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Ian Erkelens, William Bobier; Does the baseline motor response predict the short-term adaptability of phasic vergence?. Journal of Vision 2017;17(10):272. doi: 10.1167/17.10.272.
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It has been hypothesized that faster, more accurate baseline neural-motor responses result in greater adaptability to repeated external perturbations. Like saccades, phasic convergence exhibits robust adaptive behavior when exposed to double-step gap stimuli. Directional asymmetries exist in the non-adapted baseline motor response of this phasic vergence mechanism to convergent or divergent disparities. We leverage these directional asymmetries to investigate the relationship between the baseline motor response and its adaptability to a double-step convergent or divergent stimuli. 10 adults (26±3.8y/o) completed 2 study visits where baseline convergence or divergence responses to a 2° disparity step were measured and then adapted using an increasing double-step stimuli (2°+1.5°, 175ms). Individual eye movements were recorded at 250Hz with infrared video oculography, while stimuli where presented dichoptically at 40cm. Vergence kinematics of baseline and adapted responses were compared between stimulus directions. Compared to convergence, divergence exhibited significantly less adaptive changes in gain (9±2%, vs. 31±3% p=0.0005), peak velocity (4±4% vs. 32±3% p=0.0001) and peak acceleration (3±5% vs.30±6%, p = 0.006). Only divergence gain was altered after adaptation (p = 0.005); while divergence peak velocity (p = 0.36) and peak acceleration (p=0.63) were unchanged. Adapted divergence response duration increased (25±9ms, p=0.03), whereas adapted convergence duration was unchanged (-6±9ms, p=0.97). Baseline convergence peak velocity was faster (12.5±1.4°/s vs. 8.7±2.4°/s, p=0.004) than divergence in all subjects. Baseline vergence peak velocity was the strongest predictor of the adaptability of the gain and peak velocity of each system. The results demonstrate that phasic convergence adapts to systematic errors by altering all orders of the dynamic response, whereas phasic divergence adapts by altering only the duration of response output. This adaptive behavior is most strongly correlated with the initial peak velocity of the response, suggesting the baseline neural-motor function determines the degree of adaptability within this oculomotor system.
Meeting abstract presented at VSS 2017
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