The Rescorla-Wagner model: losses in associative strength in compound conditioned stimuli

This series of experiments demonstrated that compound conditioned stimuli (CSs) highly conditioned in isolation lose conditioned response strength when compound-CS-unconditioned stimulus (US) pairings are given. This loss in conditioned responding was a positive function of the number of compound-CS-US pairings and was greater for the more salient stimulus. Finally, if a previously neutral stimulus was compounded with two previously conditioned cues, the neutral stimulus could acquire conditioned inhibitory properties with only compound-CS-US pairings. These results provide support for some aspects of the Rescorla-Wagner model.     

Unequal associative changes when excitors and neutral stimuli are conditioned in compound

In four experiments a compound of a previously conditioned excitor and a neutral stimulus was either reinforced with food or nonreinforced. Two experiments used a magazine approach procedure in rats, and two used an autoshaping procedure in pigeons. All experiments employed a novel compound test procedure, which permitted evaluation of the size of the associative change that took place for the excitatory and neutral stimuli. Reinforcement of the compound resulted in greater increments in the associative strength of the neutral stimulus than of the excitor. Nonreinforcement of the compound resulted in greater decrements in the associative strength of the excitor than of the neutral stimulus. These results agree with earlier experiments with compounds of excitors and inhibitors and provide an additional challenge to contemporary error-correction models of conditioning.     

Further evidence for the summation of latent inhibition and overshadowing in rats’ conditioned taste aversion

Repeated exposures to a target taste (X) attenuated subsequent development of rats’ conditioned aversion to X (latent inhibition effect). Presentation of another taste (A) after X in conditioning (serial X-A compound conditioning) also attenuated conditioned X aversion compared with conditioning without A (overshadowing). Furthermore, the latent inhibition and overshadowing effects summed to show the least conditioned aversion in the rats given both the target preexposures and the serial X-A compound conditioning treatment. These results question the validity of the comparator hypothesis as an explanation for Pavlovian conditioning of rats’ conditioned taste aversion.     

Enhancement and summation in the perception of two successive vibrotactile stimuli

Enhancement and summation were found to be fundamentally different perceptual processes affecting the sensation magnitude of two successive vibrotactile stimuli. Enhancement, defined operationally as an increment in the subjective magnitude of one stimulus due to the presentation of a prior stimulus, and summation, defined as an increment in overall subjective magnitude of the two stimuli, were measured for sinusoidal vibration of the thenar eminence of the hand. The effect of summation was maximum when the two stimuli greatly differed in frequency, whereas maximum enhancement effects were found when both stimuli were close in frequency. The summation effect showed little decay as the interstimulus interval was increased to as much as 500 msec, whereas enhancement effects decayed to zero at approximately 500 msec. Results were similar to those obtained in comparable studies of audition and support the hypothesis that there are at least two distinct information-processing channels for the perception of cutaneous vibration.     

Elemental representations of stimuli in associative learning

This article reviews evidence and theories concerning the nature of stimulus representations in Pavlovian conditioning. It focuses on the elemental approach developed in stimulus sampling theory (R. C. Atkinson & W. K. Estes, 1963; R. R. Bush & F. Mosteller, 1951b) and extended by I. P. L. McLaren and N. J. Mackintosh (2000, 2002) and contrasts this with models that invoke notions of configural representations that uniquely code for different patterns of stimulus inputs (e.g., J. M. Pearce, 1987, 1994; R. A. Rescorla & A. R. Wagner, 1972; A. R. Wagner & S. E. Brandon, 2001). The article then presents a new elemental model that emphasizes interactions between stimulus elements. This model is shown to explain a range of behavioral findings, including those (e.g., negative patterning and biconditional discriminations) traditionally thought to be beyond the explanatory capabilities of elemental models. Moreover, the model offers a ready explanation for recent findings reported by R. A. Rescorla (2000, 2001, 2002b) concerning the way that stimuli with different conditioning histories acquire associative strength when conditioned in compound.     

Spatial summation in the evoked cortical response to auditory stimuli

Six Ss were presented monaurally and binaurally with stimuli of 0.5, 2.0, and 4.0 kHz at 40 and 70 dB sensation levels. Their computer averaged evoked potentials indicated substantially larger amplitudes (N₁ -P₂) with bilateral stimulation, regardless of frequency. Stimulation at 70 dB SL gave greater responses than that to 40 dB.     

