Taste Aversion Learning Based on Swimming and Lithium Chloride Injection in Rats: Implications From Cross-familiarization Tests and Stimulus Selectivity1

In rats, swimming causes avoidance of the taste solution consumed immediately before the swimming. Several lines of research have shown that this taste avoidance reflects Pavlovian conditioned aversion based on correlations between the taste and swimming-induced nausea. The present research compared swimming-based taste aversion learning (TAL) with conventional TAL based on nausea-inducing lithium chloride (LiCl). By exploiting cross-familiarization techniques, Experiments 1A and 1B suggested that different physiological states are induced by swimming and LiCl. This claim was supported by Experiment 2, which reports stimulus selectivity in saccharin and sucrose aversions based on swimming and LiCl.     

Failure of Retrospective Inference in Rats' Taste Aversion

Three experiments explored the possibility of retrospective inference in the rat. Experiment 1 revealed that poisoning of an element of a taste compound after single compound poisoning enhanced aversion to the other element, and that presentation of an element without poison after the compound poisoning reduced aversion to the other element. These results were opposite to those predicted by retrospective inference. Experiment 2 eliminated some confounding variables and examined the effect of element poisoning after compound poisoning. The result again was opposite to what the retrospective view predicts. The results, however, accorded with the idea that within-compound learning was established during compound presentation, and subsequent poisoning or nonpoisoning of one element affected response to the other element via the within-compound learning. In Experiment 3, the possibility of within-compound learning was reduced by using sequential presentation of tastes, but there was no indication of retrospective inference even under this condition.     

Modulation of Taste Aversions by a Pentobarbital Drug State: An Assessment of Its Transfer Properties

In a drug-discrimination procedure using conditioned taste aversions, a pentobarbital injection signaled a taste–toxin pairing while the vehicle injection signaled the same taste in the absence of the toxin. In transfer tests, drug states transferred control over consumption to other targets. If the training target was a fluid (saccharin), then transfer occurred to other fluids (both novel and familiar) but not to solid food. If the training target was food, then some transfer occurred to novel targets (both fluids and solid food) but not to familiar targets. Control rats revealed that the differential consumption seen during acquisition and during transfer tests was not due to the summation of two simple associations (i.e., drug–toxin and flavor–toxin) but rather reflected conditional control over consumption by the drug state.     

Timing at the Start of Associative Learning

Some theories of associative learning imply that time plays a fundamental role in the acquisition process. Consistent with these theories, this paper presents evidence that the time from the onset of a conditioned stimulus (CS) until presentation of the unconditioned stimulus (US) is learned very rapidly at the start of training. We report two autoshaping studies and a study on aversive conditioning in goldfish in which we examine timing at the start of conditioning. We also review data from a number of other conditioning preparations, including fear-potentiated startle, appetitive conditioning in rats, and eyeblink conditioning in rabbits, that report conditioned response (CR) timing early in training. Acquisition speed and the very first expressions of conditioned responding often show sensitivity to the time of US presentation. In instances where temporal control is slowly expressed, it is likely due to performance factors, not to slow learning about time. In fact, the learning about time may be a necessary condition for associative learning.     

味觉厌恶性条件反射建立后脑内c-Fos的表达

以新异味觉刺激糖精水的摄入为条件刺激,以腹腔注射环磷酰胺(CY,免疫抑制剂)或氯化锂(LiCl)为非条件刺激,分别使大鼠建立味觉厌恶性条件反射.在条件刺激日,糖精水在学习组大鼠下列脑区中诱发出密集的Fos表达下丘脑、杏仁核、边缘皮质等,而非学习组在这些区域中却没有或只有少量表达.另外,在丘脑前背侧核、扣带回、下丘脑外侧核、穹隆下器、压部后颗粒皮质、视上核,CY组的Fos表达明显多于LiCl组;而在伏核、杏仁基底外侧核、腹外侧隔核,LiCl组的Fos表达明显多于CY组,这种差异可能是两种药物的不同药理性质所致.     

