Wattam-Bell J
Visual Development Unit, Department of Psychology, University College London, London WC1E 6BT, UK.
Perception. 2001;30(2):159-66. doi: 10.1068/p3098.
Recent forced-choice preferential looking (FPL) experiments with random-dot patterns [Wattam-Bell, 1998 Investigative Ophthalmology & Visual Science 39(4) S885] found evidence for a perceptual asymmetry of vertical-motion processing in young infants: a preference for patterns that move downwards. This asymmetry was in the opposite direction to the asymmetry of vertical optokinetic nystagmus, which was biased towards upwards motion. However, the FPL bias was weak, and the object of present experiments was to explore the possibility that it could be enhanced by reducing stimulus contrast. In experiment 1, contrast thresholds for gratings moving upwards and downwards were compared, and no directional asymmetry at threshold was found. In experiment 2, the effect of contrast on infants' preference between simultaneously displayed upwards-drifting and downwards-drifting gratings was examined. Infants showed no preference at 5% contrast, a marked preference for downwards motion at intermediate contrasts (10% and 20%), and a similar but smaller preference at 40% contrast. These results suggest that the vertical-motion asymmetry is a result of differences in the gains of directionally selective mechanisms for upwards and downwards motion.
最近采用随机点模式进行的强迫选择优先注视（FPL）实验[瓦塔姆 - 贝尔，《Investigative Ophthalmology & Visual Science》1998年第39卷第4期，S885]发现，年幼婴儿在垂直运动处理方面存在感知不对称的证据：他们更偏好向下移动的模式。这种不对称与垂直视动性眼球震颤的不对称方向相反，后者偏向于向上运动。然而，FPL偏差很微弱，本实验的目的是探究通过降低刺激对比度是否可以增强这种偏差。在实验1中，比较了向上和向下移动光栅的对比度阈值，未发现阈值处的方向不对称。在实验2中，研究了对比度对婴儿在同时显示的向上漂移和向下漂移光栅之间偏好的影响。婴儿在5%对比度时没有偏好，在中等对比度（10%和20%）时明显偏好向下运动，在40%对比度时偏好类似但较小。这些结果表明，垂直运动不对称是向上和向下运动的方向选择性机制增益差异的结果。
