The maximum length sequence (m-sequence) has been successfully used to study the linear/nonlinear components of auditory evoked potential (AEP) with rapid stimulation. However, more study is needed to evaluate the effect of the m-sequence order in terms of the noise attenuation performance. This study aimed to address this issue using response-free electroencephalogram (EEG) and EEGs with nonlinear AEPs. We examined the noise attenuation ratios to evaluate the noise variation for the calculations of superimposed averaging and cross-correlation, respectively, which constitutes the main process in the deconvolution method using the dataset of spontaneous EEGs to simulate the cases of different orders (order 5 to 12) of m-sequences. And an experiment using m-sequences of order 7 and 9 was performed in true cases with substantial linear and nonlinear AEPs. The results demonstrate that the noise attenuation ratio is well agreed with the theoretical value derived from the properties of m-sequences on the random noise condition. The comparison of waveforms for AEP components from two m-sequences showed high similarity suggesting the insensitivity of AEP to the m-sequence order. This study provides a more comprehensive solution to the selection of m-sequences which will facilitate the feasible application on the nonlinear AEP with m-sequence method.
A new form of static random-dot stereograms free of monocular clues was designed as stimulus to elicit disparity evoked potentials in 40 normal subjects.A characteristic wide positive wave at about 250ms was consistently recorded in disparity stimulation,which may be regard as evdence of the presence of stereopsis.In constrast,recordings for monocular stimulus all demonstrated a relatively smaller and sharper positive wave with a markedly shortened latency. （Chin J Ocul Fundus Dis,1993,9:214-217）
Attention can concentrate our mental resources on processing certain interesting objects, which is an important mental behavior and cognitive process. Recognizing attentional states have great significance in improving human’s performance and reducing errors. However, it still lacks a direct and standardized way to monitor a person’s attentional states. Based on the fact that visual attention can modulate the steady-state visual evoked potential (SSVEP), we designed a go/no-go experimental paradigm with 10 Hz steady state visual stimulation in background to investigate the separability of SSVEP features modulated by different visual attentional states. The experiment recorded the EEG signals of 15 postgraduate volunteers under high and low visual attentional states. High and low visual attentional states are determined by behavioral responses. We analyzed the differences of SSVEP signals between the high and low attentional levels, and applied classification algorithms to recognize such differences. Results showed that the discriminant canonical pattern matching (DCPM) algorithm performed better compared with the linear discrimination analysis (LDA) algorithm and the canonical correlation analysis (CCA) algorithm, which achieved up to 76% in accuracy. Our results show that the SSVEP features modulated by different visual attentional states are separable, which provides a new way to monitor visual attentional states.
Objective To observe the functional state of the optic nerve and discover the injury of visual pathway function in time under general ane sthesia. The flash visual evoked potential (F-VEP) was used to monitor visual function during orbital surgery. Methods A total of 252 out of 282 patients undergoing orbital surgery under general anesthesia were successfully monitored by F-VEP during the surgery. All patients were monitored by this method under the following conditions:consious state before operation, under general anaesthesia, during and after dissection of orbital tumor and at the end of operation. Results ①There was no significant difference of wave amplitude and latency under general anesthesia and consciousness condition. ②The amplitude and latency of F-VEP were normal in the orbital surgery withou toptic nerve injury. ③Pulling and oppression of optic nerve could cause temporary wave loss, but the wave recovered after removal of the pull and oppression. ④ The wave loss of F-VEP would occur immedicately when optic nerve was severe injured and its blood supply was deficient. Since the application of the visual function monitoring, 24 cases were treated in time during disturbance of visual function and no patient has unexpected visual loss during orbital surgery. Conclusion The intraoperative monitoring of F-VEP during orbital surgery can decrease the proportion of permanent visual loss caused by orbit al surgery, and help the surgical procedures go to function-anatomy stage from experience-anatomy stage. (Chin J Ocul Fundus Dis, 2001,17:260-263)
Steady-state flsash visual evoked potentials (SFVEPs) of 30 Hz were recorded for 46 normal subjects (89 eyes )and 35 patients (51 eyes )with optic neuropathy. The visual acuities of 58.8%affected eyes were less than 0.1. The recorded waveforms were analyzed by discrete Foruier transform (DTF). The amplitudes and phases of fundamental response component and second harmonic were abstracted as characteristic values of the waveform.The total abnormal ratio was 80. 4%. The abnormal types showed the reduced amplitudes,reduced amplitude with phase change, the phases changes, and flat wave. The advantages of SFVEPs in clinical application were discussed. （Chin J Ocul Fundus Dis,1994,10:213-215）
purpose To study the visual electrophysiological changes in patients with chronic glomerulonephritis. Methods The visual evoked potentials(VEP) and electroretinogram(ERG) of 26 subjects with chronic glomerulonephritis in 51 eyes were recorded. Results Ours studies showed the patients with chronic glomerulonephritis had pathologic visual electrophysiologic abnormalities.The N 75 peak latency,b wave peak latency O 1 peak latency and total amplitude of OPs in chronic glomerulonephritis patients without fundus sign showed remarkable difference. Conclusion These changes suggested visual electrophysiological examination may be valuable in early diagnosis of retinal disfunction in patients with chronic glomerulonephritis. (Chin J Ocul Fundus Dis,1998,14:162-164)