Induction of Relational Schemas: Common Processes in Reasoning and Complex Learning

Five experiments were performed to test whether participants induced a coherent representation of the structure of a task, called a relational schema, from specific instances. Properties of a relational schema include: An explicit symbol for a relation, a binding that preserves the truth of a relation, potential for higher-order relations, omnidirectional access, potential for transfer between isomorphs, and ability to predict unseen items in isomorphic problems. However relational schemas are not necessarily coded in abstract form. Predictions from relational schema theory were contrasted with predictions from configural learning and other nonstructural theories in five experiments in which participants were taught a structure comprised of a set of initial-state,operator → end-state instances. The initial-state,operator pairs were presented and participants had to predict the correct end-state. Induction of a relational schema was achieved efficiently by adult participants as indicated by ability to predict items of a new isomorphic problem. The relational schemas induced showed the omnidirectional access property, there was efficient transfer to isomorphs, and structural coherence had a powerful effect on learning. The “learning to learn” effect traditionally associated with the learning set literature was observed, and the long-standing enigma of learning set acquisition is explained by a model composed of relational schema induction and structure mapping. Performance was better after reversal of operators than after shift to an alternate structure, even though the latter entailed more overlap with previously learned tasks in terms of the number of configural associations that were preserved. An explanation for the reversal shift phenomenon in terms of induction and mapping of a relational schema is proposed. The five experiments provided evidence supporting predictions from relational schema theory, and no evidence was found for configural or nonstructural learning theories.     

Latent Inhibition Depends on Inhibitory Attentional Learning to the Preexposed Stimulus: Evidence from Visual Search and Rule-Learning Tasks

Latent inhibition (LI) refers to findings of poorer learning with stimuli preexposed as irrelevant, compared to novel stimuli. In order to investigate the role of attention in traditional LI, two experiments with human subjects were conducted. Experiment 1 used a simplified visual-search design. As in previous studies, but now with a simpler design, there was a LI-like effect, thereby supporting the position that attentional learning to irrelevantly preexposed stimuli is reduced. Experiment 2 introduced conditions that were designed to exclude a potential contribution of novel popout to the visual-search LI-like effect. It was shown that the effect could be observed independently of contributions from novel popout. In addition, when participants were divided into good and poor attentional learners on the basis of visual-search LI scores, traditional rule-learning LI was established in good attentional learners, whereas it was absent in poor attentional learners. Together, these results indicate that visual-search procedures can be used to provide a measure for LI, and, as such, they support attention-based explanations of traditional LI.     

When All Is Revealed: A Dissociation between Evaluative Learning and Contingency Awareness

Three experiments are reported that address the issue of awareness in evaluative learning in two different sensory modalities: visual and haptic. Attempts were made to manipulate the degree of awareness through a reduction technique (by use of a distractor task in Experiments 1 and 2 and by subliminally presenting affective stimuli in Experiment 3) and an induction technique (by unveiling the evaluative learning effect and requiring participants to try to discount the influence of the affective stimuli). The results indicate overall that evaluative learning was successful in the awareness-reduction groups but not in the awareness-induction groups. Moreover, an effect in the opposite direction to that normally observed in evaluative learning emerged in participants aware of the stimulus contingencies. In addition, individual differences in psychological reactance were found to be implicated in the strength and direction of the effect. It is argued that these results pose serious problems for the contention that awareness is necessary for evaluative learning.     

Cannabinoid agonists and antagonists modulate lithium-induced conditioned gaping in rats

Considerable evidence indicates that conditioned gaping in rats reflects nausea in this species that does not vomit. A series of experiments evaluated the potential of psychoactive cannabinoid agonists, Δ-9-THC and HU-210, and non-psychoactive cannabinoids, Cannabidiol (CBD) and its dimethylheptyl homolog (CBD-dmh), to interfere with the establishment and the expression of conditioned gaping in rats. All agents attenuated both the establishment and the expression of conditioned gaping. Furthermore, the CB1 antagonist, SR-141716, reversed the suppressive effect of HU-210 on conditioned gaping. Finally, SR-141716 potentiated lithium-induced conditioned gaping, suggesting that the endogenous cannabinoid system plays a role in the control of nausea.     

