Optimum filtering for EROS measurements

The event-related optical signal (EROS) is a relatively new technology that provides noninvasive data about the time course of neural activity in circumscribed cortical areas. However, much still remains to be learned about the physiology and physics underlying the observed signals. We examined the instrumental and physiological noise observed in the intensity modulation and phase-delay measurements produced by a frequency domain oxymeter in response to steady-state auditory stimuli. We present here data on the effects of different filters on the between-subjects response consistency for amplitude and phase measurements. The results of these analyses may help explain some apparently discrepant results previously reported from different laboratories (Steinbrink et at., 2000), and illustrate differences between data from different types of measurements.