Behavioral olfactory discrimination of mixtures in the spiny lobster (Panulirus argus) based on a habituation paradigm

A habituation paradigm was used to examine behavioral aspectsof discrimination of stimulus quality in olfaction in the spinylobster (Panulirus argus). Magnitude of search response to twoconcentrations of artificial mixtures of crab, oyster, mulletand shrimp and to artificial seawater was measured in five lobstersbefore and immediately after habituation to crab mixture. Habituationto crab mixture was accomplished through 2-min presentationsof 5 ml of alternating concentrations (0.05 and 0.5 mM) of crabmixture stimulus, repeated every 5 min for a total durationof at least 3 h. This procedure resulted in at least a 42% decreasein response to any mixture, but the decrease was greatest forcrab mixture, the habituating stimulus. A habituation index,measured as post-habituation response relative to pre-habituationresponse, was used to evaluate discrimination between crab andeach of the other three mixtures. The habituation index wassignificantly greater for crab (90%) than for oyster (49%) andfor mullet (47%) mixtures. The habituation index for shrimpmixture (65%) was intermediate to these three mixtures. Thus,shrimp mixture is perceived by lobsters as being more similarto crab mixture than is either oyster or mullet mixture. Thesepatterns of discrimination parallel those reported for associativelyconditioned lobsters (Fine-Levy et al., 1987, 1988) and fora population of olfactory receptor cells (Girardot and Derby,1988).     

Perception of odor mixtures by the spiny lobster Panulirus argus

We used spiny lobsters (Panulirus argus) in a discriminationlearning procedure with aversive conditioning to examine theirbehavioral discrimination of adenosine-5'-monophosphate (AMP),betaine, L-cysteine and their binary mixtures. Our results showthat spiny lobsters can clearly discriminate among binary mixturesand their components. Lobsters aversively conditioned to avoidresponding to a binary mixture continued to respond to thatmixture's components, and lobsters that were aversively conditionedto avoid responding to a compound tended to continue to respondto binary mixtures containing that compound. Thus, responsesof conditioned lobsters to binary mixtures were not usuallyintermediate between the responses to the mixtures' components,which might be expected for response-matched compounds. Thisresult might arise from any of several factors. First, it mightresult from mixture interactions in the peripheral olfactorysystem, if the responses of olfactory receptor neurons to onecomponent of a binary mixture were suppressed by the other component,making the response to the mixture more similar to the suppressingcomponent. Electrophysiological data from a population of 50singly-recorded olfactory receptor neurons (Daniel and Derby,1994) do not consistently support this idea. A second possiblereason for the behavioral response to a binary mixture not beingintermediate between the responses to its components involveshigher order processing, such as mixture interactions generatedin olfactory interneurons in the CNS (which is known to occur:Derby et al., 1985; Ache, 1989), configural learning or associativeprocessing.     

Behavioral chemoattractants for the shrimp, Palaemonetes pugio: identification of active components in food extracts and evidence of synergistic mixture interactions

We are studying chemoattractants for the shrimp, Palaemonetespugio, to identify the active components of stimulatory foodextracts, and to determine whether the mixtures of substancesoccurring in extracts express themselves in an additive or aninteractive manner. The results of quantitative analyses ofthe specific amino acids, quaternary ammonium compounds, organicacids, nucleotides and related substances in extracts of fourorganisms (crab, shrimp, oyster, mullet) were used to formulateartificial mixtures based on the composition of each organism.Quantitative behavioral bioassays with P. pugio showed thatthe artificial mixtures based on the composition of the craband shrimp extracts were virtually as effective as the respectivenatural extracts, whereas artificial mixtures based on the compositionof the oyster and mullet extracts were far less effective. Sincethe same types of substances were included in all of the mixtures,it is apparent that the substances serving as chemoattractantsin different extracts are not constant but can vary dependingupon the source of the extract. To examine for interactionsamong the components of the four artificial mixtures, responsesto the mixtures and to their individual components were analyzedusing the additive methods of stimulus summation and responsesummation. Synergistic interactions were evident since eachmixture was markedly more effective than predicted on the basisof these additive models. The degree of synergism varied withthe composition of the mixture.     

