Long-term potential for imprinting in ducks and chickens

In the first of five experiments, three of four adult ducks who had been reared in visual isolation gradually developed strong approach responses towards a moving panel of colored lights. Experiment 2 provided evidence that the ducks' approach response reflected the same sort of social attachment that is typically formed to moving objects by newly hatched ducklings. Experiment 3 revealed that the fourth duck would not approach the moving stimulus even after additional exposure to it, but would approach a conspecific after group housing had been enforced for seven days. In Experiment 4, none of five adult chickens who had been reared in visual isolation developed approach responses towards the moving stimulus, even though in Experiment 5, newly hatched chicks approached the stimulus quite readily. Taken together, these findings (a) indicate that ducks retain the ability to form filial-type attachments to novel objects throughout their lives, and (b) offer preliminary evidence that chickens do not retain this ability into adulthood.     

Autoshaping the pigeon's gape response: acquisition and topography as a function of reinforcer type and magnitude.

The pigeon's key-pecking response is experimentally dissociable into transport (head movement) and gape (jaw movement) components. During conditioning of the key-pecking response, both components come under the control of the conditioned stimulus. To study the acquisition of gape conditioned responses and to clarify the contribution of unconditioned stimulus (reinforcer) variables to the form of the response, gape and key-contact responses were recorded during an autoshaping procedure and reinforcer properties were systematically varied. One group of 8 pigeons was food deprived and subgroups of 2 birds each were exposed to four different pellet sizes as reinforcers, each reinforcer signaled by a keylight conditioned stimulus. A second group was water deprived and received water reinforcers paired with the conditioned stimulus. Water- or food-deprived control groups received appropriate water or food reinforcers that were randomly delivered with respect to the keylight stimulus. Acquisition of the conditioned gape response frequently preceded key-contact responses, and gape conditioned responses were generally elicited at higher rates than were key contacts. The form of the conditioned gape was similar to, but not identical with, the form of the unconditioned gape. The gape component is a critical topographical feature of the conditioned key peck, a sensitive measure of conditioning during autoshaping, and an important source of the observed similarities in the form of conditioned and consummatory responses.     

Context blocking in rat autoshaping: Sign-tracking versus goal-tracking

Prior experience of unsignaled food can interfere with subsequent acquisition by birds of autoshaped key-pecking at a signal light. This has been understood to indicate that unsignaled food results in context conditioning, which blocks subsequent learning about the keylight-food relationship. In the present experiment with rats lever insertion as the conditioned stimulus (CS) preceded sucrose delivery as the unconditioned stimulus (US). Half the rats initially received unsignaled USs in the conditioning context, while the remainder did not. Both lever-presses (sign-tracking) and magazine-entries (goal-tracking) were recorded. Under immediate reinforcement conditions, prior unsignaled US interfered with sign-tracking, but had no effect on goal-tracking. In two further groups, a trace condition prevented development of sign-tracking. In this case, prior context conditioning interfered with goal-tracking. These results suggest that interference with sign-tracking may reflect response competition, while interference with goal-tracking under trace conditions may reflect failure to acquire a CS-US association.     

Extinction-induced aggression during errorless discrimination learning

Pigeons were trained to discriminate without errors between a green light and a dark key. The key-pecking response was reinforced in the presence of green, and extinction was in effect in the presence of the dark key. The duration of the dark key was gradually increased during the first few sessions of conditioning. The opportunity to attack a restrained target pigeon was also present. During discrimination training, the rate of attack in the presence of the dark key was higher for each animal than the operant level, even though most of the animals acquired the discrimination without errors. Furthermore, the rate of attack did not decrease during 45 sessions of discrimination training. Attack also occurred in the presence of the green stimulus, although to a lesser extent than during extinction. Reinforcement during green is a determinant of attack during extinction because removal of reinforcement virtually eliminated attack during extinction.     

