Material surface properties modulate vection strength Abstract Realistic appearance and complexity in the visual field are known to affect the strength of vection (visually induced self-motion perception). Although surface properties of materials are, therefore, expected to be visual features that influence vection, to date, the results have been mixed. Here, we used computer graphics to simulate self-motion through rendered 3D tunnels constructed from nine different materials (bark, ceramic, fabric, fur, glass, leather, metal, stone, and wood). There are three ways in which the new stimuli are changed from those found in previous studies: (1) as they move, their appearances interactively change with the 3D structures of the simulated world, as do all the lighting effects and 3D geometric appearances, (2) they are colored, (3) and their components covered a large portion of the visual field. The entire inner surface of each tunnel was composed from one of the nine materials, and optic flow was evoked when an observer virtually moved through the tunnel. Bark, fabric, leather, stone, and wood effectively induced strong vection, whereas, ceramic, glass, fur, and metal did not. Regression analyses suggested that low-level image features such as the lighting and amplitude of spatial frequency were the main factors that modulated vection strength. Additionally, subjective impressions of the nine surface materials showed that the perceived depth, smoothness, and rigidity were related to the perceived vection strength. Overall, our results indicate that surface properties of materials do indeed modulate vection strength.

Exercise, fatigue and proprioception: a retrospective Abstract This is an account of experiments carried out in my laboratory over more than 20 years, exploring the influence of exercise on human limb position sense. It is known that after intense exercise we are clumsy in the execution of skilled movements. The first question we posed concerned eccentric exercise, where the contracting muscle is forcibly lengthened. Such exercise produces muscle damage, and the damage might extend to the muscle’s proprioceptors, the muscle spindles, producing a disturbance of limb position sense. However, provided the exercise was sufficiently severe (20–30% fall in muscle force), comparing eccentric exercise with concentric exercise, where no damage ensues, there was no difference in the effects on position sense. After exercise of elbow muscles, the forearm was always perceived as more extended than its actual position. It led to a new hypothesis: after exercise, did the extra effort required to lift the fatigued arm provide a position signal? Findings based on spindles’ thixotropic behaviour did not support such a proposition for the elbow joint, although at the wrist an effort signal may contribute. Spindle thixotropy has also been proposed to explain the poor proprioception experienced under conditions of weightlessness. After exercise of elbow extensors or flexors, the position errors were always in the direction of forearm extension. At the knee, after exercise the lower leg was always perceived as more flexed. These findings led to the conclusion that disturbances to position sense, post-exercise, did not involve peripheral receptors, and that the effect arose within the brain.

Grip force preparation for collisions Abstract Grip force has been studied widely in a variety of interaction and movement tasks, however, not much is known about the timing of the grip force control in preparation for interaction with objects. For example, it is unknown whether and how the temporal preparation for a collision is related to (the prediction of) the impact load. To study this question, we examined the anticipative timing of the grip force in preparation for impact loads. We designed a collision task with different types of load forces in a controlled virtual environment. Participants interacted with a robotic device (KINARM, BKIN Technologies, Kingston) whose handles were equipped with force sensors which the participants held in precision grip. Representations of the hand and objects were visually projected on a virtual reality display and forces were applied onto the participant’s hand to simulate a collision with the virtual objects. The collisions were alternating between the two hands to allow transfer and learning between the hands. The results show that there is immediate transfer of object information between the two hands, since the grip force levels are (almost) fully adjusted after one collision with the opposite hand. The results also show that the grip force levels are nicely adjusted based on the mass and stiffness of the object. Surprisingly, the temporal onset of the grip force build up did not depend on the impact load, so that participants avoid slippage by adjusting the other grip force characteristics (e.g., grip force level and rate of change), therefore considering these self-imposed timing constraints. With the use of catch trials, for which no impact occurred, we further analyzed the temporal profile of the grip force. The catch trial data showed that the timing of the grip force peak is also independent of the impact load and its timing, which suggests a time-locked planning of the complete grip force profile.

