Helen Kaye

The strength of the orienting response during Pavlovian conditioning.

The strength of orienting toward a light that signaled food was studied in five experiments. Experiment 1 demonstrated that this response declined in strength during conditioning but was temporarily restored during extinction. In Experiment 2 the light was again paired immediately with the unconditioned stimulus (US), whereas in Experiments 3 and 4 it signaled a tone which in turn signaled the US. In these three experiments we again found that continuous reinforcement resulted in a decline in the strength of light orientation. These studies also revealed that under conditions of partial reinforcement, orientation to the light was sustained. Experiment 5 demonstrated that the decline in light orientation with a continuous reinforcement procedure can be retarded either by preexposing the light for a number of trials prior to conditioning or by intermixing reinforced light trials with nonreinforced presentations of a tone. This experiment also revealed that reversing the reinforcement contingency associated with the tone restored orientation to the light. This pattern of results can be most readily explained by the proposal that the strength of orientation toward the light is inversely related to the predictive accuracy of this stimulus.

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.

Hippocampal lesions attenuate latent inhibition of a CS and of a neutral stimulus

Rats with hippocampal or sham lesions were exposed extensively to a tone. Subgroups received either nonreinforced presentations of this stimulus or tone-mild footshock pairings. The subjects subsequently received pairings of the tone with a stronger footshock, and it was found that animals with hippocampal lesions learned this relationship more rapidly than did controls, regardless of whether they had received reinforced or nonreinforced prior experience with the tone. Comparisons with other control groups for which the tone was novel indicated that exposure reduced the associability of that stimulus for sham-operated rats. These results suggest that hippocampal lesions may disrupt a common mechanism underlying the loss of associability that occurs after exposure of a CS and of a neutral stimulus.

Odour of pyrazine potentiates an association between environmental cues and unpalatable taste

Abstract Two experiments examined the ability of rats, Rattus norvegicus, to discriminate an aversive quinine solution from unadulterated tap water when the presence of one of the liquids was accompanied by a pyrazine odour. Experiment 1 demonstrated that subjects would readily learn to avoid drinking in the presence of pyrazine when it had previously signalled quinine, but to drink normally when pyrazine had been paired with ‘safe’ water. In experiment 2 quinine and water were presented in discriminably different contexts. Pyrazine odour aided, or potentiated, learning about the context-taste associations compared with a control in which pyrazine was not presented during discrimination training. These results are discussed in terms of the possible roles that pyrazines and other odours might play in prey selection.

The Strength of the Orienting Response during Blocking

In two experiments rats initially received appetitive Pavlovian conditioning with an auditory conditioned stimulus (CS). Subsequently this stimulus was presented in compound with a novel light and paired with the same appetitive reinforcer. In keeping with the outcome of many such experiments on blocking, there was very little evidence of appetitive conditioning during subsequent independent presentations of the light. Of main concern in the present experiments, however, was the influence of this training on the strength of the orienting response directed towards the light. When the light was first presented it elicited a strong orienting response. The strength of this response declined rapidly when the light was presented in compound with the previously trained auditory CS but more slowly when it was paired with the reinforcer either by itself or in conjunction with an initially neutral auditory stimulus. It is suggested that the extent to which the events following the light are accurately predicted determines the strength of orientation towards this stimulus.

Strength of the orienting response during inhibitory conditioning.

The strength of the orienting response to a light was investigated in three inhibitory conditioning experiments. In Experiment 1 the occurrence of the light was negatively correlated with food delivery; this procedure resulted in a decline in the strength of the orienting response. A more rapid decline in the strength of this response was observed in rats receiving the light and food presented randomly or the light presented alone. In the remaining experiments a discrimination procedure was used in which the light was presented, nonreinforced, simultaneously with a tone. On reinforced trials the tone was presented alone and was followed either directly by food (Experiment 2) or by a clicker that signaled food (Experiment 3). The results from these studies were very similar to those of Experiment 1. It is concluded that the strength of the orienting response to a light may reflect the amount of attention or central processing that it receives, which itself is determined by the accuracy with which its immediate consequences are predicted. In a typical Pavlovian conditioning procedure, the repeated pairings of a conditioned and unconditioned stimulus (CS and US) result in the formers acquiring the capacity to elicit responses appropriate to the occurrence of the latter. In general, the CS is initially a motivationally neutral stimulus, but this is not to say that it does not possess response-eliciting properties in its own right. Pavlov (1927) observed that the presentation of a novel, neutral stimulus will result in its eliciting what he termed an investigatory reflex that brings about the immediate response in man and animals to the slightest changes in the world around them so that they immediately orientate their appropriate receptor organ in accordance with the perceptible quality in the agent bringing about the change, making the full investigation of it. (p. 12) More recently this response has become the focus of attention in research with humans and is more commonly referred to as the orienting response (OR) (cf. Sokolov, 1963). The purpose of the present article is to

A comparison of the effects of partial reinforcement schedules using a within-subject serial autoshaping procedure

Three experiments, each using a single group of pigeons, are reported. In Experiment 1 subjects were initially trained with two stimuli, one of which was always followed by food, the other being reinforced according to a 50% partial reinforcement schedule. Subsequently a serial procedure was adopted in which an additional stimulus, C, was consistently followed by the partially reinforced CS. A second additional stimulus, A, was followed on half of its occurrences by the continuously reinforced CS, its remaining presentations being followed by nothing. The rate of autoshaped keypecking was substantially greater during A than during C. In the remaining experiments subjects received first-order conditioning with a single stimulus that was either partially (Experiment 2) or continuously (Experiment 3) reinforced. The stimuli A and C were then again introduced for serial autoshaping. Stimulus A was occasionally paired with the CS and occasionally followed by nothing, whereas stimulus C was always followed by the CS. As in Experiment 1, the rate of responding during A was greater than during C. It is proposed that one influence on the rate of autoshaped keypecking during a CS is the accuracy with which the immediate consequences of that CS are predicted.

Distractor effects on latent inhibition are a consequence of generalization decrement

In two experiments rats were exposed to a novel vinegar solution and subsequently given a single conditioning trial on which consumption of vinegar was followed by an injection of lithium chloride. In conformity to other results on distractor effects, the latent inhibition produced by this treatment could be disrupted if the rats drank a second novel solution (sucrose) immediately after their initial exposure to vinegar. But latent inhibition was equally disrupted if rats were initially exposed to vinegar alone and subsequently drank vinegar immediately followed by sucrose on the conditioning trial. Thus latent inhibition was disrupted whenever there was a change between the solutions presented on initial exposure and conditioning trials. Generalization decrement seems the most parsimonious explanation of this pattern of results.

Habituation as a function of similarity and temporal location of target and distractor stimuli

Three experiments examined the habituation of rats’ neophobia to novel flavors, and the disruption of that habituation by presentation of a distractor flavor either immediately before or immediately after the target flavor. Habituation of neophobia to lemon solution was more seriously disrupted by presentation of saline as a distractor than by presentation of coffee as a distractor, and this was true whether the distractor was presented before or after the target on each habituation trial. Two further experiments established that the relative ineffectiveness of coffee as a distractor could not be attributed to its lack of salience, and was probably related to its greater similarity to the target lemon flavor. These results do not fully accord with those reported by Robertson and Garrud (1983), but are readily explained in terms of generalization of habituation between distractor and target flavors.