Science, Faculty of Science and Engineering, Waseda University, Tokyo, Japan Find articles by Katsumi Watanabe 1 , Kazutoshi Kudo Kazutoshi Kudo 2 Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan Find articles by Kazutoshi Kudo 2 Author information Article notes Copyright and License information 1 Department of Intermedia Art and Science, Faculty of Science and Engineering, Waseda University, Tokyo, Japan 2 Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan 3 Waseda Institute for Advanced Study, Waseda University, Tokyo, Japan Communicated by Bill Yates ✉ Corresponding author. Received 2025 Dec 16; Accepted 2026 Mar 17; Issue date 2026. © The Author(s) 2026 Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/ . PMC Copyright notice PMCID: PMC13065593  PMID: 41954629 Abstract Target characteristics can influence motor performance in goal-directed tasks by affecting cognitive and affective processes. This study investigated whether motor performance in a ball-throwing task differed when the target was held by a person, compared with when the target was a physical mark. Eighteen healthy adults without baseball experience participated. Each participant threw 15 fastballs across three blocks, each with a different target condition. In the Mark condition, the target was a visible mark on the net. In the Humanoid condition, the same mark was placed on a humanoid board. In the Catcher condition, the mark was held by a person. Mean ball speed, absolute error of arrival positions, pupil diameter, and subjective ease of throwing were compared across conditions. Mean ball speed and absolute error were significantly lower in the Catcher condition than in the other two conditions. Conversely, pupil diameter and subjective ease were significantly higher in the Catcher condition. These results indicate that when the target is held by a person, participants prioritized accuracy over speed. Increased pupil diameter in the pre-movement state suggests heightened arousal in the Catcher condition, which was associated with improved accuracy. Subjective ease also increased in this condition. These findings suggest that an implicit social or safety-related goal of allowing the person to catch the ball, such as safety and harm-avoidance considerations for the catcher, led participants to focus more on precise throws, contributing to the understanding of how cognitive and affective processes influence motor control. Keywords: Target, Speed, Accuracy, Motor control, Arousal, Subjective ease Introduction Accurately projecting an object (e.g., a ball) toward a target beyond one’s reach is a fundamental human motor skill. This skill, rooted in early human history, continues to be utilized and is still observed in various sports tasks such as throwing, kicking, and hitting collectively called goal-directed motor tasks, although its necessity for survival has diminished over time (Darlington 1975 ; Roach et al. 2013 ). In these tasks, various target characteristics can alter motor performance by engaging different cognitive-affective processes. For example, target size (Zahradnik et al. 2008 ; Gray et al. 2017 ), target shape (Gray et al. 2017 ),vertical or horizontal target position (Watts et al. 2004 ; Rousanoglou et al. 2015 ; van den Tillaar 2020 ), and throwing distance (Anderson and Pitcairn 1986 ; Trewartha et al. 2008 ; Zahradnik et al. 2008 ; Ramezanzade et al. 2022 ) often influence throwing motion or the accuracy of the ball arrival position, though some studies have found no effect of certain target changes or their longer-term retention (Ong et al. 2015 ; Kimura et al. 2023 ; Kusafuka et al. 2023b ). Therefore, not all characteristics of the target necessarily affect motor performance. Such effects of the target on motor performance have been investigated across a wide range of movements other than throwing, from simple laboratory motor tasks to dynamic sports tasks. However, there are many situations where balls are projected not only at objects but also at people. In fact, many previous studies have used throwing tasks aimed at a person, often referred to as a catcher (Kawamura et al. 2017 ; Kusafuka et al. 2020 , 2021 ). Notably, while previous studies have used human catchers as targets, no previous experiment has directly compared throwing toward a person and toward an inanimate target under equivalent conditions, thereby isolating the effect of human presence itself. The present study aimed at directly testing whether the presence of a human target, which integrates social presence with associated contextual constraints, modulates throwing speed, accuracy, and arousal. To minimize the confounding effects of prior skill levels and habituation to human targets, only novice participants without baseball experience were recruited. Social psychology research suggests that the mere presence of others can change an individual’s performance (social facilitation/inhibition) (Zajonc and Burnstein 1965 ; Bond and Titus 1983 ), but this has not been tested in a precise motor task context. This study addresses this gap by determining whether a thrower’s behavior changes when the target is a human. The cognitive, affective, physiological, and physical responses of humans are known to vary depending on whether other people are present (Kilner et al. 2003 ; Mukai et al. 2024 ). In a soccer penalty kick, the presence of a goalkeeper (an opponent to avoid) was found to alter kick accuracy (Navarro et al. 2013 ). Therefore, motor performance in throwing tasks may also differ accordingly. This study focused on whether the target being human or non-human constitutes a meaningful characteristic. This study examined whether motor performance in a basic aimed ball-throwing task differed when the target was held by a person, compared to when the target was a physical mark. Social psychology has long noted that the human target context can affect performance (sometimes enhancing simple skills and hindering complex ones), a phenomenon known as social facilitation (Zajonc and Burnstein 1965 ; Bond and Titus 1983 ). This study brings that question into a motor control context. In the present study, the throwing task is defined as a complex motor task reflecting a basic aimed throwing motion, as it requires the sophisticated coordination of multiple body segments to achieve both high