. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 400 500 600 Wavelength (nm) 700 Figure 3. Interpolation technique. A. Response vs. log intensity functions at 3 wavelengths: 550 nm (circles), 500 nm (triangles), and 450 nm (squares). Each set of points is fit with a linear regression func- tion, and the intensity necessary for a 5% response is determined from this. B. Average sensitivity measured by this technique. The curve is the average of three runs: vertical lines are standard errors of the mean. Spectral scan experiments This technique was inspired by electrophysiolo
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 400 500 600 Wavelength (nm) 700 Figure 3. Interpolation technique. A. Response vs. log intensity functions at 3 wavelengths: 550 nm (circles), 500 nm (triangles), and 450 nm (squares). Each set of points is fit with a linear regression func- tion, and the intensity necessary for a 5% response is determined from this. B. Average sensitivity measured by this technique. The curve is the average of three runs: vertical lines are standard errors of the mean. Spectral scan experiments This technique was inspired by electrophysiological measurements made by Franceschini (1984) and by Menzel et al. (1986). The underlying principle is to "light clamp" the response to any desired level by adjusting stimulation intensity. In our experiments, each measure- ment was taken over a 5-s interval, approximately one time constant for a typical intracellular optical response. The computer then decided whether to accept the re- sponse level or to alter the stimulation intensity and re- peat the measurement. As successive measurements oc- cur at wavelengths separated by only 10 nm, relatively little adjustm>. <'quired over most of the sensitivity band. Furttu- ny artifacts caused by animal movements are vei miikely to produce signals near the reference level, and so arc automatically rejected. The reference level of the response was generally near 10%, somewhat higher than in the previous experiments. This level was chosen to allow the measurement of both nega- tive and positive changes, and to provide some head- room for drift which might occur during a single scan. The data of an ascending spectral scan, in which the reflectance level was clamped above that mea- sured in the unstimulated condition, are plotted in Fig- ure 5A. Each time wavelength increased, a spike ap- peared in the record, which was subsequently eliminated as the scanning program brought the response to within of the refe
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