The effect of similarity between elemental stimuli and compounds in olfactory patterning discriminations

We studied the ability of honeybees to discriminate between single odorants and binary olfactory mixtures. We analyzed the effect of the number of common elements between these two stimulus classes on olfactory discrimination. We used olfactory conditioning of the honeybees' proboscis extension reflex (PER), a paradigm in which odors can be associated with a reinforcement of sucrose solution. Bees were asked to discriminate reinforced from nonreinforced olfactory stimuli. They were trained with two elemental odors (A and B) versus a binary olfactory mixture. The mixture was either AB (group 2CE, two common elements), AC (group 1CE, one common element A), or CD (group 0CE, no common element). Three groups followed a positive patterning schedule (mixture reinforced and elements nonreinforced: groups 2CE+, 1CE+, and 0CE+) and three other groups a negative patterning schedule (mixture nonreinforced and elements reinforced: groups 2CE-, 1CE-, and 0CE-). We showed that a reduction of similarity (number of common elements) between elemental odors and compounds enhanced the ability to discriminate elements from compounds and that the kind of compound processing used by the bees supports theories that assume nonelemental compound processing (i.e., that exclude the mere summation of the elemental associative strengths upon compound presentation).     

Conditions favoring superconditioning of irrelevant conditioned stimuli

Three appetitive conditioning experiments with rats found partial learning of complex XA+, XB+, XAB- (+ stands for reinforced; - stands for unreinforced) negative patterning discriminations with intermixed A+ and B+ trials (Experiment 1). AB+ trials (Experiment 2), and A+, B+, and AB+ trials (Experiment 3). In all experiments, differential responding emerged more slowly during the learning of the negative patterning discriminations than during learning of the XA+, XB+, XC- control discriminations. Additionally, the negative patterning groups responded more to X than to a separately reinforced Y on unreinforced test trials: thus, X derived superexcitatory properties. This pattern was reversed in the control groups. Results are consistent with theories that allow for different activation patterns when elements are combined.     

A modified version of the unique cue theory accounts for olfactory compound processing in honeybees

We investigated the capability of honeybees to discriminate between single odorants, binary olfactory mixtures, and ternary olfactory mixtures in olfactory conditioning of the proboscis extension reflex. In Experiment 1, three single odorants (A+, B+, and C+) and three binary mixtures of these odors (AB+, AC+, and BC+) were reinforced while the ternary compound, consisting of all three odors (ABC-), was nonreinforced. In Experiment 2, only one single odorant (A+) and one binary olfactory compound (BC+) were reinforced while the ternary compound (ABC-) consisting of the single odor and the binary compound was nonreinforced. We studied whether bees can solve these problems and whether the course of differentiation can be predicted by the unique cue theory, a modified unique cue theory, or Pearce's configural theory. Honeybees were not able to differentiate reinforced from nonreinforced stimuli in Experiment 1. However, summation to ABC observed at the beginning of training contradicts the predictions of Pearce's configural theory. In Experiment 2, differentiation between the single odorant A and the ternary compound developed more easily than between the binary compound BC and ABC. This pattern of differentiation is in line with a modified unique cue theory and Pearce's configural theory. Summation to ABC at the beginning of training, however, again was at odds with Pearce's configural theory. Thus, olfactory compound processing in honeybees can best be explained by a modified unique cue theory.     

A positive patterning advantage with complex but not simple patterning: A cue constellation approach

Determinants of a positive patterning advantage (that is, an advantage for positive patterning over negative patterning) in human causal reasoning were examined in an experiment that compared simple patterning discriminations (A, B vs. AB) to complex patterning discriminations (AB, BC, AC vs. ABC). As predicted by a cue constellation analysis of complex discriminations, a positive patterning advantage was found with complex patterning but not with simple patterning discriminations. This result may explain why some recent studies have found a positive patterning advantage where earlier studies had failed to find one. The interaction of patterning complexity with the positive patterning advantage appears to pose problems for rule-based accounts of patterning. The results support the view that associative theories of human causal reasoning are more easily distinguished from rule-based approaches when applied to conditions that make simple rules difficult to identify or implement.     

