Remaining Interpretative Problems

Several interpretative problems remain which undermine the conclusion that rats are imitating in Heyes and colleagues' bidirectional control procedure.

a) The reliability o f demonstrator-consistent responding effects. Published reports of attempts to demonstrate imitation in rats using a bidirectional control procedure have provided accounts o f a total of nine experiments. Eight o f these experiments have yielded statistically significant results which suggest that exposure to a demonstration session influences observers' directional responding in a manner dependent upon the type of outcome which follows each demonstrated response; in seven cases demonstrator-consistent responding occurred when the outcome was an appetitive reinforcer (Heyes & Dawson, 1990; Heyes et al., 1992; Heyes, Jaldow & Dawson, 1994; Heyes, Jaldow, Nokes & Dawson, 1994), and in one case demonstrator-consistent responding was inhibited when the outcome was the omission of an appetitive reinforcer (Heyes et al., 1993). The remaining experiment is not consistent with this pattern (Reed et al., 1996). In Reed et al.'s experiment, rats that had been reared in isolation were found to respond in the opposite direction to that in which their demonstrators had pushed a joystick for food reinforcement.

In fact, the nine published experiments are only a small sample of experiments that have applied a bidirectional control test to rats. The first experiment (Heyes & Dawson, 1990) has been followed by over 100 further experiments. Many of the unpublished experiments have not provided statistically significant effects in either direction. Thus, the question o f the

statistical reliability of the basic effect arises; are demonstrator-consistent responding effects in rats tested using the bidirectional control procedure a sampling artefact? One of the objectives of the Chapter 5 is to provide an answer to this question.

b) Asym m etric Local Enhancement o f the Joystick. Although the bidirectional control procedure "was designed to minimize any effects of local enhancement" (Heyes & Dawson, 1990, p. 61), such effects have not been ruled out as a putative account for demonstrator- consistent responding effects. An observational study of joystick manipulation behaviour has revealed that rats tend to deflect a bidirectional joystick using pushing movements in which either a forelimb (82% of pushes) or the snout (18% of pushes) is the effector: "The prototypical topography consisted of the rat standing facing the pole but slightly to one side, and pushing the pole away from the body with the paw adjacent to the pole" (Dickinson et al., 1996, p. 301). Therefore, joystick deflections to the left and to the right tend to result from rats having made contact with different sides of the joystick. If observers tend to be influenced by the side of the joystick that was manipulated by their demonstrator, demonstrator-consistent responding might be expected to occur, and the basic effect might be attributable to local enhancement.

While a local enhancement account has yet to be put to empirical test, it is possible to argue that behavioural concordance in the joystick paradigm is unlikely to have been due to a

visually mediated local enhancement process. Consider the nature of the visual information that is available to an observer during demonstration and test sessions. The viewpoint that an observer has of the joystick at test is different from that which it had when observing the demonstrator pushing the joystick, by virtue of the positioning of the joystick between the two animals during the demonstration session. In order to respond in the same direction as its demonstrator by a visually mediated local enhancement process, an observer would, therefore, have to represent the side of the joystick which a demonstrator had manipulated in a form that is not tied to a specific vantage point. An allocentric representation would suffice if the joystick were to remain in the same position, relative to the observers' surroundings, for testing (standard conditions), but would no longer be reliable in the joystick-transfer condition in which the joystick is moved to a new position (Heyes et al.,

Another type of local enhancement process is a more plausible untested alternative explanation for the basic bidirectional control effect. Local enhancement effects, as they have been traditionally defined, encompass more phenomena than just those resulting from socially mediated visual exposure to stimuli or locations. An extensively studied type o f local enhancement effect is one in which lasting physical products of a demonstrator's behaviour, rather than direct observation of its behaviour, results in the increased exposure o f a conspecific to a specific location or object (e.g., Galef, 1996b; Galef & Kennett, 1987; Laland & Plotkin, 1991, 1993). Some form of stable product could be asymmetrically deposited onto a joystick during a demonstration session in the bidirectional control procedure as a result of the demonstrator pushing the joystick in a single direction. When encountering these putative demonstration session products, which might be social odours or food deposits, observers could be influenced to make contact with the same side of the joystick as had their demonstrator resulting in a demonstrator-consistent responding tendency. Because the demonstrators' direction of pushing would be physically marked upon the joystick, the direction of pushing would be coded in a viewpoint-free way. Furthermore, the influence of these olfactory cues could account for a demonstrator-consistent responding bias in the rats serving in the joystick-transfer condition of Heyes et al.'s (1992) experiment if the cues were stable enough to remain asymmetrically deposited upon a joystick even after relocation of the joystick. This, non-imitative, local-enhancement account of demonstrator- consistent responding effects is consistent with evidence that olfaction, rather than vision, tends to direct the control of movement in the rat (Schultz & Tapp, 1973; Whishaw & Tomie, 1989), and is examined further in Chapter 4.

