Contrast and accentuation effects in category learning

This study examines the accentuation of perceived intercategory differences. In Experiment 1, 2 sets of trait adjectives were presented--a neutral set and a set of either favorable traits or unfavorable traits. Ss estimated the mean favorability of each set. The mean favorability of the neutral set was then increased or decreased by adding new traits. As predicted, the estimated mean favorability of the neutral set changed more when the set became more distinct from a contextual set than when it became more similar. In Experiment 2, estimated category means were displaced away from each other (contrast effect), and they moved even farther apart when new information increased the variability of trait favorability (accentuation effect). This change was illusory because the actual category means remained constant. Experiment 3, in which trait adjectives described members of 2 novel groups, replicated Experiment 2. The relevance of contrast and accentuation effects to the development and maintenance of differentiated intergroup perceptions is discussed.     

The effects of a flavour - toxicosis pairing upon long-delay, flavour aversion learning

Mackintosh (1973) has suggested that rats readily associate flavours with illnesses in cue-to-consequence studies because they have already learned that changes in internal states are unrelated to changes in external stimuli. An implication of this suggestion is that learned predispositions may also subserve the ability of rats to form long-delay, flavour-illness associations. Six experiments tested this idea by examining the strengths of aversions in a delayed flavour-toxicosis paradigm after exposure to a paired or unpaired relation between another flavour and toxicosis. Exposure to a paired relation enhanced the strengths of subsequently established flavour aversions (Experiment I). The enhanced aversions were associative in origin (Experiment II), observed with delays of 3 h and 1·5 h in, respectively, a forward (Experiment III) and backward (Experiment IV) delayed conditioning paradigm and with a 10-day interval between the flavour-toxin pairing and the delayed paradigm (Experiment V). The enhanced aversions, however, were removed by the extinction of the original flavour aversion prior to the delayed flavour-toxin pairing (Experiment VI). The results supported the idea that the ability of the rat to form long-delay, flavour-illness associations reflects an associative history involving flavours and internal changes and were discussed in terms of Mackintosh's (1975) theory of the mechanism underlying stimulus selection. The effects of a flavour-toxicosis pairing upon long-delay, flavour aversion learning.     

Palatability shifts in taste and flavour preference conditioning

Changes in palatability of tastes and flavours as a result of flavour preference conditioning were examined. In Experiment 1, when tastes were paired with glucose in a reverse-order differential conditioning paradigm, rats acquired conditioned preferences for CS + and displayed more hedonic responses to CS + than to CS - in a postconditioning taste reactivity test. In Experiment 2, rats that received oral infusions of flavours as CSs during a reverse-order conditioning procedure expressed both palatability shifts and conditioned preferences for CS + . Rats that received a forward conditioning procedure acquired a preference for CS + , but the palatability of CS + was unchanged. In Experiment 3, hungry rats drank mixtures of a flavour CS and a calorific or sweet tasting reinforcer in a long-exposure conditioning paradigm. When tested hungry, rats preferred CS + whether they had acquired flavour-calorie or flavour-taste associations. However, CS + became more palatable only for rats that acquired flavour-calorie associations. These results suggest that acquisition of flavour preferences, as measured by 2-bottle tests, may not always be accompanied by enhanced palatability.     

Perceptual learning in flavour aversion conditioning

In each of four experiments, rats drank a solution of saline or of lemon and saline shortly before receiving an injection of lithium chloride, and the generalization of the resulting aversion to sucrose or to lemon and sucrose was measured. There was little generalization from saline alone to sucrose alone, and prior exposure to the two solutions had no effect on their discriminability. An aversion conditioned to lemon-saline, however, did generalize to lemon-sucrose, and the extent of this generalization was substantially reduced by prior exposure to the two compound solutions. This perceptual learning effect was partly, but not entirely, attributable to the latent inhibition of the common element, lemon, produced by exposure to the two compounds: animals pre-exposed to lemon alone discriminated between lemon-saline and lemon-sucrose better than animals pre-exposed to saline and sucrose alone; but exposure to the three elements in isolation was not as effective as exposure to the two compound solutions in enhancing their discriminability. The final experiment established that one critical feature of compound pre-exposure is that it involves experience of saline and sucrose in the presence of the same common element. According to an associative theory of perceptual learning, this would result in the establishment of inhibitory associations between saline and sucrose, thus reducing generalization between the two compound solutions.     

