Essay // Biological Constraints in Learning By Operant Conditioning



While the “Law of Effect” has one of the most popular concepts in learning theory, the deeper applications have also been questioned. From humans to animals however, although the intelligent management of the concept of reinforcement enables learning to occur, biological factors known as the “instinctive drift” and “autoshaping” challenge the principles of learning. Instances have risen with animals, where unreinforced behaviours were noted without any particular stimulus. Such occurrences have been referred to as “misbehaviour” (Breland & Breland, 1961). The studies (Timberlake & Grant, 1975) & (Bullock & Myers, 2009) applied 2 different concepts to further understand biological constraints where the possible explanation of classical conditioning (Moore, 1973) was heavily challenged with a more sophisticated argument involving solid claims for a “behaviour-systems analysis”. The idea of “stimulus substitution” in (Moore, 1973) was also questioned by Wasserman (1973), where 3-day old chicks were observed to have adaptable responses to specific stimuli.

The 1960s, The Debate & The Effectiveness of Thorndike’s Findings

Discovered in the 1960s, the two phenomena, instinctive drift and autoshaping have created a lot of debate amongst psychologists who are in disagreement with one another in providing a concrete explanation. The main issue in behavioural therapy has been how certain animals [in some cases], would cease performing reinforced behaviours [previously shaped by trainer through operant conditioning] but instead would adopt a new pattern of unreinforced behaviours – even leading to the frequency of the behaviour increasing over time. The phenomena has caused a lot of problems and controversy in the animal behaviourist’s field; as some would see countless amount of work [requiring careful shaping and chaining] being ruined through their animal’s drift from the conditioned task. The discovery of biological constraints also raise serious questions over the effectiveness of reinforcement in modifying and controlling behaviour. Some researchers such as Timberlake in 1983 argued that the concept of reinforcement learning is inadequate and should be forgotten.

Study 1: Auto-Shaping in Rats to the Presentation of Another Rat predicting Food (Timberlake & Grant, 1975)


The hypotheses in rat experiment were tested by comparing the behaviour of an experimental group with three control groups with each consisting of five male Wistar albino rats, 90 days of age. During acquisition, each rat received 30 10-second presentation of the predictive stimulus on a variable time schedule with mean interval of 60 seconds. The stimulus-platform was driven by a motor and the cam assembly presented sideways through a flap door. For Experimental group CS+ each presentation of predictive rat was followed by one 45-mg food pellet. The CS (S) (Social) group received the same pattern of presenation but no food was delivered [since rats are highly social, grouped served as baseline for social reactivity to stimulus]. The CS(T) group was presented with stimulus rat and food randomly on two independent variable-time 60-second programs. The CS (W) (Wood) group was subjected to the same procedures as CS+ group, except predictive was a rat-sized block of wood [to separate the social and predictive effects of the stimulus rat] Rats in the CS+ group might approach the stimulus rat for its predictive quality and only engage socially due to proximity.

All rats were housed alone during experiment, and after adaptation to a 23-hour feeding schedule, each rat received 22 days of training, 2 days of pretraining, 11 days of acquisition, and 8 days of extinction. On first day of pretraining, each subject was exposed to experimental chamber for 30 minutes.

trialsratThe above figure shows that CS+ animals increased the frequency of Orient, Approach, Sniff and Social Contact during 11-day acquisition period and successfully decreased during extinction. The CS(S) animals also engaged in considerable behaviour towards stimulus rat but performance stabilized at lower level than CS+ animals (Fig 1B)

white ratFindings

These reveal that the form of contact with predictive stimulus cannot be predicted from stimulus substitution hypothesis, but seems to depend on both predictive stimulus and reward; which supports the theory of autoshaping being the reflection of a system of species-typical behaviours commonly related to the reward. The form of the behaviour [in presence of the stimulus], would thus depend on which behaviours in the conditioned system are elicited and supported by the predictive stimulus. The existence of biological constraints is confirmed.

The study proves that the animal will not necessarily associate innate behaviours linked to the primary reinforcer whatever the predictive stimulus is. Here, the predictive stimulus is another rat, and the subject rat does not treat the predictive rat [stimulus] to behaviours connected to eating.

The findings here are also supported by (Bullock & Myers, 2009) where the image of a grey square which was a predictive stimulus preceding the delivery of bananas. The video retrieved showed monkeys touching, grabbing licking and biting responses toward grey square that moved along the chamber floor, which are the typical types of behaviours observed when the monkey in its natural environment feeds itself.

