An Objective Method for Detecting Stereopsis Based on Steady-state Visual Motion Evoked Potential

Abstract

Stereopsis is the highest function of binocular vision, which can provide an accurate judgment of distance and depth. It is quantified as stereoacuity, measured in seconds of arc (arcsec). Generally, traditional assessment methods of stereopsis, such as Random-dot Stereogram and Titmus stereopsis test, which mainly depend on the subjects’ subjective perception, are very easily affected by some uncertain factors, such as low cognitive ability and impure motives. Hence, we proposed an objective method of detecting stereopsis based on steady-state motion visual evoked potential (SSMVEP).In this study, we designed a stereo SSMVEP paradigm with white noise, which used 3D shutter glasses to realize the stereo imaging based on two eyes parallax and eliminated monocular cues. The paradigm utilized periodic contraction and expansion motion to elicit SSMVEP and can change stereoscopic depth by adjusting the horizontal disparity of its two component images. Besides, the filter bank canonical correlation analysis (FBCCA) was used to analyze the electroencephalography (EEG) signals of the occipital lobe and extract relevant features to establish an index, which is corresponding to the objective stereopsis of human eyes.  Eight healthy subjects(ages 23-25 years), with normal or corrected-to-normal vision, participated in the experiments. Each experiment was divided into eight trials according to the different stereoscopic depth of the paradigm, corresponding to the zero disparity stereoacuity from 800 to 0 seconds of arc.  The experimental results show that as the stereoacuity decreases, the index value at the target stimulus frequency of SSMVEP shows a significant downward trend. Moreover, it decreases more significantly when the stereoacuity is less than 40 arcsec. The result of experiments is in accordance with the result obtained from the Random-dot Stereogram test. Our research has initially proved that the stereo paradigm based on SSMVEP can be used as a new objective and quantitative method for detecting stereopsis.