Enhanced preference for a flavour following reversed flavour—glucose pairing

In two experiments hungry rats showed enhanced preference for a flavour as a result of a procedure whereby the flavour followed presentation of 10% glucose—i.e. the reverse of the usual sequence. This provides the first example of excitatory conditioning resulting from reversed pairing involving an appetitive reinforcer. Experiment 1 compared a Cinnamon group, for which ingestion of glucose was followed after 3 min by cinnamon and on other days water was followed by wintergreen, with a Wintergreen group in which wintergreen followed glucose and cinnamon followed water. In a final 2-bottle test relative preference for cinnamon was greater in the Cinnamon than in the Wintergreen group. This effect was replicated in Experiment 2, which compared an Immediate group, for which, as above, drinking glucose was followed 3 min later by access to cinnamon, with a Delay group, for which there was a delay of 1 hr between glucose and subsequent access to cinnamon. Enhanced preference for cinnamon was found only in the Immediate group and appeared after only four glucose-cinnamon pairings. An important finding came from a choice test between glucose and saccharin in which the Immediate group showed a weaker preference for glucose than the Delay group. This indicated that a novel flavour may overshadow the association between the flavour of glucose and its consequences, which normally serves to enhance preference for glucose.     

Contrast and inhibition in discrimination learning by the pigeon: Analysis through drug effects

In a series of four experiments, pigeons were trained on either an easy, red/green discrimination with or without a penalty for errors, or a more difficult left/right discrimination with penalty. Some groups of birds were injected with chlorpromazine or desipramine prior to acquisition sessions or to sessions following learning of the discrimination. Drug injection caused substantial impairment of acquisition or retention of the left/right discrimination alone, whereas in all discriminations the behavioral contrast effect was abolished. The results suggest that inhibition of errors depends upon the difficulty of discrimination and the presence of a penalty procedure, and determines both contrast in the saline-injected groups and the extent of impairment in the drug-injected groups.     

Analysis of the perceptual learning effect in flavour aversion learning: Evidence for stimulus differentiation

Rats received exposure to two compound flavours, AX and BX, where A and B were sucrose and saline and X was acid. For group intermixed (I), exposure consisted of alternating trials with AX and BX; group blocked (B) received a block of AX trials and a separate block of BX trials. Experiment 1 showed that generalization to BX after conditioning with AX was less profound in group I than in group B. Separate examination of the elements of the compound showed that the source of this difference lay in the strength acquired by the X element. X acquired less strength in group I than in group B (Experiments 1 and 2), whereas for the A element (Experiments 3 and 4) the reverse pattern was obtained. These results support the proposal that the perceptual learning effect (restricted generalization from AX to BX in group I) depends on a process that enhances the effectiveness of unique stimulus elements (A and B) and reduces that of common elements (such as X).     

Contrast effects in maintained generalization gradients

In Experiment I, pigeons were given equal reinforcement (variable-interval 1-min) for responding during randomized presentations of eight line-orientation stimuli. Then, only responding in the vertical orientation was reinforced. Stable generalization gradients soon formed and persistent behavioral and local (transient) contrast effects appeared. Local contrast effects were not a function of relative reinforcement frequency or of any other variable known to produce contrast. Instead, they were related to average response rates associated with each stimulus. Experiment II showed that local contrast effects represent increases and decreases in response rates relative to baseline responding, and that these effects are relative; a given stimulus might enhance responding during a subsequent presentation of one stimulus, but depress responding when followed by another. These data indicate that discrimination learning is not adequately described as the acquisition of excitatory properties by some stimuli and inhibitory properties by others. A more adequate account implies that stimuli exert both excitatory and inhibitory effects related to their value.     

Implicit learning increases preference for predictive visual display

We investigated whether implicit learning in a visual search task would influence preferences for visual stimuli. Participants performed a contextual cueing task in which they searched for visual targets, the locations of which were either predicted or not predicted by the positioning of distractors. The speed with which participants located the targets increased across trials more rapidly for predictive displays than for non-predictive displays, consistent with contextual cueing. Participants were subsequently asked to rate the "goodness" of visual displays. The rating results showed that they preferred predictive displays to both non-predictive and novel displays. The participants did not recognize predictive displays any more frequently than they did non-predictive or novel displays. These results suggest that contextual cueing occurred implicitly and that the implicit learning of visual layouts promotes a preference for visual layouts that are predictive of target location.     

Acquired flavour preferences: contextual control of adaptation-level effects

This experiment investigated the role of context in the expression of conditioned flavour preferences. Rats were trained on a mixture of almond and sucrose and were then given intermixed exposures to almond in one context (Context A) and to sucrose in a second context (Context S). Finally, choice tests were given in both contexts, with one group given almond-versus-water tests and the other almond + sucrose-versus-sucrose tests. Preference for almond over water was greater in Context A than in Context S. Conversely, preference for almond + sucrose over sucrose was greater in Context S than in Context A. These results suggest that the perceived sweetness of a flavour depends on the context in which it is presented and confirm that expression of a flavour preference depends on the type of test employed.     

