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Noy, L., Weiser, N., & Friedman, J. (2017). Synchrony in Joint Action Is Directed by Each Participant's Motor Control System. Front. Psychol., 8, 531.
Abstract: In this work, we ask how the probability of achieving synchrony in joint action is affected by the choice of motion parameters of each individual. We use the mirror game paradigm to study how changes in leader�s motion parameters, specifically frequency and peak velocity, affect the probability of entering the state of co-confidence (CC) motion: a dyadic state of synchronized, smooth and co-predictive motions. In order to systematically study this question, we used a one-person version of the mirror game, where the participant mirrored piece-wise rhythmic movements produced by a computer on a graphics tablet. We systematically varied the frequency and peak velocity of the movements to determine how these parameters affect the likelihood of synchronized joint action. To assess synchrony in the mirror game we used the previously developed marker of co-confident (CC) motions: smooth, jitter-less and synchronized motions indicative of co-predicative control. We found that when mirroring movements with low frequencies (i.e., long duration movements), the participants never showed CC, and as the frequency of the stimuli increased, the probability of observing CC also increased. This finding is discussed in the framework of motor control studies showing an upper limit on the duration of smooth motion. We confirmed the relationship between motion parameters and the probability to perform CC with three sets of data of open-ended two-player mirror games. These findings demonstrate that when performing movements together, there are optimal movement frequencies to use in order to maximize the possibility of entering a state of synchronized joint action. It also shows that the ability to perform synchronized joint action is constrained by the properties of our motor control systems.
Prushansky, T., Kaplan-Gadasi, L., & Friedman, J. (2022). The relationship between thoracic posture and ultrasound echo intensity of muscles spanning this region in healthy men and women. Physiother Theory Pract, , 1–9.
Abstract: PURPOSE: Skeletal muscle echogenicity intensity (EI) is considered a measure of muscle quality, being associated with old age and pathologies. Whether EI variations can be identified in healthy adults, due to habitual shortened or elongated muscle position is unknown. Thus, this study aimed to assess the relationship between thoracic kyphosis angulation and EI scores of muscles spanning this region ((Lower Trapezius (LT), Rhomboid Major (RM), Erector Spine (ES)) in healthy young people and in addition to examine the relationship between the change in thoracic kyphosis angle from relaxed to upright position (â�� degrees ) and the EI of these muscles. METHODS: Thoracic kyphosis in relaxed and erect standing was measured using a digital inclinometer in 29 healthy adults (16 women, 13 men), aged 25-35 years. The thoracic kyphosis angles including the difference between relaxed and erect postures (â�� degrees ) were correlated to the EI scores of right and left LT, RM and ES. RESULTS: No significant differences in EI were found between the 3 muscles EI or between sides, hence they were pooled together to a total thoracic EI score (TTEI). Although the TTEI did not correlate with relaxed or erect thoracic kyphosis, it was significantly but negatively correlated with â�� degrees in the entire group: Pearson's correlation coefficient of r = -0.544; p = .01 and in men; r = -0.732; p = .01, failing to reach significance in women; r = -0.457. CONCLUSION: The negative association between the EI of the explored muscles and â�� degrees could imply a possible relationship between these muscles range of movement excursions and their composition.
Keywords: Ultrasound imaging; muscle echogenicity; posture; thoracic kyphosis
Ezrati, O., Friedman, J., & Dar, R. (2019). Attenuation of access to internal states in high obsessive-compulsive individuals might increase susceptibility to false feedback: Evidence from a visuo-motor hand-reaching task. Journal of Behavior Therapy and Experimental Psychiatry, 65, 101445.
Abstract: Background and objectives
The Seeking Proxies for Internal States (SPIS) model of obsessive-compulsive disorder (OCD) posits that obsessive-compulsive (OC) individuals have attenuated access to their internal states. Hence, they seek and rely on proxies, or discernible substitutes for these internal states. In previous studies, participants with high OC tendencies and OCD patients, compared to controls, showed increased reliance on external proxies and were more influenced by false feedback when judging their internal states. This study is the first to examine the effects of false feedback on performance of hand movements in participants with high and low OC tendencies.
