The ability of an agent to accomplish a trajectory during a certain motor task depends on the fit between external (environment) and internal (agent) constraints, also known as affordance. A model of difficulty for a generalized reaching motor task is proposed as an affordance-related measure, as perceived by a specific agent for a given environment and task. By extending the information-based Index of Difficulty of a trajectory, a stochastic model of difficulty is formulated based on the observed variability of spatial trajectories executed by a given agent during a repetitive motor task. The model is tested on an experimental walking dataset available in the literature, where the repetitive stride movement of differently aged subjects (14 “old” subjects aged 50–73; 20 “young” subjects aged 21–37) at multiple speed conditions (comfortable, ~30% faster, ~30% slower) is analyzed. Reduced trajectory variability in older as compared to younger adults results in a higher Index of Difficulty (slower: +24%, p < 0.0125; faster: +38%, p < 0.002) which is interpreted in this context as reduced affordance. The model overcomes the limits of existing difficulty measures by capturing the stochastic dependency of task difficulty on a subject’s age and average speed. This model provides a benchmarking tool for motor performance in biomechanics and ergonomics applications.

中文翻译：

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广义到达任务难度的特定于智能体的随机模型

特工在某项运动任务中完成轨迹的能力取决于外部（环境）约束与内部（特工）约束之间的契合度（也称为负担）。对于特定的环境和任务，特定的代理人认为，提出了一种广义的完成运动任务的难度模型，作为与负担相关的度量。通过扩展基于信息的轨迹的难度指数，基于观察到的由给定特工在重复性运动任务中执行的空间轨迹的可变性，来建立难度的随机模型。该模型在文献中提供的实验步行数据集上进行了测试，其中不同年龄的受试者（14个“老”受试者年龄在50-73岁； 20个“年轻”受试者年龄在21-37岁）在多种速度条件下（舒适）的重复步幅运动，分析快了约30％，慢了约30％）。与年轻人相比，老年人的轨迹变异性降低，导致难度系数更高（较慢：+ 24％，p <0.0125；更快：+ 38％，p <0.002）在这种情况下被解释为负担能力降低。该模型通过捕获任务难度对受试者年龄和平均速度的随机依赖性，克服了现有难度措施的局限性。该模型为生物力学和人体工程学应用中的电机性能提供了基准测试工具。