Data from: Contrast sensitivity and behavioural evidence for lateral inhibition in octopus

Behavioural contrast sensitivity in Octopus tetricus was measured in the
range 0.05- 12 cycles per degree (cpd) using a fixation reflex. We show
that the contrast sensitivity reaches its maximum (between 1% and 4%) at
0.3 cpd, and decreases to approximately half of the maximum value at the
lowest spatial frequency. Reduction of sensitivity at low spatial
frequency is a signature of lateral inhibition in visual systems. In
vertebrates and insects, lateral inhibition helps to overcome the
bottleneck of encoding information into spikes. In octopus, photoreceptors
generate spikes themselves and are directly connected to the brain through
their axons. Therefore, the neural processing occurring in octopus brain
cannot help to overcome the bottleneck of encoding information into
spikes. We conclude that, in octopus, the lateral inhibition occurs either
in the brain after information has been encoded into spikes, or that
photoreceptors inhibit each other. This is the first time behavioural
contrast sensitivity has been measured in a cephalopod.