The CS-Preexposure Effect in Conditioned Taste-Aversion Learning in Golden Hamsters

In Experiment 1, golden hamsters were injected with either 0.9% saline or the nausea-inducing agent, lithium chloride (LiCL), immediately after consuming a flavored diet that was either novel or familiar. The LiCl-induced aversion was strong in hamsters for which the flavored diet was novel, but no significant aversion was observed in hamsters that were familiar with the flavored diet. In Experiment 2, the strength of the LiCl-induced aversion was related inversely to the amount of conditioned-stimulus (CS) preexposure and directly to the duration of the preexposure-conditioning interval. Thus, although some previous researchers have suggested that hamsters may not demonstrate the CS-preexposure effect in a conditioned taste-aversion paradigm, they clearly did so under the conditions of the present experiments, and moreover, the characteristics of the CS-preexposure effect in hamsters were generally similar to those observed in rats.     

General Learned Irrelevance and Its Prevention

Random presentation of a tone and an electric shock to rats interfered with subsequent acquisition of a light–shock association. This interference, or “general learned irrelevance” phenomenon, however, could be prevented by prior learning of a positive relationship between the tone and the shock or that between a noise and the shock. These results strongly support the ideas that animals learn irrelevant stimulus relationships and that prior experience of stimulus relevance prevents learning irrelevance. The similarity of this observed prevention effect to an immunization effect on learned helplessness phenomena is discussed.     

Affective-Evaluative Learning in Humans: A Form of Associative Learning or Only an Artifact?

The status of evaluative conditioning (EC) as a distinct form of associative learning was called in question by Field and Davey (1997, 1998, 1999), who argued that in the typical visual EC paradigm, nonassociative visual concept learning is responsible for the evaluative changes observed. Especially, the use of only within-subject control conditions instead of independent control groups was criticized. The present three experiments show (a) that EC effects can be demonstrated within another sensory modality than visual perception and (b) that EC effects are demonstrable in a between-subject design (including a successful replication attempt). A further result was that these EC effects do not require participants' conscious awareness. The data provide no support for an artifactual account of EC but suggest an interpretation of EC as a form of associative learning.     

Lifelong estrogen exposure and cognitive performance in elderly women

Fluctuating endogenous and exogenous estrogens influence cognition in women. In this study, cognitive functioning in elderly women was examined by applying methodology used in understanding the effects of chronic estrogen exposure on hormone-sensitive tissue other than the brain. An index, combining menstrual, reproductive, and physical markers associated with estrogen levels, was developed for elderly, nondemented, predominantly Caucasian women (n = 87). This index related to better performance on two verbal factors, one attentional and one global in nature. Findings suggest that estrogen exposure across the life span plays a role in brain aging. Possible physiological mechanisms for this effect are discussed.     

Convergent cortical representation of semantic processing in bilinguals

This study examined whether semantic processes in two languages (English and Spanish) are mediated by a common neural system in fluent bilinguals who acquired their second language years after acquiring their first language. Functional magnetic resonance imaging was performed while bilingual participants made semantic and nonsemantic decisions about words in Spanish and English. There was greater activation for semantic relative to nonsemantic decisions in left and right frontal regions, with greater left frontal activation. The locations of activations were similar for both languages, and no differences were found when semantic decisions for English and Spanish words were compared directly. These results demonstrate a shared frontal lobe system for semantic analysis of the languages and are consistent with cognitive research on bilingualism indicating that the two languages of a bilingual person access a common semantic system.     

Cognitive Processing of Drawing Abilities

This critical review examines constructional apraxia from a cognitive neuropsychological perspective. To our knowledge, van Sommers (1989) is the only researcher to present a global cognitive model of drawing abilities. He organizes it into two hierarchical systems: Marr's model of visual perception and a graphic production system. The latter comprises four hierarchically organized components: depiction decisions, production strategy, contingent planning, and articulatory and economic constraints. Van Sommers' model will be discussed in light of other models and on the basis of empirical neuropsychological studies (Farah, 1984; Kosslyn & Koenig, 1992; Roncato, Sartori, Masterson, & Rumiati, 1987; van Sommers, 1989). We find that: (1) the Kosslyn and Koenig visual perception model describes more accurately the perceptual components underlying copying than the visual perception system of van Sommers' drawing model, (2) Van Sommers' arguments in favor of a depiction processing as opposed to visual imagery are not convincing, (3) Van Sommers' assumption that a production strategy is a component is unclear, and (4) articulatory and economic constraints are not cognitive components, but constraints imposed during action programming. This literature review leads to a discussion of future research topics and the specificity of constructional apraxia.     