Olfactory discrimination of complex mixtures of amino acids by the black bullhead Ameiurus melas

On the basis of previous findings of behavioural discrimination of amino acids and on the knowledge of electrophysiology of the catfish (genera Ictalurus and Ameiurus) olfactory organs, behavioural experiments that investigated olfactory discrimination of amino acid mixtures were carried out on the black bullhead Ameiurus melas. Repeated presentations of food‐rewarded mixtures released increased swimming activity measured by counting the number of turns >90° within 90 s of stimulus addition. Non‐rewarded amino acids and their mixtures released little swimming activity, indicating that A. melas discriminated between the conditioned and the non‐conditioned stimuli. Two questions of mixture discrimination were addressed: (1) Are A. melas able to detect components within simple and complex amino acid mixtures? (2) What are the smallest differences between two complex mixtures that A. melas can detect? Three and 13 component mixtures tested were composed primarily of equipotent amino acids [determined by equal electroolfactogram (EOG) amplitude] that contained L‐Cys at ×100 the equipotent concentration. Ameiurus melas initially perceived the ternary amino acid mixture as its more stimulatory component alone [i.e. cysteine (Cys)], whereas the conditioned 13 component mixture containing the more stimulatory L‐Cys was perceived immediately as different from L‐Cys alone. The results indicate that components of ternary mixtures are detectable by A. melas but not those of more complex mixtures. To test for the smallest detectable differences in composition between similar multimixtures, all mixture components were equipotent. Initially, A. melas were unable to discriminate the mixtures of six amino acids from the conditioned mixtures of seven amino acids, whereas they discriminated immediately the mixtures of four and five amino acids from the conditioned mixture. Experience with dissimilar mixtures enabled the A. melas to start discriminating the seven‐component conditioned mixture from its six‐component counterparts. After fewer than five training trials, A. melas discriminated the mixtures of nine and 10 amino acids from a conditioned mixture of 12 equipotent amino acids; however, irrespective of the number of training trials, A. melas were unable to discriminate the 12 component mixture from its 11 component counterparts.     

Behavioral discrimination of binary mixtures and their components: effects of mixture interactions on coding of stimulus intensity and quality

There is mounting evidence that mixture interactions resultin a physiological response that is different from that predictedfrom observed responses to individual mixture components. Mixtureinteractions that act to alter the neural coding of mixtureintensity (intensity mixture interactions) or quality (patternmixture interactions) may ultimately lead to dramatic differencesbetween the perceived intensities and qualities of a mixtureand its components. These perceptions could be expressed andobserved at the behavioral level. Toward examining this question,we have tested the ability of the Florida spiny lobster (Panulirusargus) to behaviorally discriminate between three odorant compounds[adenosine 5'-monophosphate (AMP), L-glutamate (Glu), and taurine(Tau)] and their binary mixtures through the use of a differentialaversive associative conditioning paradigm. Six groups of lobsterswere used, each being conditioned to avoid one of the singlecompounds or binary mixtures. Behavioral expression of intensitymixture interactions was evident. Preconditioning response magnitudesto binary mixtures were either less than those to their components(e.g. AMP + Glu) or less than predicted from responses to theircomponents (e.g. AMP + Tau). Behavioral expression of patternmixture interactions was also observed. Relationships betweenthe quality of each binary mixture and the qualities of themixture's components were determined from the results of analysisof variance and multidimensional scaling analysis. Analysesincorporated observed responses to all stimuli and ‘predicted’responses to the binary mixtures. Lobsters easily discriminatedbetween the qualities of AMP, Glu and Tau. The quality of themixture of AMP + Glu was different from either component aswell as from the predicted value for this mixture. The mixtureof AMP + Tau was intermediate between both components and wassimilar to the predicted value. The mixture of Glu + Tau, whilemore similar to Glu than to Tau, was different from the predictedvalue, and there was some indication that the Glu was actingto suppress the response to Tau. Behavioral results for AMP+ Tau, which suggest no pattern mixture interactions betweenthese compounds, are in accordance with results of recentlyconducted binding assays which indicate independent receptorsfor these compounds (Olson et al., 1992). Results, especiallyfor AMP + Glu and Glu + Tau, are consistent with results ofour electrophysiological analysis of the effects of patternmixture interactions on coding of stimulus quality and intensityby olfactory receptor cells (Derby et al., 1991a,b). This providesfurther evidence for the effects of peripherally initiated mixtureinteractions on the coding and perception of the quality ofodorant mixtures. ¹Present address: Departments of Psychology and Biology, GeorgiaState University, University Plaza, Atlanta, Georgia 30303,USA     

Characterizing psychophysical measures of discrimination thresholds and the effects of concentration on discrimination learning in the moth Manduca sexta

