Biomedical subjects

Harald Lachnit

Publications and source records attributed to Harald Lachnit.

At least 19 recordsLinked to original sources

PubMed2006

The trial-spacing effect in olfactory patterning discriminations in honeybees.

Harnessed bees conditioned to associate odors and sucrose reward learn to discriminate between olfactory mixtures and their odor components in negative (NP: A+, B+, AB-) and positive (PP: A-, B-, AB+) patterning experiments. They thus extend the proboscis to the reinforced (CS+) but not to the non-reinforced (CS-) stimuli. Using the same protocol, we studied whether or not trials, which are spaced in time, are more effective in supporting patterning discrimination than massed trials which succeed fast to each other ('trial-spacing effect'). Training followed a NP (4 A+, 4 B+, 8 AB-) or a PP (4 A-, 4 B-, 8 AB+) schedule, with a 1:1 ratio between CS+ and CS- trials (8 CS+ and 8 CS- trials). ITIs of 1, 3, 5 and 8min were used in both tasks. Increasing ITI resulted in better differentiation between reinforced and non-reinforced CSs in both NP and PP tasks. However, whereas only the longest ITI of 8min allowed discrimination in NP, PP could already be solved with an ITI of 5min. This difference might be due to the fact that NP, but not PP, would require the formation of a unique cue and thus longer processing times. We thus show that the trial-spacing effect, previously demonstrated for single stimulus conditioning, also determines performance in patterning tasks in which three different stimuli (A, B, AB) alternate so that elements have to be discriminated from their compound.

Analysis of Variance↗

PubMed2006

The comparator theory fails to account for the selective role of within-compound associations in cue-selection effects.

In a human causal learning experiment, we investigated cue selection effects to test the comparator theory (Denniston, Savastano, & Miller, 2001; Miller & Matzel, 1988). The theory predicts that the occurrence of cue selection is independent of whether the relevant learning trials are presented in a standard forward manner or in a backward manner and that within-compound associations are of equal importance in both cases. We found that the strength of the cue-selection effect was positively correlated with knowledge of within-compound associations in the backward condition but not in the forward condition. Furthermore, cue-selection effects were less pronounced in the former than in the latter condition. These results are at variance with the comparator hypothesis but are in agreement with a modified associative theory and with the suggestion that retrospective revaluation might be due to rehearsal processes.

Adult↗

PubMed2006

Contextual control in discrimination reversal learning.

In 3 human predictive learning experiments, the authors examined contextual control of responding in discrimination reversal learning. In Phase 1, a discrimination between 2 stimuli (A+, B-) was trained in Context 1. During Phase 2, participants received discrimination reversal training (A-, B+) in Context 2. Testing occurred in Context 1 and Context 2 (Experiments 1A and 1B) or in Context 1 and Context 3 (Experiment 2). During the test phase, performance in Context 1 and Context 2 reflected the contingencies trained during Phase 1 and Phase 2, respectively. When testing occurred in Context 3, there was no discriminative responding between A and B. In addition, the experiments demonstrated that discriminating stimuli with a consistent reinforcement history were also affected by contextual manipulations. Results indicate that each training context acquires the ability to control performance. Unique-cue and configural approaches account for a major part of the results.

Adolescent↗

PubMed2006

Neural representation of olfactory mixtures in the honeybee antennal lobe.

Natural olfactory stimuli occur as mixtures of many single odors. We studied whether the representation of a mixture in the brain retains single-odor information and how much mixture-specific information it includes. To understand mixture representation in the honeybee brain, we used in vivo calcium imaging at the level of the antennal lobe, and systematically measured odor-evoked activity in 24 identified glomeruli in response to four single odorants and all their possible binary, ternary and quaternary mixtures. Qualitatively, mixture-induced activity patterns always contained glomeruli belonging to the pattern of at least one of the components, suggesting a high conservation of component information in olfactory mixtures. Quantitatively, glomerular activity saturated quickly and increasing the number of components resulted in an increase of cases in which the response of a glomerulus to the mixture was lower than that to the strongest component ('suppression'). This shows global inhibition in the antennal lobe, probably acting as overall gain control. Single components were not equally salient (in terms of number of active glomeruli) and mixture activity patterns were always more similar to the more salient components, in a way that could be predicted linearly. Thus, although a gain control system in the honeybee antennal lobe prevents saturation of the olfactory system, mixture representation follows essentially elemental rules.

