Biomedical subjects
Martha Escobar
Publications and source records attributed to Martha Escobar.
Bidirectional associations in humans and rats.
In 1 experiment with humans and 3 experiments with rats, the authors sought evidence of temporal integration of independently acquired temporal relationships, including forward and backward temporal associations. The experiments were designed and analyzed in the framework of the temporal coding hypothesis (e.g., L. D. Matzel, F. P. Held, & R. R. Miller, 1988; H. I. Savastano & R. R. Miller, 1998) as a strategy toward illuminating the use of forward and backward temporal associations and assessing the directional nature of these temporal associations. The results obtained suggest that the temporal content of learning about paired events involves a single bidirectional association instead of 2 independent unidirectional, forward and backward, associations.
Competition between antecedent and between subsequent stimuli in causal judgments.
In the analysis of stimulus competition in causal judgment, 4 variables have been frequently confounded with respect to the conditions necessary for stimuli to compete: causal status of the competing stimuli (causes vs. effects), temporal order of the competing stimuli (antecedent vs. subsequent) relative to the noncompeting stimulus, directionality of training (predictive vs. diagnostic), and directionality of testing (predictive vs. diagnostic). In a factorial study using an overshadowing preparation, the authors isolated the role of each of these variables and their interactions. The results indicate that competition may be obtained in all conditions. Although some of the results are compatible with various theories of learning, the observation of stimulus competition in all conditions calls for a less restrictive reformulation of current learning theories that allows similar processing of antecedent and subsequent events, as well as of causes and effects.
Disruption of latent inhibition by interpolation of task-irrelevant stimulation between preexposure and conditioning.
Latent inhibition refers to attenuated responding to a conditioned stimulus (CS) that was repeatedly presented without reinforcement prior to the CS-unconditioned stimulus (US) pairings. Using water-deprived rats as subjects, we observed that interpolating task-irrelevant stimulation between the preexposure and conditioning phases of a latent inhibition procedure attenuated latent inhibition (Experiments 1A, 1B, and 2). Apparently, interpolated stimulation segments the preexposure and conditioning treatments into two separate experiences, much in the same way that a change of context would. Consistent with this view, the interpolated stimulation did not disrupt latent inhibition if it was also presented during both preexposure and conditioning (Experiment 3). We view these results as analogous to those of Escobar, Arcediano, and Miller (2003), who suggested that the difficulty in observing latent inhibition in human adults is related to the segmentation between preexposure and conditioning caused by the usual interpolation of instructions in preparations with humans.
Interference and time: a brief review and an integration.
Contemporary theories of associative learning have been preoccupied with the phenomenon of stimulus competition (attenuated responding to a target stimulus-outcome association if another stimulus trained together with the target is a better or more reliable predictor of the outcome). In recent years, reports of associative interference between associations trained separately have challenged associative learning theories, which provide no mechanism to account for this type of interference. Moreover, the ever-growing reports of temporal relationships between stimuli being a variable that determines the occurrence of stimulus competition and associative interference call for a reformulation of associative theory that can account for both interference and temporal learning effects. Here, we briefly review some of the central findings in stimulus competition, associative interference, and temporal learning, as well as a recently-proposed integration of these three seemingly disparate families of phenomena.
Trial number and compound stimuli temporal relationship as joint determinants of second-order conditioning and conditioned inhibition.
Two conditioned lick suppression experiments with rats used feature-negative training (A-footshock trials intermixed with nonreinforced XA presentations) to analyze the role of the number of XA compound presentations and the temporal relationship of the elements within the compound (simultaneous or serial) as determinants of the resulting behavioral control. Second-order conditioning (i.e., excitatory behavioral control by X) was observed to decline as the number of XA compound trials was increased. This decline was more rapid if X and A were presented simultaneously, as opposed to serially (i.e., X before A; Experiment 1). Conditioned inhibition to X, as assessed by a summation test (Experiment 1) and a retardation test (Experiment 2), increased with the number of XA trials and did so more quickly for simultaneous than for serial pairings of X and A. The results help to clarify previously discrepant findings regarding factors that promote excitation versus inhibition with this protocol.
