Orientation discrimination across the visual field: matching perceived contrast near threshold
Orientation discrimination across the visual field: matching perceived contrast near threshold
复制标题
DOI：
10.1016/j.visres.2004.06.004
复制
发表时间：
2004-10-01
期刊：
影响因子：
1.8
通讯作者：
Gurnsey, R
中科院分区：
文献类型：
--
作者：
Sally, SL;Gurnsey, R
通过根据F = 1 + E/E-2缩放周边呈现的刺激，通常可以使整个视野的性能相等，其中E-2是刺激大小必须加倍以维持中央凹性能水平的偏心率。以往的研究表明，当刺激呈现的对比度远高于检测阈值时，方位辨别的E-2在1.5度-20度之间。最近的心理物理和生理证据表明，在近阈值对比的感受野的空间重组。这种感受野结构的对比度依赖性变化可能会改变在整个视野中等同任务性能所需的大小缩放量。为了研究这个问题，我们测量了一系列刺激大小和偏心率（0度-15度）的方向辨别阈值。我们使用相同的程序，除了以前采用的刺激在近阈值对比。我们通过匹配程序控制了感知对比度对阈值的影响。将注视时出现的3度标准线长度设置为高于检测阈值的2个刚好可察觉的差异。所有其他刺激的感知对比度由受试者调整以匹配此刺激。然后在这些匹配的对比度下获得所有刺激大小和偏心率的方向辨别阈值。两名受试者的E-2值分别为3.42度和3.50度;这些值比以前在更高的物理对比度下呈现刺激时发现的E-2值大两倍。(C)2004爱思唯尔有限公司保留所有权利。
Performance can often be made equal across the visual field by scaling peripherally presented stimuli according to F = 1 + E/E-2 where E-2 is the eccentricity at which stimulus size must double to maintain foveal performance levels. Previous studies suggest that E-2 for orientation discrimination is in the range of 1.5degrees-2degrees when stimuli are presented at contrasts well above detection threshold. Recent psychophysical and physiological evidence suggests spatial reorganization of receptive fields at near-threshold contrasts. Such contrast-dependent changes in receptive field structure might alter the amount of size scaling necessary to equate task performance across the visual field. To examine this question we measured orientation discrimination thresholds for a range of stimulus sizes and eccentricities (0degrees-15degrees). We used the same procedure previously employed except that stimuli were presented at near-threshold contrasts. We controlled for the effects of perceptual contrast on thresholds through a matching procedure. A standard line of 3degrees in length presented at fixation was set to 2 just noticeable differences above detection threshold. The perceived contrast of all other stimuli was adjusted by the subject to match this one. Orientation discrimination thresholds were then obtained at these matching contrasts for all stimulus sizes and eccentricities. E-2 values of 3.42degrees and 3.50degrees were recovered for two subjects; these values were about a factor of two larger than E-2 values previously found for this task when stimuli were presented at higher physical contrasts. (C) 2004 Elsevier Ltd. All rights reserved.