Serial Feature-positive Discrimination Research Articles

Blockade of the M1 muscarinic acetylcholine receptors impairs eyeblink serial feature-positive discrimination learning in mice.

The serial feature-positive discrimination task requires the subjects to respond differentially to the identical stimulus depending on the temporal context given by a preceding cue stimulus. In the present study, we examined the involvement of the M1 muscarinic acetylcholine receptors using a selective M1 antagonist VU0255035 in the serial feature-positive discrimination task of eyeblink conditioning in mice. In this task, mice received a 2-s light stimulus as the conditional cue 5 or 6 s before the presentation of a 350-ms tone conditioned stimulus (CS) paired with a 100-ms peri-orbital electrical shock (cued trials), while they did not receive the cue before the presentation of the CS alone (non-cued trials). Each day mice randomly received 30 cued and 30 non-cued trials. We found that VU0255035 impaired acquisition of the conditional discrimination as well as the overall acquisition of the conditioned response (CR) and diminished the difference in onset latency of the CR between the cued and non-cued trials. VU0255035 administration to the control mice after sufficient learning did not impair the pre-acquired conditional discrimination or the CR expression itself. These effects of VU0255035 were almost similar to those with the scopolamine in our previous study, suggesting that among the several types of muscarinic acetylcholine receptors, the M1 receptors may play an important role in the acquisition of the conditional discrimination memory but not in mediating the discrimination itself after the memory had formed in the eyeblink serial feature-positive discrimination learning.

Role of Muscarinic Acetylcholine Receptors in Serial Feature-Positive Discrimination Task during Eyeblink Conditioning in Mice.

We investigated the role of muscarinic acetylcholine receptors (mAChRs) in eyeblink serial feature-positive discrimination learning in mice using the mAChR antagonist. A 2-s light cue was delivered 5 or 6 s before the presentation of a 350-ms tone paired with a 100-ms periorbital electrical shock (cued trial) but not before the tone-alone presentation (non-cued trial). Mice received 30 cued and 30 non-cued trials each day in a random order. We found that saline-injected control mice were successfully discriminating between cued and non-cued trials within a few days of conditioning. The mice responded more frequently to the tone in cued trials than in non-cued trials. Analysis of conditioned response (CR) dynamics revealed that the CR onset latency was shorter in cued trials than in non-cued trials, despite the CR peak amplitude not differing significantly between the two conditions. In contrast, scopolamine-injected mice developed an equal number of CRs with similar temporal patterns irrespective of the presence of the cue during the 7 days of conditioning, indicating in a failure to acquire conditional discrimination. In addition, the scopolamine administration to the control mice after they had successfully acquired discrimination did not impair the conditional discrimination and expression of pre-acquired CR. These results suggest that mAChRs may play a pivotal role in memory formation in the conditional brain state associated with the feature cue; however they are unlikely to be involved in the development of discrimination after conditional memory had formed in the serial feature-positive discrimination task during eyeblink conditioning.

Hippocampal lesion effects on occasion setting by contextual and discrete stimuli

Three experiments examined the role of the dorsal hippocampus (dHIPP) in occasion setting with diffuse contextual and discrete light stimuli serving as occasion setters in classical fear conditioning with rats. Both sham-operated and dHIPP-lesioned animals readily learned a L→T+, T− serial feature-positive discrimination in which a light (L) “set the occasion” for reinforcement of a tone (T+). dHIPP-lesioned animals were deficient, however, in acquiring a similar discrimination in which different contexts (A and B) served as occasion setters, i.e., A(T+) and B(T−). The lesioned animals also failed to discriminate between a context in which a tone had been partially reinforced and a context in which no conditioning had taken place, whereas sham-operated animals froze more to the tone in the conditioned context than in the novel context. Collectively, the data indicate that the dorsal hippocampus is important in processing information about the signaling value of contextual, but not discrete, stimuli.

