Predictions specify reactive control of individual digits in manipulation.
(1/504)
When humans proactively manipulate objects, the applied fingertip forces primarily depend on feedforward, predictive neural control mechanisms that depend on internal representations of the physical properties of the objects. Here we investigate whether predictions of object properties also control fingertip forces that subjects generate reactively. We analyzed fingertip forces reactively supporting grasp stability in a restraining task that engaged two fingers. Each finger contacted a plate mounted on a separate torque motor, and, at unpredictable times, both plates were loaded simultaneously with forces tangential to the plates or just one of the plates was loaded. Thus, the apparatus acted as though the plates were mechanically linked or as though they were two independent objects. In different test series, each with a predominant behavior of the apparatus and with interspersed catch trials, we showed that the reactive responses clearly reflected the predominant behavior of the apparatus. Whether subject performed the task with one hand or bimanually, appropriate reactive fingertip forces developed when predominantly both contact plates were loaded or just one of the plates was loaded. When a finger was unexpectedly loaded during a catch trial, a weak initial reactive response was triggered, but the effective force development was delayed by approximately 100 msec. We conclude that the predicted physical properties of an object not only control fingertip forces during proactive but also in reactive manipulative tasks. Specifically, the automatic reactive responses reflect predictions at the level of individual digits as to the mechanical linkage of items contacted by the fingertips in manipulation. (+info)
Kinematics and dynamics are not represented independently in motor working memory: evidence from an interference study.
(2/504)
Our capacity to learn multiple dynamic and visuomotor tasks is limited by the time between the presentations of the tasks. When subjects are required to adapt to equal and opposite position-dependent visuomotor rotations (Krakauer et al., 1999) or velocity-dependent force fields (Brashers-Krug et al., 1996) in quick succession, interference occurs that prevents the first task from being consolidated in memory. In contrast, such interference is not observed between learning a position-dependent visuomotor rotation and an acceleration-dependent force field. On the basis of this finding, it has been argued that internal models of kinematic and dynamic sensorimotor transformations are learned independently (Krakauer et al., 1999). However, these findings are also consistent with the perturbations interfering only if they depend on the same kinematic variable. We evaluated this hypothesis using kinematic and dynamic transformations matched in terms of the kinematic variable on which they depend. Subjects adapted to a position-dependent visuomotor rotation followed 5 min later by a position-dependent rotary force field either with or without visual feedback of arm position. The force field tended to rotate the hand in the direction opposite to the visuomotor rotation. To assess learning, all subjects were retested 24 hr later on the visuomotor rotation, and their performance was compared with a control group exposed only to the visuomotor rotation on both days. Adapting to the position-dependent force field, both with and without visual feedback, impaired learning of the visuomotor rotation. Thus, interference between our kinematic and dynamic transformations was observed, suggesting that the key determinant of interference is the kinematic variable on which the transformation depends. (+info)
Positive feedback, memory, and the predictability of earthquakes.
(3/504)
We review the "critical point" concept for large earthquakes and enlarge it in the framework of so-called "finite-time singularities." The singular behavior associated with accelerated seismic release is shown to result from a positive feedback of the seismic activity on its release rate. The most important mechanisms for such positive feedback are presented. We solve analytically a simple model of geometrical positive feedback in which the stress shadow cast by the last large earthquake is progressively fragmented by the increasing tectonic stress. (+info)
Defining the neural mechanisms of probabilistic reversal learning using event-related functional magnetic resonance imaging.
(4/504)
Event-related functional magnetic resonance imaging was used to measure blood oxygenation level-dependent responses in 13 young healthy human volunteers during performance of a probabilistic reversal-learning task. The task allowed the separate investigation of the relearning of stimulus-reward associations and the reception of negative feedback. Significant signal change in the right ventrolateral prefrontal cortex was demonstrated on trials when subjects stopped responding to the previously relevant stimulus and shifted responding to the newly relevant stimulus. Significant signal change in the region of the ventral striatum was also observed on such reversal errors, from a region of interest analysis. The ventrolateral prefrontal cortex and ventral striatum were not significantly activated by the other, preceding reversal errors, or when subjects received negative feedback for correct responses. Moreover, the response on the final reversal error, before shifting, was not modulated by the number of preceding reversal errors, indicating that error-related activity does not simply accumulate in this network. The signal change in this ventral frontostriatal circuit is therefore associated with reversal learning and is uncontaminated by negative feedback. Overall, these data concur with findings in rodents and nonhuman primates of reversal-learning deficits after damage to ventral frontostriatal circuitry, and also support recent clinical findings using this task. (+info)
Incorporating genetic susceptibility feedback into a smoking cessation program for African-American smokers with low income.
