Song Jaeseon, Breitmeyer Bruno G, Brown James M
Department of Psychology, University of Georgia, Athens, GA 30602, USA.
Department of Psychology, University of Houston, Houston, TX 77204, USA.
Vision (Basel). 2024 Apr 30;8(2):28. doi: 10.3390/vision8020028.
The pulsed- and steady-pedestal paradigms were designed to track increment thresholds (Δ) as a function of pedestal contrast (C) for the parvocellular (P) and magnocellular (M) systems, respectively. These paradigms produce contrasting results: linear relationships between Δ and are observed in the pulsed-pedestal paradigm, indicative of the P system's processing, while the steady-pedestal paradigm reveals nonlinear functions, characteristic of the M system's response. However, we recently found the P model fits better than the M model for both paradigms, using Gabor stimuli biased towards the M or P systems based on their sensitivity to color and spatial frequency. Here, we used two-square pedestals under green vs. red light in the lower-left vs. upper-right visual fields to bias processing towards the M vs. P system, respectively. Based on our previous findings, we predicted the following: (1) steeper Δ vs. functions with the pulsed than the steady pedestal due to different task demands; (2) lower Δs in the upper-right vs. lower-left quadrant due to its bias towards P-system processing there; (3) no effect of color, since both paradigms track the P-system; and, most importantly (4) contrast gain should not be higher for the steady than for the pulsed pedestal. In general, our predictions were confirmed, replicating our previous findings and providing further evidence questioning the general validity of using the pulsed- and steady-pedestal paradigms to differentiate the P and M systems.
脉冲和稳态基座范式分别设计用于跟踪小细胞（P）和大细胞（M）系统的增量阈值（Δ）作为基座对比度（C）的函数。这些范式产生了截然不同的结果：在脉冲基座范式中观察到Δ与 之间的线性关系，这表明是P系统的处理方式，而稳态基座范式则揭示了非线性函数，这是M系统响应的特征。然而，我们最近发现，对于这两种范式，P模型比M模型拟合得更好，我们使用了基于对颜色和空间频率的敏感度而偏向M或P系统的Gabor刺激。在这里，我们在左下和右上视野的绿光与红光下使用两个方形基座，分别使处理偏向M系统和P系统。基于我们之前的发现，我们做出了以下预测：（1）由于任务要求不同，脉冲基座的Δ与 函数比稳态基座更陡峭；（2）右上象限的Δ低于左下象限，因为右上象限偏向P系统处理；（3）颜色没有影响，因为两种范式都跟踪P系统；最重要的是（4）稳态基座的对比度增益不应高于脉冲基座。总体而言，我们的预测得到了证实，重复了我们之前的发现，并提供了进一步的证据，质疑使用脉冲和稳态基座范式区分P和M系统的普遍有效性。
