Galbraith G C, Brown W S
Lanterman Developmental Center, University of California, Los Angeles, School of Medicine, Pomona 91769.
Electroencephalogr Clin Neurophysiol. 1990 Jul-Aug;77(4):295-308. doi: 10.1016/0168-5597(90)90068-o.
Cross-correlation (CC) and latency compensation (LC) analysis were applied to the human click-evoked brain-stem auditory evoked response (BAER) and the brain-stem frequency-following response (FFR). FFRs were elicited by pure tone stimuli (230 Hz and 460 Hz) or by complex tones derived from the sum of 3rd (920 Hz), 4th (1150 Hz), and 5th (1380 Hz) harmonics of the missing 230 Hz fundamental. The lower and upper harmonics always began in sine phase, while the middle harmonic varied in starting phase, resulting in harmonically complex stimuli with differing amplitude and phase patterns. Cross-correlations were computed between individual trials and a wave form template (smoothed wave V for BAER, pure tone stimulus sinusoids for FFR). Trials were included in the analysis only if values of r2 exceeded 0.5 (negative values of r were thus included, which controlled for the chance occurrence of positive correlations). Although brain-stem recordings are noisy, requiring as many as 1000 stimuli/average, correlation analysis consistently identified more positive than negative trials (approximately 2:1 ratio). Trials were also deleted if the lag associated with the selected r2 was at the maximum shift position ('extreme lag'). Averaging trials that satisfied the correlation and lag criteria led to sizeable enhancement of BAER (mean = 114%) and FFR (mean = 68% for 230 Hz stimulus) amplitudes. LC analysis resulted in additional, albeit smaller, increases in amplitude (approximately 10%). FFRs to harmonically complex stimuli were characterized by a clear periodicity at the missing fundamental frequency (230 Hz). However, amplitudes varied according to the modulation depth of the stimulus and, in certain cases, actually exceeded that of the FFR response to a 230 Hz pure tone. The results demonstrate the effectiveness of cross-correlation and, to a lesser degree, latency compensation analysis, applied to two classes of brain-stem potentials. It is anticipated that such techniques will prove useful in the study of auditory signal processing at the level of the brain-stem.
互相关（CC）和潜伏期补偿（LC）分析应用于人类点击诱发的脑干听觉诱发电位（BAER）和脑干频率跟随反应（FFR）。FFR由纯音刺激（230Hz和460Hz）或由缺失的230Hz基频的第三（920Hz）、第四（1150Hz）和第五（1380Hz）谐波之和产生的复合音诱发。较低和较高的谐波总是以正弦相位开始，而中间谐波的起始相位变化，导致具有不同幅度和相位模式的谐波复合刺激。计算单个试验与波形模板（BAER的平滑波V，FFR的纯音刺激正弦波）之间的互相关。仅当r2值超过0.5时，试验才纳入分析（因此包括r的负值，这控制了正相关的偶然出现）。尽管脑干记录有噪声，平均需要多达1000次刺激，但相关分析始终识别出正试验比负试验更多（约2:1的比例）。如果与选定的r2相关的滞后处于最大移位位置（“极端滞后”），试验也将被删除。对满足相关和滞后标准的试验进行平均导致BAER（平均值 = 114%）和FFR（230Hz刺激的平均值 = 68%）幅度显著增强。LC分析导致幅度额外增加，尽管较小（约10%）。对谐波复合刺激的FFR以在缺失的基频（230Hz）处有清晰的周期性为特征。然而，幅度根据刺激的调制深度而变化，并且在某些情况下，实际上超过了对230Hz纯音的FFR反应幅度。结果证明了互相关以及在较小程度上潜伏期补偿分析应用于两类脑干电位的有效性。预计这些技术将在脑干水平的听觉信号处理研究中证明是有用的。