What is the spatial and temporal nature of odor representations within primary olfactory networks at the threshold of an animal's ability to discriminate? Although this question is of central importance to olfactory neuroscience, it can only be answered in model systems where neural representations can be measured and discrimination thresholds between odors can be characterized. Here, we establish these thresholds for a panel of odors using a Pavlovian paradigm in the moth Manduca sexta. Moths were differentially conditioned to respond to one odor (CS+) but not another (CS-) using undiluted odorants to minimize salience-dependent learning effects. At 24 and 48 h postconditioning, moths were tested for the presence of a conditioned response (CR) with a blank, then the CS+ and CS- (pseudorandomly) across a 5-log step series of increasing concentration. Results identified discrimination thresholds and established that differential CRs to the CS+ and CS- increased with stimulus concentration. Next, 3 separate groups of moths were differentially conditioned at either one-log step below, at, or one log step above the identified discrimination threshold. At 24 and 48 h postconditioning, moths were tested sequentially with a blank, the concentration used for conditioning, and then undiluted odor. Conditioning at one log step below the discrimination threshold established a CR, indicating both stimulus detection and learning, but was insufficient to establish evidence of discrimination. Moths conditioned at the discrimination threshold were able to discriminate but only when stimulated with undiluted odors, indicating learning, but discrimination measures were hampered. When conditioned above the discrimination threshold, moths had no difficulty in discriminating. These results establish methods for psychophysical characterization of discrimination and indicate that differential conditioning at lowered concentrations biases threshold measures.     

Maintaining accuracy at the expense of speed: stimulus similarity defines odor discrimination time in mice

Odor discrimination times and their dependence on stimulus similarity were evaluated to test temporal and spatial models of odor representation in mice. In a go/no-go operant conditioning paradigm, discrimination accuracy and time were determined for simple monomolecular odors and binary mixtures of odors. Mice discriminated simple odors with an accuracy exceeding 95%. Binary mixtures evoking highly overlapping spatiotemporal patterns of activity in the olfactory bulb were discriminated equally well. However, while discriminating simple odors in less than 200 ms, mice required 70-100 ms more time to discriminate highly similar binary mixtures. We conclude that odor discrimination in mice is fast and stimulus dependent. Thus, the underlying neuronal mechanisms act on a fast timescale, requiring only a brief epoch of odor-specific spatiotemporal representations to achieve rapid discrimination of dissimilar odors. The fine discrimination of highly similar stimuli, however, requires temporal integration of activity, suggesting a tradeoff between accuracy and speed.     

Newborn Rabbit Perception of 6-Odorant Mixtures Depends on Configural Processing and Number of Familiar Elements

Perception of odors, i.e. usually of mixtures of odorants, is elemental (the odorants'' odor qualities are perceived in the mixture) or configural (the odor quality of the mixture differs from the one of each odorant). In human adults, the Red Cordial (RC) mixture is a configurally-processed, 6-odorant mixture. It evokes a red cordial odor quality while none of the elements carries that odor. Interestingly, in newborn rabbits, the same RC mixture is weak configurally perceived: the newborns behaviorally respond to all the elements after conditioning to the whole mixture, but not to the mixture after conditioning to a single element. Thus, they perceive in the RC mixture both the odor quality of the RC configuration and the quality of each element. Here, we aimed to determine whether this perception is modulated by quantitative (number of elements) and/or qualitative bits of information (nature of elements) previously learned by the animals. Newborns were conditioned to RC sub-mixtures of different complexity and composition before behavioral testing to RC. Pups generalized their sucking-related response to RC after learning at least 4 odorants. In contrast, after conditioning to sub-mixtures of another 6-odorant mixture, the elementally perceived M^V mixture, pups responded to M^V after learning one or two odorants. The different generalization to RC and M^V mixtures after learning some of their elements is discussed according to three hypotheses: i) the configural perception of RC sub-mixtures, ii) the ratio of familiar/unfamiliar individual information elementally and configurally perceived, iii) the perception of RC becoming purely elemental. The results allow the first hypothesis to be dismissed, while further experiments are required to distinguish between the remaining two.     

