眼跳的双相调节理论的行为证据

Behavioral Evidences for the Biphasic Modulation Theory of Saccade

为了研究眼跳的双相调节理论是否适用于人类的视觉系统,本研究测量了人类被试对分别呈现在三种眼跳时间段(基线、眼跳抑制和眼跳增强)内的光栅的朝向辨别准确率。研究发现:相对于光栅呈现在基线时间段内,被试对呈现在抑制(或增强)时间段内的光栅的朝向辨别准确率显著地更低(或更高)(实验1);另外,只有使用低或中等空间频率光栅作为测试刺激时,才有这种双相调节作用(实验2)。这些结果表明:人类的视觉系统在眼跳过程中存在双相调节机制,并且这种双相调节机制具有刺激选择性。

Purposes: People shift their gaze between objects of interest using rapid pre-planned eye movements known as saccade. Humans make 2–8 saccadic eye movements per second. Saccades are very important for pointing the eye at targets in the scene, but these rapid scene shifts are not perceived. The visual stimulus generated by the saccade is omitted from our subjective awareness known as saccadic omission. Saccadic omission is important for visual system: without it, the motion on the retina would prevent us from seeing anything at all. Based on evidences coming from numerous physiological studies in behaving primates, investigators propose the biphasic modulation theory to explain the neural mechanism of saccadic omission. However, no study has reported whether the biphasic modulation theory of saccadic omission exists in the human visual system. Thus, the study examined whether the biphasic modulation theory was applicable to the human visual system(Experiment 1). Moreover, the study explored stimulus selectivity of the theory(Experiment 2). Procedures: This study included two experiments. The stimuli in both experiments were circular patches of sinusoidal gratings with a randomized phase(diameter: 2.5°;orientation:-3° or +3°, ‘-’ and ‘+’ indicated that a grating was left-or right-tilted). Spatial frequencies of gratings were different in Experiment 1(1.5 cycles/°) and in Experiment 2(0.1 cycles/°, 3 cycles/° and 6 cycles/°). In Experiment 1, the study measured the orientation discrimination accuracies of gratings for human subjects in three time periods of saccade: baseline period(over 700 ms before the onset of saccade), suppression period(100 ms before the onset of saccade – 25 ms after the saccade) and enhancement period(25 ms after the saccade – 150 ms after the saccade)). In Experiment 2, using three different spatial frequencies of gratings, the study measured the orientation discrimination accuracies of each grating for human subjects in three time periods of saccade, respectively. Results: In Experiment 1, the orientation discrimination accuracy of gratings in the suppression period was significantly lower than that in the baseline period. Meanwhile, the orientation discrimination accuracy of gratings in the enhancement period was significantly higher than that in the baseline period. In Experiment 2, when using low spatial frequency(0.1 cycles/°) grating as the test stimulus, the orientation discrimination accuracy of gratings in the suppression(or enhancement) period was significantly lower(or higher) than that in the baseline period;When using the middle spatial frequency(3 cycles/°) grating as the test stimulus, the result was the same as that using the low spatial frequency grating;However, when using the high spatial frequency(6 cycles/°) grating as the test stimulus, there was no significant difference between any two of the three conditions. Conclusions: These results indicate that the human visual system also has the biphasic modulation mechanism across saccadic eye movement. Moreover, the biphasic modulation mechanism has stimulus selectivity: Visual system selectively suppresses(in suppression period) or enhances(in enhancement period) the response to low spatial frequency gratings, but not to high spatial frequency gratings.