Abstract
The ability to track the time-varying postures of our hands and the forces they exert plays a key role in our ability to dexterously interact with objects. However, how precisely and accurately we sense hand kinematics and kinetics has not been completely characterized. Furthermore, the dominant source of information about hand postures stems from muscle spindles, whose responses can also signal isometric force and are modulated by fusimotor input. As such, one might expect that changing the state of the muscles – for example, by applying a load – would influence perceived finger posture. To address these questions, we measure the acuity of human hand proprioception, investigate the interplay between kinematic and kinetic signals, and determine the extent to which actively and passively achieved postures are perceived differently. We find that angle and torque perception are highly precise; that loads imposed on the finger do not affect perceived joint angle; that joint angle does not affect perceived load; and that hand postures are perceived similarly whether they are achieved actively or passively. The independence of finger posture and load perception contrasts with their interdependence in the upper arm, likely reflecting the special functional importance of the hand.
Highlights
Proprioception – the sense of our body’s configuration, movement, and of the forces we exert – is critical for the planning and execution of movement as evidenced by the crippling deficits that result from its loss[1,2,3]
We performed a series of experiments in which we assess the degree to which finger joint position is affected by a load applied to that joint and whether perceived load is affected by joint position
We measured the perception of joint angle and the degree to which it is influenced by a load imposed on the digit
Summary
Proprioception – the sense of our body’s configuration, movement, and of the forces we exert – is critical for the planning and execution of movement as evidenced by the crippling deficits that result from its loss[1,2,3]. Muscle spindle afferents, which are thought to be the main sources of proprioceptive signals[3,11] individually convey ambiguous information about limb position: In addition to muscle length, muscle tension and history[13] and fusimotor input[14] influence spindle responses, which likely underlies the influence of imposed torque and motor intent on perceived arm posture. The question remains whether the ambiguity between postural and load-related signals is observed for hand proprioception. To address this question, we performed a series of experiments in which we assess the degree to which finger joint position is affected by a load applied to that joint and whether perceived load is affected by joint position. We infer that the function of the hand requires a precise, unambiguous, perceptually-accessible readout of position and load and that this readout is supported by specialized processing of hand proprioception downstream of the proprioceptive afferents themselves
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