Behavioral Variability and Frequency‐dependent Selection

Abstract

In Experiment 1, two conditions were compared: (a) a variability schedule in which food reinforcement was delivered for the fourth peck in a sequence that differed from the preceding N four-peck sequences, with the value of N continuously adjusted to maintain reinforcement probability approximately constant; and (b) a control condition in which the variability constraint was dropped but reinforcement probability remained constant. Pigeons responded approximately randomly under the variability schedule but showed strong stereotyped behavior under the control condition. Experiments 2 and 3 tested the idea that variability is the outcome of a type of frequency-dependent selection, namely differential reinforcement of infrequent behavior patterns. The results showed that pigeons alternate when frequency-dependent selection is applied to single pecks because alternation is an easy-to-learn stable pattern that satisfies the frequency-dependent condition. Nevertheless, 2 of 4 pigeons showed random behavior when frequency-dependent selection was applied to two pecks, even though double alternation is a permissible and stable stereotype under these conditions. It appears that random behavior results when pigeons are unable to acquire the stable stereotyped behavior under a given frequency-dependent schedule.Key words: behavioral variability, frequency-dependent selection, Bernoulli process, Markov chain, lag analysis, response pattern, key peck, pigeon Three lines of evidence show that response variability can be modulated by reinforcement contingencies. First, when pigeons, rats, and human subjects are given reinforcers for emitting variable behavior, variability increases (Blough, 1966;Machado, 1989;Morris, 1987;Neuringer, 1986;Page & Neuringer, 1985;Pryor, Haag, & O'Reilly, 1969;Schoenfeld, Harris, & Farmer, 1966;Van Hest, Van Haaren, & Van De Poll, 1989). Second, the more variability required to obtain a reinforcer, the more is typically obtained (Machado, 1989;Morris, 1989;Page & Neuringer, 1985). Third, response variability can be placed under stimulus control (Neuringer, 1991;Page & Neuringer, 1985). These three data sets I thank John Staddon and the other L.A.B. group members for their continuous help and encouragement. The research was partially supported by grants to Duke University from NSF and NIMH (John Staddon, Principal Investigator). Experiment 1 was carried out while the author was at the Universidade de Lisboa, Portugal (my appreciation to the students who helped run the experiment). Parts of the paper were presented at the annual meeting of the Association for Behavior Analysis, Nashville, May 1990. Derivations of the functions represented in Figure 6 are available from the author upon request. Correspondence concerning this article may be sent to Armando Machado, Department of Psychology, Duke University, Durham, North Carolina 27706. suggest that variability is another operant dimension of behavior, with the same theoretical status as response force, duration, and latency. The present study was de...

Response stability and variability induced in humans by different feedback contingencies

“…However, the strategy used by the majority of the subjects consisted of repeatedly emitting fixed, relatively short sequences or even simple repetitions of single sequences, which, combined with a relatively uneven use of the different response options, did not result in a significant increase in MetVar. The latter is consistent with previous animal experiments that failed to find increases in response variability with noncontingent reinforcement (e.g., Denney & Neuringer, 1998;Machado, 1989Machado, , 1992Morgan & Neuringer, 1990;Page & Neuringer, 1985). After the shift, there was an increase in the use of rare response sequences and in MetVar.…”

“…etc. ; see Machado, 1992, for arguments that patterns of sequences may be targets of selection by reinforcement). Therefore, in the present experiments, different feedback contingencies might have a different effect on the number of trials on which specific variability criteria are met, on the behavioral strategy used, or on both.…”

Human choice among five alternatives when reinforcers decay

“…Stated differently, momentary-maximizing responding may occur when subjects can discriminate differential reinforcement, but when such discriminations are not possible, stochastic responding results. Machado (1992) initially proposed this hypothesis and our results conform to his predictions.…”

Operant variability: Some random thoughts

“…2 We know that ''directed forgetting'' is trainable (e.g., Zentall, Roper, Kaiser, & Sherburne, 1997); maybe something like this emerges as a feature of some of the random-response training procedures. There are conceptual problems with the no-memory idea (see, e.g., Machado, 1992); but, more important for present purposes, this cannot apply to the typical lag n procedures. The performances attained under these contingencies may be far from what chance would predict; as already mentioned, variation and random are not synonymous.…”

“…Surely, much data would be consistent with that device. Regarding the lag n procedures, Machado (1992) has suggested a different mechanism: frequency-dependent selection based on differential reinforcement of infrequent behavior patterns. It is not clear to me that this concept does not share the same conceptual problems of Neuringer's stochastic generator.…”