Manipulable objects can potentiate pointing and unusual grasping besides habitual grasping behaviors.

People are faster to perform a precision grip when they see a cherry (i.e., a small graspable object) than to perform a power grip, and the reverse holds true when they see an apple (i.e., a large graspable object). This potentiation effect supports that object representations could include motor components that would be simulated when a graspable object is seen. However, the nature of these motor components remains unclear. The embodied account posits that seeing an object only potentiates the most frequent actions associated with it (i.e., usual actions). In contrast, the size-coding account posits that seeing an object potentiates any actions associated to spatial codes compatible with those associated to the objects. We conducted three experiments to disentangle these two alternative accounts. We especially varied the nature of the responses while participants saw either large or small graspable objects. Our results showed a potentiation effect when participants performed the usual grasping actions (Experiment 1: power and precision grip) but also when they performed unusual grasping actions (Experiment 2: grasping between the thumb and little finger) and even when they had to perform non-grasping actions (Experiment 3: pointing actions). By supporting the size-coding account, our contribution underlines the need for a better understanding of the nature of the motor components of object representations and for using a proper control condition (i.e., pointing action) before arguing that the embodied account convincingly explains the potentiation effect of grasping behaviors.

The visual size is enough to automatically induce the potentiation of grasping behaviours.

Seeing objects usually grasped with a power or a precision grip (e.g., an apple vs a cherry) potentiates power- and precision-grip responses, respectively. An embodied account suggests that this effect occurs because object conceptual representations would lie on a motor simulation process. A new account, named the size-coding account, argues that this effect could be rather due to an overlapping of size codes used to represent both manipulable objects and response options. In this article, we investigate whether this potentiation effect could be merely due to a low-level visual feature that favours a size-coding of stimuli: the visual size in which objects are presented. Accordingly, we conducted two experiments in which we presented highly elementary and non-graspable stimuli (i.e., ink spots) either large or small rather than graspable objects. Our results showed that the mere visual size automatically potentiates power- and precision-grip responses that are in line with the size-coding account of the potentiation effect of grasping behaviours. Moreover, these results appeal to improve the methodological control of the size of stimuli especially when researchers try to support the embodied account.

The visual size of graspable objects is needed to induce the potentiation of grasping behaviors even with verbal stimuli.

Merely perceiving objects usually grasped with a power or a precision grip (e.g., an apple vs. a cherry) potentiate power-grip and precision-grip responses, respectively. According to the size-coding account, this potentiation effect is due to the compatibility between size codes associated with both stimuli and responses, rather than to the simulation of motor information stored at a conceptual level (i.e., the embodied account). At the stimulus level, size-coding would occur, because objects associated with a power grip are usually presented in a larger visual size than objects associated with a precision grip. However, this explanation is challenged by results, showing that reading nouns of objects associated with power or precision grip also leads to potentiation effects, even though the visual size of the displayed object is no longer perceived. Therefore, we designed three experiments to better understand this word-based potentiation effect and to investigate whether it relies on size codes. Our results showed a word-based potentiation effect only when the object nouns were interleaved with pictures depicting the objects in their typical visual size. We discuss the contributions of these results for both the size-coding account and the embodied account of the potentiation effect of grasping behaviors.

Anticipating the magnitude of response outcomes can induce a potentiation effect for manipulable objects.

Merely seeing large objects (e.g., apples) potentiates power grip whereas seeing small objects (e.g., strawberries) potentiates precision grip. According to the embodied cognition account, this potentiation effect reflects automatic access to object representation, including the grip usually associated with the object. Alternatively, this effect might be due to an overlap between magnitude codes used to code manipulable objects and magnitude codes used to code responses outcomes. In Experiment 1, participants saw objects usually grasped with a power or precision grip and had to press keys either with their forefinger or with their palm, each response generating a low or high tone (i.e., a large vs. small perceptual outcome, respectively). Tones were automatically delivered by headphones after the responses have been made in line with the ideomotor theories according to which voluntary actions are carried out due to the anticipation of their outcomes. Consistent with the magnitude-coding hypothesis, response times were shorter when the object and the anticipated response outcome were of the same magnitude than when they were not. These results were also consistent with a between-experiment analysis. In Experiments 2 and 3, we investigated to what extent removing or switching the outcomes during the experiment influence the potentiation effect. Our results support that the potentiation effect of grasping behaviours could be due to the compatibility between magnitude codes rather than to the involvement of motor representations. Our results also suggest a spontaneous use of the magnitude of response outcomes to code responses, as well as the flexibility of this coding processes when responses outcomes are altered.