The lack of approach to the group seems to suggest a low level of conditioning to the block of wood CS(W), but also shows that approach to predictive rat in the CS+ group was not based on its predictive value alone; conditioned approach depends on the social as well as predictive aspects of stimulus rat. Biological limitations are supported as the results seem to suggest that rats can be conditioned to approach a live rat, but not a block of wood which predicts food. Block and platform provided no social cues and could have been too large to elicit behaviour related to food. 

Study 2: The Misbehaviour of Organisms (Breland & Breland, 1961) 


In this experiment pigs were conditioned to pick up large wooden coins and deposit then in a large “piggy” bank. The coins were placed several feet from the piggy bank and the pigs were required to carry and deposit those coins to be reinforced. Generally, 4 or 5 coins would lead to a reinforcer, although the initial shaping of the pig started with 1 coin for 1 reinforcer.

Photo: Center for the History of Psychology // UOA


The pigs conditioned very rapidly and had no trouble taking ratios on top of having a famously ravenous appetite. However, gradually the same problem developed from pig to pig usually after a period of weeks or months, gradually worsening. While at first the pig would eagerly pick up dollar, carry it to the bank, then run back to get the next, and so on, until the ratio was complete. After weeks, instead of pursuing the same routine, reinforced behaviour would become slower and slower. The pig would sometimes run to pick a coin but on the way back to the bank, it would drop it, root, drop it again, root it along the way, pick it up in the air, drop it, root it some more and so on.

This change in behaviour was initially believed to be caused by a low-drive, but behaviour only increased in intensity and strength in spite of increased drive; finally going over the ratio so slow that it would be left without much to consume.

As the unreinforced behaviour increased in frequency and manifested, it was noted that the behaviour was very similar to those repertoire of food-gathering behaviours pigs usually do in their natural setting. The Brelands then concluded and referred to the behaviours as instinctive drifts as they seemed to relate to the animal’s innate responses. The subject was replaced by a Raccoon, and a similar unreinforced behaviour appeared, which caused the animal to misbehave. The initial pattern was fine when 1 coin was being given to the Raccoon, however with 2 coins the reinforced behaviour gradually deteriorated leading to Raccoon holding them together, rubbing, dipping in container and out again.  Similarly to the pigs it was deduced these movement were innate behaviour to food in natural setting [rubbing crustacean, for example]. Those behaviours were said to constitute a clear example of the failing of conditioning theory. It was evident that the animal was performing unreinforced behaviours despite the lack of reinforcer; it was concluded that coins were not food, container not a stream [dipping in and out] and no shell to remove [rubbing]. The new behaviour also produced no food, but instead delayed delivery, which makes a clear point for biological constraints in Operant Conditioning.


While the concept of operant conditioning remains a reliable method in learning [having proven to alter behaviour as a result of experience], the unpredictability of an organism seems to suggest that an element of failure in whatsoever process involving animals [living organisms] remains a possibility. On this subject, Skinner established that perhaps animal/organic behaviour is defined by both learning experiences and hereditary drives. Skinner also concluded that the odd occurrence of unreinforced behaviour would be related to phylogenetic [hereditary] and ontogenetic [learned] influences operating simultaneously.




Breland, K. & Breland, M. (1961). The misbehaviour of organisms. American Psychologist, 16, 681-684

Bullock, C. E., & Myers, T.M. (2009). Stimulus-food pairings produce stimulus-directed touch-screen responding in cynomolgus monkeys Macaca fascicularis) with or without a positive response contingency. Journal of the Experimental Analysis Behavior, 25, 127-135

Bullock, D., & Neuringer, A. (1977). Social Learning by following: An analysis. Journal of Experimental Analysis of Behaviour, 25, 127-135

Mazur, J.E. (2013). Learning and Behaviour (7th Ed.).New Jersey. Pearson, 101-126

Moore, B.R. (1973) The role of directed Pavlovian reactions in simple instrumental learning in the pigeon. In R. A. Hinde & J. Stevenson-Hinde (Eds.), Constraints of Learning. New York: Academic Press, 159-188

Timberlake, W. & Grant D.L. (1975). Auto-Shaping in Rats to the Presentation of Another Rat Predicting Food. Science, New Series, 190, 690-692

Wasserman, E. A (1973). Pavlovian Conditioning with heat reinforcement produces stimulus-directed pecking in chicks. Science, 81, 875-877


22.04.2014 | Danny J. D’Purb |


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