Deprivation and reward stimuli as compound stimuli

In Experiment 1 the experimental group was tested with a deprivation level and a reward magnitude which it had experienced previously but which it had not experienced in combination. This group was inferior in test performance to a group which had experienced the test deprivation-reward combination prior to test. These results were interpreted as indicating that deprivation stimuli and reward stimuli form a compound stimulus and training on the elements of the compound produces performance inferior to training directly on the compound. In Experiment 2, the decrement associated with two different shifts in deprivation and reward did not differ despite the different size change of total incentive involved in the two shifts. The results were interpreted as indicating that the deprivation-reward stimulus is not produced by a single underlying incentive mechanism.     

The overshadowing of background stimuli: Some effects of varying amounts of training and ucs intensity

Two experiments investigated the capacity of a nominal CS to overshadow background stimuli. Rats received CS-shock pairings in one compartment of a double compartment apparatus. After training the shock compartment was represented, but in the absence of both the CS and shock. Overshadowing was then assessed by measuring rats' latency to enter this compartment. If rats readily entered the shock compartment this indicated that the background cues in that compartment had acquired little or no associative strength during training, and overshadowing was therefore inferred. If however rats avoided the shock compartment, then this indicated that the background stimuli must have become aversive during training, and overshadowing could not then be inferred. In both experiments it was found that the capacity of a CS to overshadow background stimuli was directly related to the amount of training given. The experiments also showed that this capacity is inversely related to shock intensity. The results are discussed in terms of Rescorla and Wagner's (1972) model of conditioning.     

Generalization decrement and not overshadowing by associative competition among pairs of landmarks in a navigation task

When they are trained in a Morris water maze to find a hidden platform, whose location is defined by a number of equally spaced visual landmarks round the circumference of the pool, rats are equally able to find the platform when tested with any two of the landmarks (Prados, & Trobalon, 1998; Rodrigo, Chamizo, McLaren, & Mackintosh, 1997). This suggests that none of the landmarks was completely overshadowed by any of the others. In Experiment 1 one pair of groups was trained with four equally salient visual landmarks spaced at equal intervals around the edge of the pool, while a second pair was trained with two landmarks only, either relatively close to or far from the hidden platform. After extensive training, both male and female rats showed a reciprocal overshadowing effect: on a test with two landmarks only (either close to or far from the platform), rats trained with four landmarks spent less time in the platform quadrant than those trained with only two. Experiment 2 showed that animals trained with two landmarks and then tested with four also performed worse on test than those trained and tested with two landmarks only. This suggests that generalization decrement, rather than associative competition, provides a sufficient explanation for the overshadowing observed in Experiment 1. Experiment 3 provided a within-experiment replication of the results of Experiments 1 and 2. Finally, Experiment 4 showed that rats trained with a configuration of two landmarks learn their identity.     

Drug-preexposure effects in flavor-aversion learning: associative interference by conditioned environmental stimuli

Previous research has documented that exposure to a drug reduces the ability of the drug to support subsequent flavor-aversion learning. The four experiments reported here examined the hypothesis that this drug-preexposure effect is due to associative interference from environmental stimuli associated with the drug effects during preexposure. When distinctive environmental stimuli (confinement in a black compartment) were present during drug preexposure, these stimuli significantly disrupted subsequent flavor-aversion learning. Furthermore, flavor conditioning was not significantly disrupted when drug preexposure occurred in the absence of salient environmental stimuli or when the previously conditioned environmental stimuli were extinguished prior to flavor conditioning. It is significant, and in contrast to other published research, that flavor conditioning was not disrupted when the distinctive cues paired with the drug during preexposure were absent at the time of the flavor-drug pairing. These results are thus consistent with results from conventional studies of stimulus blocking and suggest that associative processes can play a major role in the drug-preexposure effect.     

