Delayed matching to sample: reinforcement has opposite effects on resistance to change in two related procedures

Abstract

The effects of reinforcement on delayed matching to sample (DMTS) have been studied in two within-subjects procedures. In one, reinforcer magnitudes or probabilities vary from trial to trial and are signaled within trials (designated signaled DMTS trials). In the other, reinforcer probabilities are consistent for a series of trials produced by responding on variable-interval (VI) schedules within multiple-schedule components (designated multiple VI DMTS). In both procedures, forgetting functions in rich trials or components are higher than and roughly parallel to those in lean trials or components. However, during disruption, accuracy has been found to decrease more in rich than in lean signaled DMTS trials and, conversely, to decrease more in lean than in rich multiple VI DMTS components. In the present study, we compared these procedures in two groups of pigeons. In baseline, forgetting functions in rich trials or components were higher than and roughly parallel to those in lean trials or components, and were similar between the procedures. During disruption by prefeeding or extinction, accuracy decreased more in rich signaled DMTS trials, whereas accuracy decreased more in lean multiple VI DMTS components. These results replicate earlier studies and are predicted by a model of DMTS from Nevin, Davison, Odum, and Shahan (2007).

Figure 1

The left panel presents average steady-state forgetting functions obtained by Nevin and Grosch (1990) trials with signaled large-magnitude and small-magnitude reinforcers; retention intervals varied across subjects, always in the ratios 1:2:3. The right panel shows the value of logit p, averaged across retention intervals, as a proportion of average logit p for the steady-state functions at the left, during three disruptors: Injections of sodium pentobarbital (NaPB), flashing houselight during the retention interval, and reduced sample duration. Error bars are omitted because the individual data have been lost.

Figure 2

The left panel presents average steady-state forgetting functions obtained by Odum et al. (2005) for VI DMTS components with high-probability (rich) or low-probability (lean) reinforcers. The right panel shows the value of log d, averaged across retention intervals and expressed as a proportion of average log d for the steady-state functions at the left, for two disruptors: Presentation of food during the ICI, and extinction. Standard errors are indicated by range bars.

Figure 3

The sequence of events within a trial in the VI DMTS procedure. The center key color before and after sample presentation signals the reinforcer probability. See text for complete description.

Figure 4

The sequence of events within a trial in the signaled trials procedure. The geometric figure projected on the center key throughout the trial signals the reinforcer probability. See text for complete description.

Figure 5

Forgetting functions averaged over five pigeons and pooled for 10 sessions of baseline training before each of the four resistance tests for multiple VI DMTS (left panel) and signaled trials (right panel); standard errors are indicated by range bars.

Figure 6

Values of log d during resistance tests, averaged across retention intervals and expressed as a proportion of average log d for the steady-state functions in the immediately preceding baseline in multiple VI DMTS (left panel) and signaled trials (right panel) for rich and lean components or trials for all four disruptors: Dissamp = flashing lights during samples; Discomp = flashing lights during comparisons; PF = prefeeding; and Ext = extinction. Standard errors are indicated by range bars.

Figure 7

The average differences between proportions of baseline log d in rich and lean multiple VI DMTS components and signaled trials during prefeeding and extinction (left and center-left histogram bars). Positive values signify greater resistance to disruption in rich components or trials; standard errors are indicated by range bars. The center-right and right histogram bars exhibit the differences predicted by the model of Nevin et al. (2007) when the probability of attending to the sample, p(A_s), is reduced by increasing parameter x in Equation 2 or when the probability of attending to the comparisons, p(A_c), is reduced by increasing parameter z in Equation 3; see Discussion and Appendix for explanation and calculation.

Figure 8

Time-line diagram of experimentally arranged events within a DMTS trial, and the times during which the subject is assumed to attend to the sample and comparisons. Times during which reinforcers and disruptors are assumed to operate on attending to samples or comparisons are also indicated. (Reproduced with permission from Nevin et al., 2007.)