speed and high accuracy simultaneously. However, classic social facilitation theory typically focuses on tasks with a single performance measure, and models that predict the effects of social presence on tasks requiring a trade-off between multiple indices remain scarce. Given this, it was hypothesized that the presence of a human target would differentially affect throwing speed and accuracy. From a sensorimotor perspective, the presence of a human target may also introduce specific safety constraints and risk-minimization goals. Throwing toward a person, unlike an inanimate target, may require balancing performance objectives (speed and accuracy) with the need to prevent injury to the recipient. Consistent with our focus on the trade-off between speed and accuracy, both metrics were compared between conditions involving three types of targets (ranging from a simple mark to a humanoid board and a real person). These variations were used to clearly separate the influence of human shape from the influence of the presence of a real person. Moreover, to examine mechanistic aspects of cognitive and affective processes, pupil diameter, and subjective ease of throwing were assessed. Pupil diameter was used as an index of arousal (Bradshaw 1967 ), through activation of the locus coeruleus–norepinephrine (LC-NE) system (Oliva and Anikin 2018 ), and subjective ease of throwing were focused on. Recent research suggests that the presence of others can trigger shifts in autonomic activity, where pupil diameter serves as a reliable proxy for LC–NE activation and attentional engagement (Oliva and Anikin 2018 ). Specifically, in interpersonal situations, pupil dilation has been linked to social attention and the perceived evaluative pressure of being watched (Castellotti et al. 2021 ). Therefore, pupil diameter was measured as an index of arousal to mechanistically investigate how the presence of a catcher modulates the internal state of the thrower and the performance. According to the Yerkes-Dodson Law (Yerkes and Dodson 1908 ), the relationship between arousal and performance follows an inverted-U functional shape, where an optimal level of arousal facilitates performance, but excessive arousal impairs it, particularly in complex tasks. In this study, it was hypothesized that the social presence of a human target would increase arousal, as reflected in pupil diameter. For throwing speed and accuracy, it is possible that this increase in arousal has a facilitatory effect or that the arousal exceeds the optimal threshold for fine motor control or create a cognitive distraction, thereby leading to a deterioration in performance. The results of this study provide insights into how dynamic social cues and physical attributes of targets implicitly affect the execution of motor tasks. Practically, these findings can help to design training environments. By strategically using physical targets or live catchers, throwers can practice regulating their arousal levels to maintain optimal speed and accuracy. This allows for more targeted performance enhancement that accounts for the psychological impact of a human presence. Methods Experiment Eighteen healthy adults (7 females; mean height: 1.60 ± 0.05 m, weight: 48.9 ± 4.0 kg; 11 males; mean height: 1.70 ± 0.04 m, weight: 64.6 ± 7.7 kg; mean age: 26.1 ± 2.0 years; 17 right-handed and 1 left-handed) with no baseball experience participated in the study. All the participants had never belonged to a baseball team. Their throwing style was overhand. All experiments were performed in an indoor experimental room, and a ball with a diameter of 0.065 m and a weight of 0.07 kg (a commercially available magic ball consisting of a lightweight hard core covered with high-quality nylon loop fabric for hook-and-loop adhesion) was used. It possesses sufficient strength to resist deformation even when gripped. This ball was specifically selected because its material ensures the safety of the catcher and makes it easy for novice participants to handle without injury risk. The participants warmed up by performing light throwing practice before the experiment. At the beginning of the experiment, participants were instructed on a standard grip for the ball and performed practice trials to familiarize themselves with the task. This procedure ensured that all participants, despite having no prior baseball experience, could sufficiently control the balls. Each participant threw a fastball 15 times across three blocks, each with a different target condition. In the Mark condition, the target was a visible mark on a net. In the Humanoid condition, the same mark was placed on a humanoid board. In the Catcher condition, the mark was held by a person. The mark was two-colored (pink and green) and made of hook-and-loop fastener, allowing the ball to stick upon impact. The net behind the target (approximately 2.9 m × 4.7 m), made of green polyethylene mesh, was large enough to capture all throws. There was only one experimenter (height: 1.77 m, weight: 75 kg) acting as the catcher, the same one for all participants; he held the mark with his left hand and caught the ball directly with the same hand. No bulky protective gear (e.g., a chest protector or protective glasses) was used to maintain the naturalistic social presence of the human target. The use of a soft ball, combined with the catcher’s ability to respond to incoming balls, provided sufficient protection. To ensure safety, participants were explicitly informed that the catcher was an experienced player with over 10 years of experience. The board used in the Humanoid condition was made of lightweight plywood and was painted as a matte white, life-sized human silhouette without facial or clothing details. It was created to be the same size as the catcher by modeling it after him. The target was a two-colored (pink and green) circular mark with a radius of 0.1 m, whose center was positioned 1.3 m above the floor and located 9 m from the participants (Fig. 1 ). The condition order was counterbalanced across participants using complete counterbalancing to eliminate systematic sequence effects on comparisons across conditions. The interval between throws was approximately 10 s, and a 5-minute rest period was provided between blocks to prevent fatigue. Given that the ball weight (0.07 kg) was significantly lighter than a standard baseball (approx. 