The effects upon food-reinforced pecking and treadle-pressing of auditory and visual signals for response-independent food

Seven pigeons whose key-pecking was maintained by food reinforcement on a differential-reinforcement-of-low-rates 12-sec limited-hold 4-sec schedule and 12 other pigeons whose treadle-pressing was maintained by the same schedule received appetitive Pavlovian conditioning trials superimposed upon the instrumental baseline. Half the birds in each group received a tone as the CS, and the other half received a stimulus change on the key. Each CS was 20 sec long, and was immediately followed by 10-sec access to grain. The visual CS markedly facilitated the rate of pecking on the key for the birds whose baseline response was pecking. The visual CS produced auto-shaping of the key-peck and tended to produce suppression of treadle-pressing for the birds whose baseline response was treadle-pressing. The auditory CS produced inconsistent effects across birds regardless of the baseline response. In all cases the conditioned effects extinguished when response-independent food was omitted.     

Discriminative taste aversion learning: a learning task for older chickens

The study of learning and memory using the chicken model has relied on three learning paradigms, passive avoidance learning, imprinting and the pebble floor task. Passive avoidance learning and imprinting have been used predominantly in very young chickens and cannot be used to access learning and memory in older chickens. We have established a new behavioural learning paradigm, Discriminative Taste Aversion Learning (DTAL), that can be used with both young and older animals. The task requires chickens to discriminate between food crumbs dyed either red or yellow with one colour being associated with the aversive tasting substance, methylanthranilate. Learning can be tested at various times after the training session by presenting chickens with the coloured food crumbs without an aversive taste. Both chickens tested at 5 and 15 days post-hatch learned to avoid the aversive crumbs. Furthermore, the protein synthesis inhibitor anisomycin (30 mM; 10 microl per hemisphere) injected into the intermediate medial hyperstriatum ventrale 15 min pre-training or 45 min post-training blocked long-term memory for the DTAL task when tested 24 h later. Memory for the task was unaffected by anisomycin injection 120 min post-training or in control animals injected with saline at similar times. The timing of the cellular processes of protein synthesis needed for consolidation of the DTAL appears to be similar to those described for the other behavioural paradigms in young chickens.     

Relative novelty of conditioning context influences directionality of glycemic conditioning

Previous experiments in which insulin was administered in a Pavlovian conditioning procedure obtained both hyperglycemic and hypoglycemic conditioned responses (CRs). In the present experiment the relationship of the conditioning context and the housing environment was varied. Two environments, wastebasket (WB) and metal cage (MC), were varied factorially as housing and conditioning contexts. Subgroups were injected with either insulin or saline for 6 days and then, on a test day for conditioning, all animals were administered saline. The results suggested that a hyperglycemic CR could be expected when the conditioning context is different from the housing context, but a hypoglycemic CR could be expected when the conditioning context and housing context are similar. The magnitude and reliability of conditioning were greater when it was conducted in the WB context than when conditioning was conducted in the MC context. These results are discussed in terms of stress arising from relative novelty of the conditioning environment and in terms of the salience of the conditioned stimulus (CS) used in glycemic conditioning studies.     

Role of the CS-US interval in the US preexposure effect

Theory and research suggest that long delay taste-aversion conditioning should be less affected by proximal US preexposure than short-delay conditioning. The present research tested this hypothesis by administering illness-inducing LiCl shortly before a saccharin-LiCl pairing in which the postsaccharin LiCl was administered either immediately or 20 min. after access to saccharin. The results suggest that US preexposure has a more deleterious effect on conditioning when the illness-inducing US is delayed in conditioning than when it is immediate. These results are to be expected on the basis of classical conditioning principles and question theory and research that suggest more deleterious effects of US preexposure with shorter intervals between the preexposed and conditioning US.     

Reevaluating evaluative conditioning: a nonassociative explanation of conditioning effects in the visual evaluative conditioning paradigm.

In 2 studies, the authors investigated whether evaluative conditioning (EC) is an associative phenomenon. Experiment 1 compared a standard EC paradigm with nonpaired and no-treatment control conditions. EC effects were obtained only when the conditioned stimulus (CS) and unconditioned stimulus (UCS) were rated as perceptually similar. However, similar EC effects were obtained in both control groups. An earlier failure to obtain EC effects was reanalyzed in Experiment 2. Conditioning-like effects were found when comparing a CS with the most perceptually similar UCSs used in the procedure but not when analyzing a CS rating with respect to the UCS with which it was paired during conditioning. The implications are that EC effects found in many studies are not due to associative learning and that the special characteristics of EC (conditioning without awareness and resistance to extinction) are probably nonassociative artifacts of the EC paradigm.     

