Ignacio Loy

Blocking of conditioning of tentacle lowering in the snail (Helix aspersa)

Experiment 1 established the effectiveness of an appetitive conditioning of odours procedure with snails (Helix aspersa) that was subsequently used for the study of blocking. In this important phenomenon, the conditioning of a CS1 (where CS is the conditioned stimulus) prior to conditioning of a compound, CS1CS2, blocked the conditioning to the CS2. Experiments 2a, 2b, and 2c demonstrated this associative effect using three different experimental controls. Experiments 3a and 3b replicated the blocking effect and allowed us to reject an explanation of blocking based on generalized effects of several treatments of diverse stimuli in blocking and control groups (the pseudoblocking effect). The implications of these results for the study of invertebrate cognition by means of conditioning techniques are discussed.

Conditioning of tentacle lowering in the snail (Helix aspersa): Acquisition, latent inhibition, overshadowing, second-order conditioning, and sensory preconditioning

In a series of related experiments, we studied associative phenomena in snails (Helix aspersa), using the conditioning procedure of tentacle lowering. Experiments 1A and 1B demonstrated a basic conditioning effect in which the pairing of an odor (apple) as the conditioned stimulus (CS) with the opportunity to feed on carrot as the unconditioned stimulus (US) made snails exhibit increased levels of tentacle lowering in the presence of the CS. Experiments 2 and 3 showed that the magnitude of the conditioning was reduced when snails were exposed to the CS prior to the conditioning trial (a latent inhibition effect). Experiment 4 examined the effects produced by pairing a compound CS (apple—pear) with food presentations and demonstrated the existence of an overshadowing effect between the two odors. Experiment 5 revealed that pairing one CS with another previously conditioned stimulus increased tentacle lowering to the new CS (a second-order conditioning effect). Finally, Experiment 6 showed that pairing two odors prior to conditioning of one of them promoted an increase in tentacle lowering in response to the other (a sensory preconditioning effect). The results are discussed in terms of an associative analysis of conditioning and its implications for the study of cognition in invertebrates.

Blocking in rats, humans and snails using a within-subjects design

The present research investigated the blocking effect in three different species, rats, humans and snails in formally equivalent tasks using a within-subjects design. Experiment 1 demonstrated the blocking effect in a context-flavour aversive conditioning preparation in rats: Animals failed to associate a flavour with an illness episode when it was presented in a context in which the illness was already predicted by other cues. Experiment 2 replicated this blocking effect in humans assessing their ability to learn a goal location in a virtual environment: Participants failed to learn the location of the goal in reference to a spatial cue presented alongside other pre-trained spatial cues that already indicated its location. Finally, in Experiment 3, snails failed to associate an odour with the presentation of food in the presence of other odours that already reliably predicted its presentation. The present study offers a start point for systematic comparisons between vertebrate and invertebrate species in formally equivalent tasks that produce univocal demonstrations of the blocking effect.

Conditional control of toxicosis-based conditioning by context.

This experiment with rat subjects used a conditional discrimination procedure to study the contextual control of flavour aversions. Rats were first given discrimination training with two distinctive contexts, such that a flavour was paired with lithium chloride (LiCl) in context A, alternating with presentations of the flavour alone in context B. Having learned this discrimination, the animals were now required to learn that a second flavour was followed by toxicosis in context B and nonreinforced in the other context. The rats were capable of learning to reject each of the flavours in the context where the fluid-LiCl pairings had been given, but not in the alternative context. This result is interpreted as evidence that the context acts as an occasion setter in the sense that it controls the effectiveness of a conditioned aversion in a manner independent of any direct context-illness association.

Associative learning phenomena in the snail (Helix aspersa): Conditioned inhibition

Two experiments using garden snails (Helix aspersa) showed conditioned inhibition using both retardation and summation tests. Conditioned inhibition is a procedure by which a stimulus becomes a predictor of the absence of a relevant event—the unconditioned stimulus (US). Typically, conditioned inhibition consists of pairings between an initially neutral conditioned stimulus, CS2, and an effective excitatory conditioned stimulus, CS1, in the absence of the US. Retardation and summation tests are required in order to confirm that CS2 has acquired inhibitory properties. Conditioned inhibition has previously been found in invertebrates; however, these demonstrations did not use the retardation and summation tests required for an unambiguous demonstration of inhibition, allowing for alternative explanations. The implications of our results for the fields of comparative cognition and invertebrate physiological models of learning are discussed.

Coordinating associative and ecological accounts of learning in the garden snail Cornu aspersum

Pavlovian conditioning of tentacle lowering in the snail, Cornu aspersum, as an instance of associative learning, has proven effective to show evidence of paradigmatic associative phenomena (e.g., blocking) explained by current models of conditioning. Nevertheless, the available literature questions the biological function of the conditioned response (i.e., tentacle lowering) in snails since no advantages in terms of food finding had been observed. Ecological accounts of learning claim that learning abilities contribute to the adaptation to the environmental demands, and there is experimental evidence supporting this in several species (e.g., grasshoppers, fish, or antlions). However, there is a lack of evidence in snails, which is surprising given that the conditioned response of tentacle lowering is a robust finding that fits in with several predictions of associative learning theory (e.g., blocking or conditioned inhibition). The goal of this manuscript was to test whether food detection is affected by prior experience with the food, distance, and conditioning. We found that prior experience with a food source is necessary for snails to locate the same food item; that the optimal distance to test for food detection is between 5 and 7cm and that snails seem to use different food searching strategies after conditioning depending on the stimuli that are present. The data provided constitute a small contribution to the vindication of a greater coordination between the fruitful research tool provided by the associative account of learning and the evolutionary vocation of the ecological approach of learning.

Extinction, spontaneous recovery and reinstatement in the garden snail, Helix aspersa

Extinction and its related phenomena are central to the study and development of associative learning theory. For a better understanding of the processes involved in extinction, it is important to know how general these phenomena are in different species. Extensive evidence of extinction in invertebrate species would be necessary in order to test the generality of its current theoretical and physiological accounts. We carried out three sets of experiments using terrestrial snails Helix aspersa. The repeated nonreinforced presentation of the conditioned stimulus (CS) resulted in a decrease in responding (extinction); the introduction of a delay between the extinction of a CS and its test produced an increase in responding (spontaneous recovery); and re-exposure to the unconditioned stimulus after extinction also led to an increase in responding (reinstatement). The results are discussed in relation to current interference theories of extinction.

A test of Rescorla and Wagner’s (1972) prediction of nonlinear effects in contingency learning

According to most theories, in a simple contingency learning situation, excitatory learning occurs when the probability of the unconditioned stimulus in the presence of the conditioned stimulus (p1) is higher than the probability of the unconditioned stimulus in the absence of the conditioned stimulus (p2). In Rescorla and Wagner’s (1972) model, this prediction varies, depending on the parameters used. In the following experiments, we evaluated whether the difference between p1 and p2 that is required to produce excitatory conditioning is the same, independent of the specific value of p1, or whether this difference varies proportionally to p1’s value. To do so, an appetitive procedure of Pavlovian conditioning with rats was used. In four experiments, we compared different levels of contingency (low, medium and high) and found that the difference between p1 and p2 that is required to produce excitatory conditioning increases when the value of p1 is higher. The possibility of analyzing contingency learning as a discrimination between p1 and p2 is also discussed.