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Biomedical subjects

Paul M Bays

Publications and source records attributed to Paul M Bays.

6 recordsLinked to original sources
PubMed2006

Actions and consequences in bimanual interaction are represented in different coordinate systems.

Moving one part of the body can generate interaction forces that tend to destabilize other parts of the body. However, stability is maintained by mechanisms that predict and actively oppose these interaction forces. When our body or environment changes, these anticipatory mechanisms adapt so as to continue to produce accurate predictions. In this study, we examine the acquisition of a novel predictive coordination between the arms, in a situation in which a force is produced on one hand as a consequence of the action of the other hand. Specifically, a force was applied to the left hand that depended on the velocity of the right hand. With practice, subjects learned to stabilize the perturbed left arm during right-arm movements by predicting and actively opposing the externally applied forces. After adaptation, we examined how learning generalized to a new joint configuration of the right or left arm to investigate the coordinate systems in which the internal transformation from movement to force is represented. This revealed a dissociation between the representation of the action of the right arm and the representation of its consequence, that is the force on the left arm. The movement is represented in extrinsic coordinates related to the velocity of the hand, whereas the force resulting from the movement is represented in a joint-based intrinsic coordinate system.

Adaptation, Physiological↗
PubMed2006

Attenuation of self-generated tactile sensations is predictive, not postdictive.

When one finger touches the other, the resulting tactile sensation is perceived as weaker than the same stimulus externally imposed. This attenuation of sensation could result from a predictive process that subtracts the expected sensory consequences of the action, or from a postdictive process that alters the perception of sensations that are judged after the event to be self-generated. In this study we observe attenuation even when the fingers unexpectedly fail to make contact, supporting a predictive process. This predictive attenuation of self-generated sensation may have evolved to enhance the perception of sensations with an external cause.

Adolescent↗
PubMed2005

Perception of the consequences of self-action is temporally tuned and event driven.

It has been proposed that in order to increase the salience of sensations with an external cause, sensations that are predictable based on one's own actions are attenuated [1 and 2]. This may explain why self-imposed tickle [3 and 4] or constant forces [5] are perceived as less intense than the same stimuli externally imposed. Here, subjects used their right index finger to tap a force sensor mounted above their left index finger. When a motor generated a tap on the left finger synchronously with the right tap, simulating contact between the fingers, the perception of force in the left finger was attenuated compared to the same tap experienced during rest. Attenuation gradually reduced as the left tap was either delayed or advanced relative to the active right tap. However, no attenuation was seen to left taps triggered by right-finger movements that stopped above or passed wide of the sensor. We conclude that there is a window of sensory attenuation that is broadly temporally tuned and centered on the time at which the fingers would normally make contact. That is, predictive tactile sensory attenuation is linked to specific external events arising from movement rather than to the movement per se.

Adolescent↗
PubMed2005

Interference between velocity-dependent and position-dependent force-fields indicates that tasks depending on different kinematic parameters compete for motor working memory.

Humans demonstrate motor learning when exposed to changes in the dynamics of movement or changes in the visuomotor map. However, when two opposing dynamic transformations are learned in succession, the memory of the first is overwritten by learning of the second; the same is true for two opposing visuomotor rotations. This retrograde interference is not seen for all combinations of transformations, however. When a dynamic transformation is learned subsequent to a visuomotor rotation, the presence or absence of interference appears to depend crucially on the structure of the dynamic task: a force-field dependent on the position of the hand produces interference, whereas an inertial load applied lateral to the hand does not. To explain these results, it has been hypothesized that two transformations can be learned without interference if they depend on two different kinematic parameters of movement (such as position and velocity of the hand). Here we demonstrate, contrary to this hypothesis, interference between a dynamic transformation that depends on the position of the hand and one that depends on its velocity. However, the interference was found to be incomplete, supporting the view that the ability to retain motor memories for different tasks depends on the degree to which their representations conflict in working memory.

Adaptation, Physiological↗
PubMed2005

Evidence for sensory prediction deficits in schizophrenia.

OBJECTIVE: Patients with schizophrenia experiencing delusions and hallucinations can misattribute their own actions to an external source. The authors test the hypothesis that patients with schizophrenia have defects in their ability to predict the sensory consequences of their actions. METHOD: The authors measured sensory attenuation of self-produced stimuli by patients with schizophrenia and by healthy subjects. RESULTS: Patients with schizophrenia demonstrated significantly less sensory attenuation than healthy subjects. CONCLUSIONS: Patients with a diagnosis of schizophrenia have a dysfunction in their predictive mechanisms.

Adult↗