0.145 kg), and including the rest periods, no participant reported or exhibited performance declines attributable to physical fatigue. Participants were instructed to aim at the target and throw as fast and accurately as possible. In the Catcher condition, participants were told that the error was defined as the distance from the mark’s initial position, even though the catcher would still attempt to catch balls that deviated from that position. The study was approved by the Ethics Committee of the University of Tokyo in accordance with the Declaration of Helsinki, and all participants provided written informed consent. Fig. 1. Open in a new tab Experimental setup. A speed gun and a camera positioned behind the participants were used to measure ball speed and arrival position, respectively. Pupil diameter was recorded using a wearable eye tracking device. Each participant threw fastballs across three blocks, each with a different target condition. In the Mark condition, the target was a visible mark on a net. In the Humanoid condition, the same mark was placed on a humanoid board. In the Catcher condition, the mark was held by a person. The target was a circular mark with a radius of 0.1 m, the center of which was positioned 1.3 m above the floor and located 9 m from the participants A speed gun (Stalker Pro Ⅱ, Applied Concepts Inc. / Stalker Radar, US) and a camera (DSC-RX10M4, SONY, Japan; 120 fps) positioned behind the participants, were used to measure ball speed and arrival position, respectively (Fig. 1 ). There were no markings on the ball. Consequently, the coordinates of the center of the ball were determined by manually identifying the geometric center of the ball’s silhouette from the camera images to obtain the ball arrival position. This manual digitization approach is a common practice in studies involving ball-throwing tasks (e.g., Kusafuka et al. 2023b ). To ensure high accuracy, it was confirmed that the maximum spatial error of this method was within 0.01 m, which is consistent with the precision required for performance evaluation in this field. The frames in which the ball arrived were selected by qualitative observation of the camera images. Pupil diameter was recorded using a wearable eye-tracking device (Pupil Core, Pupil Labs, Germany) at a sampling frequency of 200 Hz. The device has two eye cameras and one scene camera. The experiments were conducted in a room with constant overhead LED lighting, and all windows were covered with blinds. After completing the task, participants rated the subjective ease of throwing in each condition using the 10-point method. A score of 1 indicated that participants felt it was very difficult to throw, whereas a score of 10 indicated that it was very easy to throw. To capture the participants’ holistic experience without bias, a restrictive definition of “ease” (e.g., focusing only on muscle sensation or throwing speed) as not provided. Instead, participants were instructed to report their overall impression of each condition. The values were then z-scored for each participant to account for individual baseline differences. Data processing of ball parameters The tracking procedure used in this study to obtain the ball arrival positions was the same as in previous studies (Kusafuka et al. 2020 , 2021 , 2023b ). The position coordinates of the ball arrivals were obtained using camera images and numerical analysis software (MATLAB, MathWorks, US). The arrival points of the thrown ball in the camera images were obtained by digitizing the center of the ball at the moment of arrival. The moment of arrival was defined as the frame in which the ball hit the mark or net, even if it missed a target, since the targets were positioned on the net. In the Catcher condition, because the catcher pursued balls even when they deviated from that position, the moment of arrival was defined as the frame in which the ball hit the mark. In the Catcher condition, the arrival position was defined as the coordinates where the ball contacted the mark or the plane of the net. It should be noted that in almost all trials, the ball reached the mark or its immediate edge, ensuring that the interception point remained consistent across conditions. The instant of the ball release was identified by qualitative observation of the camera images. Three points in the horizontal direction (at intervals of 2.44 m) and three points in the vertical direction (at intervals of 1.5 m) were calibrated, giving a total of nine calibration points for transforming the position coordinates. For calibration, the marks on the net were digitized, and their measured lengths were used. The maximum error was confirmed to be 0.01 m. Arrival position coordinates were calculated using the 2D direct linear transformation (2DDLT) in MATLAB. Although the catcher’s pursuit of deviating balls could introduce slight temporal variations and potential parallax or trajectory errors due to the nature of 2DDLT, the catcher was instructed to remain as close to the plane of the first position as possible to minimize bias. Furthermore, as accuracy was measured based on the two-dimensional coordinates on the calibrated plane, these minor differences in the arrival frame are unlikely to have systematically biased the error of arrival position or pupil diameter data across conditions. The three-dimensional global orthogonal coordinates were defined as follows: the center of the throwing position on the floor was considered the origin; the x-axis was oriented to the right from the participant’s view; the y-axis was oriented toward the target right from the throwing position, and the z-axis was oriented vertically upward (Figure. 