Kramer D, Fahle M
Section of Visual Science, University Eye Clinic, Tübingen, Germany.
Vision Res. 1996 May;36(10):1411-9. doi: 10.1016/0042-6989(95)00340-1.
We measured thresholds for detecting the direction of curvature in slightly bent stimuli such as arcs and sinusoidal lines, and the direction of bend in chevrons and trapezoids in an initial experiment. Stimulus length varied over a wide range from 8.3 to 267 min arc. For sufficiently long stimuli, the angle between the stimulus and its chord was constant at 0.2-0.3 deg at detection threshold. The constant threshold implies that performance might be limited by the sensitivity of a single mechanism, in this case one that detects the orientation difference between the stimulus and its imaginary chord. In a second experiment, we investigated the two-dimensional extent of curvature sensitive units by measuring thresholds for detecting curvature of arcs that were flanked by straight lines on both sides. Thresholds remained unaffected at flank distances above 6 min arc but increased at lower distances independently of arc length, compatible with the assumption of a local, orientation sensitive mechanism. In a third experiment, we measured curvature detection with stimuli of different shapes to examine psychophysically the putative role of odd side margin receptive fields. We propose that low curvatures might be analysed by orientation sensitive units with a size around 20 x 8 min arc.
在最初的实验中，我们测量了检测诸如弧线和正弦线等轻微弯曲刺激的曲率方向，以及人字形和梯形的弯曲方向的阈值。刺激长度在8.3到267分弧度的广泛范围内变化。对于足够长的刺激，在检测阈值时，刺激与其弦之间的角度恒定在0.2 - 0.3度。这个恒定的阈值意味着性能可能受到单一机制灵敏度的限制，在这种情况下，是一种检测刺激与其假想弦之间方向差异的机制。在第二个实验中，我们通过测量检测两侧有直线的弧线曲率的阈值，研究了曲率敏感单元的二维范围。在侧翼距离超过6分弧度时，阈值保持不变，但在较低距离时，阈值会独立于弧长而增加，这与局部方向敏感机制的假设相符。在第三个实验中，我们用不同形状的刺激测量曲率检测，以从心理物理学角度检验假定的奇侧边缘感受野的作用。我们提出，低曲率可能由大小约为20×8分弧度的方向敏感单元进行分析。
