Learning with prolonged delay of reinforcement

Abstract

HARVARD MEDICAL SCHOOL AND NEUROSURGICAL SERVICE, MASSACHUSETTS GENERAL HOSPITALGustatory aversions, induced in rats by conditionally pairinfl a distinctive flavor with a noxious drug, were readily established wen when injections were delayed an hour or more. The optimal interstimulus interval and effectiveness of cues for learning appear to be a function of the specific effects of the reinforcer on the organism.It is considered axiomatic in theory and practice that no learning will occur without immediate reinforcement. For example, a hungry rat will not learn to press a lever for food unless the response is immediately followed by food (primary reinforcement) or by a signal which has been associated with food in the past (secondary reinforcement). Food can be described as rewarding, but the same general rule has been applied to punishing agents also. Delays of the order of 3 to 45 sec. have a deleterious effect upon learning in a wide variety of experimental situations. The significance of these findings for reinforcement theory was discussed by Spence (1947) and a recent review (Renner, 1964) reveals there has been no major modification of the temporal contiguity aspect. However, our data indicates that immediate reinforcement is not a general requirement for all learning. MethodYoung adult male rats (Sprague-Dawley, 300 to 400 gm)were maintained in individual cages with Purina Laboratory Chow ad lib. Drinking was restricted to a 10-min, period each day. After one week of habituation to this schedule, treatment began. In Experiment A, five groups (N = 8 each) were treated. One experimental group (Sac-Apo:inj) was given a gustatory cue in its drinking water (1 gm saccharine per liter) and after a delay was injected with a drug which produced gastriC disturbances (7mg/kg apomorphine hydrochloride I.P.). The animals were injected in serial order at I-min. intervals with the first animal injected at 5 min. and the last one at 12 min. after the saccharin water bottle was removed from the home cage. One control group (Sac-Sal:inj) drank saccharinwater and was injected with saline, while another control (Wat-Apo:inj) drank water and was injected with apomorphine. An additional experimental group (SacApo:inj) received delayed injections in serial order from 15 to 22 min. post-drinking. Other rats (Sac-Shock), immediately after drinking saccharin -water, were taken from their cages and placed in a box with an electric grid floor and three shocks (0.5 sec. pulses at 3 mal were delivered within 1 min. to the paws.All groups received four treatments, one every third day and then three extinction tests (Le. no injections or shock) on the same schedule. Between treatment days, the animals were given water for 10 min.

Changes in colored or flavored food preferences in chickens as a function of shock

“…The difference between the visual and gustatory {;onditions for the chkken, then, is in agreement with findings for the rat {Braveman & Capretta, 1965;. Capretta (1961) discussed such an effect in terms of "stimulus relevance," while Garcia, Ervin, & Koelling (1966) wisely conjectured that the bias toward associating gustatory cues with internal malaise rather than with peripheral pain is a result of natural sele{;tion acting in relation to the omnivorous feeding habits of the rat. Our fmdings for the chick would suggest a wider occurrence of the phenomenon.…”

Flavour–nutrient learning in humans: An elusive phenomenon?

“…Regardless of the cause, the finding that both FNL-H and FNL-S are less easily observed with extended rather than brief training clearly confirm that it is not possible to dismiss studies that failed to find evidence for altered behaviour to flavour CS, either in terms of liking or intake, as due to insufficient training trials. Some have argued that, as with classic findings from the study of CTA [49], the importance of learning about nutrient effects may also result in a single trial being adequate for FNL-S [9]. Since both the flavour CS and nutrient consequence are relatively long-lasting stimuli, unlike the brief stimuli used in more traditional forms of learning, this idea is not inconsistent with current theories of the nature of association learning.…”

Food preferences and aversions in human health and nutrition: how can pigs help the biomedical research?

“…Significant aversions also develop to the CS despite long delays between exposure to the CS and US (Garcia et al, 1966). However, one should keep in mind that, for practical purposes, preferences are often stronger to acquire than aversions and their acquisition often requires more than one association to achieve a strong and long-lasting effect, although some studies in rats showed that the acquisition of a preference can be rapid (Myers, 2007;Ackroff et al, 2009).…”