Is stimulus competition an acquisition deficit or a performance deficit?
Traditionally, blocking (X-outcome, followed by XY-outcome, resulting in attenuated conditioned responding to Y, relative to XY-outcome alone) has been explained in terms of the X-outcome association's preventing the acquisition of the Y-outcome association. This view is challenged by models that view stimulus competition as a deficit in the expression of the acquired Y-outcome association. Here, we provide evidence that blocking is a performance deficit in which the Y-outcome association, the to-be-blocked stimulus, can affect behavioral control by the blocking stimulus (i.e., attenuate responding to X). The results are discussed in terms of acquisition and performance models of stimulus competition.
Proactive interference between cues trained with a common outcome in first-order Pavlovian conditioning.
The nature of interference between cues (X, A) trained apart with a common outcome (O; an unconditioned stimulus) was explored by assessing proactive interference in first-order Pavlovian conditioning (i.e., A-O, X-O, resulting in attenuated responding to X). Three lick-suppression studies were conducted with water-deprived rats. Posttraining extinction of the interfering cue (A) attenuated proactive interference (Experiment 1), which mirrors the observation that extinction of the competing cue can reduce competition between cues trained together (e.g., recovery from overshadowing). Proactive interference was also attenuated with manipulations known to attenuate interference between outcomes trained apart (e.g., counterconditioning), namely reminder cues (Experiment 2) and renewal (Experiment 3). The findings suggest that similar processes underlie interference between cues trained apart, between cues trained together, and between outcomes trained apart.
Latent inhibition in human adults without masking.
Latent inhibition refers to attenuated responding to Cue X observed when the X-outcome pairings are preceded by X-alone presentations. It has proven difficult to obtain in human adults unless the preexposure (X-alone) presentations are embedded within a masking (i.e., distracting) task. The authors hypothesized that the difficulty in obtaining latent inhibition with unmasked tasks is related to the usual training procedures, in which the preexposure and conditioning experiences are separated by a set of instructions. Experiment 1 reports latent inhibition without masking in a task in which preexposure and conditioning occur without interruption. Experiments 2 and 3 demonstrate that this attenuation in responding to target Cue X does not pass a summation test for conditioned inhibition and is context specific, thereby confirming that it is latent inhibition. Experiments 3 and 4 confirm that introducing instructions between preexposure and conditioning disrupts latent inhibition.
Temporal integration and temporal backward associations in human and nonhuman subjects.
Two experiments are reported that demonstrate temporal integration of independently acquired temporal relationships, including backward associations, in both human (Experiment 1) and nonhuman (rats, Experiment 2) subjects. The experiments were designed and analyzed in the framework of the temporal coding hypothesis (e.g., Matzel, Held, & Miller, 1988; Savastano & Miller, 1998) as a strategy toward illuminating the use of temporal information and assessing the existence of temporal backward associations. Both experiments provided evidence of retrieval of associations to an event that was expected to occur prior to the moment in time at which a stimulus was presented (i.e., backward associations). In addition, Experiment 1 constitutes the first controlled demonstration of temporal integration by human subjects.
Timing in retroactive interference.
Retroactive interference is conventionally viewed as attenuated retrieval of a target association due to the training of a second association between training and testing of the target association. In three experiments in which water-deprived rats were used as subjects, we manipulated the durations of the time between cue termination and outcome onset (Experiment 1), the durations of the target and the interfering cues (Experiment 2), and the durations of the outcome used during target and interfering training (Experiment 3). Greater interference was consistently observed between associations bearing a high degree of similarity in their temporal structure, which suggests that interference occurs between complex representations that encode not only the physical attributes of the stimuli, but also their temporal characteristics.