Relative salience of species maternal calls in neonatal gallinaceous birds: a direct comparison of Japanese quail (Coturnix coturnix japonica) and domestic chickens (Gallus gallus domesticus)

Differential-approach tendencies of individual incubator-hatched chickens and Japanese quail were assayed using one exemplar of each of the species maternal calls in a simultaneous-choice paradigm. Within 24 hr after hatching, the birds received several short periods of exposure to rotating mounts of an adult female chicken and quail, which emitted the species-appropriate call. All birds were then tested with calls alone over the following 2 to 4 days. The test stimuli were played from speakers located behind pressure-sensitive panels so that approach behavior was recorded when a bird pushed against one of the panels. Both the chickens and the quail, as groups, spent significantly more time attempting to approach the exemplar of their own species maternal call, although there was considerable variation in the magnitude of the approach difference among individuals within each species. Sources of variation in preference scores are analyzed, and a simulation is used to interpret individual differences in response scores. This type of preference test is useful for a number of applications, notably for studying the behavior of quail-chick nervous system chimeras.     

The Influence of Retention Interval on the US Preexposure Effect: Changes in Contextual Blocking over Time

A number of studies manipulating the length of the interval between conditioning and testing indicate spontaneous recovery from overshadowing, suggesting that certain instances of overshadowing represent a deficit in memory retrieval rather than a failure of animals to form an association between the overshadowed stimulus and the US. The present series of experiments examined the influence of lengthening the retention interval on blocking, another stimulus selection phenomenon that is typically interpreted as an acquisition deficit. The results indicated that when subjects were tested shortly (3 days) after training conditioning to a taste blocked subsequent conditioning to an odor conditioned in compound with that taste (Experiment 1), whereas prior conditioning to an odor did not block subsequent conditioning to a taste conditioned in compound with that odor (Experiment 2). This pattern of results was essentially unchanged when testing occurred at a longer (21-day) retention interval. However, there was evidence of a US preexposure effect in Experiment 2 when subjects in the US ONLY control condition were tested at the 3-day retention interval, but not when testing occurred 21 days after conditioning. Experiments 3 and 4 examined whether this loss of the US preexposure effect over time might actually represent a change in the degree of contextual blocking as the retention interval is lengthened. Exposure to the conditioning context either during the interval between Phase 1 and Phase 2 of conditioning (Experiment 3) or prior to Phase 1 of conditioning (Experiment 4) alleviated this US preexposure effect suggesting that the loss of the US preexposure effect as the retention interval is lengthened observed in Experiment 2 is due to changes in the degree of blocking by contextual stimuli over time. The results are discussed in terms of differential susceptibility of forgetting of two functional roles played by a contextual stimuli in the current situation-context as a CS and context as a retrieval cue for other CS-US associations.     

Contextual conditioning and reinstatement of extinguished instrumental responding

In three experiments we studied the relationship between contextual conditioning and the reinstatement of extinguished lever pressing that occurs when noncontingent food is introduced following extinction. In all three experiments the non-contingent food was presented off-baseline (with the response levers not present). On subsequent tests, with the response levers present, animals that had been exposed to food showed more reinstatement of lever pressing than control animals. This finding rules out alternative mechanisms for the reinstated responding that rely on the interaction of non-contingent food and responding, such as superstitious reinforcement or the discriminative after-effects of food. In addition, in each experiment we demonstrated that manipulations known to affect contextual conditioning (signalling the food in Experiment 1, context extinction in Experiment 2, and switching contexts in Experiment 3) reduced the reinstatement. These results are consistent with the claim that contextual conditioning is important in controlling instrumental conditioning and closely parallel findings concerning the reinstatement of Pavlovian responsing following extinction.     