A comparison of event-related potentials of humans and rats elicited by a serial feature-positive discrimination task

The purpose of this experiment was to compare components of the human and rat auditory event-related potential (ERP) in a serial feature-positive discrimination task. Subjects learned to respond to an auditory target stimulus when it followed a visual feature (X → A+), but to not respond when it was presented alone (A−). Upon solving the task, the N2 component, which has been suggested to reflect the activation of inhibitory processes, was temporarily more negative in response to the target on A− than on X → A+ trials in both species. However, whereas a P3 component was present in the human participants, this component was absent in the rats. In both species, the amplitude of several ERP components, including the N2, decreased in the course of training. These results are discussed in the framework of contemporary models of associative learning.

The effects of feature type in operant serial feature-positive discriminations

In two experiments, rats were trained on two operant serial feature positive discriminations in which one feature was a flavored solution and the second feature was a visual or auditory cue. As in a previous study ( Goddard & Holland, 1996), transfer of a feature’s control to the target of the other discrimination was not observed when the flavor feature and the reinforcer were flavored sucrose solutions (Experiment 1). The performance of comparison groups showed that this lack of transfer was not due to confounded differences in the event contingencies resulting from having similar stimuli serve as feature and reinforcer. By contrast, in Experiment 2, transfer was observed between visual and flavor features when the flavor feature was unsweetened and the reinforcer was plain sucrose. These results suggest that the lack of transfer in Experiment 1 and in Goddard and Holland’s (1996) study were related to the biological significance or hedonic properties of the sucrose feature.

Feature positive discriminations in adults and children

The present experiment examined whether children and adult students differ in cognitive strategy used to solve a serial feature positive discrimination. The participants learned to make a specific response (R) to a target stimulus (T) when it was preceded by a feature stimulus (F) and to refrain from responding to T when presented alone. This discrimination can be solved in two distinctively different ways: by forming a direct relation between F and R (simple associational strategy), or by F indicating the T–R relation (higher-order relational strategy). The strategy used was examined by means of a transfer test and a counterconditioning manipulation. The results suggest that, for both the children and students, responding during the transfer test was under the control of the simple associational strategy. However, retest responding was controlled by a higher-order relational strategy more in the students than in the children. These results were discussed in the framework of previous findings in the developmental literature on age differences in type of cognitive strategy.

Intertrial interval effects in pavlovian serial feature positive discriminations

The effects of the intertrial interval (ITI) on learning and performance in Pavlovian appetitive serial feature positive (SFP) discriminations were examined in three experiments with rats. With longer ITIs, acquisition was more rapid, and there was less transfer of the feature’s behavioral control to a separately trained target cue, suggesting that longer ITIs encouraged the use of an occasion setting strategy. Behavior was also affected by discrimination-specific ITIs. Rats were trained with two SFP discriminations. The overall ITI was held constant, but the intervals between trials of one discrimination were varied by intermixing different numbers of trials from the other discrimination. Learning was more rapid when the intervals between trials of a single discrimination were longer. A sequential analyses showed that performance on a trial was impaired when it was preceded by a trial that included the same target cue but with the opposite trial outcome. The results are discussed in the frameworks of proactive interference effects and deletion-comparator processes (Cooper, Aronson, Balsam, & Gibbon, 1990.)

Latent Inhibition and Learned Irrelevance of Occasion Setting

Rats received serial feature-positive discrimination training (A → X+/X−) within a conditioned lick suppression preparation (with + representing reinforcement and − representing nonreinforcement). In Experiment 1, the feature (A) was found to modulate responding to a transfer target CS that itself had been occasion set with a second occasion setter, but not to a CS that had been partially reinforced, thereby demonstrating occasion setting with our preparation. Experiments 2–4 examined the effects on the acquisition of occasion setting of various types of pretraining exposure to A. Nonreinforced preexposure to A alone did not in any way retard acquisition and/or expression of occasion setting (Experiment 2), but feature-negative discrimination training did (Experiment 3). A feature-irrelevant pseudo-discrimination pretraining procedure produced profound retardation (Experiment 4). The results of Experiments 2 and 3 indicate that a latent inhibition-like effect for feature-positive occasion setting exists that in some ways is analogous to latent inhibition effects in Pavlovian conditioning. The results of Experiment 4 indicate that an analogue of Pavlovian learned irrelevance can be evidenced for feature-positive occasion setting. The growing parallels between occasion setting and simple Pavlovian conditioning lend support to accounts of occasion setting that view it as arising from an interaction of Pavlovian associations rather than from some distinctly different “higher order” process.

