Filters for optimal smoothing of acoustic and electric blink reflex EMG responses to determine blink response magnitude

The functional (i.e., kinematic) aspects of the blink reflex depend on the size of the integrated orbicularis oculi EMG response. Peak amplitude of smoothed rectified EMG is often used as an approximation of integrated EMG. A comparison was made between the outputs of 24 different smoothing filters, correlating peak amplitude of acoustic or electric blink reflexes with integrated EMG. The coefficient of determination (R2) was largest (i.e., ≥.95 for acoustic and ≥.90 for electric blink reflexes) when using either (1) a first-order resistor–capacitor filter with a time constant of 50 or 100 ms, (2) a boxcar filter averaging 51 or 101 data points, or (3) an unequal-weight finite impulse response filter with a cutoff frequency of 5 or 10 Hz. These filters are thus recommended when determining peak amplitude. Applying a baseline correction on peak amplitude and integrated EMG produced slightly smaller values of R2 compared with uncorrected measures.