Associative interference between cues and between outcomes presented together and presented apart: an integration.
In recent years, 'stimulus competition' in the study of acquired behavior has referred exclusively to (a) associative competition between cues trained in compound (e.g. overshadowing and blocking). Rarely cited are older experiments cast in the verbal learning tradition, now complemented with data from humans and rats in Pavlovian preparations, that demonstrate (b) competition between cues separately trained with a common outcome (i.e. proactive and retroactive interference). Similarly neglected are numerous examples of (c) competition between outcomes separately trained with a common cue within the verbal learning literature (also proactive and retroactive interference) as well as within the Pavlovian literature (i.e. counterconditioning). Recent data demonstrate (d) competition between outcomes trained in compound, thereby completing the four cells of a 2x2 matrix (competing stimuli trained together vs. trained apart and the competing stimuli being cues or outcomes) which highlights the ubiquitous nature of associative stimulus interference/competition. Most contemporary theories of acquired behavior can account for the phenomena in one or at most two cells of this matrix. Whether a common mechanism underlies the phenomena in all four cells of the matrix is currently unclear, but until such time as data preclude a common mechanism, parsimony encourages efforts to develop a model that encompasses all four cells. Here we offer a tentative model that addresses all four cells, albeit with two processes.
Associative deficit accounts of disrupted latent inhibition and blocking in schizophrenia.
Latent inhibition (attenuated responding to a signal due to signal-alone presentations preceding the signal-outcome pairings) and blocking (attenuated responding to Signal B due to Signal A being paired with the outcome prior to pairings of an AB compound with the outcome) are reportedly absent in acute schizophrenics. The common assumption that these phenomena reflect the normal functioning of attention and the observation that rats administered low doses of amphetamine show a similar disruption has resulted in the development of an animal model of attentional dysfunction in acute schizophrenia. Here, we selectively review the experimental and clinical literature concerning latent inhibition and blocking, their disruption in acute schizophrenia, and the current status of this model. We conclude that the construct validity of the model is compromised if latent inhibition and blocking are viewed in attentional terms because experimental data indicate both phenomena can be better understood in associative terms. We favor a framework in which disruption of latent inhibition and blocking in acute schizophrenics is viewed as an inability to compare and express stored representations (i.e. associative performance deficit). This change of perspective does not undermine the potential value of the model, but rather suggests that the nature of its validity should be reconsidered.
A comparison between elemental and compound training of cues in retrospective revaluation.
Associative learning theories assume that cue interaction and, specifically, retrospective revaluation occur only when the target cue is previously trained in compound with the to-be-revalued cue. However, there are recent demonstrations of retrospective revaluation in the absence of compound training (e.g., Matute & Pineño, 1998a, 1998b). Nevertheless, it seems reasonable to assume that cue interaction should be stronger when the cues are trained together than when they are trained apart. In two experiments with humans, we directly compared compound and elemental training of cues. The results showed that retrospective revaluation in the elemental condition can be as strong as and, sometimes, stronger than that in the compound condition. This suggests that within-compound associations are not necessary for retrospective revaluation to occur and that these effects can possibly be best understood in the framework of general interference theory.
Latent inhibition and contextual associations.
Attenuated responding to a conditioned stimulus (CS) after preexposure to that CS (latent inhibition) has traditionally been attributed to reductions in CS associability. Alternatively, CS-context associations formed during CS preexposure later interfere with the acquisition or expression of CS-outcome associations. Three lick suppression experiments with rats contrasted these accounts. Presumably, exposure to the context attenuates the CS-context association without altering CS associability. With a fixed amount of CS preexposure, latent inhibition decreased with increasing context exposure during or after (but not before) CS preexposure. When the ratio of context preexposure duration to CS preexposure was fixed, latent inhibition increased with CS preexposure. These results suggest that latent inhibition is a direct function of the strength of CS-context associations formed during preexposure.