 What Kirby and colleagues show is that when the initial input to a diffusion chain is a reasonably complex set of arbitrary signal/signifier pairs, e.g. one in which 27 complex signals of 6 letters are randomly assigned to 27 objects varying on dimensions of color, kind of motion, and shape, what is transmitted becomes more and more compositional over iterated transmission. Here, ‘compositional’ is being used to refer to the high degree to which sub-strings of the signals come to be systematically paired with specific phenomenal sub-features of what is signified. The transmission conditions in these experiments were free of noise, and for each iteration of the learning task only half of the possible 27 signifier/signified pairs were presented to participants. Under this kind of transmission bottleneck a high degree of sign/signified structure emerged.