Modificación del polímero VKVx24 con un derivado de ciclooctino

The subjects were 40 male hooded Lister rats, obtained from the same supplier, maintained under the same conditions, and of approximately the same age as those from Experiment 1.

O f these, 8 had been trained to be, and performed as, demonstrators in an earlier experiment. The other 32 were experimentally naïve, and served as observers.

The animals were trained and tested in the same four operant chambers that had been used in Experiments 1-3. However, the experimental room in which these chambers was situated was blacked out for the course o f Experiment 4; E could not see anything in the room after light adaptation.

Procedure

The demonstrators and observers were prepared for testing in the same way as those that served in Experiment 3, except that, in preparation for an earlier experiment, equal numbers

(n = 4) o f the demonstrators had been trained, by conventional methods, to respond discriminatively either to the left, or to the right. These demonstrators were given two sessions o f top-up training prior to serving in Experiment 4.

Demonstration and Testing. The observers were subjected to the conventional NDR procedure, as described in Experiment 1, with the following exceptions.

Regardless o f the subjects' group assignment, demonstration sessions commenced and were ended in darkness. Just before the demonstration session was started, and with the observers already in place, demonstrators were introduced into the test compartments in complete darkness; no light entered the operant chamber from the blacked out experimental room and the houselights within the operant chambers were switched off. At the end of each demonstration session, and with the house light again off, demonstrators were removed from the test compartments in darkness. This procedure ensured that no animals were able to observe a demonstrator manipulate the joystick either before or after a demonstration session.

Three factors, each with two levels, were factorial manipulated between subjects. The 4 observers living in each of eight housing cages were randomly assigned to one of the resulting eight groups. The location of putative lasting effects of demonstration sessions laid down by the demonstrator to which the subject had been exposed was manipulated in the following manner. Observers assigned to groups in which the last coding term was "L"

(Groups li-(L)-L, li-(R)-L, dk-(L)-L and dk-(R)-L) were present in the observation chamber while one of the demonstrators that had been trained to push the joystick to the left completed a demonstration session in which left responses were reinforced. The remaining observers, those assigned to groups in which the last coding term was "R" (Groups li-(L)-R, li-(R)-R, dk-(L)-R and dk-(R)-R), were exposed to a session in which right responses made by one of the right trained demonstrators were reinforced.

Whether observers had visual access to the direction that its demonstrator had pushed the Joystick was also manipulated. Observers assigned to groups in which the first coding term was "li" (Groups li-(L)-L, li-(L)-R, li-(R)-L and li-(R)-R) did have visual access to their demonstrator during the demonstration session. The houselight was illuminated at the beginning o f the demonstration session, and was switched off when the final reinforcer had been collected. In contrast, the houselight remained off during the demonstration session for observers assigned to groups in which the first coding term was "dk" (Groups dk-(L)-L, dk- (L)-R, dk-(R)-L and dk-(R)-R) so that these animals were not able to observe their demonstrator responding.

An additional manipulation was the location of any lasting effects of the demonstration session prior to the one to which the observer had been exposed. This was carried out by balancing the order in which the animals were tested, such that the direction in which the immediately preceding demonstrator had pushed the joystick was independently varied. Observers assigned to groups in which the middle coding term was "(L)" (Groups li-(L)-L, li-(L)-R, dk-(L)-L and dk-(L)-R) had demonstration and test sessions immediately after an observer that had been exposed to a left responding demonstrator had been tested. Observers assigned to groups in which the middle coding term was "(R)" (Groups li-(R)-L, li-(R)-R, dk- (R)-L and dk-(R)-R) followed the testing of an observer that had been exposed to a right responding demonstrator.

Results and Discussion

Six of the observers failed to make 50 reinforced responses during 40 minutes of testing and were excluded from the analysis. These animals had been assigned to the following groups: 2 from Group li-(L)-R, and 1 from each of Groups li-(R)-R, dk-(L)-L, dk-(L)-R and dk-(R)-

Figure 4.1: Mean discrimination ratios (responses to the left / responses to the left + responses to the right) for all groups from Experiment 4. "li", demonstration session illuminated; "dk", demonstration session in the dark; "(L)", previous demonstrator pushed to the left; "(R)", previous demonstrator pushed to the right; L, exposure to left demonstration; R, exposure to right demonstration. Error bars represent SEM.

L (Left) □ R (Right)

%

L. In all but 2 of the demonstration sessions to which the remaining 26 observers had been exposed, the demonstrators showed perfect discrimination. In the remaining demonstration sessions, to observers from Groups ü-(R)-L and dk-(R)-L, the demonstrators made only one response in the untrained and unreinforced direction.

