Fig. 1.

Intracellular recording from a cell classified as a UV receptor. a The sequence starts with a spectral scan of 23 approximately isoquantal light pulses from 300 to 740 nm spaced 20 nm apart. This is followed with a scan going back from 740 to 300 nm. The responses in the green wavelength region are slightly hyperpolarising, possibly due to an ERG artefact or electrical crosstalk from neighbouring green receptors. The intensity calibration scan consists of responses to light pulses at 380 nm, covering an intensity range of 4 log units, increasing in 0.25 log unit steps. The polarisation sensitivity scan was also performed at 380 nm. It starts with five adaptation prepulses, which are followed by 36 pulses with the polariser being rotated in 10° steps. The duration of each of the three protocols was ~40 s. b Estimation of effective intensity of the light pulses. The background waterfall plot shows the root mean square difference (RMSD) profiles (see Fig. 2e, f). The RMSD minima are estimates of effective intensities obtained by the RWC method (black circles). Open squares show the estimates obtained by reverse transformation of a Hill sigmoid