Figure 8.

(A) Mean choice frequencies of fish 3, which was trained to discriminate between a pyramid (S+) and a cube. Both objects were made from clay and were painted with varnish, which sealed them to water. Objects were placed at different distance from their gates (abscissa). Fish were tested either with visible lights on (light grey columns), or in complete darkness (infrared illumination; dark grey columns). Sigmoid curves were fi tted to the two data sets (solid line = dark conditions, dashed line = lights on) N > 45. (B) Same as in (A) but with clay objects, which were not painted and therefore were soaked with water. This hampered their detection through active electrolocation. Dots within each column give mean choice latencies with standard deviation (right ordinate). N > 33.