The motor system computes well but remembers poorly

The psychological approach to human voluntary movements advocated by F. Mechsner (2004) can be aligned with the view that motor commands are generated afresh but are not retrieved from memory. This movement-generation hypothesis gains indirect support in the findings Mechsner reviewed and obtains more direct support from the results of studies of memory for movement and computational modeling of motor planning.     

Interlimb Coordination: Real Constraints and False Dichotomies

Despite the recent advances in the field of coordination dynamics addressing the interplay of constraints of different natures in the emergence of human coordination, F. Mechsner (2004) invites us to revive hierarchical and dichotomous thinking by offering again his exclusive position that coordinated movements are (purely) perceptual-cognitive/psychological in nature. In this comment, the authors address a number of theoretical and methodological issues that might potentially puzzle the readers of Mechsner's article. They contend that the dichotomy proposed by Mechsner (i.e., perceptual-cognitive vs. motor) constitutes a restrictive framework for understanding human coordination.     

On the perceptual control of bimanual performance

The author compares some critical findings of F. Mechsner and his colleagues with related results from other laboratories to point out that when higher levels of representation are available, those levels might come to be the focus of attention and control motor actions by overriding constraints at lower levels of the system.     

The cognitivist's revenge?

The recent articles by F. Mechsner (2004) and his colleagues (F. Mechsner, D. Kerzel, G. Knoblich, & W. Prinz, 2001) have once again fuelled the cognition vs. motor debate. In this commentary, the author takes an historical perspective and argues that Mechsner' stance represents just another phase in this continuing dialogue. Finally, the value of such false dichotomies in the progress of the field is questioned.     

Interlimb coordination: real constraints and false dichotomies

Despite the recent advances in the field of coordination dynamics addressing the interplay of constraints of different natures in the emergence of human coordination, F. Mechsner (2004) invites us to revive hierarchical and dichotomous thinking b y offering again his exclusive position that coordinated movements are (purely) perceptual-cognitive/psychological in nature. In this comment, the authors address a number of theoretical and methodological issues that might potentially puzzle the readers of Mechsner's article. They contend that the dichotomy proposed by Mechsner (i.e., perceptual-cognitive vs. motor) constitutes a restrictive framework for understanding human coordination.     

On the Perceptual Control of Bimanual Performance

The author compares some critical findings of F. Mechsner and his colleagues with related results from other laboratories to point out that when higher levels of representation are available, those levels might come to be the focus of attention and control motor actions by overriding constraints at lower levels of the system.     

Psychology has to deal with efferences too

The authors argue that F. Mechsner's (2004) perceptual-cognitive approach is an important contribution to the current discussion of motor control. Mechsner presents convincing evidence against direct motor control. Nevertheless, the mechanisms by which perceptual-cognitive representations determine efferent commands must still be clarified.     

Symmetry and the devil

F. Mechsner (2004) bases his argument for the primacy of perception on a simplified interpretation of phase transition findings. The authors show that attention to the details of phase transition analysis, as well as consideration of findings from steady-state experiments and the tools of symmetry theory, necessitate a theory of bimanual coordination that includes both perceptual and motor processes.     

Psychology Has to Deal with Efferences Too

The authors argue that F. Mechsner's (2004) perceptual-cognitive approach is an important contribution to the current discussion of motor control. Mechsner presents convincing evidence against direct motor control. Nevertheless, the mechanisms by which perceptual-cognitive representations determine efferent commands must still be clarified.     

Control is good; prediction is better?

Franz Mechsner (2004) suggests that movements are exclusively controlled with respect to the effects that they cause in the external world and that motor control can be reduced to prediction of movement effects. Although predictive mechanisms certainly deserve a lot more attention than they have received in the past, the author argues here that prediction and control must necessarily work together to build a flexible and effective motor system.     

Postintentional Neglect

F. Mechsner (2004) seems to deny a functional importance of postintentional processes, except that their characteristics can be taken into account at the perceptual-cognitive level of control. In that perspective, processes that are critical for the understanding of motor control and its limitations are neglected. On the other hand, the functional importance of task conceptions or task sets, which can vary and affect performance even for tasks that appear identical to an observer, is emphasized.     

Postintentional neglect

F. Mechsner (2004) seems to deny a functional importance of postintentional processes, except that their characteristics can be taken into account at the perceptual-cognitive level of control. In that perspective, processes that are critical for the understanding of motor control and its limitations are neglected. On the other hand, the functional importance of task conceptions or task sets, which can vary and affect performance even for tasks that appear identical to an observer, is emphasized.     

A simple and unified approach to human voluntary movements

In his provocative article, F. Mechsner (2004) advances the thesis that human voluntary movements are subject to "psychological" or "perceptual-cognitive" control and are thus organized "without regard to efferent patterns" (p. 355). Rather than considering in detail the experiments that he proffered by way of support, the present author discusses the degree to which that supposition has appeal on the grounds of simplicity and is defined in terms that are compatible with a unified science.     

Perceptual-cognitive control as a special case in equivalent multisensory-sensorimotor interactions

In his primary thesis on the purely perceptual-cognitive nature of movement control, F. Mechsner (2004) entirely neglects, or in fact negates, the influences of action on perception. In this commentary, the author follows the logical steps of Mechsner, illustrates what he conceives to be an error in Mechsner's reasoning, and synthesizes those arguments in favor of a hypothesis of a system of equivalent elements (senses and effectors) in interaction.     

