Pardhan S
Department of Optometry and Ophthalmic Dispensing, Anglia Polytechnic University, CB1 1PT, Cambridge, UK.
Vision Res. 2003 May;43(11):1249-55. doi: 10.1016/s0042-6989(03)00093-2.
Spatial frequency thresholds for recognition were measured for binocular and monocular viewing conditions at two contrast levels (95% and 7%). Measurements were obtained at the fovea and at four different eccentric retinal locations. Each eccentric retinal location was 8 degrees from the fovea, one on the horizontal axis (180 degrees ), and the other three in the superior field on retinal axes of 90 degrees, 45 degrees and 135 degrees. For the superior and horizontal retinal locations, the orientations of the gratings tested were horizontal (180 degrees ) and vertical (90 degrees ). For the retinal points on the oblique axes, the orientations of the gratings were 45 degrees and 135 degrees. Measurements were also obtained at the fovea for all four different grating orientations at both levels of contrast. Recognition threshold was defined as the highest spatial frequency at which luminance gratings were perceived vertically. At the fovea, binocular summation ratios (binocular spatial frequency/monocular spatial frequency) showed no significant differences for gratings of either contrast levels or for any orientation (p>0.05). In the superior periphery, significantly higher summation ratios were shown by low contrast vertical gratings (p<0.05), and in the horizontal periphery by low contrast horizontal gratings (p<0.05). On the oblique axis, low contrast gratings that were parallel to the oblique meridian showed higher summation ratios compared to those at right angles to it. High contrast gratings, at least at 8 degrees eccentricity, did not show this effect. Data suggest that meridional organisation of the retina (e.g. vertical gratings seen maximally in the superior field) occurs for resolution and that it is evidenced closer to the fovea than previously shown.
在两种对比度水平(95%和7%)下,分别测量了双眼和单眼观察条件下的识别空间频率阈值。测量是在中央凹以及视网膜上四个不同的偏心位置进行的。每个偏心视网膜位置与中央凹相距8度,一个在水平轴(180度)上,另外三个在视网膜轴为90度、45度和135度的上半视野中。对于视网膜上半部分和水平位置,所测试光栅的方向为水平(180度)和垂直(90度)。对于斜轴上的视网膜点,光栅的方向为45度和135度。在两种对比度水平下,还在中央凹测量了所有四种不同光栅方向的情况。识别阈值定义为垂直感知亮度光栅的最高空间频率。在中央凹,对于任何对比度水平或任何方向的光栅,双眼总和比(双眼空间频率/单眼空间频率)均无显著差异(p>0.05)。在上半周边区域,低对比度垂直光栅显示出显著更高的总和比(p<0.05),在水平周边区域,低对比度水平光栅显示出显著更高的总和比(p<0.05)。在斜轴上,与斜子午线平行的低对比度光栅比与之成直角的光栅显示出更高的总和比。高对比度光栅,至少在偏心8度时,未显示出这种效应。数据表明,视网膜的子午线组织(例如,在上半视野中垂直光栅看得最清楚)与分辨率有关,并且在比以前所示更靠近中央凹的位置就有证据表明这一点。