视觉诱发电位(VEP)对不同频率条纹的反差敏感性

VISUAL—EVOKED POTENTIALS ON CONTRAST SENSITIVITY

本实验利用条纹发生器产生正弦调制的条纹作视觉刺激,用NICOLETCA—1000平均仪,从枕骨隆起上方沿中线5cm处记录瞬态视觉诱发电位。实验用四种不同反差,十种空间频率,四名被试。结果表明瞬态视觉诱发电位(C_1—C_2)的峰值随反差的增加而变化,其在空间频率上有一定的分布,最敏感处落在3—5C/deg。在阈上刺激时,被试个体有差异,但分布趋势相似,最敏感处也为3—5C/deg,这和心理物理实验获得的调制传递函数(MTF)结果很吻合。从实验结果可以看到(C_1—C_2)值对反差变化是敏感的,它反映了人视觉系统对不同空间频率上的反差敏感性,可以把它与MTF相类比。

Gratings, the luminance profiles of which varied sinusoidally, wereflashed and displayed on a monitor. An electrode recording thetransient visual-evoked potential was placed 5 cm above inion. Fourhealthy subjects wete tested on four levels of contrast of gratings atten spatial frequencies and VEP was recorded by NICOLET CA-1000system. The result shows that amplitude of (C_1-C_2)differs with differentspatial frequencies, and becomes larger as contrast increases. The maximum amplitude of VEP is at approximately 3-5 c/deg,which tallies with the results of Modulation Transfer Function (MTF)obtained in psychophysical experiment. It is found that the amplitude of(C_1-C_2)is sensitive to contrast change. From VEP, one can see that in human visual system, sensitivitydiffers with different spatial frequencies, which is similar to the resultsof MTF.