Feature-positive Research Articles

Serial feature positive and feature negative discrimination learning in a taste avoidance preparation: implications for interoceptive control of behavior.

Psychoactive drugs produce interoceptive stimuli that can guide appropriate behaviors by initiating or inhibiting responding. The current study investigated whether an interoceptive morphine state produces similar patterns of serial feature positive (FP) and feature negative (FN) discrimination learning under comparable conditions in a taste avoidance design. Male Sprague-Dawley rats were trained under 10 cycles of FP or FN discrimination. In the FP task, morphine (10 mg/kg, IP) signaled that a saccharin solution was followed by LiCl (1.2 mEq, IP), while the vehicle (saline) signaled that the LiCl was withheld. In the FN task, the contingency was reversed. The FP-trained rats acquired the discrimination after three training cycles, consuming significantly less saccharin on morphine, than on vehicle, sessions (P < 0.05). The FN-trained rats acquired the discrimination after six training cycles, consuming more on morphine than on vehicle sessions (P < 0.05). However, FN-trained rats never recovered saccharin consumption to baseline levels and 40% of the rats continued to avoid saccharin (consuming 0 ml) on morphine sessions. Control rats that never received LiCl consumed high levels of saccharin on morphine and vehicle sessions, indicating that morphine did not produce unconditioned suppression of saccharin consumption. The difficulty to acquire FN discrimination might reflect the limitations of learning about safety contingencies in the taste avoidance design. The rapidity of FP learning when a drug state signals an aversive contingency may have implications for the general role of interoceptive stimuli in the control of behavior.

Sex differences in the discriminative stimulus characteristics of a morphine occasion setter in rats

The current study investigated whether the stimulus effects of morphine can function as a positive and negative feature in a Pavlovian occasion setting drug discrimination preparation in male and female rats. Sprague-Dawley rats were assigned to a feature positive (FP) or feature negative (FN) training group and all received intermixed morphine (3.2 mg/kg, IP) or saline injections 15 min before 20-min daily training sessions. For FP rats, on morphine sessions, each of eight 15-s white noise (WN) presentations was followed by 4-s access to sucrose (0.01 ml, 26% w/v); on saline sessions, sucrose was withheld. FN rats learned the reverse contingency. FP discrimination was acquired somewhat sooner than FN discrimination, and females, but not males, became sensitized to the locomotor effects of morphine, which did not influence conditioned responding. Rats then entered dose generalization testing. There was no sex difference in dose generalization for FN groups (ED50 1.26 for males and 1.57 for females). Yet for FP rats, the dose response curve for females was shifted to the right compared to males (ED50 0.54 for males and 1.94 for females). FP females exhibited enhanced responding at a dose higher than that of their original training. These findings reveal the need to reassess our notions of drug stimuli that guide appropriate associative behaviours from the perspective of sex differences.

Can the discriminative stimulus effects of nicotine function concurrently as modulatory opponents in operant and pavlovian occasion setting paradigms in rats?

Nicotine promotes interoceptive changes in the nervous system. Such interoceptive stimuli play important roles in modulating addictive behavior. Operant and Pavlovian stimulus control modulate responsiveness to environmental stimuli related to drug-seeking and self-administration. Nicotine functions as a discriminative stimulus in modulating operant behavior as well as Pavlovian feature stimuli in modulating the conditional responding (CR) to exteroceptive CS→US contingencies. Elucidation of the interaction of these interoceptive stimulus control functions is vital for a comprehensive understanding of nicotine use/abuse, which might lead to better behavioral treatment strategies. This experiment evaluated the interaction among Pavlovian feature positive (FP) and feature negative (FN) effects of nicotine on concurrently occurring operant SD and SΔ effects. Sixteen rats were trained in a Pavlovian and operant bidirectional contingency paradigm, using nicotine (0.3 mg/kg) and non-drug (saline) states as interoceptive cues for operant discriminative stimulus conditions (SD and SΔ) as well as Pavlovian FP and FN for a light-CS, either leading to a shared food pellet outcome or non-outcome. Nicotine and saline sessions were intermixed. For one group of rats (n = 8), nicotine served as an SD for lever pressing (variable interval 60 s) and simultaneously functioned as an FN for CS-light→noUS relation on the same sessions. On intermixed sessions, saline served as the SΔ for lever pressing (non-reinforced) and FP, during which the 8-sec light preceded delivery of the food pellet (variable time ITI = 60 s). For the other group (n = 8) nicotine served as the SΔ (lever pressing non-reinforced) and FP for the CS, with saline serving in the reverse roles. Consecutive brief non-reinforcement tests revealed that: A) rates of lever pressing were significantly greater in SD than SΔ with nicotine and saline suggesting strong operant discriminative stimulus control; B) FP responding to the light CS with nicotine and saline was evident; and C) FN suppression of the CR with nicotine was not evident but weak under saline. These data suggest that nicotine can function as an interoceptive context that hierarchically can enter into concurrently opposing modulatory relations in Pavlovian and operant drug discrimination procedures.