Motor affordance and its role for visual working memory: evidence from fMRI studies

We examined the role of motor affordances of objects for working memory retention processes. Three experiments are reported in which participants passively viewed pictures of real world objects or had to retain the objects in working memory for a comparison with an S2 stimulus. Brain activation was recorded by means of functional magnetic resonance imaging (fMRI). Retaining information about objects for which hand actions could easily be retrieved (manipulable objects) in working memory activated the hand region of the ventral premotor cortex (PMC) contralateral to the dominant hand. Conversely, nonmanipulable objects activated the left inferior frontal gyrus. This suggests that working memory for objects with motor affordance is based on motor programs associated with their use. An additional study revealed that motor program activation can be modulated by task demands: Holding manipulable objects in working memory for an upcoming motor comparison task was associated with left ventral PMC activation. However, retaining the same objects for a subsequent size comparison task led to activation in posterior brain regions. This suggests that the activation of hand motor programs are under top down control. By this they can flexibly be adapted to various task demands. It is argued that hand motor programs may serve a similar working memory function as speech motor programs for verbalizable working memory contents, and that the premotor system mediates the temporal integration of motor representations with other task-relevant representations in support of goal oriented behavior.     

Mood, memory, and motor performance and the severity of tardive dyskinesia

This study tested the hypothesis that the features of tardive dyskinesia were associated with motor slowing, memory impairment, and depressive apathy all of which are considered to characterize the so-called subcortical dementias. In a sample of 48 psychiatric patients all fulfilling research criteria for tardive dyskinesia and without other signs of organic illness age-independent correlations were observed between severity of orofacial dyskinesia and measures of memory, motor performance and mood providing some empirical support for the hypothesis.     

The roles of sequencing and verbal working memory in sentence comprehension deficits in Parkinson's disease

Studies of sentence comprehension deficits in Parkinson's disease (PD) patients suggest that language processing involves circuits connecting subcortical and cortical regions. Anatomically segregated neural circuits appear to support different cognitive and motor functions. To investigate which functions are implicated in PD comprehension deficits, we tested comprehension, verbal working memory span, and cognitive set-switching in a non-linguistic task in 41 PD patients; we also obtained speech measurements reflecting motor sequencing processes that may be involved in articulatory rehearsal within working memory. Comprehension of sentences with center-embedded or final relative clauses was impaired when they could not be understood from lexical semantic content alone. Overall comprehension error rates correlated strongly with impaired set-switching and significantly with reduced working memory span and speech motor sequencing deficits. Correlations with comprehension of different sentence structures indicate that these impairments do not represent a single deficit; rather, PD comprehension deficits appear to arise from several independent mechanisms. Deficits in cognitive set-switching or underlying inhibitory processes may compromise the ability to process relative clauses. Deficits in verbal working memory appear to impair comprehension of long-distance dependencies. Speech sequencing correlated with neither set-switching nor verbal working memory span, consistent with their being supported by independent, segregated cortico-subcortical circuits.     

A note on schema and exemplar approaches to motor skill representation in memory

Given the need for a memory representation of well-learned motor skills, a common assumption in motor behavior is that this knowledge is stored in a central, abstracted form. Active production of motor skills has not been used in experimental designs that have provided empirical support for this view of representation, however. Much of the faith in centralized, abstracted forms of memory representation for motor skills is due to the popularity of Schmidt's schema theory, which has adapted the prototype abstraction model from category learning research to the representation of motor skills. Since schema theory was proposed, however, an alternative view that seriously questions the preeminence of the prototype abstraction model for the central representation of knowledge has arisen in the category learning literature. This particular view, termed the specific exemplar model, has led a number of researchers in cognition to develop mixed models that involve both prototypic abstraction and specific exemplar elements. This note, then, identifies what can be perceived as a gap in the empirical knowledge base in motor behavior and discusses the possibility of using the debate about representation for category learning as a stimulus for initiating a similar investigation into the representation of motor skills. A hypothetical specific exemplar model for the memory representation of motor skills is outlined, and possible empirical comparisons between this model and the schema abstraction model are suggested.     

Perception—Action Coupling during Bimanual Coordination: The Role of Visual Perception in the Coalition of Constraints That Govern Bimanual Action

Constraints pertaining to interlimb coordination have been studied extensively in the past decades. In this debate, F. Mechsner (2004) has taken a provocative position by putting primary emphasis on perceptual principles that mediate coordinative stability. Whereas the present authors agree that the role of perceptual principles is of critical importance during coordination, they take issue with Mechsner's extreme position and with the evidence forwarded to support a purely perceptual-cognitive approach to bimanual coordination. More specifically, the authors emphasize that current knowledge about brain function argues against a dualism between perception and action, criticize the presented evidence that posture manipulations during coordination provide decisive evidence against motoric and muscular constraints, and report on potential pitfalls associated with the use of visual transformation procedures to support complex coordination patterns.     

Perception-action coupling during bimanual coordination: the role of visual perception in the coalition of constraints that govern bimanual action

Constraints pertaining to interlimb coordination have been studied extensively in the past decades. In this debate, F. Mechsner (2004) has taken a provocative position by putting primary emphasis on perceptual principles that mediate coordinative stability. Whereas the present authors agree that the role of perceptual principles is of critical importance during coordination, they take issue with Mechsner's extreme position and with the evidence forwarded to support a purely perceptual-cognitive approach to bimanual coordination. More specifically, the authors emphasize that current knowledge about brain function argues against a dualism between perception and action, criticize the presented evidence that posture manipulations during coordination provide decisive evidence against motoric and muscular constraints, and report on potential pitfalls associated with the use of visual transformation procedures to support complex coordination patterns.