Errors and episodes of “freezing” seen during mirror writing by adults can be incorporated into the model suggested in Thelen et al.'s target article This requires assigning an important role to internal inverse models stored in memory. The strongly anti-dualism position of Thelen et al.'s leaves little room for the Bernsteinian notion of activity.

Exclusively focused on data that are consistent with the proposed ideas, the target article misses an opportunity to review data that are inconsistent with them. Weaknesses of the emulation theory become especially evident when one tries to incorporate physiologically realistic muscle and reflex mechanisms into it. In particular, it fails to resolve the basic posture-movement controversy.

Motor control schemes should have an element of control and an element of coordination. The former is a source of initiative and a zroduct of the brain's work (mind, intelligence, or ) while the latter can be viewed as a process with constraints emerging at a hierarchically lower, autonomous level. Limiting scientific analysis to an object smaller than the universe necessarily leads to a hierarchical (cybernetic) approach.

The equilibrium-point hypothesis (the λ-model) is superior to all other models of single-joint control and provides deep insights into the mechanisms of control of multi-joint movements. Attempts at associating control variables with neurophysiological variables look confusing rather than promising. Probabilistic mechanisms may play an important role in movement generation in redundant systems.

Plamondon & Alimi's derivation of the kinematic model is mathematically flawed. By simply naming a particular parameter combination the model fails to explicate the sources of variability. As a result, the model cannot distinguish between various sources of error, such as those resulting from task demands and those resulting from movement execution.

We criticize the synaptic theory of long-term memory and the inappropriate usage of physical notions such as in motor control theories. Motor control and motor memory hypotheses should be based on explicitly specified hypothetical control variables that are sound from both physiological and physical perspectives. [HOUK et al.; SMITH; THACH].