Cue interactions in flavor preference learning: a configural analysis

Four experiments showed that the preference normally established to a neutral flavor cue that was paired with maltodextrin was attenuated when that cue was conditioned in compound with another flavor--overshadowing. Furthermore, two experiments showed that the preference for a neutral flavor conditioned as part of a compound was further attenuated if the other element in that compound was separately paired with the reinforcer--blocking. These results stand in contrast to a number of previous compound flavor preference conditioning experiments, which have not revealed reliable cue competition effects. These discrepant findings are discussed in terms of the effects of within-compound associations and a configural perspective on potentiation. Modeling of this configural perspective predicts that a compound of two separately trained cues will elicit a similar response to the individual cues themselves--absence of summation. Two experiments confirmed this prediction.     

Acquired flavour preferences: Contextual control of adaptation-level effects

This experiment investigated the role of context in the expression of conditioned flavour preferences. Rats were trained on a mixture of almond and sucrose and were then given intermixed exposures to almond in one context (Context A) and to sucrose in a second context (Context S). Finally, choice tests were given in both contexts, with one group given almond-versus-water tests and the other almond + sucrose-versus-sucrose tests. Preference for almond over water was greater in Context A than in Context S. Conversely, preference for almond + sucrose over sucrose was greater in Context S than in Context A. These results suggest that the perceived sweetness of a flavour depends on the context in which it is presented and confirm that expression of a flavour preference depends on the type of test employed.     

Contrast effects in multiple fixed-interval reinforcement schedules

Pigeons were exposed to a multiple fixed-interval one-minute fixed-interval three-minute schedule of reinforcement following training on either a multiple fixed-interval one-minute fixed-interval one-minute schedule or a multiple fixed-interval three-minute fixed-interval three-minute schedule. For all birds, large negative local contrast effects developed during the first of four three-minute intervals in a component; response rate was depressed and postreinforcement pause lengthened in this interval. Positive local contrast effects were evident during the first of 12 one-minute intervals in a component for five of six birds; at asymptote, the pause was very short and response rate slightly elevated during this interval. Overall positive contrast was generally transient and varied considerably across subjects, while overall negative contrast effects, if they occurred, appeared only after a large number of sessions.     

Contrast effects in judgments of health hazards

Researchers commonly use 2 models to explain contrast effects (CEs): the standard-of-comparison model and the set-reset model. The 2 models focus on the role of categorization to predict when a CE (instead of an assimilation effect) will happen, while minimizing the role of knowledge accessibility and relevance in determining whether any effect will occur. A 3rd model, the selective-accessibility model (F. Strack & T. Mussweiler, 1997), focuses on knowledge accessibility and relevance, but it is a model of assimilation effects in the anchoring bias. In the present study of CEs, the authors tested 3 predictions implied by the selective-accessibility model. The authors found a CE only when anchor- and target-rating dimensions matched and only in the 1st of multiple targets rated. The CE required a minimum amount of attention to the anchor. These results support the account that selective knowledge accessibility and relevance play an important role in CEs.     

An analysis of learning data which distinguishes between initial preference and learning ability

Several sets of learning data furnished by I. Krechevsky have been analyzed in terms of meaningful parameters of the learning curve, and the changes in the frequency distributions of these parameters with changes in the experimental conditions have been studied. One of the parameters represents the animal's initial preference for the light or dark, the other represents learning ability. The analysis shows that destruction of about ten or fifteen per cent. of the cortex, increases the animal's preference for the light and decreases the learning ability slightly. By ordinary methods of analysis, it is not possible to discover thatboth initial preference and learning ability have been changed by any given factor.The author wishes to acknowledge financial assistance from the Social Science Research Committee of the University of Chicago in the completion of this study.     

Observing inefficient action can induce infant preference and learning

‘Motionese’ can be defined as an exaggerated and repetitive action. It induces preference and learning in infants. However, which action component of motionese promotes infants’ preference and learning remains largely unknown. In this study, we focused on inefficiency and toward-ness of action. Our study demonstrates that observing an inefficient holding out action can induce a visual preference in 4-month-old infants and learning in 10-month-old infants through eight experiments (N = 192). We found that when infants observe inefficient holding out action, the action attracts their attention and facilitates learning about the identity of the toy object accompanying it, especially when people direct inefficient actions towards them. Our findings indicate that both action efficiency and toward-ness may be key factors in infant learning.