Avoidance conditioning in bamboo sharks (Chiloscyllium griseum and C. punctatum): behavioral and neuroanatomical aspects

Animals face different threats; to survive, they have to anticipate how to react or how to avoid these. It has already been shown in teleosts that selected regions in the telencephalon, i.e., the medial pallium, are involved in avoidance learning strategies. No such study exists for any chondrichthyan. In nature, an avoidance reaction may vary, ranging from a ‘freeze’ reaction to a startling response and quick escape. This study investigated whether elasmobranchs (Chiloscyllium griseum and C. punctatum) can be conditioned in an aversive classical conditioning paradigm. Upon successful conditioning, the dorsal, medial and lateral pallium were removed (group 1) and performance tested again. In a second group, the same operation was performed prior to training. While conditioning was successful in individuals of both groups, no escape responses were observed. Post-operative performance was assessed and compared between individual and groups to reveal if the neural substrates governing avoidance behavior or tasks learned in a classical conditioning paradigm are located within the telencephalon, as has been shown for teleosts such as goldfish.     

Can Honey Bees Learn the Removal of a Stimulus as a Conditioning Cue?

Experiments investigated a Pavlovian conditioning situation where the presence and absence of the stimulus are reversed temporally with respect to the presentation of a reward. Instead of a conditioned stimulus (e.g. odor) signaling the presence of a reward, the stimulus (e.g. odor) is present in the environment except just prior to the presence of the reward. Thus, the absence of the stimulus, or offset of the stimulus (e.g. absence of odor), serves as a conditioned stimulus and is the reward cue. Honey bees (Apis mellifera) were used as a model invertebrate system, and the proboscis‐conditioning paradigm was used as the test procedure. Using both simple Pavlovian conditioning and discrimination‐learning protocols, animals learned to associate the onset of an odor as conditioned stimuli when paired with a sucrose reward. They could also learn to associate the onset of a puff of air with a sucrose reward. However, bees could not associate the offset of an order stimulus with the presentation of a sucrose reward in either a simple conditioning or a discrimination‐learning situation. These results support the model that a very different cognitive architecture is used by invertebrates to deal with certain environmental situations, including signaled avoidance.     

Behavioral determination of stimulus pair discrimination of auditory acoustic and electrical stimuli using a classical conditioning and heart-rate approach

Acute animal preparations have been used in research prospectively investigating electrode designs and stimulation techniques for integration into neural auditory prostheses, such as auditory brainstem implants and auditory midbrain implants. While acute experiments can give initial insight to the effectiveness of the implant, testing the chronically implanted and awake animals provides the advantage of examining the psychophysical properties of the sensations induced using implanted devices. Several techniques such as reward-based operant conditioning, conditioned avoidance, or classical fear conditioning have been used to provide behavioral confirmation of detection of a relevant stimulus attribute. Selection of a technique involves balancing aspects including time efficiency (often poor in reward-based approaches), the ability to test a plurality of stimulus attributes simultaneously (limited in conditioned avoidance), and measure reliability of repeated stimuli (a potential constraint when physiological measures are employed). Here, a classical fear conditioning behavioral method is presented which may be used to simultaneously test both detection of a stimulus, and discrimination between two stimuli. Heart-rate is used as a measure of fear response, which reduces or eliminates the requirement for time-consuming video coding for freeze behaviour or other such measures (although such measures could be included to provide convergent evidence). Animals were conditioned using these techniques in three 2-hour conditioning sessions, each providing 48 stimulus trials. Subsequent 48-trial testing sessions were then used to test for detection of each stimulus in presented pairs, and test discrimination between the member stimuli of each pair. This behavioral method is presented in the context of its utilisation in auditory prosthetic research. The implantation of electrocardiogram telemetry devices is shown. Subsequent implantation of brain electrodes into the Cochlear Nucleus, guided by the monitoring of neural responses to acoustic stimuli, and the fixation of the electrode into place for chronic use is likewise shown.     