Animals↗

PubMed2006

Tracking stimulus processing in Pavlovian pupillary conditioning.

The aim of the present study was to evaluate whether the anticipatory pupillary dilation response is a useful indicator for the examination of complex differential conditioning problems like patterning. A human fear conditioning procedure with six groups (n=20 each) was used to examine conditioned stimulus (CS) processing when a compound stimulus was reinforced, but not its elements (positive patterning) or when the elements were reinforced, but not the compound (negative patterning), as well as modifications in which the compound was replaced by either a new compound or by a new element. We found evidence for conditioning within 2 s after CS onset. Group differences in differential conditioning indicated systematic differences in CS processing due to different discrimination task difficulties. This study showed that the pupil response is a suitable indicator for human Pavlovian conditioning with high time resolution within and between trials.

Adolescent↗

PubMed2006

Extinction of conditioned inhibition through nonreinforced presentation of the inhibitor.

In previous studies that have tried to extinguish conditioned inhibition through nonreinforced presentations of the inhibitor, researchers have repeatedly failed to find evidence for such extinction. The present study revealed that extinction can be achieved through nonreinforcement of the inhibitor, depending on properties of the reinforcer. In a human causal learning experiment, we found complete extinction in a scenario in which the reinforcer could take on negative values. Thereby, this scenario reflected the assumed symmetrical continuum on which associative strength can vary, according to the Rescorla-Wagner theory of associative learning. In contrast to this, the inhibitory cue retained its inhibitory potential in another condition, in which the scenario did not allow negative values of the reinforcer.

Attention↗

PubMed2005

The experimental task influences cue competition in human causal learning.

Participants were shown A+ and C- trials followed by AB+ and CD+ trials. These trials were embedded in a causal learning task in which participants had to learn either the relationship between different foods and allergic reactions or the relationship between different stocks and an increase in the stock market index. The authors orthogonally varied the manner in which the different cues were presented to participants during training. Cue competition was related to the causal learning scenario but not to the manner in which the different cues were presented. These results question claims of a human bias toward configural processing that were based on difficulties in finding cue competition in some previous causal learning experiments.

Adult↗

PubMed2004

Within-compound associations in retrospective revaluation and in direct learning: a challenge for comparator theory.

In three human causal learning experiments we investigated the role of within-compound associations in learning about absent cues versus learning about present cues. Different theoretical approaches agree that within-compound associations are essential for learning about absent cues-that is, for retrospective revaluation. They differ, however, with regard to the role of within-compound associations for learning about present cues-that is, for direct learning. A memory test was used to assess within-compound associations. Experiment 1 used a blocking/release from overshadowing design, Experiment 2 used a conditioned inhibition design, and Experiment 3 used a higher-order cue selection design. In all experiments, first-order retrospective revaluation was significantly correlated with within-compound associations, but no significant correlations were found for the direct learning conditions. In addition to this, second-order retrospective revaluation in Experiment 3 was positively correlated to joint knowledge of first-order and second-order within-compound associations. Furthermore, cue selection effects were stronger for direct learning conditions than for retrospective learning conditions. These results are at variance with the comparator hypothesis but are in agreement with a modified associative theory and with the suggestion that retrospective revaluation might be due to rehearsal processes.

Adolescent↗

PubMed2003

The effect of cumulative experience on the use of elemental and configural visual discrimination strategies in honeybees.

We addressed the question of whether the amount of individual experience determines the use of elemental or configural visual discrimination strategies in free-flying honeybees Apis mellifera. We trained bees to fly into a Y-maze to collect sucrose solution on a rewarded stimulus presented in one of the arms of the maze. Stimuli were colour disks, violet (V), green (G) or yellow (Y), which were of equal psychophysical salience for honeybees. Training followed an A+, BC+ design, followed by an AC versus BC test. Training consisted of 6 (3 A+ and 3 BC+), 20 (10 A+ and 10 BC+) or 40 (20 A+ and 20 BC+) acquisition trials. Elemental models of compound processing predict a preference for the non-trained stimulus AC while configural models predict a preference for the trained stimulus BC. Our results show that increasing the number of acquisition trials results in a change of the internal representation of stimuli. After six training trials, bees favoured an elemental strategy and preferred AC to BC during the tests. Generally, increasing the number of training trials resulted in an increase of the choice of BC. Thus, short training favoured processing of the compound as the sum of its elements (elemental account) while long training favoured its processing as being different from the sum of its elements (configural account). Additionally, we observed that the change in stimulus processing was also influenced by stimulus similarity. Colour perceptual similarity favoured configural processing with increasing experience.