1). Ball arrival positions were defined based on the x-axis and z-axis of this global coordinate system. The absolute error of the ball arrival position was defined as the distance between the ball arrival position and the center of the target. In the Catcher condition, the error was also defined as the distance from the first position, which was checked with a ruler to be the same as in the other conditions for each trial. Ball speed was defined as the magnitude of the velocity at ball release obtained by the speed gun. Data processing of pupil parameters Measured pupil diameters were analyzed using Pupil-Player (Pupil Labs, v 1.15). Although subtle fluctuations in ambient luminance may have occurred depending on the time of day, a within-subject design was utilized to ensure that ambient light remained relatively stable during each participant’s session. The start and end of each condition for each participant were identified by visual inspection of the video taken by the scene camera mounted on Pupil Core, and the data in the interval between them were used for the analysis. The Pupil Labs guidelines recommend that detection data be used only when the confidence value of the pupil’s center location is more than 60% ( https://docs.pupil-labs.com/core/software/pupil-player/#raw-data-exporter ). In this experiment, all pupil data with confidence value less than 70% were excluded (40.9% of total data), following Pupil Labs guidelines, to improve the reliability of the analysis. Valid sample proportions were similar across conditions (Mark: 41.2%, Humanoid: 40.1%, Catcher: 41.1%). Due to rapid head movements during the throwing execution, data points with low confidence values were objectively excluded. The exclusion was based on software confidence rather than a fixed temporal window. Consequently, the analyzed high-confidence data primarily reflect the pre-movement state of a period of relative stability where the participant focuses on the target immediately before the initiation of the throw. Thus, the current results primarily reflect sustained tonic pupil diameter during this preparatory phase, rather than phasic, time-locked responses at ball release. The current results primarily reflect the tonic pupil diameter and pre-movement states rather than phasic, time-locked responses at the moment of ball release. Given that this data loss occurred consistently across conditions, the observed differences were consider to be representative of the sustained physiological arousal associated with each context. Statistical analysis A priori power analysis was conducted to ensure sufficient sensitivity to indicate the sample size ( n = 18) is appropriate for a within-subject design. Based on a medium-large expected effect size (Cohen’s d = 0.8) and α = 0.05 (two-tailed), the planned sample size yields an estimated statistical power of 0.87 for detecting differences between conditions. An effect size of d = 0.8 was selected based on Cohen’s (1988) widely-used conventions for a “large” effect, which are applied when field-specific estimates are unavailable. This value represents a theoretically and practically meaningful difference that our experimental manipulation was designed to detect. For each participant, the data from the fifteen trials in each condition were averaged to produce a single mean value per condition. The mean ball speed, absolute error of arrival positions, pupil diameter, and subjective ease of throwing were compared across conditions using pairwise t-tests. Data normality was assessed using the Shapiro-Wilk test and visual inspection of Q-Q plots. As the data satisfied the assumption of normality (all ps > 0.05), paired-samples t-tests were employed for all comparisons. This approach of planned comparisons was chosen to directly examine the specific contrasts between conditions while strictly controlling for the family-wise error rate via the Holm-adjustment method. The All Holm-adjusted p-values are reported. Paired-samples effect sizes (d₍z₎) with 95% CIs for each contrast were additionally reported. Statistical significance was defined as p < 0.05. In addition, repeated measures correlations were performed for ball speed and absolute error of ball arrival position, subjective ease of throwing and mean ball speed, and subjective ease of throwing and the mean absolute error of ball arrival position. They were implemented using the rmcorr package in R (Bakdash & Marusich, 2017 ). The unit of analysis was participant × condition means, and all p-values for these correlations were adjusted for multiplicity using the Holm method to ensure reproducibility and statistical rigor. The purpose of analyzing the relationship between ball speed and absolute error was to evaluate correlations at the trial level (within-participant) in addition to the condition level (between-participant). Results Ball parameters Figure 2 shows the mean ball speed and the absolute error of ball arrival position in each condition. The plots represent the value of each participant. The mean ball speed and mean absolute error of arrival positions were significantly lower in the Catcher condition compared to the other two conditions (Mark: 15.4 ± 5.9 m/s (= 55.4 ± 21.3 km/h), Humanoid: 15.2 ± 5.5 m/s (= 54.7 ± 19.9 km/h), Catcher: 14.4 ± 4.9 m/s (= 51.9 ± 17.8 km/h); Mark: 0.76 ± 0.41 m, Humanoid: 0.76 ± 0.36 m, Catcher: 0.65 ± 0.33 m). Pairwise t-tests confirmed that the differences between Catcher and Mark were significant (Ball speed: t(17) = 3.40, p < 0.01, d₍z₎ = 0.80, 95%CI[0.23 1.37]; Absolute error: t(17) = 2.95, p = 0.01, d₍z₎ = 0.70, 95%CI[0.14 1.25]), as were the differences between Catcher and Humanoid (Ball speed: t(17) = 2.65, p = 0.02, d₍z₎ = 0.62, 95%CI[0.08 1.17]; Absolute error: t(17) = 2.59, p = 0.02, d₍z₎ = 0.61, 95%CI[0.07 1.15]). No significant differences were observed between Mark and Humanoid (Ball speed: t(17) = 0.88, p = 0.39, d₍z₎ = 0.21, 95%CI[-0.30 0.71]; Absolute error: t(17) = 0.60, p = 0.56, d₍z₎ = 0.14, 95%CI[-0.36 0.64]). Fig. 2. Open in a new tab Mean ball speed and absolute error of ball arrival position. The graphs show the mean ball speed and absolute error of ball arrival position in each condition. Error bars indicate mean ± SD. The gray plots represent the value of each participant. * p < 0.05 Figure 3 shows the relationship between ball speed and the absolute error of ball arrival position per trial for each participant. The range in the correlations calculated across the participants was r = -0.33 to 0.17. There was no significant correlation between ball speed and the absolute error of ball arrival position in any of the participants. These results demonstrate the absence of a trial-level speed-accuracy trade-off, indicating that higher ball speeds did not systematically lead to increased positional errors in this task. Figure 4 shows the relationship between the mean ball speed and the mean absolute error of ball arrival position of all