Hippocampal lesions interfere with Pavlovian negative occasion setting.

Rats were trained with either a serial feature positive (L-->T1+ T-) or a serial feature negative (L-->T1-, T1+) discrimination, intermixed with training on another, nonconditional discrimination (T2+, N-), using a Pavlovian appetitive conditioning preparation with multiple response measures. Among rats trained with the serial feature positive discrimination, neurotoxic lesions of the hippocampus produced a transient impairment in the acquisition of that discrimination, but did not affect acquisition of the nonconditional discrimination. In contrast, among rats that received serial feature negative discrimination training, hippocampal lesions produced enduring deficits in the acquisition of both discriminations. The results of transfer tests indicated that both lesioned and control rats used a conditional learning strategy (occasion setting) to solve the feature positive and feature negative discriminations. Furthermore, lesioned rats, especially those that received training with the feature negative discrimination, displayed increasingly higher levels of general activity as training progressed. The results suggest that hippocampal lesions particularly interfere with inhibitory learning (negative occasion setting) about both explicit and contextual cues.

Temporal control in Pavlovian occasion setting

Rats were trained with two Pavlovian serial feature positive discriminations (X→A+/A− and Y→B+, B−), in which the target stimuli (A and B) were reinforced when they were preceded by the feature stimuli (X and Y), but not when they were presented alone. In one discrimination the feature-target interval was 10 s, and in the other discrimination that interval was 30 s. In a series of tests in which the feature target interval varied in ten steps between 5 and 50 s, performance was better when the targets were presented at their usual training times after the feature, rather than earlier or later. Training with the shorter FTI (10 s) resulted in both greater peak responding at the training interval and steeper temporal gradients than training with the longer FTI (30 s). Presentation of a compound feature comprised of both the 10 s and 30 s feature elements shifted the time of peak target responding to an intermediate value, 15 s. In contrast, simple conditioning controlled by the features (measured in the empty intervals between feature and target presentations) showed temporal control but no evidence for stimulus averaging. Most of these results are consistent with scalar timing, but may imply separate temporal codes or timing mechanisms for simple conditioning and occasion setting.

Temporal specificity in serial feature-positive discrimination learning.

Two experiments examined the temporal specificity of learning in operant serial feature-positive discriminations (feature-->target+/target-). Test performance was better when the target cues were presented at their customary times after the features than when they were presented at earlier or later times. When features trained with one feature-target interval were combined with targets trained with another interval, performance was best when the test interval was the same as the interval associated with the feature, suggesting that the temporal information was coded with the feature cue. Finally, the temporal specificity of the responding controlled by occasion setters was unaffected by feature extinction. Implications for the nature of learning in occasion setting are discussed.

Temporal specificity in serial feature-positive discrimination learning.

Temporal specificity in serial feature-positive discrimination learning.

Type of feature affects transfer in operant serial feature-positive discriminations

In two experiments, the effects of feature identity in operant serial feature-positive discriminations were examined with rats. Rats were trained with two serial feature-positive discriminations (F1 → T1+/ T1− and F2 → T2+/ T2−), in which different operants were reinforced with delivery of a sucrose solution during two auditory target cues (T1 and T2). The features (F1 and F2) were two visual cues, two flavored sucrose solutions, or one visual cue and one sucrose solution. Transfer of a feature’s control to the target of the other discrimination was observed only when the features were from the same modality. When observed, transfer responding was of the form originally trained to the target, rather than the feature, and was preserved after feature extinction. Control groups showed that the differential transfer was not solely the consequence of differential feature generalization. Implications for theories of occasion setting are discussed.

The effects of intertrial and feature-target intervals on operant serial feature-positive discrimination learning

The effects of intertrial interval (ITI) and feature-target interval (FTI) on the nature of learning in discrete-trial operant serial feature-positive (feature → target+ / target−) discrimination training were examined in two experiments with rats. Discrimination performance was acquired more rapidly with longer ITIs and shorter FTIs. In contrast, transfer to a separately trained target was greater with shorter ITIs regardless of FTI. Persistence of discrimination performance after feature extinction was greater with longer ITIs. Only the last of these performance measures showed evidence for invariance with constant ITI/FTI ratios. The results are discussed in the context of theories of occasion setting.

