Kingdom F A
McGill Vision Research Unit, Department of Ophthalmology, Montreal, Quebec, Canada.
Spat Vis. 1996;10(3):285-97. doi: 10.1163/156856896x00178.
Previous studies have reported that the magnitude of induced brightness in Craik-Cornsweet-O'Brien (CCOB) figures is greater for decrement compared with increment figures. Moulden and Kingdom (Spatial Vision, 1990, 5, 101-121) suggested this was due to larger Off-centre compared with On-centre receptive fields. Such an explanation would also predict an increment-decrement difference in the contrast threshold for discriminating a CCOB stimulus from its step-edge equivalent. To test this prediction contrast thresholds were measured for discriminating 'cusp' from 'square-bar' stimuli, for both increment and decrement forms. Contrary to prediction however, no difference was found between increment and decrement discrimination thresholds. These findings suggest that On- versus Off-centre receptive field size differences are unlikely to underlie the polarity-based asymmetry in induced brightness in CCOB figures. More generally they demonstrate that the magnitude of induced brightness in CCOB figures does not have a direct parallel in the ability of observers to discriminate those stimuli from their step-edge equivalents. The significance of these findings for models of brightness coding is discussed.
先前的研究报告称，与增量图形相比，Craik-Cornsweet-O'Brien（CCOB）图形中诱导亮度的幅度在减量时更大。莫尔登和金登（《空间视觉》，1990年，第5卷，第101 - 121页）认为，这是由于离中心感受野比中心感受野更大。这样的解释也会预测在区分CCOB刺激与其等效阶跃边缘时，对比度阈值存在增量 - 减量差异。为了检验这一预测，测量了区分“尖点”和“方条”刺激（增量和减量形式）的对比度阈值。然而，与预测相反，增量和减量辨别阈值之间未发现差异。这些发现表明，中心与离中心感受野大小差异不太可能是CCOB图形中基于极性的诱导亮度不对称的基础。更普遍地说，它们表明CCOB图形中诱导亮度的幅度与观察者区分这些刺激与其等效阶跃边缘的能力没有直接的对应关系。讨论了这些发现对亮度编码模型的意义。