Can the early visual processing of others' actions be related to social power and dominance?

Although goals often drive action understanding, this ability is also prone to important variability among individuals, which may have its origin in individual social characteristics. The present study aimed at evaluating the relationship between the tendency to prioritize goal information over grip information during early visual processing of action and several social dimensions. Visual processing of grip and goal information during action recognition was evaluated in 64 participants using the priming protocol developed by Decroix and Kalénine (Exp Brain Res 236(8):2411-2426, 2018). Object-directed action photographs were primed by photographs sharing the same goal and/or the same grip. The effects of goal and grip priming on action recognition were evaluated for different prime durations. The same participants further fulfilled questionnaires characterizing the way individuals deal with their social environment, namely their sense of social power, dominance, perspective taking, and construal level. At the group level, results confirmed greater goal than grip priming effects on action recognition for the shortest prime duration. Regression analyses between the pattern of response times in the action priming protocol and scores at the questionnaires further showed that the advantage of goal over grip priming was associated with higher sense of social power, and possibly to lower dominance. Overall, data confirm that observers tend to prioritize goal-related information when processing visual actions but further indicate that this tendency is sensitive to individual social characteristics. Results suggest that goal information may not always drive action understanding and point out the connection between low-level processing of observed actions and more general individual characteristics.

Size coding of alternative responses is sufficient to induce a potentiation effect with manipulable objects.

The mere perception of manipulable objects usually grasped with a power-grip (e.g., an apple) or a precision-grip (e.g., a cherry) potentiate power-grip- and precision-grip-responses, respectively. This effect is seen as to be driven by automatic access of the representation of manipulable objects that includes a motor representation of usually performed grasping behaviors (i.e., the embodied view). Nevertheless, a competing account argues that this effect could be due to an overlapping of size codes used to represent both manipulable objects and response options. Indeed, objects usually grasped with a power- and a precision-grip (e.g., an apple vs. a cherry) could be coded as large- and small-objects, respectively; and power- and precision-grip responses as large- and small-responses, respectively. We conducted 4 experiments to test this hypothesis. In Experiment 1, the response device usually used in studies reporting a potentiation effect is fixed horizontally (the grasping component of responses was removed). We instructed participants to press the small-switch with their index-digit and the large-switch with their palm-hand. In line with the size-coding-hypothesis, responses on the small-switch performed with the index-digit led to shorter RTs when objects usually associated with a precision-grip (e.g., a cherry) were presented compared to objects usually associated with a power-grip (e.g., an apple). A reverse pattern was obtained for responses on the large-switch performed with the palm-hand. In Experiments 2, 3 and 4, we went further by investigating which factors of Experiment 1 allow the size coding of responses: the size of switch and/or the size of the effector part used. Data confirmed the critical involvement of the size of switches and the possible involvement of the size of the effector part used. Thus, data support the possibility that the potentiation of grasping is due to a compatibility/incompatibility between size codes rather than involving motor representations of usually performed grasping behaviors as advocated in several embodied views. Moreover, data support the possibility that responses are coded thanks to a size code that extends the Theory of Event Coding.

Action Effects on Visual Perception of Distances: A Multilevel Bayesian Meta-Analysis.