Thirty-four participants with high OC tendencies and 34 participants with low OC tendencies were asked to perform accurate hand reaches without visual feedback in two separate sessions of a computerized hand-reaching task: once after valid feedback training of their hand location and once with false-rotated feedback. We assessed the accuracy and directional adaptation of participants' reaches.
As predicted, high OC participants evidenced a larger decrease in their hand positioning accuracy after training with false feedback compared to low OC participants.
The generalization of our findings to OCD requires replication with a clinical sample.
These results suggest that in addition to self-perceptions, motor performance of OC individuals is prone to be overly influenced by false feedback, possibly due to attenuated access to proprioceptive cues. These findings may be particularly relevant to understanding the distorted sense of agency in OCD.
Keywords: Obsessive-compulsive disorder; Movement; Agency; Proprioception; Proxies
Raveh, E., Portnoy, S., & Friedman, J. (2018). Adding vibrotactile feedback to a myoelectric-controlled hand improves performance when online visual feedback is disturbed. Hum Mov Sci, 58, 32–40.
Abstract: We investigated whether adding vibrotactile feedback to a myoelectric-controlled hand, when visual feedback is disturbed, can improve performance during a functional test. For this purpose, able-bodied subjects, activating a myoelectric-controlled hand attached to their right hand performed the modified Box & Blocks test, grasping and manipulating wooden blocks over a partition. This was performed in 3 conditions, using a repeated-measures design: in full light, in a dark room where visual feedback was disturbed and no auditory feedback – one time with the addition of tactile feedback provided during object grasping and manipulation, and one time without any tactile feedback. The average time needed to transfer one block was measured, and an infrared camera was used to give information on the number of grasping errors during performance of the test. Our results show that when vibrotactile feedback was provided, performance time was reduced significantly, compared with when no vibrotactile feedback was available. Furthermore, the accuracy of grasping and manipulation was improved, reflected by significantly fewer errors during test performance. In conclusion, adding vibrotactile feedback to a myoelectric-controlled hand has positive effects on functional performance when visual feedback is disturbed. This may have applications to current myoelectric-controlled hands, as adding tactile feedback may help prosthesis users to improve their functional ability during daily life activities in different environments, particularly when limited visual feedback is available or desirable.
Zopf, R., Friedman, J., & Williams, M. A. (2015). The plausibility of visual information for hand ownership modulates multisensory synchrony perception. Experimental Brain Research, 233(8), 2311–2321.
Abstract: We are frequently changing the position of our bodies and body parts within complex environments. How does the brain keep track of one’s own body? Current models of body ownership state that visual body ownership cues such as viewed object form and orientation are combined with multisensory information to correctly identify one’s own body, estimate its current location and evoke an experience of body ownership. Within this framework, it may be possible that the brain relies on a separate perceptual analysis of body ownership cues (e.g. form, orientation, multisensory synchrony). Alternatively, these cues may interact in earlier stages of perceptual processing—visually derived body form and orientation cues may, for example, directly modulate temporal synchrony perception. The aim of the present study was to distinguish between these two alternatives. We employed a virtual hand set-up and psychophysical methods. In a two-interval force-choice task, participants were asked to detect temporal delays between executed index finger movements and observed movements. We found that body-specifying cues interact in perceptual processing. Specifically, we show that plausible visual information (both form and orientation) for one’s own body led to significantly better detection performance for small multisensory asynchronies compared to implausible visual information. We suggest that this perceptual modulation when visual information plausible for one’s own body is present is a consequence of body-specific sensory predictions.
Keywords: Multisensory perception; Temporal synchrony perception; Virtual hand; Body representations; Body ownership; Sensory predictions