PubMed · 5454574
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A V Reader. 1970. Conditional reflexes and learning machines.. https://doi.org/10.1016/0001-6918(70)90008-9
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To achieve a given motor task a single trajectory must be chosen from the infinite set of possibilities consistent with the task. To investigate such motor planning in a natural environment, we examined the kinematics of reaching movements made around a visual obstacle in three-dimensional space. Within each session, the start and end points of the movement were uniformly varied around the obstacle. However, the distribution of the near points, where the paths came closest to the obstacle, showed a strong anisotropy, clustering at the poles of a preferred axis through the center of the obstacle. The preferred axes for movements made with the left and right arms were mirror symmetric about the midsagittal plane, suggesting that the anisotropy stems from intrinsic properties of the arm rather than extrinsic visual factors. One account of these results is a sensitivity model of motor planning, in which the movement path is skewed so that when the hand passes closest to the obstacle, the arm is in a configuration that is least sensitive to perturbations that might cause collision. To test this idea, we measured the mobility ellipse of the arm. The mobility minor axis represents the direction in which the hand is most inertially stable to a force perturbation. In agreement with the sensitivity model, the mobility minor axis was not significantly different from the preferred near point axis. The results suggest that the sensitivity of the arm to perturbations, as determined by its inertial stability, is taken into account in the planning process.
Recent research in the area of stimulus equivalence suggests that transfer of function via members of stimulus equivalence classes may have relevance to human emotional responding and the development and generalization of certain psychological disorders. This study investigated the transfer of avoidance evoking functions through equivalence classes. Eight subjects were trained in the necessary relations for two-four member stimulus equivalence classes to emerge. Next, using an on-baseline classical conditioning procedure, one member of one class was paired with shock while one member of the other class was presented without shock. Then, while subjects engaged a key-press task, a differential, signalled avoidance task was introduced wherein shock was avoided if a response occurred to the stimulus previously associated with shock. The remaining stimuli from both classes were then presented. The behavior of all eight subjects showed the differential transfer of the avoidance evoking function. The clinical and theoretical implications of the results are discussed.
Previous research on anxiety and some recent reports on chronic pain suggest that the response to aversive stimuli may be influenced by expectations rather than actual experience. This study examined the contributions of four expectancy-related variables to the tolerance and avoidance of pain: pain expectancy, response expectancy, self-efficacy expectancy, and danger expectancy. Chronic pain sufferers volunteered to undergo cold pressor pain on two trials (the first for practice, and the second to determine tolerance) and then faced the prospect of a third trial (to determine avoidance). It was found that expected tolerance (or response expectancy) significantly predicted actual tolerance, whereas expected danger significantly predicted avoidance. These findings are in partial agreement with previous research. Among the clinical implications are that chronic pain sufferers generally associate pain with damage and they predict their pain tolerance well; they do not necessarily escape from a compulsory activity that produces pain, but given the chance they would rather avoid it in the first place.