The association of hemoglobin A1c and high risk plaque and plaque extent assessed by coronary computed tomography angiography.

The objective of this study was to investigate the relationship of Hemoglobin A1c (HbA1c) and plaque characteristics including high risk plaque and plaque extent. We retrospectively examined 1079 consecutive coronary computed tomography (CT) angiography scans and the HbA1c results. We divided the patients into four groups by the HbA1c status: non-diabetic, ≤6.0; borderline, 6.1-6.4; diabetic low, 6.5-7.1; diabetic high, >7.1. We determined segment involvement score >4 as extensive disease. High risk plaque was defined as two feature positive (FP) plaque which consists of positive remodeling (remodeling index >1.1) and low attenuation (<30 HU). Univariate and multivariate analysis including conventional cardiovascular risk factors, symptoms and medication was performed. Univariate analysis showed that diabetic patients as well as borderline patients were significantly related with 2FP plaque and extensive disease. Although the relationship of borderline patients and 2FP plaque was marginal in multivariate analysis [odds ratio (OR) 1.53, 95% confidence interval (CI) 0.95-2.40, p = 0.07], the elevation of HbA1c was strongly associated with 2FP plaque (diabetic low, OR 2.19, 95% CI 1.37-3.45, p < 0.005; diabetic high, OR 4.14, 95% CI 2.57-6.67, p < 0.0005). The association of HbA1c elevation and extensive disease was quite similar between borderline and diabetic patients (borderline, OR 1.96, 95% CI 1.29-2.95, p < 0.005; diabetic low, OR 1.94, 95% CI 1.25-3.01, p < 0.005; diabetic high, OR 2.19, 95% CI 1.39-3.43, p < 0.005). Patients with elevated HbA1c of >6.0 are potentially at risk for future cardiovascular events due to increased high risk plaque and extensive disease, even below the diabetic level of 6.5. Coronary CT could be used for risk stratification of these patients.

Asymmetries in time-based and feature-based discriminations in humans: linking the long+ and feature-positive effects.

Three experiments examined time-based and feature-based discrimination learning in a video game task with human participants. Each participant played the role of gunner on a space ship. Participants were told that a periodically presented target object might or might not be hiding an enemy alien, which would appear briefly once the target disappeared. Points were given for 'shooting' at the target that hid the enemy alien, and were taken away if the target was ultimately not hiding an alien. In Experiment 1, either a relatively long (4 s) or a relatively short (1 s) intertrial interval (ITI) predicted whether an alien would be hiding behind the next target. Participants anticipated enemy aliens more readily when the long ITI predicted the enemy alien than when the short ITI did so, establishing a long+ effect for the first time in humans. In Experiment 2, a friendly alien was added on the negative trials, so that a different event, rather than no event, occurred on the negative trials. This eliminated the long+ effect; that is, participants now found it equally easy to predict the target enemy aliens whether they uniquely followed long or short ITIs. Experiment 3 examined whether a similar treatment reduced the theoretically related feature-positive (FP) effect. In that experiment, a unique visual image, rather than the ITI duration, served as the predictor. An FP effect occurred when the discrimination was between trials with an outcome versus no outcome, but not when the discrimination was between an outcome versus a different outcome. The findings connect the long+ and the FP effects, and suggest that both can be reduced by making the negative trials more salient.

