Does the phenomenon of blocking enable us to identify which animals have expectations?

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David Beisecker. Photo courtesy of University of Nevada, Las Vegas.

A useful way to resolve the question of whether operant conditioning should be envisaged in mentalistic terms or purely causal terms would be to examine the phenomena linked with it, and ascertain whether the key concepts invoked to explain these them can be defined using a mind-neutral intentional stance or requires a mentalistic explanation.

One phenomenon - blocking - has been proposed by Beisecker as an example of behaviour that expectation-generating animals would engage in. I shall discuss this particular claim in detail, as it is a highly unusual prediction of one model of associative learning - the Rescorla-Wagner model - whose central ideas are usually expounded using mentalistic terminology.

While the Rescorla-Wagner model is not able to explain all phenomena connected with classical conditioning, it is still regarded as "the 'best' theory of classical conditioning" (Jackson, 2002). Its basic principle is that "the amount of conditioning depends on how surprising the association between the CS and US is. Surprise determines not only if conditioning occurs but how much conditioning occurs. The more unexpected or surprising the US, the more conditioning will occur" (Lipp, 1998, italics mine). Surprise surely qualifies as a mental state.

Blocking, which is readily explained by the model, has been interpreted by some learning theorists as evidence that animals form expectations and hence have mental states. Beisecker describes how it works:

Several learning theorists have argued that the apparent educability of some creatures is best explained in terms of the adjustment of "expectation-like" structures mediating between sensory input and behavioral output. For example, expectations are a reasonable explanation for the blocking phenomena often observed in actual creatures. Animals that have been trained to associate a conditioned stimulus with an unconditioned stimulus will subsequently fail to associate other stimuli with the unconditioned stimulus, when the latter are presented along with the original conditioned stimulus. For example, rats that have been trained to associate a bell tone with an electric shock will not come to associate a red light with a shock, as long as the red light is consistently paired with the bell tone. The prior conditioning prevents (or "blocks") subsequent conditioning to other, co-varying stimuli. If learning were merely a function of the frequency of stimulus-pairing, then one would expect the animal to become conditioned to the new stimulus as well. One would expect the rats eventually to associate the red light with a shock, as indeed they do when they aren't subjected to the earlier training. Many learning theorists have argued that the failure of previously conditioned animals to become conditioned to the new stimulus arises because the animal already uses the original conditioned stimulus to successfully predict the occurrence of the unconditioned stimulus. When a previously conditioned rat encounters the compound tone and light stimulus, it expects that the shock will occur (because it heard the bell tone), and so the subsequent shock isn't a surprise. Since events are as they were expected to be (they were not novel), there is no pressure to develop new associations, hence no subsequent conditioning to the light. Thus these theorists conclude that the rats are responding to surprise, to things not being as they expected them to be (Beisecker, 1999, pp. 298-299, italics mine).

The ability to form expectations is certainly a sufficient condition for having mental states, and if Beisecker's account of belief is correct, it is a necessary condition as well. If blocking indicates the presence of expectations, then can we use the phenomenon of blocking to distinguish those animals with minds from those without?

According to Dr Bjorn Brembs, blocking has not been confirmed in any invertebrates.
Photo courtesy of Professor J. Byrne, Department of Neurobiology and Anatomy, The University of Texas Health Science Center at Houston.

There are two good reasons for caution here. First, associative learning is widespread in the animal kingdom: even simple worms have been shown to be capable of it. The evidence for operant conditioning is less clear, but it is well-documented for many kinds of insects, and we have already discussed tentative evidence that worms such as C. elegans may be capable of it. However, most kinds of animals that are capable of operant conditioning have not yet been shown to exhibit blocking (see Appendix for further discussion). There have been no confirmed reports of blocking in worms, and its occurrence even in so-called "higher" invertebrates (honeybees) remains controversial. If Beisecker wishes to propose blocking as a litmus test of cognitive mental states, then he has will have to limit these states to invertebrates.

A second reason for caution is that blocking may turn out to be explicable in non-mentalistic terms, in any case. As one neurobiologist who does research in this field commented (Menzel, personal email communication, 21 July 2003):

Expectation is a term that I am also using in these papers but not with a high order cognitive meaning. It is my impression that scientists in my field are considering expectation as a function that results from former learning and creates a status of retrieved memory without implications about any separate cognitive state other than memory retrieval. There are even concepts that try to explain blocking as a function of peripheral sensory integration.

We have already seen that sensory capacities and memory can be explained by adopting a goal-centred intentional stance, without the need for a richer, mentalistic account. If many scientists believe that these capacities are sufficient to explain blocking, then (pace Beisecker) it would be unwise to invoke blocking as evidence of mental states.

L.13 The occurrence of blocking in an organism does not provide a sufficient warrant for our ascription of cognitive mental states to it.

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