A note on behavioural contrast and frustration

The suggestion has been made that positive contrast, the increase in response rate in one successively-presented stimulus following a change in conditions that decreases responding in the other, may not depend on differential stimulus control. Evidence is reviewed suggesting that contrast effects on most multiple interval schedules do depend upon discrimination, but that effects similar to contrast that result from the omission of reinforcement on fixed-interval schedules (the frustration/omission effect) reflect other factors. The link between contrast and the omission effect is the discrimination mechanism which allows animals to respond only at times or places correlated with food delivery. Contrast is a direct result of this mechanism; but the omission effect depends on the difference between the inhibitory discriminative after-effects acquired by food on fixed-interval schedules, and those acquired by a “neutral” stimulus presented in its place.     

Determinants of cumulative successive contrast in saltiness intensity judgments

When all stimuli elicit the same taste quality, solutions preceded by a high concentration level are judged to be significantly less intense than solutions preceded by a low concentration level. After repetitious stimulation with a different tasting stimulus, the intensity of the present stimulus is overestimated. This phenomenon is called “successive contrast.” In the present study, the cumulative effects of three identical stimuli on the saltiness ratings for a test stimulus are investigated. The preceding stimuli are manipulated with regard to taste quality, saltiness intensity, total taste intensity, and complexity. Whether the size of the cumulative contrast effect is associated with the degree of dissimilarity between preceding stimuli and test stimulus, or with the saltiness or total taste intensity of the preceding stimuli, is investigated. The size of the contrast effect depends on the type of preceding stimulus, its intensity, and the type of test stimulus. No association was found with judgments of the degree of dissimilarity between the preceding stimuli and the test stimulus. For nonsalty preceding stimuli, the contrast effects are independent of concentration level. When the preceding stimuli taste at least partly salty, the total intensity appears to determine the size of the contrast for an unmixed salty test stimulus.     

Transfer and non-transfer successive incentive contrast effects in the rat

Recent evidence concerning successive incentive contrast suggests the occurrence of both positive and negative contrast effects under both non-transfer and transfer conditions. There are three types of explanation for these contrast effects, based on frustration theory, sequential theory and adaptation level theory (perceptual accounts). One of the critical experiments favouring perceptual accounts, Collier and Marx (1959), is subject to a number of methodological criticisms. This experiment was repeated, with modifications to take account of these criticisms, and extended to include transfer, as well as non-transfer, conditions. There was no evidence of contrast. In a further experiment using Collier and Marx's procedure with lever pressing and panel pushing, positive and negative, transfer and non-transfer effects were found using Noyes pellets rather than sucrose as reward. It is suggested that these results contribute some support to perceptual accounts of incentive contrast, although no present theory is entirely satisfactory.     

A reappraisal of successive negative contrast in two populations of domestic dogs

When an anticipated food reward is unexpectedly reduced in quality or quantity, many mammals show a successive negative contrast (SNC) effect, i.e. a reduction in instrumental or consummatory responses below the level shown by control animals that have only ever received the lower-value reward. SNC effects are believed to reflect an aversive emotional state, caused by the discrepancy between the expected and the actual reward. Furthermore, how animals respond to such discrepancy has been suggested to be a sign of animals’ background mood state. However, the occurrence and interpretation of SNC effects are not unequivocal, and there is a relative lack of studies conducted outside of laboratory conditions. Here, we tested two populations of domestic dogs (24 owned pet dogs and 21 dogs from rescue kennels) in a SNC paradigm following the methodology by Bentosela et al. (J Comp Psychol 123:125–130, 2009), using a design that allowed a within-, as well as a between-, subjects analysis. We found no evidence of a SNC effect in either population using a within- or between-subjects design. Indeed, the within-subjects analysis revealed a reverse SNC effect, with subjects in the shifted condition showing a significantly higher level of response, even after they received an unexpected reduction in reward quality. Using a within-, rather than a between-, subjects design may be beneficial in studies of SNC due to higher sensitivity and statistical power; however, order effects on subject performance need to be considered. These results suggest that this particular SNC paradigm may not be sufficiently robust to replicate easily in a range of environmental contexts and populations.     

Percentage body weight and the successive negative contrast effect in rats

In two runway experiments employing rats the successive negative contrast effect was evaluated for animals maintained at high or low body weights. In both experiments the effects on performance of shifting reward magnitude were independent of body weight. These results contrast with those of previous studies in which the successive negative contrast effect occurred only under low body weight. It was suggested that when conditions are maximal or near maximal for production of the successive negative contrast effect, as they were here but not in previous investigations, body weight will not influence the size of this effect.     

