Fig. 3. (A) Comparison of the e-vector angle-response amplitudes of a colour receptor (row 4P R6), a hemispheric receptor (DH R1) and a `high PS cell' (row 2D R2). All photoreceptors shown here possess similar response amplitudes to unpolarized white light, and nearly parallel response-intensity (R-log I) functions. They are all most sensitive to an e-vector orientation of linearly polarized light (_max) of approximately +45°. (B) Intracellular recordings of the e-vector angle-response curves of two neighbouring photoreceptors (R3 and R4) within row 5. The two cells possess 90° phase-shifted _max (_max(R4)=+45° and _max(R3)=-45°). Slight re-positioning of the microelectrode after completing the recording and staining of the first cell (R3) resulted in a 90° phase-shift of _max. Subsequent Lucifer Yellow injection showed that the microelectrode tip had moved from R3 into the neighbouring retinula cell R4. R4 belongs to Group I and R3 to Group II cells amongst R1-R7, and they have their microvilli arranged at right angles. (C) To determine the polarization sensitivity of a photoreceptor, two R-log I curves were recorded at _max and _min, respectively. In this example, the intensity shift (i) of 0.72 log units between the linear parts of the two fitted standard Rushton intensity-response functions corresponds to a polarization sensitivity of 5.2.