Inefficient licking during forced spout alternation in rats: violation of the law of effect?

The efficiency of the neural control of licking was assessed in rats (n = 6) allowed 30-min daily access to water in a box equipped with two retractable drinking spouts. After completion of a photoelectrically monitored lick, the contacted spout was withdrawn by an electromechanical device which simultaneously made the other spout available at an adjacent wall opening. Although economy of behavior required the animals to lick at each spout only once, computer monitored licking showed that the rats emitted 2.9 +/- 0.2 and 2.5 +/- 0.1 licks per spout presentation (LPSP) on the first and fifth days of training, respectively. The transition time between spouts and the interlick interval were not significantly changed. Separation of the spouts by a vertical partition extending 24 mm into the box prolonged the transition time and increased LPSP to 3.9 and 3.3 on Days 1 and 4 of training, respectively. These values were not changed when the length of the partition was increased to 40 mm. The failure of rats to maximize reward by emitting single licks probably reflects limited control of the generator of licking and/or the tendency to avoid its frequent switching on and off.