We studied response biases to visual stimulation using a new experimental t
echnique. The subjects (hens, Gallus gallus domesticus) were confronted wit
h several rewarding and non-rewarding patterns on a computer screen. In con
trast with standard discrimination tasks the rewarding patterns were not id
entical and varied in a dimension differentiating them from the non-rewardi
ng patterns. The rewarding patterns changed in response to hens' biases in
selection of patterns. The aim of the study was to examine the possibility
of receivers being a driving farce in signal evolution. In one of the exper
iments a clear-cut result was obtained. During the course of the experiment
the rewarding patterns became gradually more different from the non-reward
ing one, a result expected from theoretical studies of the effect of respon
se bias in signal evolution. A second similar experiment was less conclusiv
e, with ceiling and floor effects influencing the results.