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Travel into the Future: anticipatory coding and prediction






 

The famous innovative thinker and mathematician in Victorian Britain Charles Babbage said in 1840 that “…intelligence would be measured by the capacity for anticipation”.

The capacity to anticipate is necessary for survival, and contributes to the success of every organism. As a consequence, animals and humans behave as if the confirmation of an expectation makes the same anticipation more certain in the future. They behave in a predictive manner: what happened once will occur again.

Recently, a growing number of researchers have identified and emphasised the importance of anticipation as the basis of models of animal learning and behaviour. In this section we will concentrate on animals’ capacity to predict future states in time in which their actions are embedded.

In no doubts, species are not equal in their abilities to anticipate future events. If a mouse disappears into its hole it no longer exists for a snake, while a cat, for instance, remains in front of the whole and waits for the mouse to re-appear.

Chimpanzees seem to be able to plan their behaviour in the light of future events which they can predict basing on their personal experience. De Waal (1982) reported an incident in the Arnhem Zoo where Van Hoff established the chimpanzee colony. “It is November and the days are becoming colder. On this particular morning Franje collected all the straw from her cage (sub-goal) and takes it with her under her arm so that she can make a nice warm nest for herself outside (goal). Franje did not react to the cold, but before she can have actually felt how cold it is outside”. (p. 192)

Once more an anecdote concerns Lucy, the chimp reared in Temerlin’s family. She often accompanied the family in their trip to a ranch. The ape was very much afraid of bridges especially those of them which she considered unsteady. Long before coming near such “bad bridges” she began whimper, tremble with fear and grasp a driver by the hand in order to stop the car (Temerlin, 1975).

These and analogous naturalistic observations raise a question of how long animals can travel into the future.

Bischof (1978) and Bischof-K`hler (1985) suggest an explicit limit on the extent to which animals can represent the future. Their hypothesis is that animals other than humans cannot anticipate future needs or drive states, and are therefore bound to a present that is defined by their current motivational state. More recent, the so-called mental time-travel hypothesis (Suddendorf and Corballis 1997), states that the cognitive time-window for non-humans animals is restricted to the immediate past, the present, and the immediate future. According to this hypothesis, animals are incapable of taking action in the present on the basis of either the recollection of specific past episodes (retrospective cognition) or the anticipation of future states of affairs (prospective cognition).

Some recent investigations question these assumptions about episodic memory and future planning. In fact, this is a part of a general problem of whether our species is alone in a cognitive niche, a question with which we will face more than once in this book. In this issue experimental results on animal capability of planning future events will be analysed in terms of cognition and adaptiveness.

In scientific literature in general, anticipation refers to attempt of the prediction of behavioural consequences. Anticipatory behaviour refers to behaviour that is influenced by expectations about the future, such as future states of the environment, future actions, or merely anticipations about the way things work in a given situation. Although it is natural to assume that at least some species of animals are capable of anticipating future events, it was believed for a long time that animals only possess planning for present needs which is called immediate planning; planing for the future is called anticipatory planning (Gulz, 1991). Although it may appear obvious that Pavlovian and instrumental learning tasks would result in organisms learning to anticipate future events on the basis of current stimuli or present actions, respectively, the notion that animals can anticipate future events was strongly resisted by the majority of learning theorists from the early 1900s to the late 1960s (Grant and Kelly, 2001).

Some distinct behavioural evidences of expectation and participation came from Hunter’s (1912) experiments, in which chimpanzees definitely demonstrated their disillusionment when more desired rewards were replaced in the boxes with less attractive items. More contemporary research in both Pavlovian and instrumental conditioning demonstrated that organisms learned something in addition to, or, more likely, other than stimulus-response habits.

Particularly definitive evidence for anticipation has been provided by studies in which the value of the consequent has been modified after conditioning (Holland and Straub, 1979; Dickinson et al., 1996). In these studies, initially a stimulus or an action had been established as a reliable predictor of an outcome (food pellets). Subsequently, the value of the consequent has been reduced (e.g., by satiating the animal on that consequent, or by making the consequent aversive by pairing it with induced illness). During testing in which the consequent is no longer presented, animals react to the predictor, whether stimulus or action, in a way clearly revealing that they had learned what is predicted by that stimulus or action. For example, rats that had initially reacted with agitated excitement to a tone paired with sucrose, show little excitement to the tone following devaluation of the sucrose. Similarly, rats that had earlier eagerly pressed a lever to obtain sucrose pellets, will, after devaluation of sucrose, be reluctant to press the lever.

