It is now well established that signal receivers have a key role in the evolution of animal communication: the suite of sensory and cognitive processes by which animals perceive and learn about their environment can have a significant impact on signal design. A crucial property of these information-processing mechanisms is the emergence of 'receiver bias' in the behavioural responses to signals. Whereas most research has focussed on receiver biases in the sensory system, more recent studies show that biases can also arise from learning about signals. Here, we highlight how learning-based biases can arise, and how these differ from biases emerging from sensory systems in their impact on signal evolution.