The Automatic Processing Of Visual Information In Different Visual Acuity Levels: An ERP Preliminary Study

Purpose: To explore whether visual mismatch negativity(v MMN) or P3 a could be evoked by optotypes in different visual acuity levels, and hope to provide theoretical basis to explore the possibility of ERP in assessment of subjective(cognitive) visual acuity.Method: A cross-modal three stimulus Oddball paradigm was used in the present study. Subjects(n=15) with appropriate visual acuity(0.2-0.8) were presented with optotypes stimuli in the center of the visual field while they were required to response to the auditory stimuli in serious-minded. The experiment of each participant consisted of three different visual acuity conditions as follows, supra-threshold(legibly visible stimuli) condition, threshold(hazily visible stimuli) condition and sub-threshold(invisible stimuli) condition.Results:(1) In temporo-occipital electrodes, the parameters(amplitudes and latencies) of P1, N1 and P2 components between standards and deviants of three visual acuity conditions did not yield any significant results. And among three visual acuity conditions, the parameters of P1, N1 and P2 components elicited by standards did not yield any significant differences either.(2) In the 270-430 ms post-stimulus range, v MMN responses to deviant optotypes were found in supra-threshold and threshold conditions over bilateral temporo-occipital electrodes, and there was no statistic difference of v MMN amplitudes and latencies in these two conditions.(3) In the 480-570 ms post-stimulus range, P3 a component was found in supra-threshold and threshold conditions at bilateral centro-parietal and temporal scalp sites. Besides, the P3 a amplitude of supra-threshold condition was much larger than that of threshold conditions.(4) Neither v MMN nor P3 a component was elicited by deviant stimuli under sub-threshold condition in the corresponding time windows.Conclusions: These data demonstrated that(1) P1 component evoked by our paradigm was not sensitive to the visual acuity,(2) the emergence of v MMN could only reflect the automatic detection of orientation-changes in the supra-threshold and threshold conditions,(3) whereas the P3 a amplitude could reflect the different processing between supra-threshold and threshold stimuli.