Figure 4.1 displays the group-mean discrimination ratio for each group. Discrimination ratios were computed by dividing the number of left responses by the total number o f responses made in the test session. These data appear to indicate that, in this experiment, manipulation o f the direction o f demonstrator responding to which observers were exposed was not sufficient to result in demonstrator-consistent responding; the discrimination ratios for observers from groups that had been exposed to left pushing demonstrators (Groups li-(L)-L, li-(R)-L, dk-(L)-L and dk-(R)-L) do not appear to have tended to be greater than those from groups that had been exposed to right pushing demonstrators (Groups li-(L)-R, li-(R)-R, dk- (L)-R and dk-(R)-R). This appears to have been the case both for those groups in which observers had been exposed to their demonstrator in the dark, and for those groups in which observers had additionally had visual access to the responses made by their demonstrator.

However, the data illustrated in Figure 4.1 do suggest that manipulation of the direction of responding of the demonstrator that had served in the previous demonstration session may, under certain circumstances, influence observers' direction of responding. For those observers in groups exposed to a demonstration session in the dark, a stronger left preference appeared to have occurred if they had followed the testing of an observer that had been exposed to a left pushing demonstrator (Groups dk-(L)-L and dk-(L)-R) than if they had followed observers exposed to right pushing demonstrator (Groups dk-(R)-L and dk-(R)-R). This type of demonstrator-consistent responding effect did not appear to be present for those groups in which observers were able to view their demonstrators' responses.

These impressions were supported when the data were subjected to a three factor ANOVA of exposed-demonstrator's direction x availabihty of visual information x previous- demonstrator's direction. This revealed no main effects of exposed-demonstrator's direction or availability of visual information, both Fs < 1. However, those observers in groups following the testing of an animal exposed to a left pushing demonstrator tended to make more left responses than those observers in groups that had followed the testing o f an animal

exposed to a right pushing demonstrator, F (l,1 8 ) = 4.60, p = 0.046. This main effect of previous-demonstrator's direction should be interpreted in light o f the only interaction which approached statistical significance, that between previous-demonstrator's direction and availability of visual information, F (l,1 8 ) = 3.57, p = .075. When this interaction was examined further with simple effects, this demonstrator-consistent responding effect was found to be confined to observers from groups that had been exposed to their demonstrator responding in the dark. Observers fi*om Groups dk-(L)-L and dk-(L)-R tended to make more left responses than those from Groups dk-(R)-L and dk-(R)-R, F (l,1 8 ) = 8.31, p = .010, while observers from Groups li-(L)-L and li-(L)-R did not differ in directional preference from those from Groups li-(R)-L and li-(R)-R, F < 1.

On the whole, the results of Experiment 4 were disappointing. Observers' directional joystick pushing was not found to be influenced by the responding direction of the demonstrator to which they had been exposed. This lack of a demonstrator-consistent responding effect was found to be just as absent for the groups of observers that had visual access to demonstrated responses as it was for the groups of observers that could not observe these responses. Testing after exposure to an illuminated demonstration session was expected to result in demonstrator-consistent responding, because it was a prediction of the odour hypothesis as well as the conventional imitation account of the findings of bidirectional control experiments. While these null results do not provide differential support for either hypothesis, they are consistent with the suggestion that the bidirectional control procedure is not a sensitive measure of putative imitation effects (see Chapters 3, 5, and 6).

One intriguing finding, which has implications for the odour hypothesis, was the novel demonstrator-consistent responding effect of previous demonstrator direction. For half the observers, those firom groups which were exposed to a demonstration session that occurred in darkness, directional responding tended to be consistent with that of the demonstrator that had performed in the test chamber one demonstration session earlier. This effect provides some support for the odour hypothesis. Demonstration sessions which these observers had not been able to witness had an effect on the directionality of their joystick pushing. This suggests that detectable physical traces of a demonstration session can result in demonstrator-consistent responding, and that these deposits have a relatively long lasting influence, vindicating the decision to control running order. However, the failure to find a

similar effect for the remaining observers, those from groups which were able to watch the joystick pushes of their demonstrator, is difficult to interpret. It might suggest that exposure to demonstration session deposits and observation of joystick pushing have different types o f influence upon observers' behaviour which are prone to subtle interactions, but the nature o f this interaction is not obvious. Because the results of Experiment 4 encourage further investigation of the odour hypothesis, a discussion of the relative roles played by exposure to demonstration session products and visual information in producing demonstrator- consistent responding effects is postponed until later in this chapter.