Flitcroft D I
University Laboratory of Physiology, Oxford University, UK.
Ophthalmic Physiol Opt. 1991 Jan;11(1):81-90.
Static accommodation responses to sinusoidal grating stimuli that displayed temporal modulations in luminance contrast (i.e. contrast flicker) were measured with a laser speckle optometer. The effects of a variety of temporal waveforms were investigated including square-wave modulations, sinusoidal modulations, and band-pass filtered noise. The effects of altering both the amplitude and the temporal frequency (0.4-30 Hz) of the contrast flicker and the spatial frequency of the stimulus (0.77-9.2 c/deg) were also examined. All the flicker waveforms investigated (square wave, sinusoidal and band-pass noise) reduced accommodative accuracy, the effect being most apparent at lower spatial frequencies (0.77-1.15 c/deg). With band-pass filtered noise the effects of flicker were most apparent with frequencies in the range 1-4 Hz, at both lower (0.4 Hz) and higher flicker frequencies (8-32 Hz) accommodations was less affected. It was found that flicker impaired accommodation under conditions where the contrast was at all times suprathreshold. This is incompatible with the proposal that flicker reduces accommodation responses because for part of each flicker cycle the stimulus was below threshold. However, these results are compatible with the alternative hypothesis that flicker impairs the ability of the accommodation system to utilize temporal cues such as those derived from the higher frequency component (1-2 Hz) of accommodative oscillations.
使用激光散斑验光仪测量了对在亮度对比度上显示时间调制(即对比度闪烁)的正弦光栅刺激的静态调节反应。研究了各种时间波形的影响,包括方波调制、正弦调制和带通滤波噪声。还研究了改变对比度闪烁的幅度和时间频率(0.4 - 30Hz)以及刺激的空间频率(0.77 - 9.2周/度)的影响。所研究的所有闪烁波形(方波、正弦波和带通噪声)均降低了调节精度,在较低空间频率(0.77 - 1.15周/度)时这种影响最为明显。对于带通滤波噪声,闪烁的影响在1 - 4Hz频率范围内最为明显,在较低(0.4Hz)和较高闪烁频率(8 - 32Hz)时调节受影响较小。研究发现,在对比度始终高于阈值的条件下,闪烁会损害调节。这与闪烁降低调节反应是因为在每个闪烁周期的部分时间刺激低于阈值这一观点不相符。然而,这些结果与另一种假设相符,即闪烁会损害调节系统利用时间线索的能力,例如那些源自调节振荡的高频成分(1 - 2Hz)的线索。