Conditioning ewes and lambs to increase consumption of spotted knapweed

Spotted knapweed (Centaurea maculosa Lam.) is an invasive plant that alters species composition and grazing value of rangelands in the northwestern United States. The spread of invasive plants may be reduced by using livestock as a biological control. We determined if mature ewes and their lambs (n = 34 ewe/lamb pairs) consume more spotted knapweed when ewes and/or lambs are conditioned to fresh-cut spotted knapweed. Ewe/lamb pairs were randomly assigned to one of four conditioning treatments: ewes and lambs not conditioned to spotted knapweed (N), conditioned ewes with non-conditioned lambs (E), non-conditioned ewes with conditioned lambs (L), or conditioned ewes and lambs (both—B). Then, ewes and lambs were observed together for 5 days (Trial 1); 11 days later, lambs were observed for 4 days without their mothers (Trial 2). During conditioning, intake by conditioned and non-conditioned ewes and lambs varied over time (as-fed basis, treatment by day interaction; ewes P = 0.03; lambs P = 0.05). Overall, non-conditioned lambs (N, E) consumed more than conditioned lambs (L, B; P = 0.02). In Trial 1, N ewes consumed similar amounts of spotted knapweed and bromegrass (Bromus inermis Leyss.) as the E, L, and B ewes (P = 0.67). E ewes spent more time eating spotted knapweed than L ewes (P = 0.001), and E ewe/lamb pairs consumed more spotted knapweed than L ewe/lamb pairs (P = 0.02). In Trial 2, N lambs consumed less spotted knapweed than E, L, and B lambs (P = 0.06). L lambs consumed more than E lambs (P = 0.007). Conditioning ewes, lambs, or ewes and lambs did not increase time spent eating spotted knapweed when both grazed together in a drylot, but conditioned lambs, without their mothers present, consumed more spotted knapweed 11 days later than non-conditioned lambs. Conditioning lambs only in a group setting with their peers may have the greatest potential to enhance consumption of spotted knapweed, because of social facilitation and the predilection for young animals to try novel feeds.     

Conditioning of active type avoidance in the rat : effect of the interval between conditioned stimulus and unconditioned stimulus

Lengthening the time interval between the conditioned stimulus and the unconditioned stimulus increases the number of active avoidance conditioned responses in subjects that have been trained to a stable level of performance in many previous conditioning sessions. In the present research, rats chosen from a population specially selected for low rates of avoidance conditioning have been used. In addition to this characteristic, subjects were chosen for the exhibition of an apparent absence of retention from one day to another. The dependency of the number of conditioned responses on the time interval between conditioned stimulus and unconditioned stimulus may lead to wrong evaluation of the subjects' conditioning level. In fact, the level of conditioning may be attributed to either learning or memory processes when in many cases it is determined only by the latency time of the conditioned response. The conditioned response has no possibility of manifesting itself when its latency time exceeds in length the time interval between conditioned stimulus and unconditioned stimulus.     

大鼠尾壳核的GABA能传递在条件性行为调控中的作用

本工作采用了行为和脑内注射相结合的方法研究了大鼠尾壳核的 GABA 能传递在条件性行为调控中的作用。在分辨学习的基础上训练大鼠完成条件性回避任务,以比较药物对分辨学习和条件性回避的不同效应。实验结果表明,于大鼠双侧尾壳核内分别注入 γ-氨基丁酸(GABA)(每侧100μg/μl)和 GABA 受体激动剂蝇蕈醇(Muscimol)(每侧0.1μg/μl)后可暂时抑制条件性回避反应的出现,但分辨学习无明显影响。作为对照,于尾壳核内注入等量的生理盐水则既不影响条件性回避反应,也不影响分辨学习。在条件性回避反应被 Muscimol抑制后于尾壳核内再注入 GABA 受体阻断剂印防己毒素(PTX)(每侧0.1μg/μl)则可拮抗Muscimol 的行为抑制效应,即条件反应的出现率可恢复到或接近注射前水平。实验结果表明,大鼠尾壳核的 GABA 能传递在条件性行为调控中的重要作用。     

Reversing Stimulus Timing in Visual Conditioning Leads to Memories with Opposite Valence in Drosophila

Animals need to associate different environmental stimuli with each other regardless of whether they temporally overlap or not. Drosophila melanogaster displays olfactory trace conditioning, where an odor is followed by electric shock reinforcement after a temporal gap, leading to conditioned odor avoidance. Reversing the stimulus timing in olfactory conditioning results in the reversal of memory valence such that an odor that follows shock is later on approached (i.e. relief conditioning). Here, we explored the effects of stimulus timing on memory in another sensory modality, using a visual conditioning paradigm. We found that flies form visual memories of opposite valence depending on stimulus timing and can associate a visual stimulus with reinforcement despite being presented with a temporal gap. These results suggest that associative memories with non-overlapping stimuli and the effect of stimulus timing on memory valence are shared across sensory modalities.     

