The study of dual task interference has gained increasing attention in the literature for the past 35 years, with six MEDLINE citations in 1979 growing to 351 citations indexed in 2014 and a peak of 454 cited papers in 2013. Increasingly, researchers are examining dual task cost in individuals with pathology, including those with neurodegenerative diseases. While the influence of these papers has extended from the laboratory to the clinic, the field has evolved without clear definitions of commonly used terms and with extreme variations in experimental procedures. As a result, it is difficult to examine the interference literature as a single body of work. In this paper we present a new taxonomy for classifying cognitive-motor and motor-motor interference within the study of dual task behaviors that connects traditional concepts of learning and principles of motor control with current issues of multitasking analysis. As a first step in the process we provide an operational definition of dual task, distinguishing it from a complex single task. We present this new taxonomy, inclusive of both cognitive and motor modalities, as a working model; one that we hope will generate discussion and create a framework from which one can view previous studies and develop questions of interest.

Background: A decline in manual dexterity is a common phenomenon in elderly individuals. Often, simple daily activities such as handling coins and preparing meals become challenging. A substantial decline in manual dexterity may impact one’s ability to live independently. Thus, understanding the underlying causes of these impairments is essential. Considerable attention has been given to the regulation of fingertip forces during object grasp, lift and transport in the elderly. Objective: Here we review studies on fingertip force coordination in the elderly, with an emphasis on the relationship between the degree of change in elderly grip force control and the nature of the tasks performed. Methods: A literature search was performed using Medline, Pubmed, and Web of Science electronic databases covering studies from 1985 to 2009, inputting combinations of the following key words: grip force, grasp force, fingertip forces, precision grip, aging, elderly, and hand motor control. Results: Studies show a consistent elevation in grip force magnitudes that may easily lead to fatigue. These force increases may represent a compensation for increased skin slipperiness or a reduction in tactile information. In contrast, anticipatory grip force control (planning) remains relatively intact. Age-related changes in anticipatory control seem to emerge only during more complex tasks. Conclusion: The relationship between task complexity and degree of age-related changes suggests that results from simple, laboratory-based tasks may only partially explain impairments observed during the performance of activities of daily living, since the latter ones are typically more complex. A better understanding of impaired manual dexterity experienced by elderly individuals could be achieved by expanding experimental paradigms so that they more closely resemble the complexities encountered in functional daily tasks. Subsequently, these findings could be used in clinical settings to develop treatment approaches that consider grasp control in the context of behaviorally meaningful tasks.

An interesting feature of the muscular organization of the human hand is that the main flexors and extensors of the fingers are compartmentalized and give rise to multiple parallel tendons that insert onto all the fingers. Previous studies of motor-unit synchrony in extensor digitorum and flexor digitorum profundus indicated that synaptic input to motor neurons supplying these multitendoned muscles is not uniformly distributed across the entire pool of motor neurons but instead appears to be partially segregated to supply subsets of motor neurons that innervate different muscular compartments. Little is known, however, about the organization of the synaptic inputs to the motor neurons supplying another multitendoned finger muscle, the flexor digitorum superficialis (FDS). Therefore in this study, we estimated the extent of divergence of last-order inputs to FDS motor neurons by measuring the degree of short-term synchrony among motor units within and across compartments of FDS. The degree of synchrony for motor-unit pairs within the same digit compartment was nearly twofold that of pairs of motor units in adjacent compartments and more than fourfold that of pairs in nonadjacent compartments. Therefore like other multitendoned muscles of the hand, last-order synaptic inputs to motor neurons supplying the FDS appear to primarily supply subsets of motor neurons innervating specific finger compartments. Such an organization presumably enables differential activation of separate compartments to facilitate independent movements of the fingers.

Freezing of Gait (FOG) is an impairment that affects the majority of patients in the advanced stages of Parkinson’s Disease (PD). FOG can lead to sudden falls and injuries, negatively impacting the quality of life for the patients and their families. Rhythmic Auditory Stimulation (RAS) can be used to help patients recover from FOG and resume normal gait. RAS might be ineffective due to the latency between the start of a FOG event, its detection and initialization of RAS. We propose a system capable of both FOG prediction and detection using signals from tri-axial accelerometer sensors that will be useful in initializing RAS with minimal latency. We compared the performance of several time frequency analysis techniques, including moving windows extracted from the signals, handcrafted features, Recurrence Plots (RP), Short Time Fourier Transform (STFT), Discreet Wavelet Transform (DWT) and Pseudo Wigner Ville Distribution (PWVD) with Deep Learning (DL) based Long Short Term Memory (LSTM) and Convolutional Neural Networks (CNN). We also propose three Ensemble Network Architectures that combine all the time frequency representations and DL architectures. Experimental results show that our ensemble architectures significantly improve the performance compared with existing techniques. We also present the results of applying our method trained on a publicly available dataset to data collected from patients using wearable sensors in collaboration with A.T. Still University.

Background It is unclear how young and older adults modulate dual-task mobility under changing postural challenges. Aim To examine age-related changes in dual-task processing during specific phases of dual-task Timed Up-and-Go (TUG_dual-task). Method Healthy young and older adults performed the Timed Up-and-Go (TUG) with the following dual-task conditions: (1) serial-three subtractions, (2) carrying cup of water, (3) combined subtraction and carrying water, and (4) dialing cell phone. The primary outcome was the dual-task cost on performance of TUG (percent change from single- to dual-task) based on duration and peak trunk velocity of each phase: (a) straight-walk, (b) sit-to-stand, (c) turn, (d) turn-to-sit. Mixed-design univariate analysis of variance was performed for each type of task. Results Older adults had more pronounced mobility decrements than young adults during straight-ahead walking and turns when the secondary task engaged both cognitive and manual modalities. Simple cognitive or manual tasks during TUG_dual-task did not differentiate young from older participants. Subtraction performance during simple and complex cognitive conditions differed by phase of the TUG. Manual task performance of carrying water did not vary by phase or age. Discussion Our findings suggest that dual-task processing is dynamic across phases of TUG_dual-task. Aging-related dual-task decrements are demonstrated during straight-ahead walking and turning, particularly when the secondary task is more complex. Conclusion Older adults are susceptible to reduced dual-task mobility during straight-ahead walking and turning particularly when attentional loading was increased.