The main thrust of Dr. Shelhamer’s work is in the area of vestibular and oculomotor adaptation. This includes studies of the error signals that drive adaptation, ways to improve adaptation, and context-specific adaptation. This line of investigation uses a dynamic-systems approach, leading to the study of the statistical properties (fractal correlations) of sequences of responses. This began with the finding that sequences of consecutive predictive saccades are highly correlated, reflecting the need to store past performance to program a movement with the proper parameters (timing, amplitude). The correlations exhibit power-law decay, which is a form of fractal scaling and suggests a process that optimally balances flexibility and stability. The most recent results of this work demonstrate that the strength and extent of the inter-trial correlations are directly related to the ability to adaptively alter saccade gain. This has been extended to adaptive control of the VOR. These results are among the first that demonstrate the potential to forecast an individual’s predictive ability, which might be used to tailor adaptation and training paradigms. This work is now being expanded more broadly, based on multi-system adaptation of humans to environmental perturbations such as extended space flight. The challenges of understanding, assessing, and promoting adaptation to space flight are similar to those involved with compensation from injury or disease, and both aspects can be studied in normal subjects exposed to controlled sensorimotor perturbations: this is the guiding hypothesis of ongoing research. The overall theme of this work is resilience: the ability to reorganize physiological processes to recover from injury, pathology, and environmental perturbation.
Technology Expertise Keywords
sensorimotor assessment, ambulatory monitoring
Shelhamer M. Nonlinear Dynamics in Physiology: A State-Space Approach. Singapore: World Scientific, 2007.
Shelhamer M, Joiner W. Saccades exhibit abrupt transition between reactive and predictive, predictive saccade sequences have long-term correlations. J Neurophysiol, 2003, 90:2763-2769.
Shelhamer M. Sequences of predictive saccades are correlated over a span of ~2 s and produce a fractal time series. J Neurophysiol, 2005, 93:2002-2011.
Shelhamer M. Sequences of predictive eye movements form a fractional Brownian series - implications for self-organized criticality in the oculomotor system. Biol Cybern, 2005, 93:43-53.
Wong AL, Shelhamer M. Sensorimotor adaptation error signals are derived from realistic predictions of movement outcomes. J Neurophysiol, 2011, 105:1130-1140.
Wong AL, Shelhamer M. Exploring the fundamental dynamics of error-based motor learning using a stationary predictive-saccade task. PLoS ONE, 2011, 6:e25225.
Wong AL, Shelhamer M. Similarities in error processing establish a link between saccade prediction at baseline and adaptation performance. J Neurophysiol, 2014, 111:2084-2093.
Shelhamer M. Trends in sensorimotor research and countermeasures for exploration-class space flights. Front Syst Neurosci, 2015, 9:115.
Shelhamer M. A call for research to assess and promote functional resilience in astronaut crews. J App Physiol, 2016, 120:471-472.