Differential cortical activation during the perception of moving objects along different trajectories Abstract Detection of 3D object-motion trajectories depends on the integration of two distinct visual cues: translational displacement and looming. Electrophysiological studies have identified distinct neuronal populations, whose activity depends on the precise motion cues present in the stimulus. This distinction, however, has been less clear in humans, and it is confounded by differences in the behavioral task being performed. We analyzed whole-brain fMRI, while subjects performed a common time-to-arrival task for objects moving along three trajectories: moving directly towards the observer (collision course), with trajectories parallel to the line of sight (passage course), and with trajectories perpendicular to the line of sight (gap closure). We found that there was substantial overlap in the pattern of activation associated with each of the three tasks, with differences among conditions limited to the human motion area (hMT+), which showed greater activation extent in the gap closure condition than for either collision or passage courses. These results support a common substrate for temporal judgments of an object’s time-to-arrival, wherein the special cases of object motion directly toward, or perpendicular to, the observer represent two extremes within the broader continuum of 3D passage trajectories relative to the observer.

Two-step actions in infancy—the TWAIN model Abstract In this paper, we propose a novel model—the TWAIN model—to describe the durations of two-step actions in a reach-to-place task in human infants. Previous research demonstrates that infants and adults plan their actions across multiple steps. They adjust, for instance, the velocity of a reaching action depending on what they intend to do with the object once it is grasped. Despite these findings and irrespective of the larger context in which the action occurs, current models (e.g., Fitts’ law) target single, isolated actions, as, for example, pointing to a goal. In the current paper, we develop and empirically test a more ecologically valid model of two-step action planning. More specifically, 61 18-month olds took part in a reach-to-place task and their reaching and placing durations were measured with a motion-capture system. Our model explained the highest amount of variance in placing duration and outperformed six previously suggested models, when using model comparison. We show that including parameters of the first action step, here the duration of the reaching action, can improve the description of the second action step, here the duration of the placing action. This move towards more ecologically valid models of action planning contributes knowledge as well as a framework for assessing human machine interactions. The TWAIN model provides an updated way to quantify motor learning by the time these abilities develop, which might help to assess performance in typically developing human children.

Embodying their own wheelchair modifies extrapersonal space perception in people with spinal cord injury Abstract Despite the many links between body representation, acting and perceiving the environment, no research has to date explored whether specific tool embodiment in conditions of sensorimotor deprivation influences extrapersonal space perception. We tested 20 spinal cord injured (SCI) individuals to investigate whether specific wheelchair embodiment interacts with extrapersonal space representation. As a measure of wheelchair embodiment, we used a Body View Enhancement Task in which participants (either sitting in their own wheelchair or in one which they had never used before) were asked to respond promptly to flashing lights presented on their above- and below-lesion body parts. Similar or slower reaction times (RT) to stimuli on the body and wheelchair indicate, respectively, the presence or absence of tool embodiment. The RTs showed that the participants embodied their own wheelchair but not the other one. Moreover, they coded their deprived lower limbs as external objects and, when not in their own wheelchair, also showed disownership of their intact upper limbs. To measure extrapersonal space perception, we used a novel, ad hoc designed paradigm in which the participants were asked to observe a 3D scenario by means of immersive virtual reality and estimate the distance of a flag positioned on a ramp. In healthy subjects, errors in estimation increased as the distance increased, suggesting that they mentally represent the physical distance. The same occurred with the SCI participants, but only when they were in their own wheelchair. The results demonstrate for the first time that tool embodiment modifies extrapersonal space estimations.

Dual-mode dopamine increases mediated by 5-HT 1B and 5-HT 2C receptors inhibition, inducing impulsive behavior in trained rats Abstract Patients with eating disorders exhibit problems with appetitive impulse control. Interactions between dopamine and serotonin (5-HT) neuron in this setting are poorly characterized. Here we examined 5-HT receptor-mediated changes in extracellular dopamine during impulsive appetitive behavior in rats. Rats were trained to perform a cued lever-press (LP) task for a food reward such that they stopped experiencing associated dopamine increases. Trained rats were administered the mixed 5-HT1B/2C-receptor antagonist metergoline, the 5-HT2A/2C-receptor antagonist ketanserin, and p-chlorophenylalanine (PCPA). We measured dopamine changes in the ventral striatum using voltammetry and examined the number of premature LPs, reaction time (RT), and reward acquisition rate (RAR). Compared with controls, metergoline increased premature LPs and shortened RT significantly; ketanserin decreased premature LPs and lengthened RT significantly; and PCPA decreased premature LPs, lengthened RT, and decreased RAR significantly. Following metergoline administration, rats exhibited a fast phasic dopamine increase for 0.25–0.75 s after a correct LP, but only during LP for an incorrect LP. No dopamine increases were detected with ketanserin or PCPA, or in controls. After LP task completion, metergoline also caused dopamine to increase slowly and remain elevated; in contrast, ketanserin caused dopamine to increase slowly and decrease rapidly. No slow dopamine increase occurred with PCPA. Inhibition of 5-HT1B- and 5-HT2C-receptors apparently induced dual modes of extracellular dopamine increase: fast phasic, and slow long-lasting. These increases may be associated with the suppression of acquired prediction learning and retention of high motivation for reward, leading to impulsive excessive premature LPs.