Previous studies have suggested that action constraints influence visual perception of distances. For instance, the greater the effort to cover a distance, the longer people perceive this distance to be. The present multilevel Bayesian meta-analysis (37 studies with 1,035 total participants) supported the existence of a small action-constraint effect on distance estimation, Hedges's g = 0.29, 95% credible interval = [0.16, 0.47]. This effect varied slightly according to the action-constraint category (effort, weight, tool use) but not according to participants' motor intention. Some authors have argued that such effects reflect experimental demand biases rather than genuine perceptual effects. Our meta-analysis did not allow us to dismiss this possibility, but it also did not support it. We provide field-specific conventions for interpreting action-constraint effect sizes and the minimum sample sizes required to detect them with various levels of power. We encourage researchers to help us update this meta-analysis by directly uploading their published or unpublished data to our online repository ( https://osf.io/bc3wn/ ).

Motor simulation in tool-use effect on distance estimation: A replication of Witt and Proffitt (2008).

Witt and Proffit (Human Perception and Performance, 34 (6), 1479-1492, 2008) hypothesized that when people intend to reach a target, they run a motor simulation allowing them to anticipate potential reaching constraints and outcomes, which in turn affects spatial perception. They reported that participants estimated targets to be closer to them when they intended to use a reach-extending tool, but only when they did not perform a concurrent motor task. The authors concluded that the concurrent motor task prevented the simulation of tool-use and its effect on perception. Reported here is a replication that extends their work through an additional control group and a larger sample size. Our results failed to support either the role of motor simulation in the tool-use effect on distance estimation or the tool-use effect itself. Moreover, a reanalysis of Witt and Proffitt's data suggested that they should have been more nuanced in their own conclusions. Further replications are needed in order to elucidate the existence, nature, boundary conditions, and underlying mechanisms of the action constraint effects on space perception.

Pre-Calibrated Visuo-Haptic Co-Location Improves Execution in Virtual Environments.

A common approach to visio-haptic human-machine interfaces adopts a simpler design by shifting grounded force feedback away from the virtual scene. The alternative design favors intuitiveness by displaying visual and grounded force feedback at the same location (i.e. visuo-haptic co-location) but requires a sensibly more complex implementation and a tedious kinematic conception. The benefits of one approach over the other had not been fully investigated. Notably, (i) while users seem to better operate under co-located condition, it's not always the case. (ii) In the case of a desktop interface, the cost of a complex implementation to achieve co-location is challenged. We aim here to resolve (i) by conducting a user-centered experiment in which participants performed two generic tasks in co-located and delocated configurations, and comparing their performances. Additionally, we intend to fill the gap (ii) by testing a design without continuous head tracking, i.e., with static co-location. Participants' performances are assessed in terms of execution time, accuracy and force variation, while their subjective experiences are collected via a survey. Findings indicate that co-located configurations lead to shorter execution times, more accurate motions, better management of forces and are largely preferred by users, even when the co-location is pre-calibrated statically.

The Action Constraints of an Object Increase Distance Estimation in Extrapersonal Space.

This study investigated the role of action constraints related to an object as regards allocentric distance estimation in extrapersonal space. In two experiments conducted in both real and virtual environments, participants intending to push a trolley had to estimate its distance from a target situated in front of them. The trolley was either empty (i.e., light) or loaded with books (i.e., heavy). The results showed that the estimated distances were larger for the heavy trolley than for the light one, and that the actual distance between the participants and the trolley moderated this effect. This data suggests that the potential mobility of an object used as a reference affects distance estimation in extrapersonal space. According to embodied perception theories, our results show that people perceive space in terms of constraints related to their potential actions.

When combined spatial polarities activated through spatio-temporal asynchrony lead to better mathematical reasoning for addition.