Dissociations Between ABA-, ABC-, and AAB-Renewal of Pavlovian Modulation in Human Sequential Feature Positive Discrimination Learning

Using a conditioned suppression preparation, we investigated extinction and aba-, abc-, and aab-renewal of Pavlovian modulation in human sequential Feature Positive (FP) discrimination learning, X → A+/A-. Extinction treatment was administered in the acquisition context a (aaa- and aab-groups) or in a new context b (aba- and abc-groups) and comprised X → A- extinction trials. Discriminative X → A/A responding was lost in all groups when tested in the extinction context. In the aba-group, the discriminative X → A/A responding totally recovered when retested in the acquisition context a. For the aaa-, the aab-, and the abc-group, discriminative X → A/A responding did not reappear when tested for renewal in, respectively, contexts a, b, and c. The demonstration of aba-renewal of extinguished modulation, but not abc- and aab-renewal, suggests that extinction in a context different from the acquisition context and a return to the original acquisition context might both be critical for renewal of Pavlovian modulation in human FP-discrimination learning.

Methamphetamine functions as a positive and negative drug feature in a Pavlovian appetitive discrimination task

This research determined the ability of methamphetamine to serve as a positive or negative feature, and assessed the ability of bupropion, cocaine, and naloxone to substitute for the methamphetamine features. Rats received methamphetamine (0.5 mg/kg, intraperitoneally) or saline 15 min before a conditioning session. For the feature positive (FP) group, offset of 15-s cue lights was followed by access to sucrose on methamphetamine sessions; sucrose was withheld during saline sessions. For the feature negative (FN) group, the light offset was followed by sucrose on saline sessions; sucrose was withheld during methamphetamine sessions. During acquisition, the FP group had higher responding on methamphetamine sessions than on saline sessions. For the FN group, responding was higher on saline sessions than on methamphetamine sessions. Conditioned responding was sensitive to methamphetamine dose. For the FP group, bupropion and cocaine fully and partially substituted for methamphetamine, respectively. In contrast, both drugs fully substituted for methamphetamine in the FN group. Naloxone did not substitute in either set of rats. FP-trained rats were more sensitive to the locomotor stimulating effects of the test drugs than FN-trained rats. This research demonstrates that the pharmacological effects of methamphetamine function as a FP or FN in this Pavlovian discrimination task and that training history can affect conditioned responding and locomotor effects evoked by a drug.

The feature positive effect in the face of variability: Novelty as a feature.

Past literature has shown, across various methods and species, that feature positive (FP) tasks (AB-/B+) are learned more easily than are feature negative (FN) tasks (AB-/B+), giving rise to what is known as the feature positive effect (FPE). Experiment 1 was intended to assess the role of expected absence in the FPE through manipulation of the context (constant vs. varied common elements) that was paired with the feature. The results indicate that novel contextual elements (varied common elements) may be salient enough to eliminate the FPE, creating a feature negative effect (FNE). Experiment 2 replicated the FNE. The addition of a testing phase confirmed that participants in the FN task judged novel stimuli to be strong positive predictors whereas participants in the FP task did not, thus producing a novelty FPE. These results are problematic for contemporary associative learning models.

Extinction and renewal of Pavlovian modulation in human sequential Feature Positive discrimination learning

Using a conditioned suppression task, we investigated extinction and renewal of Pavlovian modulation in human sequential Feature Positive (FP) discrimination learning. In Experiment 1, in context a participants were first trained on two FP discriminations, X-->A+/A- and Y-->B+/B-. Extinction treatment was administered in the acquisition context a (aaa group) or in a new context b (aba group), and comprised X-->A- extinction and Y- control trials. Discriminative X-->A/A responding was lost in both groups when tested in the extinction context, but partially recovered in the aba and not in the aaa group when tested in the acquisition context, suggesting extinction and renewal of extinguished modulation. The same was observed for the Y-->B/B control pair, however, questioning whether the loss of discriminative X-->A/A responding represented genuine extinction of modulation. In Experiment 2, including only aba groups, participants were trained in context a on two FP discriminations, X-->A+/A- and Y-->B+/B-, after which the group "Extinction" was exposed to X-->A- extinction trials in context b, whereas the group "Control" was exposed to X- control trials; concurrently, both groups received further Y-->B+/B- training. In the group Control, differential Y-->B/B and X-->A/A responding were acquired and maintained throughout the experiment. In the group Extinction, while Y-->B/B responding was also maintained throughout, differential X-->A/A responding disappeared because of X-->A- extinction treatment when tested in the extinction context b, but partially reappeared when tested in the acquisition context a. This evidences aba-renewal of extinguished modulation.