participants. There was no significant correlation between them ( r = 0.12, p = 0.46, 95%CI[-0.21 0.43]). Fig. 3. Open in a new tab Correlation between the ball speed and the absolute error of arrival position. The graphs show the correlation between mean ball speed and absolute error of ball arrival position per trial for each participant. The x-axis shows the ball speed and the y-axis shows the absolute error of arrival position. The colored points indicate the values for each trial, whose color corresponds to the condition. Across participants, the trial-level relationships did not show a consistent speed–accuracy trade-off Fig. 4. Open in a new tab Correlation between the mean ball speed and the mean absolute error of ball arrival position. The graphs show the correlation between the mean ball speed and the mean absolute error of ball arrival position of all the participants. The x-axis shows the ball speed and the y-axis shows the absolute error of arrival position. The colored points indicate the mean values for each condition of each participant, whose color corresponds to the condition. Note that these correlations reflect between-participant variability rather than within-participant control-policy shifts Pupil parameters and subjective index Figure 5 shows the mean pupil diameter and the mean subjective ease of throwing in each condition. The mean pupil diameter and mean subjective ease of throwing were significantly higher in the Catcher condition compared to the other two conditions (Mark: 3.82 × 10 − 3 ± 0.65 × 10 − 3 m, Humanoid: 3.86 × 10 − 3 ± 0.58 × 10 − 3 m, Catcher: 4.01 × 10 − 3 ± 0.68 × 10 − 3 m; Mark: -0.46 ± 0.73 pt, Humanoid: -0.22 ± 0.70 pt, Catcher: 0.68 ± 0.58 pt). Pairwise t-tests confirmed that the differences between Catcher and Mark were significant (Pupil diameter: t(17) = 3.98, p < 0.01, d₍z₎ = 1.06, 95%CI[0.34 1.79]; Subjective ease: t(17) = 4.31, p < 0.01, d₍z₎ = 1.02, 95%CI[0.40 1.63]), as were the differences between Catcher and Humanoid (Pupil diameter: t(17) = 3.20, p = 0.01, d₍z₎ = 0.85, 95%CI[0.18 1.53]; Subjective ease: t(17) = 3.58, p < 0.01, d₍z₎ = 0.84, 95%CI[0.27 1.42]). No significant differences were observed between Mark and Humanoid (Pupil diameter: t(17) = 0.66, p = 0.52, d₍z₎ = 0.18, 95%CI[-0.41 0.76]; Subjective ease: t(17) = 0.78, p = 0.45, d₍z₎ = 0.18, 95%CI[-0.32 0.68]). Fig. 5. Open in a new tab Mean pupil diameter and subjective ease of throw. The graphs show the mean pupil diameter and subjective ease of throw in each condition. Error bars indicate mean ± SD. The gray plots represent the value of each participant. *p < 0.05. Pupil data with a confidence value less than 70% were excluded from the analysis (representing 40.9% of the total data). The valid sample proportions were consistent across conditions (Mark: 41.2%, Humanoid: 40.1%, Catcher: 41.1%) Figure 6 shows the relationship between the mean subjective ease of throwing, and the mean ball speed and the mean absolute error of ball arrival position, respectively. There was no significant correlation between the mean subjective ease of throwing and the mean ball speed ( r = -0.24, p = 0.14, CI[-0.53, 0.09]). In contrast, there was a significant negative correlation between mean subjective ease of throwing and the mean absolute error of ball arrival position ( r = -0.54, p < 0.01, CI[-0.74, -0.26]). The lower the absolute error of ball arrival position, the higher the subjective ease of throwing. Fig. 6. Open in a new tab Correlation between the mean subjective ease of throw, and mean speed and mean absolute error of ball arrival position. The graphs show the correlation between the mean subjective ease of throw and the mean ball speed and mean absolute error of ball arrival position of all the participants, respectively. The values are z-scored for each participant. The x-axis shows the subjective ease of throw and the y-axis shows the ball speed and the absolute error of arrival position, respectively. The colored points indicate the mean values for each condition of each participant, whose color corresponds to the condition. The solid yellow line represents the common regression slope derived from the repeated measures correlation analysis, illustrating the within-participant association, accounting for individual differences in baseline ratings. Note that subjective ease ratings were collected after each block; thus, they may reflect the perceived performance and outcome feedback rather than real-time effort alone Discussion This study focused on whether motor performance in a ball-throwing task differed when the target was held by a person, compared to when the target was a physical mark. The findings provide insights into how dynamic social cues and physical attributes of targets implicitly affect the execution of motor tasks. The ball speed and absolute error of arrival positions were significantly lower in the Catcher condition compared to the other two. Conversely, the pupil diameter and subjective ease of throwing were significantly higher in the Catcher condition. These results indicate that when the target is held by a person, participants prioritized accuracy over speed. Although all participants received the same instructions across the conditions, such performance changes occurred. Humans sometimes unconsciously change the emphasis on speed or accuracy of their movements in response to goals. In goal-directed motor tasks, accuracy has been considered the dominant factor (Bruening et al. 2024 ). Faster movements are generally associated with a loss of accuracy, which prompts individuals to reduce their speed when high accuracy is required. This tendency to decelerate is often attributed to the increased accuracy constraints imposed by the task, as slower movements are typically thought to facilitate greater precision in reaching the target (Fitts 1954 ; Ketcham et al. 2002 ). In this study, the implicit social goal of allowing the person to catch the ball led participants to perceive a higher demand for accuracy and to focus more on precise throws. Participants might also have been subconsciously cautious about not injuring the catcher by throwing too hard. This psychological factor, likely unique to inexperienced throwers who do not accurately recognize their own abilities or the abilities of the catcher, may have further reinforced the