Transfer of occasion setting across stimulus and response in operant feature positive discriminations

Two experiments examined transfer of stimulus control after discrete-trial operant serial feature positive discrimination (X → A+ A− ) training in rats. Transfer of the X feature's ability to facilitate responding to a subsequent target cue was nearly complete if the transfer target had been trained as the target in another serial feature positive discrimination, even if that target controlled a different operant than controlled by the original A target. Repeated presentations of X alone had little effect on performance to either the original or transfer test compounds. In contrast, transfer to a separately trained and extinguished target was smaller and occurred only if the original and transfer target controlled the same operant. Furthermore that transfer was eliminated by nonreinforced feature presentations. Implications of these data for hypotheses about the nature of occasion setting in operant conditioning were discussed.

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.

Asymmetrical Effect of a Temporal Gap between Feature and Target Stimuli on Pavlovian Serial Feature-Positive and Feature-Negative Discriminations

Four pigeons were trained with two serial feature-positive discrimination tasks (A−, X→A +, B−, Y→g→B +), in which two diffuse feature stimuli (X and Y) signaled that one of two target keylights (A and B) was followed by food. One of the discrimination tasks had a temporal gap (g) between the feature and the target. The birds learned both of these two discriminations, producing pecks exclusively to the target preceded by the feature. Another group of four birds was trained with two serial feature-negative discrimination tasks (A +, X→A−, B +, Y→g→B−), in which two diffuse features signaled that one of two target keylights was not followed by food. One of the tasks also had a temporal gap. The birds learned the discrimination without the gap, producing pecks exclusively in the target alone trials. However, they did not show any sign of discrimination with the gap and produced many responses to the target (B) preceded by the feature and the gap, as well as that not preceded by them.

Preweanling and adult rats treat conditioned light-tone combinations differently

Ontogenetic differences in processing light-tone compounds were discovered in preweanling (17-day-old) and adult (60–80-day-old) rats. Suppression of general activity was used as an index of the magnitude of conditioned fear following a single training session in which a CS+ was paired with mild footshock. In Experiment 1, rats were trained on discriminations in which the CS− consisted of a light and the CS+ was either a tone alone (simple discrimination) or a light-tone compound (simultaneous feature-positive discrimination). Adults and preweanlings given each type of discrimination were then tested for fear of the CS− and a target stimulus (tone alone or light-tone compound). Adults in all groups displayed greater fear of the target than of the CS−. Preweanlings, however, discriminated the CS− from the target only when the target was the same as the original CS+. Experiment 2 revealed that age-related differences in conventional stimulus generalization is not a likely explanation for the pattern of results found in Experiment 1. Experiment 3 revealed age-related differences in expressed fear of a serial feature-positive discrimination; adults, but not preweanlings, showed greater fear of the compound than of the CS−. Alternative interpretations of the results from these experiments are discussed, and the general conclusion is that adults appear more inclined to process elements of a compound stimulus selectively, whereas preweanlings seem more likely to process the compound unselectively, with roughly equivalent processing of each element.

Retraction of Ross and LoLordo findings concerning blocking in serial feature-positive discriminations.

Retraction of Ross and LoLordo findings concerning blocking in serial feature-positive discriminations.

Retraction of Ross and LoLordo findings concerning blocking in serial feature-positive discriminations.

Findings concerning the effectiveness of stimuli from various conditioning procedures in blocking conditioned excitation and occasion-setting functions of an added stimulus in a serial feature-postive discrimination training procedure (LoLordo & Ross, 1987; Ross & LoLordo, 1986, 1987) are retracted. Videotapes on which the published data were based were rescored by 2-5 people, most of whom were uninformed about group memberships of the subjects. In no case did the rescoring confirm any of the orginal findings of blocking. Possible factors contributing to the discrepancies are discussed. The experiments should be repeated with feature stimuli that are less similar to each other and with several scorers, at least one of whom is unaware of the group assignment of the subjects.