Fig. 7. Intracellular recordings in the retina of a posterio-median eye of the spider Drassodes cupreus. Left and right response–intensity curves are recorded with light polarized parallel (Para) and perpendicular (Perp) to the long axis of the eye, respectively. The log intensity shift of 0.96 between the two curves translates to a polarization sensitivity of 9.1 (a unitless quantity). (This figure was published as supplementary information in Dacke et al., 1999; http://www.nature.com/nature/journal/v401/n6752/suppinfo/401470a0.html).