context dependent prioritization of accuracy over speed. These motives – helping the person succeed and avoiding harm – likely coincide with one another, leading to the observed cautious (but accurate) throws. A previous study showed that when throwing a handball with an emphasis on ball speed or accuracy, a change in ball speed but no change in accuracy was observed (Van Den Tillaar and Ettema 2006 ). This result indicates that ball speed can be consciously altered, whereas accuracy cannot be consciously altered in a throwing task. Since the same target was used across conditions in the previous study, changing the target may have unconsciously altered accuracy in this study. This shift suggests that participants adopted a more nuanced, strategic motor plan when faced with a live human. Another possible reason for the increased accuracy is that the participants may have felt reassured, since they knew that the catcher would go after even balls that deviated from the mark’s initial position. This interpretation is further supported by the participants’ reports of an increase in the subjective ease of throwing in this condition. In this study, the catcher was permitted to move to catch deviating balls, a design choice made to ensure participant safety and maintain ecological validity, as a stationary human target would be both hazardous and unnatural. Participants received immediate visual feedback in all conditions by observing the ball’s arrival. In the Catcher condition, the successful catch provided salient feedback, which reflects real-world dynamics but may have introduced a confounding factor by providing participants with psychological reassurance. This safety net effect could have contributed to the observed increase in accuracy and should be considered when interpreting the differences between human and non-human conditions. The fact that performance changes occurred only in the Catcher condition suggests that they were not driven by the target’s human-like shape, but rather by the presence of a real person. Subjective ease of throwing increased in this condition. At the between-condition level, speed decreased while accuracy improved with a human catcher, consistent with a speed–accuracy trade-off (Fitts 1954 ). However, within participants at the trial level, speed and absolute error were not significantly correlated, indicating that faster trials were not necessarily less accurate. This result suggests that a trade-off relationship within each trial is not necessarily present, consistent with previous studies (Indermill and Husak 1984 ; Freeston et al. 2007 ; Urbin et al. 2011 , 2012 b; Freeston and Rooney 2014 ). Consequently, the overall shift toward lower speed and higher accuracy in the Catcher condition suggests that participants adopted a different throwing strategy, which resembles a trade-off at the between-condition level. In addition, there was no significant correlation between the mean ball speed and the mean absolute error of ball arrival position across all participants. While not statistically significant, the data showed a slight tendency toward a negative correlation rather than a trade-off; that is, some participants with faster ball speeds also tended to exhibit higher accuracy. This suggests that at the individual level, superior speed does not necessarily preclude high accuracy. This result is due to differences in skill levels among participants. Although this study focused only on people with no baseball experience, ball speeds ranged widely from approximately 30 km/h to 110 km/h. In throwing movements, longer training periods lead to better reproduction of the ball arrival position without decreasing throwing speed (García et al. 2013 ; Kawamura et al. 2017 ). Moreover, some studies have reported that skilled individuals do not show the typical tradeoff between speed and accuracy in overarm throwing, and that the reproducibility of the ball arrival position does not necessarily decrease as movement speed increases(Van Den Tillaar and Ettema 2003 ; Tillaar and Ettema 2006 ). Therefore, the speed-accuracy trade-off appears to be dependent on the level of analysis. Based on the results of this study, a clear trade-off was observed in the between-condition analysis (inter-condition strategic adjustment), but not within participants at the trial level (intra-subject variability). Our findings are consistent with the notion that arousal via the LC–NE system may be associated with enhanced accuracy by sharpening attention. Pupil dilation is an accepted proxy for LC–NE activity (Aston-Jones and Cohen 2005 ; Sara 2009 ; Oliva and Anikin 2018 ; Ricou et al. 2024 ); thus, the larger pupils in the Catcher condition suggest that participants were in a heightened arousal state. Moderate arousal has been theorized to be linked to optimized performance (up to a point) by increasing focus on task-relevant cues. In this case, the social presence of the catcher likely evoked an arousal boost that might have helped participants concentrate on aiming accurately at the target (Castellotti et al. 2021 ). This potentially focused attention may help explain the improved accuracy, even as throwing speed was willingly reduced. Similar mechanisms are discussed in adaptive gain theory, where the LC dynamically adjusts gain to favor either exploitation (focused task engagement) or exploration (Tae-Ho Lee et al. 2018 ). It is possible that participants shifted into a focused exploitative mode, prioritizing accuracy (exploitation of the learned throwing aim) when a person was to receive the ball. Increased pupil diameter during the initial state before the movement begins may serve as a critical foundation. While the final spatial-temporal accuracy of a throw is physically determined within a brief window of a few milliseconds during the ball release (Hore and Watts 2011 ; Matsuo et al. 2018 ), performance in throwing is not determined solely by the final instant, rather, it is the result of a continuous motor process where errors and adjustments are integrated throughout the entire movement (e.g., Kusafuka et al. 2023a ). The heightened preparatory arousal may optimize attentional engagement and stabilize the initial set of the movement to ensure precise control during the rapid, high-speed execution phase. However, as gaze behavior (e.g., fixation location