Somatosensory control of precision grip during unpredictable pulling loads

Abstract

In the previous paper regarding the somatosensory control of the human precision grip, we concluded that the elicited automatic grip force adjustments are graded by the amplitude of the imposed loads when restraining an 'active' object subjected to unpredictable pulling forces (Johansson et al. 1992a). Using the same subjects and apparatus, the present study examines the capacity to respond to imposed load forces applied at various rates. Grip and load forces (forces normal and tangential to the grip surfaces) and the position of the object in the pulling direction (distal) were recorded. Trapezoidal load force profiles with plateau amplitudes of 2 N were delivered at the following rates of loading and unloading in an unpredictable sequence: 2 N/s, 4 N/s or 8 N/s. In addition, trials with higher load rate (32 N/s) at a low amplitude (0.7 N) were intermingled. The latencies between the start of the loading and the onset of the grip force response increased with decreasing load force rate. They were 80 +/- 9 ms, 108 +/- 13 ms, 138 +/- 27 ms and 174 +/- 39 ms for the 32, 8, 4 and 2 N/s rates, respectively. These data suggested that the grip response was elicited after a given minimum latency once a load amplitude threshold was exceeded. The amplitude of the initial rapid increase of grip force (i.e., the 'catch-up' response) was scaled by the rate of the load force, whereas its time course was similar for all load rates. This response was thus elicited as a unit, but its amplitude was graded by afferent information about the load rate arising very early during the loading. The scaling of the catch-up response was purposeful since it facilitated a rapid reconciliation of the ratio between the grip and load force to prevent slips. In that sense it apparently also compensated for the varying delays between the loading phase and the resultant grip force responses. However, modification of the catch-up response may occur during its course when the loading rate is altered prior to the grip force response or very early during the catch-up response itself. Hence, afferent information may be utilized continuously in updating the response although its motor expression may be confined to certain time contingencies. Moreover, this updating may take place after an extremely short latency (45-50 ms).(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of grip force with load force during point-to-point arm movements

“…This finding adds to evidence garnered by Johansson and colleagues (Johansson and Westling 1984;Johansson et al 1992) that grip force is programmed in advance of voluntary manipulations of mechanically predictable objects. Thus, not only do grip force adjustments anticipate environmental demands imposed by the properties of the object (Johansson and Westling 1984), they also anticipate the consequences of our own actions.…”

“…This finding might appear to contradict the results of Johansson and colleague (e.g. Johansson and Westling 1984;Johansson et al 1992), showing that the ratio of grip force to load force is nearly constant when manipulating objects. However, it should be noted that the variation in baseline grip force we observed was not related to the properties of the object.…”

“…Johansson and Westling (1984) demonstrated that grip force and load force change in parallel when subjects move a spring-loaded object where the load force increases with displacement. More recently, Johansson et al (1992) reported that changes in grip force parallel changes in load force when pulling on a stiff, fixed object where the load depends on the isometric force exerted by the hand. However, the coupling between grip force and load force during arm movements with inertial loads has not been systematically documented.…”

Somatic Sensation of Hand-Object Interactive Movement Is Associated with Activity in the Left Inferior Parietal Cortex

“…Previous studies on the neuronal basis of object manipulation and tool use have addressed this issue mainly from a motor control perspective (Jeannerod et al, 1995;Binkofski et al, 1999;Ehrsson et al, 2000). However, the tactile and kinesthetic signals from the hand and the fingers are critically important for manual performances (Rothwell et al, 1982;Johansson and Westling, 1984;Johansson et al, 1992). In particular, information about the spatial relationship between the hand and a hand-held object is important when we handle the object.…”

Effect of laparoscopic grasper force transmission ratio on grasp control

“…If an unpredictable load force (unknown tissue stiffness) occurs during barehanded grasping, humans are able to adjust their pinch force to prevent slippage while avoiding exceedingly large forces [3][4][5][6][7][8][9][10].…”