(5/504)
PURPOSE: Markers of genetic susceptibility to tobacco-related cancers could personalize harms of smoking and motivate cessation. Our objective was to assess whether a multicomponent intervention that included feedback about genetic susceptibility to lung cancer increased risk perceptions and rates of smoking cessation compared with a standard cessation intervention. EXPERIMENTAL DESIGN: Our design was a two-arm trial with eligible smokers randomized in a 1:2 ratio to Enhanced Usual Care or Biomarker Feedback (BF). Surveys were conducted at baseline, 6, and 12 months later. The setting was an inner city community health clinic. African-American patients who were current smokers (n = 557) were identified by chart abstraction and provider referral. All smokers received a self-help manual and, if appropriate, nicotine patches. Smokers in the BF arm also were offered a blood test for genotyping the GST(3) gene (GSTM1), sent a test result booklet, and called up to four times by a health educator. Prevalent abstinence was assessed by self-report of having smoked no cigarettes in the prior 7 days at the 6- and 12-month follow-ups and sustained abstinence, i.e., not smoking at either follow-up or in-between. RESULTS: Smoking cessation was greater for the BF arm than the Enhanced Usual Care arm (19% versus 10%, respectively; P < 0.006) at 6 months but not at 12 months. CONCLUSIONS: Smokers agreed to genetic feedback as part of a multicomponent cessation program. Although the program increased short-term cessation rates compared with standard intervention, genetic feedback of susceptibility may not benefit smokers with high baseline risk perceptions. (+info)
Methods for pre-testing and piloting survey questions: illustrations from the KENQOL survey of health-related quality of life.
(6/504)
Part of the assertion that any survey researcher can make about the validity of their results needs to contain an analysis of questions and their responses from the respondent's viewpoint. Claims concerning the validity, reliability and sensitivity of health-related quality of life measures tend to be based on the quantitative approach of psychometrics, which fails to identify when respondents: misinterpret questions; do not recall the information requested; or give answers that present themselves in a better or worse light. The paper presents some approaches to pre-testing and piloting survey questionnaires to check the interpretation of survey questions, using illustrations from the KENQOL project. The paper describes: how the intended referential and connotative meaning of each question was established; the criteria to judge the appropriateness of each question; the methods used to make those judgements; and the process of reviewing questions based on findings. The role of piloting is highlighted, and further reading is suggested for readers wishing to develop a model for their own investigation. (+info)
A real-time state predictor in motor control: study of saccadic eye movements during unseen reaching movements.
(7/504)
Theoretical motor control predicts that because of delays in sensorimotor pathways, a neural system should exist in the brain that uses efferent copy of commands to the arm, sensory feedback, and an internal model of the dynamics of the arm to predict the future state of the hand (i.e., a forward model). We tested this theory under the hypothesis that saccadic eye movements, tracking an unseen reaching movement, would reflect the output of this state predictor. We found that in unperturbed reaching movements, saccade occurrence at any time t consistently provided an unbiased estimate of hand position at t + 196 msec. To investigate the behavior of this predictor during feedback error control, we applied 50 msec random-force perturbations to the moving hand. Saccades showed a sharp inhibition at 100 msec after perturbation. At approximately 170 msec, there was a sharp increase in saccade probabilities. These postperturbation saccades were an unbiased estimator of hand position at saccade time t + 150 msec. The ability of the brain to guide saccades to the future position of the hand failed when a force field unexpectedly changed the dynamics of the hand immediately after perturbation. The behavior of the eyes suggested that during reaching movements, the brain computes an estimate of future hand position based on an internal model that relies on real-time proprioceptive feedback. When an error occurs in reaching movements, the estimate of future hand position is recomputed. The saccade inhibition period that follows the hand perturbation may indicate the length of time it takes for this computation to take place. (+info)
Vocal memory and learning in adult Bengalese Finches with regenerated hair cells.
(8/504)
Critical learning periods are common in vertebrate development. In many birds, song learning is limited by a critical period; juveniles copy songs from adult birds by forming memories of those songs during a restricted developmental period and then using auditory feedback to practice their own vocalizations. Adult songs are stable over time regardless of exposure to other birds, but auditory feedback is required for the maintenance of stable adult song. A technique was developed to reversibly deafen Bengalese Finches by destruction and regeneration of inner ear auditory hair cells. With this approach, we asked two questions about the plasticity of song information stored in the adult brain. First, do adult birds store memories or "templates" of their songs that exist independent of auditory reinforcement? Such memories could be used to control vocal output by acting as fixed models of song to which ongoing vocalizations are matched. Second, can adult song learning, which does not normally occur in this species, be induced by removing and then restoring hearing? Studying changes in adult song behavior during hair cell loss and regeneration revealed two findings: (1) adult birds store memories or templates of their songs that exist independent of auditory input and can be used to restore normal vocal behavior when hearing is restored; (2) under experimental circumstances, adult birds can be induced to acquire song material from other birds. Results suggest that, in Bengalese Finches, the degree of behavioral and neural plasticity in juvenile and adult birds may be less distinct that previously thought. (+info)