Configural olfactory learning in honeybees: negative and positive patterning discrimination

In an appetitive context, honeybees (Apis mellifera) learn to associate odors with a reward of sucrose solution. If an odor is presented immediately before the sucrose, an elemental association is formed that enables the odor to release the proboscis extension response (PER). Olfactory conditioning of PER was used to study whether, beyond elemental associations, honeybees are able to process configural associations. Bees were trained in a positive and anegative patterning discrimination problem. In the first problem, single odorants were nonreinforced whereas the compound was reinforced. In the second problem, single odorants were reinforced whereas the compound was nonreinforced. We studied whether bees can solve these problems and whether the ratio between the number of presentations of the reinforced stimuli and the number of presentations of the nonreinforced stimuli affects discrimination. Honeybees differentiated reinforced and nonreinforced stimuli in positive and negative patterning discriminations. They thus can process configural associations. The variation of the ratio of reinforced to nonreinforced stimuli modulated the amount of differentiation. The assignment of singular codes to complex odor blends could be implemented at the neural level: When bees are stimulated with odor mixtures, the activation patterns evoked at the primary olfactory neuropile, the antennal lobe, may be combinations of the single odorant responses that are not necessarily fully additive.     

Positive and negative patterning in human causal learning

Investigations of patterning discriminations by nonhuman animals have generally found that positive patterning is easier to learn than negative patterning. Studies of patterning discriminations in human causal learning tasks have failed to document any differences between positive and negative patterning. In the present study, human participants predicted an outcome on trials involving either a compound cue or its elements. Positive and negative patterning problems were successfully solved in a within-subjects design; negative patterning problems proved to be more difficult when an additional, 50% contingent cue was included (Experiment 2), but not when it was excluded (Experiment 1). Possible reasons for these results are discussed. The discussion concludes with an analysis of exemplar models (e.g., Pearce, 1994) of human causal learning and considers the conditions under which these models do and do not anticipate our results.     

Probing the Time Course of Nonlinear Discriminations during Human Electrodermal Conditioning

Animal-based theories of Pavlovian conditioning propose that patterning discriminations are solved using unique cues or immediate configuring. Recent studies with humans, however, provided evidence that in positive and negative patterning two different rules are utilized. The present experiment was designed to provide further support for this proposal by tracking the time course of the allocation of cognitive resources. One group was trained in a positive patterning schedule (A−, B−, AB+) and a second in a negative patterning schedule (A+, B+, AB−). Electrodermal responses and secondary task probe reaction time were measured. In negative patterning, reaction times were slower during reinforced stimuli than during nonreinforced stimuli at both probe positions while there were no differences in positive patterning. These results support the assumption that negative patterning is solved using a rule that is more complex and requires more resources than does the rule employed to solve positive patterning.     

Configural learning in two species of marsupial (Setonix brachyurus and Sminthopsis crassicaudata)

Four experiments examined the ability of quokkas (Setonix brachyurus) and fat-tailed dunnarts (Sminthopsis crassicaudata) to solve 2 configural tasks: transverse and negative patterning. Transverse patterning requires the simultaneous solution of 3 overlapping discrimination problems (A+ B-, B+ C-, C+ A-). Both species could solve the nonoverlapping (elemental) version of this task (U+ V-, W+ X-, Y+ Z-), but only dunnarts solved the transverse patterning task. Negative patterning requires conditioned responses to 2 stimuli when presented separately but not together (A+, B+, AB-). Both species formed a selective conditioned response to A+ and B+ stimuli and inhibited responding to a simple nonreinforced stimulus (C-), but only dunnarts successfully inhibited responding to the AB- compound to solve the negative patterning task. These experiments are the first to demonstrate configural learning in a marsupial.     

Summation effects in human learning: evidence from patterning discriminations in goal-tracking

Participants in two human goal-tracking experiments were simultaneously trained with negative patterning (NP) and positive patterning (PP) discriminations (A+, B+, AB–, C–, D–, CD+). Both elemental and configural models of associative learning predict a PP advantage, such that NP is solved less readily than PP. However, elemental models like the unique cue approach additionally predict responding in AB– trials to be initially stronger than that in A+ and B+ trials due to summation of associative strength. Both experiments revealed a PP advantage and a strong summation effect in AB– trials in the first half of the experiments, irrespective of whether the same US was used for both discriminations (Experiment 1) or two different USs (Experiment 2). We discuss that the correct predictions of the unique cue approach are based on its assumptions of non-normalized and context-independent stimulus processing rather than elemental processing per se.     

Acquisition of a unique cue in positive and negative patterning?

