Abstract
How stable and general is behavior once maximum learning is reached? To answer this question and understand post-acquisition behavior and its related individual differences, we propose a psychological principle that naturally extends associative models of Pavlovian conditioning to a dynamical oscillatory model where subjects have a greater memory capacity than usually postulated, but with greater forecast uncertainty. This results in a greater resistance to learning in the first few sessions followed by an over-optimal response peak and a sequence of progressively damped response oscillations. We detected the first peak and trough of the new learning curve in our data, but their dispersion was too large to also check the presence of oscillations with smaller amplitude. We ran an unusually long experiment with 32 rats over 3,960 trials, where we excluded habituation and other well-known phenomena as sources of variability in the subjects' performance. Using the data of this and another Pavlovian experiment by Harris et al. (2015), as an illustration of the principle we tested the theory against the basic associative single-cue Rescorla–Wagner (RW) model. We found evidence that the RW model is the best non-linear regression to data only for a minority of the subjects, while its dynamical extension can explain the almost totality of data with strong to very strong evidence. Finally, an analysis of short-scale fluctuations of individual responses showed that they are described by random white noise, in contrast with the colored-noise findings in human performance.
Highlights
How stable is behavior when there is nothing more to learn? Much debate has been flourished around this basic question since the earliest studies of animal conditioning (Pavlov, 1927), especially after the first efforts to make the discipline theoretically quantitative with a mathematical approach (Hull, 1943)
We can subtract the number of unconditioned stimulus (US), to the total number of licks per session and we identify v = − . (6)
Whenever we talk about licks during the conditioned stimulus (CS) in sessionby-session data, we imply that the number of unconditioned responses has been discounted
Summary
How stable is behavior when there is nothing more to learn? Much debate has been flourished around this basic question since the earliest studies of animal conditioning (Pavlov, 1927), especially after the first efforts to make the discipline theoretically quantitative with a mathematical approach (Hull, 1943). In the context of discrimination experiments of operant conditioning, extended training was studied in relation with behavioral contrast and the peak-shift effect. In an experiment lasting 64 sessions, Hearst (1971) did not observe this decrease from peak responding, sometimes called overtraining effect (as a reduction in behavioral contrast), inhibition with reinforcement, or post-peak depression (see Kimmel and Burns, 1975, for an early review and Behavior Stability in Pavlovian Conditioning other references). An attenuated conditioned responding with extended reinforced training has been observed in the case of Pavlovian conditioning, where it is modulated by the context (Overmier et al, 1979; Bouton et al, 2008; Urcelay et al, 2012). The experiments with dogs by Overmier et al (1979) showed response decrease on a time scale of 300 trials. On the other extreme of the spectrum, response fluctuations have been registered on the very short time scale of trial by trial (Ayres et al, 1979)
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