A test of the visual acuity of the locust eye

Targets consisting of solid rectangles (bright on a dark ground), of a range of widths, or pairs of thin lines of separation equal to the width of each rectangle, were used to evoke on, or movement responses in, the DCMD and other visual interneurones in the locust (Schistocerca gregaria). It was found that, judged from the discharges in these interneurones, both types could distinguish solid from paired-line figures of identical subtense, down to an angle of 0.4 degrees. Such an angle is well within the values of the eye parameters DeltaP and Deltaphi. Similar results were obtained with figures of the reversed contrast, showing that acuity was maintained even in the presence of a bright surrounding.