Domestic chicks perceive stereokinetic illusions

Stereokinetic illusions occur when certain 2-D patterns are set in slow rotation in a plane perpendicular to the line of sight. Such phenomena have never been investigated in animal species other than our own. We used the domestic chick (Gallus gallus) to check whether these illusions are experienced by non-human species, taking advantage of filial imprinting. Newly hatched visually naive chicks were individually exposed for 4 h to 2-D stimuli producing, to a human observer, the perception of a stereokinetic cone (experiment 1) or of a stereokinetic cylinder (experiment 2). Thereafter, each chick underwent a free-choice test between a solid 3-D cone and a solid 3-D cylinder. A control group of newly hatched but not imprinted chicks underwent the same testing procedure, to check for the presence of any spontaneous preference for one or other of the two solid objects. Imprinted chicks approached the 3-D stimulus closely resembling the stimulus they had been exposed to during imprinting (the cone in experiment 1 and the cylinder in experiment 2). Non-imprinted chicks did not show any preference. These results suggest that domestic chicks experience stereokinetic illusions.     

A response-spacing effect: an absence of responding during response-feedback stimuli

In most studies of operant reinforcement a response-feedback stimulus is used which is so brief that the nature of the responding during it is virtually undetectable. The present study investigated the nature of this responding by lengthening an initially brief feedback stimulus. The key-pecking responses of pigeons were maintained by a variable-interval schedule of food reinforcement. Each response produced a brief stimulus light in addition to the usual auditory response feedback. When the duration of the feedback stimulus light was gradually increased, it was found to control a nearly zero rate of responding. The result was a paced, metronomic-like performance in which the pigeon made a single response, paused until the stimulus terminated, and then responded again. As a result, the overall response rate was greatly reduced; the mean interresponse time approximated the stimulus duration. A plausible interpretation is that brief feedback stimuli acquire control over responding because they coincide with few responses and few reinforcers. These findings show that in addition to their known functions as conditioned-reinforcing stimuli and discriminative stimuli, response-feedback stimuli also exert direct stimulus control: responding is reduced during the feedback stimulus itself.     

Metyrapone reveals that previous chronic stress differentially impairs hippocampal-dependent memory

Chronic stress facilitates fear conditioning in rats with hippocampal neuronal atrophy and in rats in which the atrophy is prevented with tianeptine, a serotonin re-uptake enhancer. The purpose of this study was to determine whether the lack of dissociation between fear conditioning performance and hippocampal integrity was masked by the presence of endogenous corticosteroids during training. As in previous studies, rats were stressed by daily restraint (6 h/day for 21 days), trained in the conditioning chamber (day 23), and then assessed for conditioned fear (day 25) at a time when hippocampal dendritic atrophy persists. On the training day, half of the control and stressed rats were. injected with metyrapone to reduce corticosterone release. Two hours later, two paired or unpaired presentations of tone and footshock were delivered. Although metyrapone reduced conditioned fear in all rats, only stressed rats showed dissociated fear conditioning (i.e. tone conditioning was reduced while contextual conditioning was eliminated). Chronically stressed rats, regardless of metyrapone treatment displayed more rearing in the open field when tested immediately after the completion of fear conditioning. These data support the hypothesis that increased emotionality and enhanced fear conditioning exhibited by chronically stressed rats maybe due to endogenous corticosterone secretion at the time of fear conditioned training. Moreover,these data suggest that chronic stress impairs hippocampal-dependent processes more robustly than hippocampal-independent processes after metyrapone to reduce corticosterone secretion during aversive training.     

对条件化恐惧反应的抑制效应:指导性与习惯性情绪调节的作用

为了考察实验室指导性与个体习惯性情绪调控策略对恐惧反应的影响,先使用问卷调查了81名大学生的习惯性重评与抑制水平,随后将被试分为两组,指导其在条件化恐惧习得过程中进行主动的情绪调节或自然观看,24h后进行恐惧的表达测试。结果发现,习惯性抑制水平与恐惧习得及表达水平呈显著负相关,且指导性情绪调节与习惯性抑制均显著降低了恐惧习得及表达水平。这提示指导性与习惯性情绪调节策略均能够削弱应激的伤害以保护个体。     

