Kukkonen H, Näsänen R, Rovamo J
Department of Vision Sciences, University of Aston, Birmingham, United Kingdom.
Invest Ophthalmol Vis Sci. 1994 Jun;35(7):3111-8.
In the studies of spatial integration an increase in the spatial extent of the stimulus usually results in a decrease in the spatial frequency bandwidth of the stimulus. The authors investigated separately the effects of these two factors on contrast detectability.
Efficiencies were measured for a circular grating at 4 c/deg and for bandpass-filtered point stimuli having a constant center frequency at 4 c/deg and bandwidths of 0.25, 0.5, 1, and 2 octaves. The phase range of these two-dimensional stimuli was increased from zero to 90, 180, 270, and 360 degrees by replacing the original zero phase at each spatial frequency component by a random number with zero mean. This procedure left the spatial frequency bandwidth unaffected.
The increase in phase range and decrease in spatial frequency bandwidth caused a progressively larger proportion of the contrast energy of the point stimuli to spread into their surroundings. As a result, detection efficiency decreased with increasing bandwidth and phase range for all point stimuli. However, a change in the stimulus bandwidth affected efficiency only when it altered stimulus area. The area of the circular grating and its detection efficiency remained almost constant irrespective of the phase range. When efficiency was plotted in semi-logarithmic coordinates as a function of stimulus area expressed in terms of the spatial spread of contrast energy, the line of least squares explained 85% of the total variance.
The primary determinant of detection efficiency for stimuli with constant center spatial frequency is not stimulus bandwidth but stimulus area expressed in terms of the spatial spread of contrast energy.
在空间整合研究中，刺激的空间范围增加通常会导致刺激的空间频率带宽减小。作者分别研究了这两个因素对对比度可检测性的影响。
测量了4周/度的圆形光栅以及中心频率恒定为4周/度、带宽分别为0.25、0.5、1和2倍频程的带通滤波点刺激的效率。通过用均值为零的随机数替换每个空间频率分量处的原始零相位，将这些二维刺激的相位范围从零增加到90、180、270和360度。此过程不影响空间频率带宽。
相位范围的增加和空间频率带宽的减小导致点刺激的对比度能量中越来越大的比例扩散到其周围环境中。结果，所有点刺激的检测效率均随带宽和相位范围的增加而降低。然而，只有当刺激带宽改变刺激面积时，其变化才会影响效率。圆形光栅的面积及其检测效率几乎保持不变，与相位范围无关。当以半对数坐标绘制效率与以对比度能量的空间扩散表示的刺激面积的函数关系时，最小二乘线解释了总方差的85%。
对于中心空间频率恒定的刺激，检测效率的主要决定因素不是刺激带宽，而是以对比度能量的空间扩散表示的刺激面积。
