Memory representations underlying motor commands used during manipulation of common and novel objects

Abstract

1. While subjects lifted a variety of commonly handled objects of different shapes, weights, and densities, the isometric vertical lifting force opposing the object's weight was recorded from an analog weight scale, which was instrumented with high-stiffness strain gauge transducers. 2. The force output was scaled differently for the various objects from the first lift, before sensory information related to the object's weight was available. The force output was successfully specified from information in memory related to the weight of common objects, because only small changes in the force-rate profiles occurred across 10 consecutive lifts. This information was retrieved during a process related to visual identification of the target object. 3. The amount of practice necessary to appropriately scale the vertical lifting and grip (pinch) force was also studied when novel objects (equipped with force transducers at the grip surfaces) of different densities were encountered. The mass of a test object that subjects had not seen previously was adjusted to either 300 or 1,000 g by inserting an appropriate mass in the object's base without altering its appearance. This resulted in either a density that was in the range of most common objects (1.2 kg/l) or a density that was unusually high (4.0 kg/l). 4. Low vertical-lifting and grip-force rates were used initially with the high-density object, as if a lighter object had been expected. However, within the first few trials, the duration of the loading phase (period of isometric force increase before lift-off) was reduced by nearly 50% and the employed force-rate profiles were targeted for the weight of the object.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation of a long-term memory for visuomotor adaptation following only a few trials of practice

“…If visuomotor adaptation serves as an example of the initial, explicit stage of this process, one task that may serve as a model for this process following more practice is adjustment of grip and load forces for lifting objects of unusual densities. This task is ostensibly similar to visuomotor adaptation, given that both show signs of long-term memory formation following only brief periods of initial practice (Gordon et al 1993;Flanagan and Beltzner 2000;Flanagan et al 2008). However, visuomotor adaptation is known to be subserved by both explicit and implicit processes (Mazzoni and Krakauer 2006;Taylor et al 2014), while adjustment of grip and load forces during lifting seems to be largely implicit, evidenced by the fact that the size-weight illusion persists after appropriate motor adjustments have been made (Flanagan and Beltzner 2000).…”

Visual and Somatosensory Information about Object Shape Control Manipulative Fingertip Forces

“…scaling of the force output to the weight of common objects in Gordon et al, 1993). Alternatively, subjects may have used vision in a "computational" sense, relying on implicit general knowledge about relationships of the shapes of objects and required force coordination.…”

“…First, when humans handle common objects, the force development in the dynamic phase of the lifting action is appropriately scaled for the weight of the current object despite different weights, sizes, and densities of such objects (Gordon et al, 1993). That is, memories from previous manipulative experiences are used to scale the force output to an expected weight before explicit sensory information about the weight is available at liftoff.…”

“…That is, the development of the finger forces may be determined initially by a process involving visual identification of the object and the retrieval of implicit memory information concerning its physical properties in terms of the forces to apply. So far, this has been shown to apply to the adaptation of the force output to the weights of objects when we lift objects of different weights, sizes, and densities (Gordon et al, 1991(Gordon et al, , 1993.…”

Lighter or Heavier Than Predicted: Neural Correlates of Corrective Mechanisms during Erroneously Programmed Lifts

“…We registered brain activity in healthy subjects associated with individual lifts using functional magnetic resonance imaging (fMRI). By comparing the brain activity from trials performed with a heavy weight, but programmed for a lighter weight, with trials that were adequately programmed for the heavy weight, we could elucidate the neural substrates responsible for the slow, discontinuous increases in fingertip force that occur after the initial program for the light weight has failed to lift the object (Johansson and Westling, 1988;Gordon et al, 1991Gordon et al, , 1993. Likewise, by comparing the brain activity in trials performed with a light weight, but programmed for a heavier weight, with trials that were adequately programmed for a light weight, we could elucidate the neural substrates responsible for the abrupt termination of the fingertip force that occurs after the premature lift off (Johansson and Westling, 1988).…”