Similar Odor Discrimination Behavior in Head-Restrained and Freely Moving Mice

A major challenge in neuroscience is relating neuronal activity to animal behavior. In olfaction limited techniques are available for these correlation studies in freely moving animals. To solve this problem, we developed an olfactory behavioral assay in head-restrained mice where we can monitor behavioral responses with high temporal precision. Mice were trained on a go/no-go operant conditioning paradigm to discriminate simple monomolecular odorants, as well as complex odorants such as binary mixtures of monomolecular odorants or natural odorants. Mice learned to discriminate both simple and complex odors in a few hundred trials with high accuracy. We then compared the discrimination performance of head-restrained mice to the performance observed in freely moving mice. Discrimination accuracies were comparable in both behavioral paradigms. In addition, discrimination times were measured while the animals performed well. In both tasks, mice discriminated simple odors in a few hundred milliseconds and took additional time to discriminate the complex mixtures. In conclusion, mice showed similar and efficient discrimination behavior while head-restrained compared with freely moving mice. Therefore, the head-restrained paradigm offers a relevant approach to monitor neuronal activity while animals are actively engaged in olfactory discrimination behaviors.     

Disruption of GABAA in the insect antennal lobe generally increases odor detection and discrimination thresholds

Studies of olfactory function show that disruption of GABA A receptors within the insect antennal lobe (AL) disrupts discrimination of closely related odors, suggesting that local processing within the AL specifically enhances fine odor discrimination. It remains unclear, however, how extensively AL function has been disrupted in these circumstances. Here we psychophysically characterize the effect of GABA A blockade in the AL of the moth Manduca sexta. We used 2 GABA A antagonists and 3 Pavlovian-based behavioral assays of olfactory function. In all cases, we used matched saline-injected controls in a blind study. Using a stimulus generalization assay, we found that GABA A disruption abolished the differential response to related odors, suggesting that local processing mediates fine odor discrimination. We then assessed the effect of GABA A antagonist on discrimination thresholds. Moths were differentially conditioned to respond to one odor (reinforced conditioned stimulus [CS+]) but not a second (unreinforced conditioning stimulus [CS-]) then tested for a significant differential conditioned response between them across a series of increasing concentrations. Here, GABA A blockade disrupted discrimination of both similar and dissimilar odor pairs as indicated by generally increased discrimination thresholds. Finally, using a detection threshold assay, we established that GABA A blockade also increases detection thresholds. Because detection is a prerequisite of discrimination, this later finding suggests that disrupted discrimination may be due to impairment of the ability to detect. We conclude that the loss of ability to detect and subsequently discriminate is attributable to a loss of ability of the AL to provide a clear neural signal from background.     

Second-Order Conditioning and Conditioned Inhibition: Influences of Speed versus Accuracy on Human Causal Learning

In human causal learning, excitatory and inhibitory learning effects can sometimes be found in the same paradigm by altering the learning conditions. This study aims to explore whether learning in the feature negative paradigm can be dissociated by emphasising speed over accuracy. In two causal learning experiments, participants were given a feature negative discrimination in which the outcome caused by one cue was prevented by the addition of another. Participants completed training trials either in a self-paced fashion with instructions emphasising accuracy, or under strict time constraints with instructions emphasising speed. Using summation tests in which the preventative cue was paired with another causal cue, participants in the accuracy groups correctly rated the preventative cue as if it reduced the probability of the outcome. However, participants in the speed groups rated the preventative cue as if it increased the probability of the outcome. In Experiment 1, both speed and accuracy groups later judged the same cue to be preventative in a reasoned inference task. Experiment 2 failed to find evidence of similar dissociations in retrospective revaluation (release from overshadowing vs. mediated extinction) or learning about a redundant cue (blocking vs. augmentation). However in the same experiment, the tendency for the accuracy group to show conditioned inhibition and the speed group to show second-order conditioning was consistent even across sub-sets of the speed and accuracy groups with equivalent accuracy in training, suggesting that second-order conditioning is not merely a consequence of poorer acquisition. This dissociation mirrors the trade-off between second-order conditioning and conditioned inhibition observed in animal conditioning when training is extended.     

Change in the signal properties of a conditioned stimulus during two-way avoidance conditioning in rats

Acquisition of two components of conditioned active avoidance behavior by rats was studied. First presentations of electroshock evoked a number of different behavioral reactions. However, after five trials many rats learned to escape punishment running away to another part of a shuttle-box. The efficiency of the avoidance reaction conditioning significantly depended on the ability of an animal to learn the correct escape reaction to the unconditioned stimulus. However, some animals were incapable for acquisition of the conditioned reaction despite their high level of successful escapes. Increase in the number of negative reactions to the conditioned stimulus (light) at the next stage of learning suggests that the conditioned stimulus becomes the signal of forthcoming punishment. The ability of an animal to identify the conditioned stimulus as a signal significantly affected the efficiency of conditioned avoidance acquisition.