Successive positive contrast in one-way avoidance learning

The main finding of these experiments was a positive contrast effect in one-way avoidance learning. Experiment 1 showed that increasing safety time during one-way avoidance training led to improved performance, surpassing that of a control group that had received the high reward (safe time) from the beginning of training. Experiment 2 showed that a similar positive contrast effect occurred when the time spent in the danger compartment before the onset of the warning signal was shortened. These results suggest that time spent in a safe context acts as a reinforcer of the avoidance response; however, its incentive value depends not only on its duration, but also on the length of the time spent in the danger compartment before the onset of the signal. Overall, results also suggest that the avoidance response is a mixture of flight (motivated by fear) and approach (to a safe place) behaviour. The specific weight of the flight or approach component may be a function of the time and the amount of activation of each emotional state (fear or relief) due to opponent homeostatic compensatory processes that occur in the danger and safe compartments during one-way avoidance learning.     

Some limitations on behavioral contrast and induction during successive discrimination

A pigeon's rate of pecking on a red key, reinforced at a constant frequency, may be changed by increasing or decreasing the frequency of reinforcement of pecking on a successively presented green key. The changes in the rate of pecking on red, called interactions, are of two types: contrast, in which the changes in the rates of pecking on the two colors are in opposite directions; and, induction, in which the changes in the rates are in the same direction. In previous data, a change in the frequency of reinforcement associated with the green key produced a corresponding change in the rate of pecking the green key and an opposite change (contrast) in the rate of pecking on the red key. The present data suggest that the magnitude of contrast is very small if pecking on the red key is reinforced at a high enough frequency (about 40 reinforcements per hr in the present experiment). Also, given that interactions occur, induction rather than contrast may result from small changes in a low frequency of reinforcement associated with green.     

Within-subjects positive and negative contrast effects in rats.

Rats were given alternating 1-min. access periods to 2 tubes containing either 32% or 4% sucrose solutions for daily 6-min. test sessions. Lick rate for 32% was higher under comparison (32 vs. 4) than noncomparison (32 vs. 32) conditions; and lick rate for 4% was lower under comparison conditions (4 vs. 32) than under noncomparison conditions (4 vs. 4). All sucrose conditions were varied within subjects and both positive and negative contrast were obtained with a small n. In addition to lick rate, intake and latency measures also revealed contrast effects. Deprivation conditions altered latency but not lick rate measures of contrast. Reducing the test session to 3 min. (alternating 30-sec. access periods) did not greatly affect contrast. Additional experiments provided evidence for distinct within-days and between-days contrast effects, as well as a between-groups contrast effect.     

Spontaneous recovery of consummatory behavior, but not of consummatory successive negative contrast

Five experiments were designed to study spontaneous recovery (SR) in two situations involving consummatory behavior: consummatory successive negative contrast (cSNC) and consummatory extinction (cE). SR of consummatory suppression should occur if incentive downshift induces an egocentric memory encoding information about the emotional reaction to the downshift that is counterconditioned or extinguished during exposure to the downshifted reward. SR of cSNC failed to occur after resting periods of 24, 96, or 336 h interpolated following complete (Experiment 1) and incomplete (Experiment 2) recuperation of consummatory behavior, and was not induced by the opioid-receptor antagonist naloxone (2 mg/kg), known to enhance cSNC (Experiment 3). However, SR of consummatory behavior occurred across sessions in cSNC (Experiment 3) and cE (Experiments 4-5). Furthermore, naloxone facilitated cE without affecting SR (Experiments 4-5). These results are discussed in relation to evidence for the development of an egocentric memory of the aversive downshift experience in consummatory situations.     

Behavioural contrast does not occur with continuous reinforcement in the positive component

An experiment reported by Jenkins (1961) obtained positive behavioural contrast in a discrimination with continuous reinforcement of the positive stimulus. A large body of research, however, has failed to obtain positive contrast with this type of schedule. Jenkins's experiment was repeated with an added control group matched to the discrimination group in number of nonreinforced components. No positive contrast was obtained, and it was concluded that Jenkins's result could not be interpreted as positive contrast. The implications of this result for some theoretical accounts of positive contrast were discussed.