Animals↗

PubMed2003

Non-elemental processing in olfactory discrimination tasks needs bilateral input in honeybees.

In patterning discriminations, animals have to differentiate a compound stimulus AB from each of its elements A and B. In positive patterning (PP), the compound is reinforced whilst the single elements are non-reinforced. In negative patterning (NP), single elements are reinforced whilst the compound is non-reinforced. Using olfactory conditioning of the proboscis extension response (PER), we asked whether honeybees (Apis mellifera) can solve these patterning problems when odorants are given unilaterally as well as bilaterally to the antennae. Separating the olfactory input space of bees into two independent zones using plastic walls placed between the antennae, we conditioned bees in PP and NP procedures, with input on one side, on both sides, or in an ambiguous problem where bees had to solve PP on one side and NP on the other side. We found that bees with simultaneous bilateral input solve both patterning tasks efficiently. In contrast, PP but not NP was learned by bees receiving unilateral olfactory input. Bees subjected to the ambiguous NP/PP problem only solved PP. As PP can be solved through mere elemental processes, but NP is critically dependent on the use of non-elemental learning processes, our results suggest that bilateral olfactory input is necessary for non-elemental processing to take place in the bee brain.

Animals↗

PubMed2003

Effects of practice and transfer in the detection of embedded figures.

Gottschaldt's (1926) study on embedded figures serves as the foundation for the claim that Gestalt factors limit the impact of experience on perception. The present experiments studied the effects of practice and transfer on the detection of embedded figures. Experiment 1 showed the clear effects of practice that might have been due to recognition. Moreover, it demonstrated the effects of transfer, thus reducing the potential impact of recognition. Experiment 2 replicated practice effects and extended them to other types of part and whole figures. It was conducted to evaluate the specificity of the transfer in more detail. In Experiments 1 and 2, transfer between old and new items only occurred when either the figures and their basic elements were of the same kind or the same search strategies could be used. Thus, perceptual abilities improve by training even when Gestalt factors are at work. Possible sources of these improvements are discussed with special attention to a distinction between figural and procedural aspects.

Adolescent↗

PubMed2003

Asymmetric interference in patterning discriminations: a case of modulated attention.

In sequential training positive patterning hinders negative patterning, but not vice versa. This asymmetry was attributed to interference of two different rules. In a Pavlovian skin conductance response conditioning experiment with humans, we further investigated this effect. Two groups performed sequential training of positive and negative patterning with a reduced number of trials per training schedule. In Group PNP, the sequence was positive patterning (A-, B-, AB+), negative patterning (C+, D+, CD-), followed by positive patterning (E-, F-, EF+). Group NPN consisted of negative patterning (A+, B+, AB-), positive patterning (C-, D-, CD+), and negative patterning (E+, F+, EF-) again. As predicted by an attentional explanation we found no interference. Hence, the asymmetry observed earlier had been due to less attention to specific stimuli in consequence of an extensive use of the numerosity-rule.

Adolescent↗

PubMed2003

Similarity and discrimination in human Pavlovian conditioning.

We report three Pavlovian eyelid conditioning experiments with humans, designed to experimentally decide between elemental and configural learning theories. We used two different designs originally proposed by Redhead and Pearce (1995). In Experiments 1 and 2, three stimulus elements, A, B, and C, were presented in all possible combinations. All patterns were reinforced except for pattern ABC (A/B/C+, AB/AC/BC+, ABC-). According to elemental learning theories, response proportions on A/B/C+ trials should be smaller than on AB/AC/BC+ trials, whereas configural learning theory makes the opposite prediction. The results confirmed neither prediction. In Experiment 3, the A/B/C+, AB/AC/BC+, and ABC- trials were interspersed by D/E/F-, DE/DF/EF-, DEF+ trials. Again, neither prediction was confirmed. We suggest a modification of configural learning theory as a possible explanation of our results.