Several recent studies have supported the existence of a link between spatial processing and some aspects of mathematical reasoning, including mental arithmetic. Some of these studies suggested that people are more accurate when performing arithmetic operations for which the operands appeared in the lower-left and upper-right spaces than in the upper-left and lower-right spaces. However, this cross-over Horizontality × Verticality interaction effect on arithmetic accuracy was only apparent for multiplication, not for addition. In these studies, the authors used a spatio-temporal synchronous operand presentation in which all the operands appeared simultaneously in the same part of space along the horizontal and vertical dimensions. In the present paper, we report studies designed to investigate whether these results can be generalized to mental arithmetic tasks using a spatio-temporal asynchronous operand presentation. We present three studies in which participants had to solve addition (Study 1a), subtraction (Study 1b), and multiplication (Study 2) in which the operands appeared successively at different locations along the horizontal and vertical dimensions. We found that the cross-over Horizontality × Verticality interaction effect on arithmetic accuracy emerged for addition but not for subtraction and multiplication. These results are consistent with our predictions derived from the spatial polarity correspondence account and suggest interesting directions for the study of the link between spatial processing and mental arithmetic performances.

Getting a tool gives wings: overestimation of tool-related benefits in a motor imagery task and a decision task.

Two experiments examine whether people overestimate the benefits provided by tool use in motor tasks. Participants had to move different quantities of objects by hand (two at a time) or with a tool (four at a time). The tool was not within reach so participants had to get it before moving the objects. In Experiment 1, the task was performed in a real and an imagined situation. In Experiment 2, participants had to decide for each quantity, whether they preferred moving the objects by hand or with the tool. Our findings indicated that people perceive tool actions as less costly in terms of movement time than they actually are (Experiment 1) and decide to use a tool even when it objectively provides less time-based benefits than using the hands (Experiment 2). Taken together, the data suggest that people overestimate the benefits provided by tool use.

Within reach but not so reachable: obstacles matter in visual perception of distances.

A large number of studies have shown that effort influences the visual perception of reaching distance. These studies have mainly focused on the effects of reach-relevant properties of the body and of the objects that people intend to reach. However, any influence of the reach-relevant properties of the surrounding environment remains still speculative. We investigated this topic in terms of the role of obstacle width in perceiving distances. Participants had to estimate the straight-line distance to a cylinder located just behind a transparent barrier of varying width. The results showed that participants perceived the straight-line distance to the cylinder as being longer when they intended to grasp the cylinder by reaching around a wide transparent barrier rather than by reaching around narrower ones. Interestingly, this effect might be due to the anticipated effort involved in reaching. Together, our results show that reach-relevant properties of the surrounding environment influence perceived distances, thereby supporting an embodied view of the visual perception of space.

Tool use and perceived distance: when unreachable becomes spontaneously reachable.

An interesting issue about human tool use is whether people spontaneously and implicitly intend to use an available tool to perform an action that would be impossible without it. Recent research indicates that targets presented just beyond arm's reach are perceived closer when people intend to reach them with a tool rather than without it. An intriguing issue is whether this effect also occurs when people are not explicitly instructed to use a tool to reach targets. To address this issue, we asked participants to estimate distances that were beyond arm's reach in three conditions. Participants who held passively a long baton underestimated the distances as compared to participants with no baton (Experiment 1). To examine whether this effect resulted from holding the baton, we asked participants to estimate distances while holding passively a shorter baton (Experiment 2). We found that holding this short baton did not influence distance perception. Our findings demonstrate that when people aim at performing a task beyond their action capabilities, they spontaneously and implicitly intend to use a tool if it substantially extends their action capabilities. These findings provide interesting insights into the understanding of the link between the emergence of tool use, intention, and perception.

Close to me? The influence of affective closeness on space perception.

Recent data show that psychosocial factors affect visual perception. We tested this hypothesis by investigating the relationship between affective closeness and the perception of apertures between two people. People feel discomfort when they are near someone they are not affectively close to. Therefore, we predict that they will be less likely to perceive that they can pass between two people not affectively close to them. Participants had to imagine passing through the aperture between two life-size classmate pictures. We found that the closer participants felt to their classmates, the more they felt able to pass between them. This provides the first evidence of a relationship between affective closeness and the perception of aperture between two people, suggesting that psychosocial factors constrain space perception.