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9: Counter-hypothesis to "Genetically based differences..".

Two factors is part of this counter-hypothesis: a phenomenon named Autoshaping and the conditions under which the animals are housed.

Autoshaping is too called "Superstitious behaviour" and can emerge by two different types of learning:

During Operant Learning (in the discipline "Fixed Time reinforcement procedure") a hungry individual is feed a reward after a certain time (e.g. 15 seconds) no matter what behaviour is actually performed. Since the individual in question usually is doing something when the reward is given one will be able to observe after a while that this behaviour is reinforced (more dominant) until a point where it is practically the only behaviour performed. It is generally assumed that the individual in some way (falsely) associates this special behaviour with being rewarded and because of that performs the behaviour (NB - reconsider for a moment the 3rd criteria in the definition of stereotypic behaviour: the apparent lack of obvious purpose...)

The other way autoshaping can be taught is via the Classical (or Pavlovian) conditioning (=learning).

Pavlov made a distinction between two types of reflexes; unconditional- and conditional reflexes. Pavlov admitted that other terms could have served as well: Unconditional reflexes might have been referred to as inborn, unlearned, or species reflexes; conditional reflexes could have been called acquired, learned, or individual reflexes. However, the terms conditional and unconditional caught on and are still used today. The unconditional reflexes is usually permanent and present among practically all individuals within the specie. The conditional reflexes are learned, relatively short-lasting and shows considerably individual variation.

The famous textbook example of Pavlovian reflexes is where an unconditional stimulus (a so-called US - e.g. food) gives rise to an unconditional response (a so-called UR - e.g. increased flow of saliva). If an object (e.g. a food-machine) is presented immediately before the US, the research subject will eventually develop salivation just by the sight of the object: the food-machine has now become a conditional stimulus (CS) and the response it cause (salivation) is now called a conditional response (CR).

It seems that the time which passes between presentation of the CS (the food-machine) and the US (the food) is significant in predicting which type of response the research subject displays (Figure 3). A short delay (seconds) causes the CR (salivating) but a longer delay (e.g. an hour) can provoke a locomotoric response. To take a hungry rat, a short delay will typically make it close in on the opening from which the food will emerge (appetitive behaviour) but if the delay is longer, the rat can instead start to run in an exercise wheel, if such is present.

Figure 3 shows what the first factor in the counter-hypothesis is about. A locomotoric response is probably caused by an appetitive phase after which the response undergo an internal moderation during some time maybe in the form of Sensitization of neuron paths and/or motor programs or that the behaviour becomes more placed under central (= conscious) control .

Stereotypic behaviours can then be hypothesised to emerge as a result of such moderation.

 

Figure 3

The second factor concerns the conditions under which mink and pigs are housed at the production farms. These conditions are summarized in Table 4.

Tabel 4

Housing conditions	Mink	Pig
Feeding schedule	Irregular	Regular
Size of accommodation	Good	Poor
Limitated in accessibility of food	No	Yes
Relative size of stomach/intestine	Small	Large
General state of hunger	Satisfied/full	Hungry
Extra allotment of sugar beet =>	N.A. for obvious reasons	Reduces stereotypic behaviour.
Ad libitum feeding	No effect	Large reduction in stereotypies (approaching zero).

Mink: The studies published until now concerning mink has generally been carried out on large farms with 2-4.000 animals. Feeding on such farms is done using food-trolleys, which drive between the long rows of cages. The mink keepers controls the route for these food-trolleys and often shows the behaviour of letting them start a different points of departure and at different times. A food-trolley can therefore easily drive past a certain cage without delivering a portion of food.

The feedings are therefore irregular and the maximal time span, from which the mink hears the food-trolley, until it actually gets a portion, can be between 1 and 4 hours - in other words a suitable time span if the objective is to provoke a locomotoric response (see figure 3).

Mink typically engage in stereotypic activities pre-feeding with a limited number of stereotypies post-feeding. These stereotypes, as mentioned before, mainly consist of pacing, jumpings, backward somersaultings etc. Minks can do these stereotypes because they are very athletic and capable of using all three dimensions in their cage. They have relatively speaking (relative to the condition for the pigs) good space in their cages.

Mink are not restrained or limited in their access to food, since there is no special economical incitement for this. Compared to the pig, they have a relatively small stomach/intestine making it impossible for a mink to eat all it's ration in one sitting. They eat for a couple of minutes, rest, eat again and so on. Generally speaking, mink on farms are full most of the time.

Turning to stereotypies, it has been observed that mink on small farms exhibit a significantly lower level of stereotypies than mink on larger farms and a reason for that might be that the feed follows the sight/sound of the food-trolley considerably faster.

Pigs and on the other hand typically stabled in very small boxes (stalls) - sometimes tethered which naturally leads to a limited freedom to move. There stereotypies are typically oral (no Pacing for obvious reasons) and is mainly seen post-feeding. They typically experience limitations in food supplies (pregnant sows to around 60% of the ad libitum consumption) and are therefore in a state of chronic hunger. A pig will eat its ration in 15 minutes and then spend a considerable amount of time rooting in the empty trough and perform other types of stereotypies.

These kinds of observations have then spawned the idea that the pig gets too little negative feedback in the consummatoric phase due to insufficient filling of the stomach. An experimental supplement of sugar beats to the food reduced the amount of stereotypies and using ad libitum addition feeding the stereotypies were reduced to zero.

The phenomenon of Autoshaping paired with the conditions within the farm could therefore easily explain the difference in these two species regarding stereotypic activities without having to mobilize the existence of genetic predispositions [that the tendency to stereotype lately seems to have a heritable element among mink is a different story - note from 2006].

In other words, it seems that food-motivation can explain at least some of both the amount and difference in timing of stereotypies between these two species, but data from experiments using other species are few.

Other motivations have been examined, e.g. the motivation to move, but here data is a bit more conflicting. I studies using horses, certain primates and in one study using pigs (sham-chewing) it seemed as if an increase in the available area reduced the stereotypies. In other studies, using other primates, an increase in available area had no effect on the stereotypies and in the same study with pigs as above, the stereotypies chain chewing and polydipsia (excessive drinking) were not seen to be reduced.

[Note: personally I am inclined to question that polydipsia among pigs in large farms should be classified as stereotypic in nature. I am not especially thinking along the lines of diabetes, but polydipsia seem to me to be suited to serve the purpose of filling the stomach of a hungry pig]

Next topic: Hypothesis: "Stereotypies acts as Reinforcers".