Background: Almost all major aspects of daily life revolve around the completion of movements such as locomotion, reaching and grasping. Often these movements are performed in complex and distracting environments with specific goals in mind. Traditionally, habitual motor tasks such as walking have been viewed as unrelated to the cognitive domain; however, there is growing evidence of cognitive-motor interaction (CMI), perhaps associated with the inability to allocate attentional resources during dual tasking and/or damage within shared neural tracts of the brain. Inquiries into the manifestation, mechanisms and implications of CMI are ecologically relevant as we commonly perform tasks concurrently, such as walking and talking on a phone or attempting to recall a shopping list while traversing the grocery store. Moreover, cognitive-motor interactions have been shown to be related to adverse outcomes such as falling in health and disability. It is also apparent that dual tasking can further compound the impairments commonly observed in individuals with neurological disorders. Ultimately, a deeper understanding of CMI could lead to strategies for improving multitasking performance through targeted intervention, training and/or rehabilitation.
Specific Aims: The purpose of the current work was to examine a theoretical basis of CMI through the implementation of experimental manipulations based on an individual, environment and task (IET) centered motor control framework. This work is of both theoretical and clinical importance. The primary aim of this analysis was to present an in depth theoretical examination of CMI that to date has not been explicitly performed in any population. By carrying out an analysis of this nature, future studies examining CMI may be better informed in regards to the responsible mechanisms related to particular observations. Additionally, a better understanding of the individual, environmental, and task factors that relate to CMI could help enhance current dual task interventions and rehabilitation techniques.
Methods: Three experiments were carried out, with each examining manipulations of the key areas outlined in the IET framework. That is, the foundation of this work was to manipulate task and environmental constraints during dual tasking in multiple clinical populations with neurodegenerative disease or injury and healthy control subjects to provide a comprehensive analysis of the driving factors that lead to altered performance when multitasking.
Experiment one aimed to determine the effect of varying environmental complexity (i.e. risk levels) on both task perception and CMI during dual tasking. Participants were asked to simultaneously walk and think in environments with varied difficulty (e.g. narrow walkways, obstacles) to determine how an added environmental stimulus alters dual task performance. Experiment two examined the attentional demands of movement through the use of probe reaction times during different mobility/stability tasks. Participants completed five tasks (sitting, standing, stationary cycling, leaning to stability limits and walking) requiring a range of stability and mobility control while simultaneously responding to randomly presented auditory cues. Experiment three considered the effect of explicit task instructions towards cognitive or motor prioritization and their effect on observed CMI behavior. Participants were asked to walk and think while given instructions on which domain (e.g. cognitive or motor) to prioritize.
Results: All three experiments included samples of both healthy individuals and individuals with neurological impairment (e.g. multiple sclerosis and Parkinson's disease) The primary result of the present work was a direct comparison of the attentional capacity model, a neuro-resource based framework of dual tasking, compared to the behaviorally based self-awareness prioritization model. Examining the results from the three experiments as a whole suggests that the capacity model in and of itself may not fully describe the changes to gait and balance during concurrent performance. Contrarily, measures similar to the hazard estimate and postural reserve constructs of the prioritization model commonly displayed congruence with the observed CMI outcomes. Additionally, these relationships were primarily present across all groups, healthy and clinical samples, indicating that the level of physiological and/or cognitive impairment in an individual may be more pertinent to dual task costs than the disease or injury that is the root of those impairments.
Conclusions: The current results have worthwhile clinical import. First, they suggest that studies of CMI should consider utilizing methodology that limits task bias in order to get the most valid understanding of prioritization as possible. Moreover, it was determined in the current analysis that in total, the participants tended to adopt a posture second approach for simple motor conditions and later shift this focus towards posture as task difficulty increased. This behavior suggests that cognitive flexibility is present in both the healthy and clinical populations and ultimately could be a target for intervention if possibly unsafe dual task strategies are observed. Additionally, it is of note that overall measures of physiological fall risk, cognition and balance confidence were commonly related to observed DTCs. This suggests that symptoms and not the underlying neurological disorder may drive CMI behavior. Ultimately, the current results serve to provide exciting new evidence in regards to the theoretical underpinnings of CMI
