Chsptsr 2 Animal sequence learning
2.3 Associative Sequence learning (ASL) Theory
Hayes and Ray (1998) recently proposed a new theory of imitation known as Associative Sequence learning theory (ASL). ASL theory represents actions as being made up of sequences of smaller actions or 'action units'. Consider the example cited earlier in this section regarding a gorillas consumption of the nettle
Laportea alatipes (Byrne and Russon 1996). Here, in order to ensure safe consumption of the nettle gorillas employed a process of manipulations which when carried out in the correct order resulted in harmful stings being kept away from the mouth upon eating. This provides a rather hefty example of an action which comprises smaller units of actions in order to complete, however, ASL theory states that all actions no matter how small can be considered as comprising smaller 'action units'.
Using Heyes and Ray's example, when an observer sees a sequence of hand movements i.e. point, splay then victory, which combine to provide a novel combination of movement, two associative processes, the first being of a sensory nature and the second dealing with representations of the motor components of the action sequence are activated. The sensory links form a representation of the visual aspects of the sequence so that the observer knows what each item in the sequence looks like and can recognise sequence components if necessary. In addition, these sensory units are connected to each other according to factors such as context or time which provide cues to allow reproduction of the correct order of sequence items. Once some kind of sensory representation of each item in a sequence is formed, an associative link between each of these units and the motor units, which contain kinaesthetic information regarding performance of the motor programme, are formed. These motor components are assumed to be already present in the repertoire of the observer. Links between the sensory units and the motor units are suggested to be brought about through the observer seeing a sequence executed and completed, however, these connections can also be brought about indirectly. For example, consider the sequence item 'point'. On one
occasion an observer may see another person pointing with their finger and hear the word 'point' at the same time, on another occasion the observer may be making the hand movement 'point' and then hear the word 'point'. Therefore information about the motor and sensory aspects of the sequence item may have been formed in the absence of one and other and become connected via an "acquired equivalence" route to imitation.
Heyes' theory combines for the first time, learning about sequences and learning by observation which have hitherto been treated separately experimentally. Most importantly it allows certain predictions to be made about animal learning. ASL theory proposes that if an animal is capable of stimulus learning and in addition has prior experience of the individual actions which comprise a sequence then it may be able to learn to reproduce any action sequence in the correct order and using the same actions which it has seen demonstrated. Using a task akin to the two action tasks which have been mentioned earlier it would be possible to test this empirically. For example, an experimenter might wish to pretrain rats to execute a number of individual lever presses and then expose these rats to demonstrators that have been trained to press one or other combination of lever presses. On test the observer rats would be given the levers and scored as to how closely their lever pressing resembles the sequences of lever presses they had seen demonstrated. If they manage to reproduce the correct combination of lever presses and with the same method e.g. paw or mouth then one could conclude imitation of sequence execution. If however, they only manage to reproduce the correct order of lever presses but without the concomitant action then this still informs us that this species are capable of learning about sequences of stimuli by observation.
2.4 Summary
To summarise: it appears that animals other than Homo sapiens are indeed capable of stimulus learning by observation, of learning about objects and events. Undoubtedly animals can learn about single stimuli by observation, and can learn
about stimulus and response sequences by direct exposure to the target events. Less clear is whether they can learn about single responses by observation (imitation), or whether they can learn about sequences of stimuli or responses by observation.
Whiten (1998) provides the only firm evidence of observational sequence learning in animals (chimps), which is most likely to be as a result of learning about sequences of stimuli rather than learning about sequences of responses. If this is the case it is suggested that this may be mediated by an associative mechanism.
The experiments reported in Chapter 6 sought evidence of stimulus sequence learning by observation in rats using a two action test under free operant and fixed trial conditions.