or dwell time) was not formally analyzed, these attentional interpretations remain speculative. For instance, while the focused exploitative mode could have resulted in an external focus of attention compared to an internal focus of attention, the rich social context of the Catcher condition might also have shifted the participants’ aiming strategy—from focusing on a geometric “point” to a broader “person/zone.” Future research incorporating gaze data and post-task interviews regarding aiming strategies would be necessary to distinguish between these mechanisms. Some previous studies have shown better accuracy in goal-directed motor tasks by focusing externally relative to internally (Wulf and Prinz 2001 ; Wulf 2013 ). Conversely, since previous research indicates that participants with larger baseline pupil diameters had lower accuracy in tasks involving moving a cursor to targets on a screen (Naber and Murphy 2020 ), it is possible that the relationship between changes in pupil diameter within individuals and between individuals is not necessarily aligned. In this study, since the environment was not as controlled as in a perceptual experimental setting (although the brightness of the room was constant, all windows were covered with blinds, but light from outside still entered causing changes in the morning and evening), only changes in pupil diameter within each individual were analyzed. While the observed change in pupil diameter reflects a relative increase in arousal (Beatty 1982 ), the absolute magnitude of this change should be interpreted with caution. Pupillary responses are highly sensitive to task-specific demands and individual physiological baselines, making them more effective as relative measures rather than absolute ones (Kahneman 1973 ). Thus, the observed change in the Catcher condition suggests a shift in focus and social alertness, but it is difficult to define a universal arousal level based on the magnitude of pupillary dilation alone. In addition, because the possibility cannot be completely excluded that differences in the pupillary light reflex influenced our results (e.g., differences between the human receiver and the matte-white board), the interpretation of larger pupil diameter as an indicator of heightened arousal remains suggestive and should be interpreted with caution. Regarding arousal, the decrease in throwing speed in the Catcher condition, despite improved accuracy, can be interpreted in two ways. First, participants may have strategically managed the speed-accuracy trade-off, prioritizing the reliability of the catch and participant safety over speed. In this view, optimal performance was defined by the success of the accuracy. Second, from the perspective of the Yerkes-Dodson law, it is possible that the participants’ arousal levels remained in a sub-optimal range. While the presence of a human target was sufficient to increase focus and accuracy, it may not have reached the threshold required to facilitate maximal force or speed. This cautious physiological state, coupled with the motive to avoid injury, likely led to the observed prioritization of accuracy over power. Subjective ease of throwing tended to be related not to ball speed but to ball arrival position (the smaller the absolute error of ball arrival position, the easier the trial is to throw). It might be possible to discuss which senses come into play in motor tasks (Kusafuka et al. 2022 ). Since participants rated the subjective ease of throwing in each condition after completing the task, they might have responded post-dictionally that it was easier to throw under conditions in which the throw was accurate rather than fast. In this experiment, participants could receive visual feedback related only to the arrival position. Therefore, the subjective ease of throwing might be influenced more by visual feedback of the arrival position than by feedback from other modalities (e.g., proprioceptive, tactile, and pressure sensations) related to ball speed. Performing the same experiment under conditions in which participants can receive feedback related to both ball speed and arrival position might be necessary to clarify this point. Regarding the construct validity of the subjective measure, it is important to note that our findings suggest this rating represents an integrated perception of performance rather than a pure motoric sensation. Since participants were not instructed to isolate their physical sensations from the task outcome, their ratings likely reflected a postdictive evaluation based on motor outcome. This indicates that in the context of this throwing task, “subjective ease” is a composite construct where visual feedback outweighs proprioceptive or kinematic feedback. It reveals the psychological structure of “ease” in this specific motor task—showing that subjective ease is more strongly tied to perceived success than to pure sensations. Although the precise mechanisms underlying the increased accuracy remain unclear, the present findings would contribute to understanding how cognitive and affective processes influence motor control. While this is one piece of evidence that social situation influences motor behavior, there have been very few studies showing how these effects manifest in rapid goal-directed motor tasks such as throwing, in which both speed and accuracy can be examined. The findings provide empirical evidence that the human target context can modulate specific parameters of motor performance, namely throwing speed, accuracy, and arousal. In addition, they show that the influence operated in opposite directions for speed and accuracy, and the social context does not simply alter all performance output similarly. Throwers change the speed of their throws depending on target type, thus demonstrating that speed is a parameter that may be dependent on social aspects of the situation. However, the manipulation of the social factor is confounded with other factors. The accuracy of throws is higher for the human catcher, which is linked to a larger pupil diameter and a larger subjective ease. Since all these parameters are connected, as the significant correlations indicate, it is difficult to say which parameter is the one that is adjusted and which of the others just follow. For example, this study does not allow us to decide whether