An agent-specific stochastic model of generalized reaching task difficulty

Andrea Lucchese, Salvatore Digiesi, Kübra Akbaś, Carlotta Mummolo

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


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.

Original languageEnglish (US)
Article number4330
JournalApplied Sciences (Switzerland)
Issue number10
StatePublished - May 2 2021

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • Instrumentation
  • General Engineering
  • Process Chemistry and Technology
  • Computer Science Applications
  • Fluid Flow and Transfer Processes


  • Affordance
  • Foot trajectory
  • Gait variability
  • Index of difficulty
  • Reaching motor task
  • Trajectory complexity
  • Young and elderly gait


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