Forty college students received a classical differential conditioning procedure involving both positive and negative patterning, each of these being associated with a different pair of stimuli. In positive patterning, elemental stimuli, A and B, were presented without an unconditioned stimulus while their compound, AB, was paired with electric shock. In negative patterning, elemental stimuli, C and D, were paired with shock while their compound, CD, remained unpaired. Thirty of these subjects then received a negative patterning transfer test on new stimuli, while ten subjects received a positive patterning transfer test. First interval response (FIR) and second interval response (SIR) were measured. During initial acquisition, positive patterning occurred in both dependent measures, but negative patterning was present only in the SIR. The transfer tests showed almost significant transfer of positive patterning in FIR and SIR. Negative patterning showed significant transfer neither in FIR nor SIR. It was concluded that, although elementary models of conditioning can explain positive patterning on the basis of summation of excitation from the elements to the compound, the occurrence of negative patterning in the SIR and the almost significant transfer of positive patterning in FIR and SIR appear to require the additional assumption of a unique cue.     

Configural associations in discrimination learning

In 4 experiments, Sprague-Dawley rats and homing pigeons received training with an A+ AB0 BC+ discrimination, in which food (+) accompanied trials with A and BC. Food was not presented (0) on trials with the compound AB. Subsequent test trials revealed that responding during C by itself, or the compound ABC, was slower than during either A or BC. Responding during the ABC compound was also found to be slower after training with the A+ AB0 BC+ than an A0 AB+ BC+ discrimination. We argue that these findings demonstrate the importance of configural associations in discrimination learning. Two accounts for the way in which these associations exert their influence are considered.     

Rats are sensitive to ambiguity

In the present study, we investigated response decisions made under conditions of incomplete information in rats. In Experiment 1, rats were trained on either a positive patterning (PP; A-, B-, AB+) or a negative patterning (NP; A+, B+, AB-) instrumental lever-press discrimination. Subjects that had learned an NP discrimination responded less to Cue A when Cue B was covered at test. The cover did not, however, affect test responses to Cue A in the PP condition. In Experiment 2, rats received concurrent training on both PP and NP discriminations. After concurrent training, responses to Cue A were different with B covered versus uncovered for both NP and PP discriminations. We discuss possible accounts for why exposure to a nonlinearly soluble discrimination (NP) may have affected sensitivity to cue ambiguity produced by the cover. These results have interesting implications for representational processes engaged in problem solving.     

Solving XOR

Three experiments examined the way in which exclusive-or (XOR) problems are solved by rats. All rats first received food-rewarded positive and negative patterning problems with two stimulus sets: either A+, B+, AB- and C-, D-, CD+, or A-, B-, AB + and C+, D +, and CD-. Subsequently, rats received revaluation trials in which A was paired with shock and C was not, prior to generalization test trials with B, D, AB, and CD (Experiments 1 & 2); or received A-->shock trials prior to tests with B and CD (Experiment 3). There was greater generalized fear to B than to either D (Experiments 1 & 2) or AB (Experiment 2) and CD (Experiments 2 & 3). These results are inconsistent with configural, connectionist models, but are consistent with an alternative connectionist model that can represent the logical structure of XOR problems.     

Similarity and Discrimination Learning

The role played by similarity in discrimination learning was examined in four experiments using compound stimuli. In Experiment 1, pigeons received training in which food was presented after stimulus A, compound AB, but not compound ABC—A+ BC+ ABCo. The A+ ABCo discrimination was acquired more readily than was the BC+ ABCo discrimination. In the remaining experiments, training was of the form, A+ B+ C+ AB+ AC+ BC+ ABCo. The discrimination between the single stimuli A+ B+ C+ and ABCo consistently developed more readily than between the pairs of stimuli AB+ AC+ BC+, and ABCo. The results are shown to be more consistent with a configural than with an elemental theory of conditioning.     

Upshifted decision criteria in attentional blink and repetition blindness

A large number of “unawareness” phenomena have been explained and quantified in terms of sensitivity (d′) fluctuations, with very few attempts at addressing an alternative putative cause, i.e., fluctuations of subjects’ response criteria (c). Response criteria fluctuations are particularly likely under dual-task paradigms with unbalanced sensitivities (Gorea & Sagi, 2000) such as those used in evidencing attentional blink (AB) and repetition blindness (RB) phenomena. The present study inquires into whether AB and RB are indeed prone to a deviant decisional behaviour. AB and RB were studied with a yes/no task allowing the assessment of d′ and c for the detection (presence/absence) of a target letter T2 as a function of its temporal lag relative to the presentation of another (AB) or of the same (RB) letter, T1 (Experiment 1). A significant criterion increase was observed in both cases. Additional experiments demonstrate that this criterion effect is typical of these dual-task AB and RB paradigms as it is not observed in a standard contrast detection task with mixed contrasts (Experiment 2), in a “control” AB design stripped off its first task T1 (Experiment 3), or in a metacontrast experiment (Experiment 4). We propose that the observed criterion shifts are the consequence of the inherent dual-task AB and RB designs (where observers have to judge two events of unequal saliencies) and that they entail an enhancement of the AB and RB effects as long as these effects are assessed via subjective (yes/no or matching) procedures.     

