Tuning the power spectrum of physiological finger tremor frequency with flickering light.

Fast Fourier Transform analyses were performed on finger tremor movements at 0.2-Hz intervals from 0.4 to 40 Hz in 10 human subjects, under a flickering light condition of 4-15 Hz and an unstimulated control condition. Under the control condition, the power spectrum showed an essentially normal curve distribution, except for an early frequency component in the histogram. In contrast, when the flickering light stimulus was presented, the power of specific frequency components at 8-11 Hz was strongly enhanced. This effect was induced exclusively at a frequency of 8, 9, or 11 Hz of flickering light, and this flickering frequency producing the enhancement effect differed from subject to subject. There existed a significant correlation between the frequencies of flicker and tremor at the tuned frequency. These findings demonstrate that a specific frequency of flickering light can intensify a specific frequency of physiological finger tremor, and that different individuals exhibit different optimal "tuning" frequencies.