Sequential and simultaneous feature positive discriminations: Occasion setting and configural learning in human Pavlovian conditioning.

Using a conditioned suppression preparation, the authors investigated sequential (X --> A+/A-) versus simultaneous (XA+/A-) feature positive (FP) discrimination learning in humans. The sequential discrimination was expected to be resolved by means of a Feature X Modulated Target A-US association and the simultaneous discrimination by a feature X-US association. After sequential FP training, extinction of Feature X did not affect discriminative X --> A/A responding (Experiment 1), and X transferred its modulatory ability only to new targets, B, that had also been modulated (Experiment 2). This suggests that the sequential FP discrimination indeed resulted in occasion setting. Unlike expected, Feature X Extinction did not affect discriminative XA/A responding after simultaneous FP training (Experiment 3), while at the same time Feature X did show the predicted nonselective transfer to new targets, B (Experiment 4). J. M. Pearce's (1987) configural learning theory can account for most but not all findings of Experiments 3 and 4.

Neither Extended Sequential nor Simultaneous Feature Positive Training Result in Modulation of Evaluative Flavor–Flavor Conditioning in Humans

In previous attempts to induce Pavlovian modulation of human evaluative flavor–flavor associations, the recurrent finding was that exposure to a Feature Positive (FP) schedule (XA+/A−), in which flavor A was reinforced by the aversive flavor Tween20 if and only if it was accompanied by a feature stimulus X, did not result in the expected X-modulated dislike for target A, but in simple unconditional A-US associations. The first experiment reported here investigated if more extended training results in a shift from simple A-US learning to the development of X-modulated A-US associations. Participants were exposed to a 32-trial, 4-session sequential FP schedule using flavors both for feature and target stimuli. The modulatory and/or excitatory power of the stimuli was assessed after each training session. After initial training, participants again acquired a simple unmodulated target A-US association. Contrary to expectations, the additional training sessions did not result in participants gradually learning the XA+/A− discrimination, but rather seemed to corroborate the already established A-US association. This was true whether or not participants acquired valid explicit knowledge about the conditional X→(A-US) relation. The second experiment tested the hypothesis that what can be described as conditional flavor preferences may actually be based on a configural learning process. Participants were exposed to a single-session, eight-trial XA+/A− simultaneous discrimination schedule, the parameters of which were selected so as to enhance the probability of configuring XA, while simultaneously making it likely to observe a pattern of evaluations similar to an X-modulated dislike for A (X was less salient than A). Even though there was good evidence that participants noticed flavor X, they again failed to solve the XA+/A− discrimination and most probably acquired an association between the more salient flavor A and the US. The possibility is discussed that evaluative learning, unlike expectancy learning, might ultimately prove not to be subject to modulation.

Behavioural control by simultaneous and serial features in feature-positive and feature-negative discriminations

Two experiments with rats examined behavioural control by feature stimuli in appetitive conditioning using latency of food-magazine visits as the dependent measure. In experiment 1, a feature-positive (FP) discrimination was presented in which a target stimulus was consistently followed by food when preceded by a serial feature and accompanied by a simultaneous feature, and not followed by food when presented alone. The reverse condition, a feature-negative (FN) discrimination procedure, was in effect in experiment 2. Groups of rats differed in the physical identity of the stimuli used as target and features. In the FP discrimination, all groups came to respond faster on reinforced than on nonreinforced trials. Subsequent tests revealed that the serial feature was responsible for this performance in all groups, whereas the simultaneous feature had not acquired significant control in all groups. Only one half of the groups solved the FN discrimination and they did this on the basis of only the simultaneous feature, which was a relatively intense stimulus in these groups. These results suggest a propensity to use the serial feature in FP discriminations and the simultaneous feature in FN discriminations.