Negative patterning is easier than a biconditional discrimination

Two groups of rats were trained for 50 days on different discriminations in a magazine approach paradigm. One group was trained with a negative patterning schedule and a positive patterning schedule concurrently: they received intermixed trials of A+, B+, AB-, C-, D-, CD+ (A, B, C, and D are four distinct stimuli; the plus sign denotes reinforcement with food, and the minus sign denotes nonreinforcement). The second group of rats was trained with the same four stimuli arranged as compounds and reinforced according to the biconditional schedule AB+, CD+, AC-, and BD-. The first group learned the positive patterning schedule much more quickly than the negative patterning schedule, but they learned the negative patterning schedule more effectively than the second group learned the biconditional schedule. The authors discuss the implications of these findings for models of stimulus representation.     

Overshadowing and blocking procedures in latent inhibition

Three experiments used rats as subjects and a flavour-aversion procedure to examine the effect of compound flavour (AB) pre-exposure on the extent of latent inhibition to an element (A) of that compound. In Experiment 1 a group of rats exposed to AB exhibited less latent inhibition to stimulus A than a group for which A was presented in isolation or than a group that received A followed by a second stimulus, B, during the pre-exposure phase. Experiment 2 and Experiment 3 showed that the effectiveness of B during compound pre-exposure depended on its novelty. Thus a group that received exposure to stimulus B prior to AB pre-exposure showed more latent inhibition than a group that did not receive prior experience of the B stimulus. Two explanations for these effects were considered: that compound pre-exposure might reduce effective processing of the elements of that compound during the pre-exposure phase; alternatively, that exposure to an element as a part of a compound may modify the way in which that element is perceived.     

Backward and forward blocking in human electrodermal conditioning: Blocking requires an assumption of outcome additivity

Blocking was observed in two human Pavlovian conditioning studies in which colour cues signalled shock. Both forward (Experiment 1) and backward (Experiment 2) blocking was demonstrated, but only when prior verbal and written instructions suggested that if two signals of shock (A+ and B+) were presented together, a double shock would result (AB++). In this case, participants could assume that the outcome magnitude was additive. Participants given non-additivity instructions (A+ and B+ combined would result in the same outcome, a single shock) failed to show blocking. Modifications required for associative models of learning, and normative statistical accounts of causal induction, to account for the impact of additivity instructions on the blocking effect, are discussed. It is argued that the blocking shown in the present experiments resulted from the operation, not of an error-correction learning rule, nor of a simple contingency detection mechanism, but of a more complex inferential process based on propositional knowledge. Consistent with the present data, blocking is a logical outcome of an A+/AB+ design only if participants can assume that outcomes will be additive.     

The effects of using stimuli from three different dimensions on autoshaping with a complex negative patterning discrimination

In two experiments pigeons received a complex negative patterning discrimination, using autoshaping, in which food was made available after three stimuli if they were presented alone (A, B, C), or in pairs (AB, AC, BC), but not when they were all presented together (ABC). Subjects also received a positive patterning discrimination in which three additional stimuli were not followed by food when presented alone (D, E, F), or in pairs (DE, DF, EF), but they were followed by food when presented together (DEF). Stimuli A and D belonged to one dimension, B and E to a second dimension, and D and F to a third dimension. For both problems, the discrimination between the individual stimuli and the triple-element compounds developed more readily than that between the pairs of stimuli and the triple-element compound. The results are consistent with predictions that can be derived from a configural theory of conditioning.     

Pavlovian conditioning and rule learning

The experiment reviewed here was an attempt to show that two differential Pavlovian conditioning designs, namely positive and negative patterning, can best be understood as rule learning. First, it is shown that positive patterning is equivalent to the logical rule of conjunction (AND) and that negative patterning is equivalent to the logical rule of exclusive disjunction (XOR). It is assumed that in order to learn both kinds of discrimination subjects learn to use the according rule. If this is the case, the observed differentiation should be independent of the number of reinforcements for each individual stimulus. Second, subjects should be able to transfer the rule to new stimuli. Forty human subjects were randomly divided into four groups (N=10 each). Two factors were manipulated independently between subjects: (1) positive vs negative patterning, and (2) 2 vs 4 pairs of trained stimuli. Second interval skin conductance responses were measured. During initial acquisition positive as well as negative patterning occurred independently of number of pairs of trained stimuli (with total amount of training kept constant). Furthermore, AND as well as XOR could be transfered to new stimuli.