c) A n effect o f exposure to the movements o f the manipulandum? The status of demonstrator-consistent responding as a measure of imitation has been questioned because, in the bidirectional control procedure, behavioural concordance is identified with types of joystick displacement that are recorded automatically without the presence of an investigator to observe the movements of the animals (Byrne & Tomasello, 1995). Directional concordance was considered by Byrne & Tomasello to be trivial, revealing little about the specificity with which observers' movements match those of their demonstrators. Dickinson et al.'s (1996) observational study has shown that there is some variability in the topography o f rats' joystick pushing; while the most commonly used method of moving a joystick is a push with a forepaw, some joystick displacements are brought about by rats' snouts.

Therefore, the use o f directionality to define sameness might tend to obscure non­ concordance in movements when they are described at a finer level o f description. In an exchange o f views with Byrne and Tomasello on the issue of how matching behaviour should be defined, Heyes (1995) has argued that concordance of movements described at the level of directionality is sufficient for a demonstration of imitation. The danger with this approach is that directionally-consistent responding could be described as an effect o f exposure to the movements of the manipulandum, rather than the movements of a demonstrator, if a mechanism could be postulated which, unlike egocentric or allocentric observational autoshaping, could account for demonstrator-consistent responding when the joystick is relocated (the Joystick-transfer condition, Heyes et al., 1992).

At least two accounts have recently been proposed for demonstrator-consistent responding in the joystick-transfer condition that take this finding to be an effect of exposure to the movements of a manipulandum. The following coding process was advanced by Byrne and Tomasello:

the joystick itself, and its position relative to a wall (any wall) is used as a landmark for orientation. Then...the observer notes the position of the stick and how it moves relative to the wire grid wall and then transfers that orientation to the joystick in its new position relative to the new wall it is up against.

(Byrne & Tomasello, 1995, p. 1419). Byrne and Tomasello's mechanism is too poorly specified to explain the difference in behaviour of observers of left and right pushing. As Heyes (1995) noted, joystick movement was parallel to the nearest wall for observers from both groups. In contrast, Heyes' most recent interpretation of the findings of the joystick-transfer condition could account for the difference in directional responding found for observers of left and right pushing demonstrators, and does so in terms of a sensitivity to the direction o f joystick movement rather than a sensitivity to the pushing movements of a demonstrator:

At minimum, they seem to be using the demonstrator's body, perhaps its vertical body axis, as a point of reference defining direction o f joystick movement, and identifying their own body as being at that reference point on test

(Heyes, 1996b, p. 376). In other words, demonstrator-consistent responding could be explained if observers represented the direction of joystick movement, and did so, not in relation to their own viewpoint at observation (egocentrically), nor in relation to their surroundings

(allocentrically), but in relation to the position from which the joystick could be manipulated by an agent (agentcentrically).

The foregoing analysis suggests that two conceptually distinct hypotheses remain as putative accounts for demonstrator-consistent responding in the bidirectional control procedure, if this effect were assumed to be caused by exposure to observable events occurring within a demonstration session. According to the imitation hypothesis, the key observed events are agentcentric representations o f demonstrators' movements. According to the alternative hypothesis, the key observed events are agentcentric representations o f joystick motion. B ecause the latter possibility might be described as the coding of the affordance of the joystick manipulandum, this non-imitative account will, following Tomasello et al. (1987), be referred to as the emulation hypothesis.

While these hypotheses can be conceptually distinguished in terms o f the content of agentcentric representations (body movements vs movements of the joystick), it is less clear how they might be ençirically distinguishable within the bidirectional control procedure (see Heyes, 1996b). This difficulty in finding differential predictions for the imitation and emulation accounts of demonstrator-consistent responding appears to underlie Heyes' willingness, in a defence of the bidirectional control procedure as evidence of imitation, to propose that the observers were sensitive to the movements o f the joystick. Indeed, when discussing how imitation should be defined, the empirical accessibility o f a psychological process identified with imitation was taken to be the primary consideration in the "realist" approach advocated by Heyes (see, e.g., Hull, 1984, for a discussion of realist and alternative positions in the philosophy of science). One reaction to this problem might be to suggest that imitation should be understood to involve a process through which events are represented relative to the point of reference of an agent, irrespective of whether the content of these representations are movements of the agent or changes in its inanimate world.

Alternatively, if the imitation and emulation hypotheses are, truly, untestable in the bidirectional control procedure, the weakness may be with the use o f this procedure as a research tool rather than with the hypotheses themselves. The reproduction o f object directed movements and the reproduction of non-object directed movements might be mediated by different psychological mechanisms, and this idea is pursued in Chapter 8. If this

w ere the case, the emulation hypothesis would be a credible alternative, non-imitative, account for demonstrator-consistent responding in the bidirectional control procedure.

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