Biomedical subjects

Anthony P McLean

Publications and source records attributed to Anthony P McLean.

4 recordsLinked to original sources

PubMed2006

The sampling distribution of kappa.

Research on Herrnstein's single-schedule equation contains conflicting findings; some laboratories report variations in the k parameter with reinforcer value, and others report constancy. The reported variation in k typically occurs across very low reinforcer values, and constancy applies across higher values. Here, simulations were conducted assuming a wide range of reinforcer values, and the parameters of Herrnstein's equation were estimated for simulated responding. In the simulations, responses controlled by current reinforcement contingencies were added to other responses ('noise'), controlled by the experimental environment and by contingencies in effect at other times. Expected reinforcer rates were calculated by entering simulated responding into a reinforcement feedback function. These were then fitted using Herrnstein's hyperbola, and the sampling distributions of the two fitted parameters were studied. Both k and Re were underestimated by curve fitting when low-deprivation or reinforcer-quality conditions were simulated. Further simulations showed that k and Re were increasingly underestimated as the assumed noise level was increased, particularly when low-deprivation or reinforcer quality was assumed. It is concluded that reported variations in k from single schedules should not be taken to indicate that the asymptotic rate of responding depends on reinforcement parameters.

Animals↗

PubMed2006

Rapid acquisition in concurrent chains: evidence for a decision model.

Pigeons' choice in concurrent chains can adapt to rapidly changing contingencies. Grace, Bragason, and McLean (2003) found that relative initial-link response rate was sensitive to the immediacy ratio in the current session when one of the terminal-link fixed-interval schedules was changed daily according to a pseudorandom binary sequence (e.g., Schofield & Davison, 1997). The present experiment tested whether the degree of variation in delays across sessions had any effect on acquisition rate in Grace et al.'s (2003) rapid-acquisition procedure. In one condition ("minimal variation"), the left terminal link was always fixed-interval 8 s and the right terminal link was either fixed-interval 4 s or fixed-interval 16 s. In the other condition ("maximal variation"), a unique pair of fixed-interval values was used in each session. Responding was sensitive to the current-session immediacy ratio in both conditions, but across subjects there was no systematic difference in sensitivity. These results challenge the view that initial-link responding in the rapid-acquisition procedure is determined by changes in the learned value of the terminal-link stimuli, and suggests instead that a process resembling categorical discrimination may control performance. A decision model based on the assumption that delays are categorized as short or long relative to the history of delays provided a good account of the data and shows promise in being able to explain other choice phenomena.

Animals↗

PubMed2005

Integrated versus segregated accounting and the magnitude effect in temporal discounting.

Temporal discounting rates in humans generally decrease as the amount of reward increases, a phenomenon known as the magnitude effect. In the present study, we examined whether temporal discounting and the magnitude effect are related to segregation of choices in terms of gains or losses for waiting for or expediting receipt of a reward. Subjects (N = 24) responded to a series of hypothetical choices about amounts of money available either immediately or after a delay. The immediate and delayed amounts either were presented as integrated amounts in the baseline condition or were segregated as differential gains or losses for choosing delayed or expedited consumption (delay and speedup conditions, respectively). Temporal discounting rates decreased in the segregated conditions, in accord with the standard discounted utility model but contrary to the hypothesis that the subjects were choosing on the basis of reward differentials in the baseline condition. The size of the magnitude effect was comparable in the baseline and the delay conditions but decreased in the speed-up condition. These results challenge explanations of the magnitude effect in terms of an increasing proportional sensitivity property of the utility function (Loewenstein & Prelec, 1992) and the hypothesis that subjects choose on the basis of differentials even when the rewards are presented as integrated amounts.

Accounting↗

PubMed2003

Rapid acquisition of preference in concurrent chains.

We report two experiments using a concurrent-chains procedure in which one terminal-link schedule was fixed-interval 8 s and the alternative schedule changed randomly from day to day. In Experiment 1, the alternative schedule varied between 4 s and 16 s according to a pseudorandom binary sequence similar to the one used by Hunter and Davison (1985). Similar to results with concurrent schedules, pigeons' response allocation in the initial link was most sensitive to the schedules arranged in the current session, although some effect of prior history was evident. Overall sensitivity was lower than for comparable data from steady-state research. In Experiment 2, a unique value between 2 s and 32 s was used for the alternative-schedule delay in each session. Sensitivity levels were similar to Experiment 1 and remained unchanged across 61 sessions of training. For all subjects, sensitivity was greater when the alternative-schedule delay was greater than 8 s compared with when it was less than 8 s. Generalized-matching plots revealed evidence of clustering of data points into two groups for some pigeons, suggesting that a process similar to a categorical discrimination may have at least partly determined response allocation. Overall, this research shows that pigeons' initial-link response allocation can adjust rapidly to frequent changes in the terminal links.

Animals↗