Adult↗

PubMed2002

Configural learning in human Pavlovian conditioning: acquisition of a biconditional discrimination.

Previous studies of conditioning have shown that non-human animals are able to master discrimination problems which cannot be solved on the basis of elemental associations. Most of these discrimination problems, however, have not yet been investigated in human Pavlovian conditioning. In a skin conductance conditioning experiment we therefore assessed whether humans can solve a biconditional discrimination. Participants underwent conditioning with an AB+, CD+, AD-, CB- design and successfully mastered this discrimination. Thus, they were able to learn about the relationship of specific configurations of stimuli with the reinforcer. The results extend previous findings of configural learning in humans.

Adult↗

PubMed2002

Differential conditioning of anticipatory pupillary dilation responses in humans.

The purpose of the present experiments was to demonstrate conditioning of anticipatory pupillary dilation responses in humans as previous efforts to condition pupillary dilation had yielded inconsistent results. In those studies, using an aversive unconditioned stimulus (US) had yielded more promising results than using non-aversive USs. In three experiments we utilized a reaction time task as a non-aversive US and observed reliable differential conditioning of anticipatory pupillary dilation. Differential responding was evident within very few trials and was largest late in the anticipatory interval. Experiment 4 replicated these findings using an aversive US (electric shock). In measuring anticipatory responses in a differential conditioning preparation all four experiments provided clear evidence for Pavlovian conditioning of pupillary dilation in humans.

Adult↗

PubMed2002

The effect of stimulus probability on pupillary response as an indicator of cognitive processing in human learning and categorization.

Stimuli presented with a low probability of occurrence elicit larger pupillary dilations than those presented with a high frequency. Utilizing this stimulus probability effect, we conducted two Go/NoGo reaction time experiments to analyze category learning and compound coding in the context of associative learning. Experiment 1 showed no stimulus probability effect when participants used an abstract rule to classify stimuli with different probabilities into the same category. When no rules could be applied, however, the stimulus probability effect was observed. Hence, this effect can be utilized to identify the application of rules in category learning. Experiment 2 demonstrated that the stimulus probability effect can also be used in determining whether compounds are processed in terms of elemental stimuli or as new entities. The results of Experiment 2 supported elemental rather than configural processing. Obviously, the probability effect can be used as a tool for the evaluation of categorization and compound processing.

Adult↗

PubMed2002

Evidence for the utilization of distinctive features in nonlinear discrimination problems.

There is evidence that in human Pavlovian conditioning positive patterning (A-, B-, AB+) as well as negative patterning (A+, B+, AB-) are solved by applying abstract rules. In the present report we further investigated how humans solve patterning discriminations by conducting two Go/NoGo reaction time experiments that utilized the stimulus probability effect: stimuli presented with a low probability of occurrence elicit larger pupil dilations than those presented with a high frequency. In decreasing the ratio of compound and elemental trials from 1/1 (24 A, 24 B, 48 AB) in Experiment 1 to 1/2 (32 A, 32 B, 32 AB) in Experiment 2 we manipulated stimulus probability. The results of both experiments indicate that humans utilize distinctive features such as number information in order to classify the stimuli.

Adult↗

PubMed2002

The impact of reinforcement density on response differentiation in configural discrimination problems.

Two human Pavlovian conditioning experiments investigated the impact of reinforcement density (the number of reinforced trials divided by the total number of trials) on discrimination learning. Experiment 1 used a negative patterning problem (A+, B+, AB-) and Experiment 2 used a positive patterning problem (A-, B-, AB+). In both experiments, reinforcement density varied across four levels. Response differentiation between reinforced and non-reinforced stimuli was linearly related to the decrease in reinforcement density. Responses to nonreinforced stimuli did not differ between the four groups in either experiment. In contrast to this, responses to reinforced stimuli were considerably more pronounced in conditions with lower reinforcement density. For negative patterning, this replicates and extends similar observations from other species. For positive patterning, this is a finding that has not yet been reported in other experiments. The results are in agreement with the comparator hypothesis (Miller & Matzel, 1988) and with Wagner's (1981) "standard operating procedures" (SOP) model.

Adult↗