Long-term retention of Pavlovian serial feature-positive and feature-negative discriminations

Fifteen pigeons were concurrently trained with Pavlovian serial feature-positive (F-P) and feature-negative (F-N) discrimination tasks (A−, X→A+; B+, Y→B−), and retention of these discriminations was tested after a 2-week interval. The birds maintained the discriminations. After retraining of the original tasks, seven birds were tested with a one-month interval. Reliable deterioration was observed in the both discriminations due to increases in responding on the nonreinforced trials (A− for the F-P discrimination and Y→B− for the F-N discrimination). The remaining eight birds also were tested after a one-month interval, but they received 3-day retraining of the target stimuli (A− and B+) before the test. There was no loss of the discriminations in these birds, suggesting reactivation of discriminations by the target retraining.

No Evidence for Modulation of Evaluative Flavor–Flavor Associations in Humans

In four experiments using a human evaluative flavor–flavor association paradigm, we investigated whether the acquisition of stimulus valence may be subject to Pavlovian modulation or occasion setting. In all studies, subjects (Ss) were exposed to a feature-positive (FP) (XA+/A−) schedule (or a modified version of it), in which flavor A was reinforced by the aversive flavor Tween 20 if and only if it was accompanied by a feature stimulus X. It was expected that Ss would develop an X-dependent dislike for A. In Experiment 1, for half of the Ss a quasi-sequential FP schedule was used, whereby the color of the liquids functioned as X. The other half of the Ss were exposed to a positive-patterning (PP) (XA+/A−/X−) schedule, in which unreinforced color (X−) trials were added to the FP schedule. Both schedules resulted in an unmodulated dislike for flavor A. In Experiment 2, Ss were exposed to a modified FP schedule, in which flavor A was reinforced by Tween 20 when presented with color X, while A was reinforced with positive sugar when presented colorless. Ss again demonstrated an unmodulated dislike for A. Experiment 3, using a sequential FP (X → A+/A−) schedule in which a flavor functioned as X, also resulted in an unmodulated dislike for A. Finally, in Experiment 4, Ss were exposed to the modified FP schedule, in which flavor A was presented with Tween 20 when preceded by flavor X, while A was reinforced with Sugar when not preceded by X. For those Ss liking sugar, no valence shifts were observed, whereas for those not liking sugar, the standard unmodified dislike for A was obtained. Some suggestions are provided with respect to variables which might be related to the absence of modulation.

Contextual control of pavlovian feature-positive and feature-negative discriminations

Three pigeons were trained with a Pavlovian serial feature-positive (F-P) discrimination task in a light context, in which the houselight was on, and with a Pavlovian serial feature-negative (F-N) discrimination task in a dark context, in which the houselight was off. Three other pigeons were trained with the F-P task in the dark context and the F-N task in the light context. These two contextual conditions were changed randomly trial by trial. The former birds learned the tasks within 60 sessions, by responding exclusively to the target keylight after the feature tone in the light context and by responding exclusively to the target not preceded by the feature in the dark context. Two of the latter birds required separate training of the F-P and the F-N tasks to acquire the discrimination: responding exclusively to the target after the feature in the dark context and responding exclusively to the target not preceded by the feature in the light context. The third bird, however, failed to learn the discrimination even with separate training. These results indicate that the four-term contingency (the context-feature-target-food relationship) controlled the birds’ behavior in the Pavlovian setting. The insertion of a temporal gap between the feature and the target impaired the F-N discrimination, although it had little effect on the F-P discrimination.

The ontogeny of the feature-positive effect in young chicks

The wide generality of the feature-positive effect (FPE) has caused speculation that the FPE may represent innate biases in the stimulus control of discriminative responding. There is little experimental evidence to date ragarding this possibility. In the present study, 1- or 4-day-old chicks were trained on a feature-positive (FP) or feature-negative (FN) discrimination with heat reinforcement. After the acquisition phase, these subjects received extinction training followed by a reacquisition phase. The FP performance was superior to the FN performance in both age groups. Extinction resulted in improved discrimination performance in both the FP and FN conditions. Unmasking of FN learning by the extinction treatment suggests that the FPE represents a deficit in performance, rather than an inability to learn the FN task. These data demonstrate that adult-like performance on feature discriminations is evident as early as the first day post-hatch.