The influence of pacer-movement continuity and pattern matching on auditory-motor synchronisation Abstract People commonly move along with auditory rhythms in the environment. Although the processes underlying such sensorimotor synchronisation have been extensively investigated in the previous research, the properties of auditory rhythms that facilitate the synchronisation remain largely unclear. This study explored the possible benefits of a continuity matching between auditory pacers and the movement produced as well as of a spatial pattern matching that has been previously demonstrated with visual pacers. Participants synchronised either finger tapping or forearm oscillations with either discrete or continuous pacers. The pacers had either a spatial pattern (left–right panning) that matched the movement pattern produced or no spatial pattern. The accuracy and variability of synchronisation were assessed by the mean and standard deviation of the asynchronies, respectively, between participant’s movement and the pacers. Results indicated that synchronisation was more accurate and less variable for discrete pacers and continuous movement (i.e., forearm oscillations). The interaction between those two factors involved a more complex relationship than a simple continuity match benefit. Although synchronisation variability increased with continuous pacers for both types of movement, this increase was smaller for continuous movement than discrete movement, suggesting that continuous movement is more beneficial only for continuous pacers. Moreover, the results revealed limited benefits of spatial pattern matching on auditory-motor synchronisation variability, which might be due to lower spatial resolution of the auditory sensory modality. Together, these findings confirm that sensorimotor synchronisation is modulated by complex relations between pacer and movement properties.

Alteration of perceived emotion and brain functional connectivity by changing the musical rhythmic pattern Abstract The arrangement of musical notes and their time intervals, also known as musical rhythm is one of the core elements of music. Nevertheless, the cognitive process and neural mechanism of the human brain that underlay the perception of musical rhythm are poorly understood. In this study, we hypothesized that changes in musical rhythmic patterns alter the emotional content expressed by music and the way it is perceived, that assumably causes specific changes in the brain functional connectome. Therefore, 18 male children aged 10–14 years old were recruited and exposed to 12 musical excerpts while their brain’s electrical activity was recorded using a 32-channel EEG recorder. The musical rhythmic patterns were changed by manipulating only note values in beats while keeping time signature and other elements in a fixed state. The experienced emotions were assessed using a 2-dimensional self-assessment manikin questionnaire. The behavioral data showed that an increase in the complexity of musical rhythmic patterns significantly enhances perceived valence and arousal levels. In addition, the pattern of brain functional connectivity was also estimated using the weighted phase lag index and their association with behavioral changes was calculated. Interestingly, the behavioral changes were mainly associated with alteration of brain functional connectivity at the alpha band in the fronto-central connections. These results emphasize the important role of the motor cortical site-fronto-central connections, in the perception of musical rhythmic pattern. These findings may improve conception of the underlying brain mechanism involved in the perception of musical rhythm. Graphic abstract

Does spatial cognitive style affect how navigational strategy is planned? Abstract People orient themselves in the environment using three different, hierarchically organized, spatial cognitive styles: landmark, route, and survey. Landmark style is based on a representation encompassing only visual information (terrain features); route style is based on a representation that connects landmarks and routes using an egocentric (body-centred) frame of reference; survey style is based on a global map-like representation that mainly involves an allocentric (world-centred) frame of reference. This study was aimed at investigating whether individual spatial cognitive style affected the way to plan a path when searching for a lost object. Participants with landmark, route, and survey style were assessed with an ecological navigational planning task (the Key Search Task), which required planning a strategy to search for the lost key in a hypothetical wide squared field. Results showed that spatial cognitive styles were associated to different navigational planning strategies, although the time to complete the Key Search Task was comparable across the styles. As revealed by the Key Search Task score, survey style individuals were the best navigational planners, route style individuals were less efficient and landmark style individuals were the least efficient. These results suggest that spatial cognitive style has effects on navigational planning. Implications for clinical settings, such as for developmental topographical disorientation, are discussed.