Using tools with real and imagined tool movements

New Ideas in Psychology

Modern technologies progressively create workplaces in which the execution of movements and the observation of their consequences are spatially separated. Challenging workplaces in which users act via technical equipment in a distant space include aviation, applied medical engineering and virtual reality. When using a tool, proprioceptive/tactile feedback from the moving hand (proximal action effect) and visual feedback from the moving effect point of the tool, such as the moving cursor on a display (the distal action effect) often do not correspond or are even in conflict. If proximal and distal feedback were equally important for controlling actions with tools, this discrepancy would be a constant source of interference. The human information processing system solves this problem by favoring the intended distal action effects while attenuating or ignoring proximal action effects. The study presents an overview of experiments aiming at the underlying motor and cognitive processes and the limitations of visual predominance in tool actions. The main findings are, that when transformations are in effect the awareness of one’s own actions is quite low. This seems to be advantageous when using tools, as it allows for wide range of flexible sensorimotor adaptations and – may be more important – it evokes the feeling of being in control. Thus, the attenuation of perceiving one’s own proximal action effects is an important precondition for using tools successfully. However, the ability to integrate discordant perception-action feedback has limits, especially, but not only, with complex transformations. When feature overlap between vision and proprioception is low, and when the existence of a transformation is obvious proximal action effects come to the fore and dominate action control in tool actions. In conclusion action–effect control plays an important role in understanding the constraints of the acquisition and application of tool transformations.

Human dexterity with tools is believed to stem from our ability to incorporate and use tools as parts of our body. However tool incorporation, evident as extensions in our body representation and peri-personal space, has been observed predominantly after extended tool exposures and does not explain our immediate motor behaviours when we change tools. Here we utilize two novel experiments to elucidate the presence of additional immediate tool incorporation effects that determine motor planning with tools. Interestingly, tools were observed to immediately induce a trial-by-trial, tool length dependent shortening of the perceived limb lengths, opposite to observations of elongations after extended tool use. Our results thus exhibit that tools induce a dual effect on our body representation; an immediate shortening that critically affects motor planning with a new tool, and the slow elongation, probably a consequence of skill related changes in sensory-motor mappings with the repeated use of the tool.

When using a tool, proximal action effects (e.g., the hand movement on a digitizer tablet) and distal action effects (e.g., the cursor movement on a display) often do not correspond to or are even in conflict with each other. In the experiments reported here, we examined the role of proximal and distal action effects in a closed loop task of sensorimotor control. Different gain factors perturbed the relation between hand movements on the digitizer tablet and cursor movements on a display. In the experiments, the covert hand movement was held constant, while the cursor amplitude on the display was shorter, equal, or longer, and vice versa in the other condition. When participants were asked to replicate the hand movement without visual feedback, hand amplitudes varied in accordance with the displayed amplitudes. Adding a second transformation (Experiment 1: 90°-rotation of visual feedback, Experiment 2: 180°-rotation of visual feedback) reduced these aftereffects only when the discrepancy between hand movement and displayed movement was obvious. In conclusion, distal action effects assimilated proximal action effects when the proprioceptive/tactile feedback showed a feature overlap with the visual feedback on the display.

Experimental Brain Research, 2012

PLoS ONE, 2013

Understanding the interactions of visual and proprioceptive information in tool use is important as it is the basis for learning of the tool's kinematic transformation and thus skilled performance. This study investigated how the CNS combines seen cursor positions and felt hand positions under a visuo-motor rotation paradigm. Young and older adult participants performed aiming movements on a digitizer while looking at rotated visual feedback on a monitor. After each movement, they judged either the proprioceptively sensed hand direction or the visually sensed cursor direction. We identified asymmetric mutual biases with a strong visual dominance. Furthermore, we found a number of differences between explicit and implicit judgments of hand directions. The explicit judgments had considerably larger variability than the implicit judgments. The bias toward the cursor direction for the explicit judgments was about twice as strong as for the implicit judgments. The individual biases of explicit and implicit judgments were uncorrelated. Biases of these judgments exhibited opposite sequential effects. Moreover, age-related changes were also different between these judgments. The judgment variability was decreased and the bias toward the cursor direction was increased with increasing age only for the explicit judgments. These results indicate distinct explicit and implicit neural representations of hand direction, similar to the notion of distinct visual systems.

Psychonomic Bulletin & Review, 2020

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 reachextending 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.

The present study examined what participants perceive of their hand movements when using a tool. In the experiments different gains for either the x-axis or the y-axis perturbed the relation between hand movements on a digitizer tablet and cursor movements on a display. As a consequence of the perturbation participants drew circles on the display while their covered hand movements followed either vertical or horizontal ellipses on the digitizer tablet. When asked to evaluate their hand movements, participants were extremely uncertain about their trajectories. By varying the amount of visual feedback, findings indicated that the low awareness of one’s own movements originated mainly from an insufficient quality of the humans’ tactile and proprioceptive system or from an insufficient spatial reconstruction of this information in memory.

Human Factors: The Journal of the Human Factors and Ergonomics Society

Objective: We explored constraints in responding to spatially variable stimuli when hand movements are transformed into inverse movements of a tool. Background: Generally, the spatial compatibility between stimuli and responses is a powerful determinant of performance. However, many tasks require the use of simple tools such as first-class levers that transform hand movements into inverted movements of a tool. What types of compatibility effects arise with such tools? Method: Participants moved the tip of a pointer to the left or right according to the color of a stimulus. The pointer was manipulated either directly, so that a hand movement caused a pointer movement in the corresponding direction, or indirectly, so that the hand moved the pointer in the opposite direction. Results: Responding was faster when the location of stimulus and the movement direction of the tool corresponded than when they did not correspond, independent of the movement direction of the hand. This occurred when stimulus location was task relevant (Experiment 1) as well as when it was task irrelevant (Experiment 2). Furthermore, responding was delayed when the hand and the relevant end of the tool moved in noncorresponding rather than corresponding directions. Conclusion: These results point to two distinct compatibility effects in tool use: one that relates to the transformation of stimuli into goals and one that relates to the transformation of goals into movements. Application: Potential applications of this research include the prediction and possibly manipulation of unwanted “fulcrum effects” in laparoscopic surgery and other first-class lever movements.

Journal of motor behavior, 2004