Feature-positive and feature-negative discrimination learning maintained by negative reinforcement in rhesus monkeys

Rhesus monkeys were trained to press panels to escape or avoid shock. Escape and avoidance training were combined factorially with feature-positive (FP) and feature-negative (FN) discriminations. In the FP situation, S+ trials were characterized by one red and two green panel displays and S− consisted of an all green panel array. In the FN arrangement, S+ and S− arrays were reversed. When compared properly, FP discriminations were learned more readily than FN discriminations in both escape and avoidance training conditions. Positive tracking was associated with FP discriminations, and feature avoidance characterized the FN tasks. These data suggest that in primates, feature responses (i.e., tracking behaviors) are more a function of the operant contingency than of the Pavlovian correlation.

Feature-negative effect in rats’ discrimination learning in the runway

In two experiments, rats were trained on a successive go/no-go discrimination problem in the runway in which the positive (8+) and negative (8-) discriminanda were differentiated by the presence or absence of a distinctive feature. The feature in Experiment 1 was a series of flash­ ing lights over the runway. In Experiment 2, the feature was a pretrial reinforcement (Phase 1), or pretrial reinforcement versus pretrial nonreinforcement (Phase 2). The feature signaled S+ trials in feature-positive (FP) groups and S- trials in feature-negative (FN) groups. The original discrimination was reversed in Phase 2 of both experiments. With the exception of the pretrial nonreinforcement groups in Experiment 2, there was an asymmetry in discrimination learning in both phases of both experiments favoring superior discrimination learning by FN subjects over FP subjects, a feature-negative effect. Implications of the results for an informa­ tion processing account of asymmetries in learning feature discriminations are discussed. Jenkins and Sainsbury (1969) reported an asym­ metry in pigeons' learning of a successive go/no-go discrimination in which the positive (S+) and neg­ ative (S-) discriminanda were differentiated by a distinctive stimulus (feature), presented on S+ trials in the feature-positive (FP) case and on S- trials in the feature-negative (FN) case, in the direction of faster learning of FP discriminations than FN dis­ criminations. This asymmetry, called the feature­ positive effect (FPE), is quite pervasive, having been obtained across a considerable range of experimental procedures, learning tasks, types of features, and species (see Hearst, 1978, in press, for reviews). The generality of the FPE has been taken to indicate that a fundamental psychological principle (or bias), per­ haps due to the innate organization of the nervous system, underlies its occurrence (Hearst, 1978; Newman, Wolff, & Hearst, 1980). Hearst (in press) has suggested that the FPE may be related to some effects in human learning and information process­ ing characterized by a bias favoring the presence over the absence of a stimulus as a source of information. The two experiments reported here investigated feature-discrimination learning in rats, employing for the first time a successive go/no-go discrimina­ tion problem in the runway. Previous feature-learning experiments with rats have demonstrated a FPE in appetitive barpress situations (Crowell & Bernhardt, 1979; Halgren, 1974, Lea, 1974) and in conditioned suppression (Reberg & Leclerc, 1977). Whether the

Effects of Stimulus Contact on the Feature-Positive Effect

Fourteen pigeons were taught to discriminate displays differentiated by the presence or absence of a distinctive feature. Feature-positive (FP) birds were reinforced for responses to displays containing the feature, while feature-negative (FN) birds were reinforced for responses to displays containing only the elements common to both stimulus displays. Both control and experimental birds were required to respond to a spatially separate operant key, while experimental animals were also required to contact the individual elements of the display. A planned comparisons test indicated that FP performance was superior to FN performance only for the control animals. No difference was found between the performance of the experimental FP and FN birds. Consideration of the elements of the display toward which the FN birds orient was offered as an explanation of these results.

The feature-positive effect and sign-tracking behavior during discrimination learning in the rat

Feature-positive (FP) and feature-negative (FN) successive discrimination learning was investigated in the rat. When a discrete, visual element serving to differentiate the discriminanda belonged to S+ (FP), rats acquired the discrimination more rapidly than when it formed a part of S− (FN). During the course of training, FP rats developed a tendency to direct their responding toward the differentiating feature in S+ while FN rats shifted their responding away from this element in S−. These findings were discussed in terms of the conceptions of stimulus-reinforcer relations and “sign-tracking” behavior.