Machado, A. (1997).
Increasing the variability of response sequences in pigeons by adjusting the frequency of switching between two keys.
Journal of the Experimental Analysis of Behavior,
68, 1-25.
Three experiments compared the amounts of behavioral variability
generated with two reinforcement rules. In Experiments 1 and 2
pigeons received food whenever they generated a sequence of eight
pecks, distributed over two keys, provided that the sequence
contained a certain number of changeovers between the keys.
Although no variability was required - the birds could obtain all
reinforcers by repeating the same sequence - the pigeons emitted
a large number of different sequences. In Experiment 3 pigeons
received food whenever they generated a sequence that had not
occurred during the last 25 trials. After prolonged training, the
birds showed more sequence variability than in the first two
experiments. The analysis of the internal structure of the
response sequences revealed that, in general, (a) the location of
the first peck was highly stereotyped; (b) as the trial advanced,
the probability of switching to the initially preferred key
decreased whereas the probability of switching to the other key
increased; and (c) a first-order Markov chain model with
transition probabilities given by a logistic function accounted
well for the internal structure of the birds' response sequences.
These findings suggest that, to a large extent, the variability
of response sequences is an indirect effect of a djustments in
changeover frequency.
Key words: behavioral variability, switching behavior,
nonstationary Markov chain model, response sequence, key peck,
pigeon