throwers throw more accurately, producing more positive feedback which widens the pupil, or does the presence of the catcher induce a larger arousal (wider pupil), enabling them to throw more accurately. Therefore, it remains unclear which parameters are directly influenced by the presence of the catcher, and which are just side effects. Future work will experimentally manipulate arousal (e.g., auditory startle) and feedback visibility to test directionality. Two methodological issues from this study, which should be considered in future studies, are presented. The first point was that the relationship between the participant and the catcher, and their characteristics might affect the outcome. In this study, although only one experimenter acted as the catcher for all participants, his relationship with the participants varied. Participants represent a wide range of relationships, such as close friends, colleagues, and first-time acquaintances. In addition, whether any catcher, for example a less skilled, younger, or smaller catcher induces the same effects is unclear. A thrower may not throw a ball at high speed at a person who appears less skilled. Therefore, it is still possible that an effect of the presumed skill level of a catcher rather than general social effect of the mere presence of a catcher. Furthermore, individual differences in personality traits related to social interaction might have influenced the present findings. For instance, traits such as agreeableness or empathy could affect the extent to which a participant prioritizes the catcher’s success over their own speed. Since this study did not assess participants’ personality profiles, future research should investigate how these internal traits interact with social contexts to shape motor performance. The second issue is that the experiments were conducted under limited laboratory conditions, and it is not clear whether the present findings can be generalized to competitive sport situations involving opponents, psychological pressure, or strategic aiming. The participants were individuals with no baseball experience only. Non-experienced throwers were recruited to minimize the confounding effects of prior skill levels and diverse past experiences. In skilled throwers, diverse backgrounds—including the length of experience and past positive or negative reinforcement in throwing to human—could introduce significant inter-individual variation, potentially obscuring the experimental effects. The current findings, obtained from non-experienced throwers, suggest that in practice scenarios such as baseball pitching, aiming toward a human catcher could potentially enhance accuracy by modulating arousal and strategic focus. However, the extent to which these findings apply to different tasks, such as darts, or to highly skilled athletes remains to be determined. All experiments were conducted in an indoor experimental room, and the distance between the participant and target was fixed at 9 m. The number of trials in this study was relatively small (15 trials per condition, totaling 45 trials) compared to previous studies using throwing tasks, as the design accounted for potential fatigue effects on participants. The effect of target type on throwing performance in more diverse environments and conditions should be investigated in future studies. Conclusion This study examined whether motor performance in a ball-throwing task in novice participants would differ when the target was held by a person, compared to when the target was a physical mark. Mean ball speed, absolute error of arrival positions, pupil diameter, and subjective ease of throwing were compared across three blocks each with a different target condition. Consequently, ball speed and absolute error of arrival positions were significantly lower in the Catcher condition than in the other two. Conversely, pupil diameter and subjective ease of throwing were significantly higher in the Catcher condition. These results indicate that when the target is held by a person, these participants prioritized accuracy over speed. This finding suggests that the implicit social goal of allowing the person to catch the ball may have led participants to focus more on precise throws than speed. The increased pupil diameter is consistent with heightened arousal/cognitive load in the Catcher condition, which was associated with improved accuracy. Subjective ease of throwing also increased in this condition. While these findings are limited to novices, they provide insights into how dynamic social cues and physical attributes of targets affect the execution of motor tasks, contributing to an understanding of how cognitive and affective processes implicitly influence motor control. Acknowledgements The authors would like to thank Mr. R. Yamamoto for his cooperation in conducting the preliminary experiments. We would also like to thank members of Kudo lab and Nakazawa lab at the University of Tokyo, and Watanabe lab at Waseda University for inspiring discussions. This work was in part supported by Japan Science and Technology Agency and JSPS KAKENHI 24K02825 and 25H01237. Author contributions A.K., D.Y., T.O., S.T., K. W., and K.K. contributed conception and design of the study. A.K., D.Y., Y.S., T.O., T.M., and S.T. performed experiments. A.K. performed the analysis. A.K. wrote the first draft of the manuscript. K.W. and K.K. revised partially the manuscript. All authors contributed to manuscript revision, and read and approved the submitted version. All authors contributed to the article and approved the submitted version. Funding This work was in part supported by Japan Science and Technology Agency and JSPS KAKENHI 24K02825 and 25H01237. Data availability The anonymized datasets and analysis code used during the current study are available from the corresponding author on reasonable request. Declarations Conflict of interest The authors declare no competing interests. Footnotes Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. References Anderson M, Pitcairn T (1986) Motor control in dart throwing. Hum Mov Sci 5:1–18. 10.1016/0167-9457(86)90002-3 [ Google Scholar ] Aston-Jones G, Cohen JD (2005) An integrative theory of locus coeruleus-norepinephrine function: Adaptive gain and optimal performance. 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