Enkephalins and learning and memory: a review of evidence for a site of action outside the blood-brain barrier

A series of studies indicate that enkephalins exert dramatic influences on learning and memory in rats and mice, when studied with conditioning tasks that are both negatively and positively motivated. Pharmacological analysis of these enkephalin actions on conditioning suggests that the [leu]enkephalin acts through a delta opioid receptor which is located outside the blood-brain barrier. Control studies indicate that enkephalins do not simply affect the performance of a conditioned response through actions on shock sensitivity or locomotor activity. Characterization of the peripheral enkephalin mechanism that affects behavior suggests an action through an enzymatic system that controls the concentrations of enkephalin present at its receptors in the periphery. This enzymatic mechanism is sensitive to experience, since its activity changes following conditioning, which suggests that it may be a regulatory mechanism for behavior.     

Some effects of discriminative training with equated frequency of reinforcement

Pigeons were exposed to a multiple schedule which provided equally frequent reinforcement in the presence of two stimuli but which produced markedly different rates of key-pecking. Generalization gradients were displaced away from the stimulus associated with the lower rate of key-pecking. Another group of pigeons had similar training, except that a low rate of key-pecking was established in a stimulus with a much higher frequency of food reinforcement. In this case, the generalization gradients were not affected by the training on the schedule producing a low response rate.     

Genetic background differences and nonassociative effects in mouse trace fear conditioning

Fear conditioning, including variants such as delay and trace conditioning that depend on different neural systems, is widely used to behaviorally characterize genetically altered mice. We present data from three strains of mice, C57/BL6 (C57), 129/SvlmJ (129), and a hybrid strain of the two (F(1) hybrids), trained on various versions of a trace fear-conditioning protocol. The initial version was taken from the literature but included unpaired control groups to assess nonassociative effects on test performance. We observed high levels of nonassociative freezing in both contextual and cued test conditions. In particular, nonassociative freezing in unpaired control groups was equivalent to freezing shown by paired groups in the tests for trace conditioning. A number of pilot studies resulted in a new protocol that yielded strong context conditioning and low levels of nonassociative freezing in all mouse strains. During the trace-CS test in this protocol, freezing in unpaired controls remained low in all strains, and both the C57s and F(1) hybrids showed reliable associative trace fear conditioning. Trace conditioning, however, was not obtained in the 129 mice. Our findings indicate that caution is warranted in interpreting mouse fear-conditioning studies that lack control conditions to address nonassociative effects. They also reveal a final set of parameters that are important for minimizing such nonassociative effects and demonstrate strain differences across performance in mouse contextual and trace fear conditioning.     

Effects of ventral and dorsal CA1 subregional lesions on trace fear conditioning

Recent lines of research have focused on dissociating function between the dorsal and ventral hippocampus along space and anxiety dimensions. In the dorsal hippocampus, the CA1 subregion has been implicated in the acquisition of contextual fear as well as in the trace interval in trace fear conditioning. The present study was designed to test the relative contributions of dorsal (dCA1) and ventral CA1 (vCA1) in trace fear conditioning. Long-Evans rats received ibotenate lesions of the ventral CA1 (n=7), dorsal CA1 (n=9), or vehicle control lesions (n=8) prior to trace fear conditioning acquisition. Results suggest dCA1 and vCA1 groups show no significant deficits during acquisition when compared to control groups. dCA1 and vCA1 both show deficits in the retention of contextual fear when tested 24 h post-acquisition (P<.05 and P<.01, respectively), and vCA1 was impaired relative to dCA1 (P<.05). This is suggestive of a graded involvement in contextual retention between the dorsal and ventral aspects of CA1. dCA1 showed no deficit for retention of conditioned fear to the tone or the trace when tested 48 h post-acquisition, whereas vCA1 did show a significant deficit for the trace interval and a slight, non-significant reduction in freezing to the tone, when compared to the control group (p<.05). Overall the data are suggestive of a graded involvement in retention of fear conditioning between the dorsal and ventral aspects of CA1, but it is likely that vCA1 may be critically involved in retention of trace fear conditioning.