In the early 1980s, several investigators recognised that the information or code which mediates short-term retention in delayed matching-to-sample could have either a retrospective or prospective content (Grant, 1981; Honig and Thompson, 1982; Riley et al., 1981; Roitblat, 1980). In particular, the animal could retain features of the sample stimulus during the delay, a retrospective or " backward-looking" code. During testing, the retrospective code, in combination with the rules learned during simultaneous matching, would be sufficient to generate accurate choice performance. Alternatively, the rules learned during simultaneous matching could be activated during sample presentation to generate an anticipatory code. That is, the code could represent features of the correct choice stimulus, a prospective or " forward-looking" code. This approach has generated experiments devoted to what is called prospective memory in animals.

Grant and Kelly (2001) reviewed a great deal of findings including their own experiments designed to answer the question of whether an anticipation of a future action and/or event can function as an effective mediator of short-term retention in pigeons. They found that the literature provides only moderate evidence of the role of anticipation in mediation of short-term retention in these subjects. The strong evidence for anticipatory memory-mediation comes from the study of Zentall et al. (1990) devoted to memory for spatial locations. They found that a delay interpolated after four of five locations had been chosen produced less disruption in performance than a delay interpolated after two or three locations had been chosen. This finding provides compelling evidence that, as the trial progressed, pigeons re-coded from remembering previously chosen locations to remembering not yet chosen locations.

The scheme of experiment was as follows. An array of five pecking keys was illuminated at the onset of a trial. Choosing (i.e., pecking) a particular key was correct if that key had not been chosen previously on that trial. An error was to choose a key which had been previously chosen on that trial, and resulted in a 2.5-s blackout after which the keys were again illuminated for a choice. A trial ended when all five keys had been chosen. The data relevant to the issue of prospective code content came from trials in which a delay was inserted at some point in the choice sequence. Across trials, the delay occurred after 1, 2, 3, or 4 correct choices had been made. The authors found that the delay caused more errors when it was interpolated after choice 2 than when it was interpolated after choice 1. This result suggests that the amount of information that the bird had to retain was greater after having made two choices than after having made only one choice. Hence, this result suggests that the animal begins the trial using a code with retrospective content; that is, early in the trial the animal remembers which locations it has previously chosen. Interestingly, however, a delay interpolated after choice 3 produced approximately the same amount of forgetting as a delay interpolated after choice 2, suggesting that the memory load was equivalent after either two and three choices had been made. Equivalent memory load after two or three choices could be obtained if pigeons remembered retrospectively after having made two choices (and hence remembered the two locations previously chosen) and remembered prospectively after having made three choices (and hence remembered the two locations not yet chosen). Further support for the notion that pigeons switched to prospective coding later in the trial was provided by the finding that a delay interpolated after choice 4 produced less forgetting than a delay interpolated after choice 2 or 3 and, moreover, produced about the same amount of forgetting as a delay interpolated after choice 1. This result is expected if the animal codes prospectively later in the trial because the memory load after choice 4 (i.e., 1 item) is equivalent to that after choice 1 and is less than that after choice 2 or 3 (i.e., 2 items). Hence, the results of Zentall et al.'s (1990) experiment provides evidence that codes having prospective or anticipatory content can mediate retention in pigeons.

A similar experiment employing rats was carried out by Cook, Brown, and Riley (1985). They investigated the content of the memory used by rats in mediating retention intervals interpolated during performance in a 12-arm radial maze. The delay occurred following either the 2nd, 4th, 6th, 8th, or 10th choice. A 15-min delay had the greatest disruptive effect when interpolated in the middle of the choice sequence and less of an effect when it occurred either earlier or later. This pattern of results was obtained when both a free- choice or forced-choice procedure was used prior to the delay and regardless of whether post-delay testing consisted of completion of the maze or two-alternative forced-choice tests. Assuming that the disruptive effect of a delay is a function of memory load, this implies that the rats used information about previously visited arms (retrospective memory) following an earlier interpolated delay but information about anticipated choices (prospective memory) following a delay interpolated late in the choice sequence.

In Reznikova’s (1983) experiments red wood ants showed high standard of temporal interpolation in the 12-arm radial maze adapted for insects in such a way that the ants had to visit one of 12 cardboard strips consequently in order to find a drop of syrup there. The ten-minute delay occurred after each choice. Each time the next arm (a strip) was baited so the ants were requested to predict the appearance of the reward not on that strip they had visited before but on the next one. 19 series of trials were conducted with the interval of two days between series, and the bait ran through the whole cycle during each series. Since the second series ants behaviour was not chaotic: they chose that strip where they found syrup last time but having failed to find food, they proceeded to the next one. During fourth series of trials the insects demonstrated that they can predict when the syrup ought to be. They visited the next strip ahead each time, not that one on which they found the food previously. During 20-24-th series the maze was shifted from vertical to horizontal position. The ants coped with this task successfully since the second series with the new position.

 






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