Roles of the qualities and locations of stimuli and responses in simple associative learning

The Quality-Location Phenomenon is defined by the previous research of Lawicka (1964 and 1969) in which dogs easily learn go/no-go tasks to differences in stimulus quality and go-left/go-right tasks to differences in stimulus location whereas the opposite pairings of tasks and stimulus attributes are difficult to learn. The Lawicka-Konorski explanation in terms of drive differentiation and response selection is described, and a new hypothesis, the Quality-Location Hypothesis, is offered. This hypothesis states that the quality of a stimulus best serves as a cue for the quality of a response, whereas the location of a stimulus best serves as a cue for the location of a response. The evidence for the hypothesis is reviewed, and experimental considerations for its evaluation are mentioned.     

Size-weight interaction in judgements of compound stimuli

Recent work in the fields of multidimensional information transmission and perceptual accentuation due to value has led to theories concerning unidimensional judgements of compound stimuli. The present study attempts to explore these theories, adding the dimension of size to judged weight, following negative results with judgements of size when brightness is varied.

Three sets of stimulus objects were prepared. Variation of weight was the same in each set. However, the size of the objects was the same in one set, while in another set size increased with weight, and in a third set size and weight were negatively correlated. Three groups of 16 subjects were asked to make replicated absolute judgements of the weights in each set.

It appeared that judgements of weight are more affected by density when density varies than when changes of size produce constant density. As predicted, contrast between successive stimuli is greatest when size and weight are negatively correlated, and least with positive correlation. The extent of the judged scales, and the means of these scales, follow the same pattern. Differences in discriminability between the three series, whilst in the expected direction, are not significant. The hypothesis that these effects would be more apparent in the psychologically linked dimensions of size and weight, than in the relatively neutral case of size and brightness, was largely confirmed. These findings both amplify and modify the previous suggestions concerning compound stimuli.     

Auditory–Visual stimuli: Effects on derived relations with compound stimuli

This research explored the effect of teaching conditional discriminations with three procedures on the derivation of 36 stimuli relations (derived relations). The stimuli used consisted of three characteristics musical instruments, along with the corresponding picture. In the first experiment six university students were trained with simple stimuli and tested with compound auditory–visual samples; therefore, a one‐to‐many structure was used. In the second experiment, auditory stimuli were replaced by visual stimuli, for the samples used, for new students. A third experiment was implemented with an extra phase of training with compound stimuli for six new students. The structure of the experiments was: pretests (Xbcd–A; Xacd–B; Xabd–C; Xabc–D), training (A–B; A–C; A–D), and posttests (same as pretests). The difference between these conditions was the kind of stimuli used and a new phase of teaching used in condition 3: (Xbcd–A). The results indicate that training with simple stimuli on discriminations that include stimuli that are easy to discriminate from each other (words and sounds) is a sufficient condition for good posttest performance. However, when comparisons are made difficult (words only), participants show better performance on new tests if they have a learning history with compound stimuli.     

Emergent conditional discrimination in children: Matching to compound stimuli

This study reports two experiments that first taught preschool children identity-matching to compound sample and compound comparison stimuli. A compound stimulus consisted of a colour and a form superimposed on one another. Test sessions assessed whether children related the form and colour elements of a particular compound stimulus. The test for this was matching to sample in which an arbitrary conditional discrimination was required. A majority of the children selected the correct colour comparison in the presence of each form sample. The children also showed the reverse sample-comparison relations: they matched form comparisons to the corresponding colour samples, respectively. In the context of these arbitrary relations, new colours were paired with the form elements of the samples (Experiment 1), and new form elements were paired with the colour elements of the comparisons (Experiment 2). Subsequent tests assessed whether the new stimulus elements had control over responding when presented as single samples or comparisons. Test results showed that most subjects were able to relate the new stimulus elements to the corresponding colour and form elements, respectively. The study demonstrated that matching to compound stimuli in training and testing conditionsMaygenerate conditional relations between the individual stimulus elements.     

Response summation to a compound stimulus in a context of choice

Key pecks by two groups of pigeons were reinforced on concurrent schedules. For group Ē, pecks were reinforced during either a visual or an auditory stimulus; for group E, an additional, extinction component was available, during which both visual and auditory stimuli were absent. After training, both groups were given a compound test to measure preference among four stimuli, the three used in training plus a compound of the visual and auditory stimulus. Group E showed preference for the compound, emitting more pecks and spending more time in this stimulus than in other stimuli. Group Ē showed no preference between the compound and visual stimulus, nor between the auditory stimulus and the absence of both stimuli, but preferred the former pair over the latter pair of stimuli.