Selective attention and interhemispheric response competition in the split-brain

The interfering effect of an unattended stimulus on processing of an attended item was studied in a single split-brain participant (LB) and in normal controls. Pairs of letters were presented to the left visual field (LVF), right visual field (RVF), or bilaterally. Participants attended to the rightmost letter while attempting to ignore the leftmost letter. Responses associated with the attended and to-be-ignored letters could be compatible or incompatible. Manual response latencies were generally slower on Response Incompatible compared to Response Compatible trials. Notably, LB displayed this effect on Bilateral trials, where target and distractor were presented to opposite visual fields. LB was unable to perform a same-different matching task with bilateral letter stimuli, but was able to name bilateral letters accurately. Hence, in the bilateral condition, the ability to cross-compare letters was dissociated from attentional interference and from letter naming. Implications of these findings are discussed.     

Reproducibility of fMRI-determined language lateralization in individual subjects

This study investigated within-subject test-retest reproducibility (i.e., reliability) of language lateralization obtained with fMRI. Nine healthy subjects performed the same set of three different language tasks during two fMRI sessions on separate days (verb generation, antonym generation, and picture naming). A fourth task analysis was added in which the three tasks were analyzed conjointly (combined task analysis, CTA). The CTA targets brain areas that are commonly used in different language tasks, aiming more selectively at language-critical structures. The number of active voxels (i.e., robustness) and calculated lateralization index (LI) were compared across sessions, tasks, subjects, and two a priori defined volumes of interest (classical language regions versus whole hemisphere) for a wide range of statistical thresholds. Robustness and reliability strongly varied between task analyses. The CTA was a robust detector of language-related brain activity, in contrast to the single task approaches. The CTA and verb generation task allowed for reliable calculation of the LI. Higher thresholds yielded a clear increase in left lateralization, which was largest when calculated from active voxels in classical language regions.     

Arrows of time in infancy: the representation of temporal-causal invariances

Many transformations that take place over time can only occur in one temporal direction, and adults are highly sensitive to the differences between forward and backward presentations of such events. In seven experiments using two selective-looking paradigms, 4- and 8-month-olds were shown forward and backward videotapes of events involving the effects of gravity on liquids and solid objects and of the separation of whole objects into pieces. Four-month-olds showed a significant preference for the forward version of liquid pouring from a beaker to a glass. Eight-month-olds looked longer at the forward versions of this and four other gravity-related events but showed no directional preferences for the separation events. Several experiments indicate that longer looking at the forward versions of the gravity stimuli is not a product of attraction to specific perceptual features of the stimuli. A model based on the development of representations of types of events is presented and evaluated.     

Grammatical Encoding in Aphasia: Evidence from a “Processing Prosthesis”

Agrammatic aphasia is characterized by severely reduced grammatical structure in spoken and written language, often accompanied by apparent insensitivity to grammatical structure in comprehension. Does agrammatism represent loss of linguistic competence or rather performance factors such as memory or resource limitations? A considerable body of evidence supports the latter hypothesis in the domain of comprehension. Here we present the first strong evidence for the performance hypothesis in the domain of production: an augmentative communication system that markedly increases the grammatical structure of agrammatic speech while providing no linguistic information, functioning merely to reduce on-line processing demands. Copyright 2000 Academic Press and Unisys Corporation.     

Effects of Change in Social Content of Video Rewards on Response Patterns of Bonnet Macaques

Three individually housed bonnet macaques, with long-term experience in performing a joystick task with a reward choice of either viewing color video of a single bonnet group or obtaining a banana-flavored food treat, were presented with images of a new group when they chose to view social video. The change produced absolute increases in responding for social video and enhanced preference for viewing social video relative to obtaining the food treat, supporting the view that the monkeys were strongly attending to the social content of the videos.