Discrimination of coherent and incoherent motion by pigeons: an investigation using a same-different motion...

We trained seven pigeons to discriminate arrays of 8 identical icons that made small random movements in the same direction (coherent movement) from arrays of 8 identical icons that made small random movements in different directions (incoherent movement), with each icon moving within its own cell in an invisible 4×4 grid. During initial training, one specific configuration of icons (a fixed array) was used. The pigeons learned this discrimination and were later trained with successively introduced novel fixed arrays, and finally with novel arrays of random spatial arrangements (random arrays). Four pigeons successfully learned the final version of the task and were tested with random arrays containing different numbers of icons (from 2 to 12). Discrimination accuracy rose as the number of icons increased. These and other findings suggested that the pigeons had discriminated the visual displays by relying on the relative motion of the icons. Nevertheless, motion signals from individual icons (i.e., absolute motion) did interfere with discriminative performance to arrays of coherently moving icons. These results were considered in light of findings from another experiment in which pigeons had to search for a static icon among identical icons that moved coherently or incoherently as in the present study.