Fortune Brad, Hood Donald C
Discoveries in Sight, Devers Eye Institute, Portland, Oregon 97232, USA.
Invest Ophthalmol Vis Sci. 2003 Mar;44(3):1364-75. doi: 10.1167/iovs.02-0441.
To compare conventional pattern-reversal visual evoked potentials (cVEPs) with multifocal VEPs (mfVEPs).
mfVEPs and cVEPs were recorded during the same session in 12 normal subjects with an active electrode at Oz referenced to the inion (Oz-In) or to a midfrontal position, Fz (Oz-Fz). The mfVEP stimulus, a 60-sector dartboard, had a mean luminance of 100 cd/m(2) and a diameter of 42.2 degrees. The cVEP checkerboard stimulus subtended 21 degrees, had a mean luminance of 75 cd/m(2) and a contrast of 90%. Transient responses (2.5 Hz) were recorded for check sizes ranging from 12 to 50 minutes of arc (minarc). White cardboard masks were used to isolate upper and lower hemifields, within various field windows, for comparison with corresponding parts of the mfVEP. In a second experiment, VEPs were obtained using slowed m-sequences (8 and 16 video frames per m-step), as well as square-wave periodic reversals (2.4 Hz), for both the scaled dartboard display and an unscaled checkerboard display (check size of 50 minarc).
The mfVEPs to fast m-sequence stimulation showed a strong polarity reversal between waveforms from the upper versus the lower hemifield. The cVEPs had larger amplitudes (approximately 3x) and longer implicit times (approximately 15-20 ms) and did not show the polarity reversal. Amplitude asymmetry between upper and lower hemifields was larger for cVEPs than for mfVEPs. As the stimulation rate was slowed, response amplitudes and implicit times of the major features increased, the upper versus lower polarity reversal was generally lost, and asymmetry of hemifield amplitudes grew. The same pattern of results was observed for scaled and unscaled spatial displays and for Oz-Fz and Oz-In signal derivations.
Full-field cVEPs cannot be simply related to the sum of mfVEPs when each are recorded under their typical conditions. The stimulation rate has the largest influence on the differences between the two response types. The findings suggest that contributions from extrastriate sources are greater with the cVEP paradigm or the slowed mfVEP sequence than with the standard mfVEP paradigm.
比较传统模式翻转视觉诱发电位（cVEP）与多焦视觉诱发电位（mfVEP）。
在同一时段对12名正常受试者记录mfVEP和cVEP，使用置于枕区（Oz）的活动电极，参考点为枕外隆凸（Oz-In）或额中部位置Fz（Oz-Fz）。mfVEP刺激为60扇区的飞镖靶，平均亮度为100 cd/m²，直径为42.2度。cVEP棋盘格刺激的视角为21度，平均亮度为75 cd/m²，对比度为90%。记录了视角范围从12到50分视角（minarc）的瞬态反应（2.5 Hz）。使用白色硬纸板面罩在不同视野窗内分离上半视野和下半视野，以便与mfVEP的相应部分进行比较。在第二个实验中，对于缩放后的飞镖靶显示和未缩放的棋盘格显示（视角为50 minarc），使用慢m序列（每m步8和16个视频帧）以及方波周期性翻转（2.4 Hz）来获得视觉诱发电位。
快速m序列刺激下的mfVEP显示，上半视野与下半视野波形之间存在强烈的极性反转。cVEP的波幅更大（约3倍），潜伏期更长（约15 - 20 ms），且未显示出极性反转。cVEP上半视野与下半视野之间的波幅不对称性比mfVEP更大。随着刺激速率减慢，主要特征的反应波幅和潜伏期增加，上半视野与下半视野的极性反转通常消失，半视野波幅的不对称性增大。对于缩放和未缩放的空间显示以及Oz-Fz和Oz-In信号推导，观察到相同的结果模式。
当在各自典型条件下记录时，全视野cVEP不能简单地与mfVEP的总和相关联。刺激速率对两种反应类型之间的差异影响最大。研究结果表明，与标准mfVEP范式相比，cVEP范式或减慢的mfVEP序列中来自纹外区域的贡献更大。
