Ontogenetic changes in the visual acuity ofSepia officinalismeasured using the optomotor response

Abstract

For many organisms vision is of fundamental importance to many aspects of their lives. Here we present the first study to examine the effects of ontogeny and light intensity on the vision of a cephalopod. We measured the visual acuity of four size classes of Sepia officinalis L., 1758 (common cuttlefish) under four light intensities. We used an optomotor testing system in which we recorded the unconditioned whole-body movements exhibited by individuals when placed inside a rotating cylinder lined with vertical black and white stripes. By varying the width of these stripes to determine the minimum width associated with a positive response, we were able to estimate the visual acuity angle or minimum separable angle (MSA). We found a significant effect of both body size and light intensity; larger animals had greater visual acuity, while individuals of all size classes discriminated more detail at higher light intensities. The minimum recorded MSA for S. officinalis was 34' of arc (0.57°) for the largest animals (80 mm) at the highest light intensity used (15 µW·cm–2). Decreasing light intensity from 15 to 4.5 µW·cm–2affected animals of all sizes to approximately the same degree, reducing their visual acuity by approximately 55%.