The pigeons had extensive previous experience working on concurrent schedules (Cowie, Elliffe & Davison, 2013; Cowie et al., 2014; Davison & Baum, 2010), so no pre-training was required. Sessions were conducted in the pigeons’ home cages in a time-shifted environment in which the room lights were lit from 12 midnight until 4 p.m. Sessions for all six pigeons began at 1.00 a.m. Sessions were conducted daily, starting with the left- and right-key lights lit red, signaling the availability of a variable-interval (VI) schedule on each key. Sessions lasted 60 min or until 60 food deliveries had occurred, whichever occurred first.