Negative Discriminative Stimulus Research Articles

Does a negative discriminative stimulus function as a punishing consequence?

The study and use of punishment in behavioral treatments has been constrained by ethical concerns. However, there remains a need to reduce harmful behavior unable to be reduced by differential-reinforcement procedures. We investigated whether response-contingent presentation of a negative discriminative stimulus previously correlated with an absence of reinforcers would punish behavior maintained by positive reinforcers. Across four conditions, pigeons were trained to discriminate between a positive discriminative stimulus (S+) signaling the presence of food, and a negative discriminative stimulus (S-) signaling the absence of food. Once learned, every five responses on average to the S+ produced S- for a duration of 1.5 s. S+ response rate decreased for a majority of pigeons when responses produced S-, compared to when they did not, or when a neutral control stimulus was presented. In Condition 5, choice between two concurrently presented S+ alternatives shifted away from the alternative producing S-, despite a 1:1 reinforcer ratio. Therefore, presenting contingent S- stimuli punishes operant behavior maintained on simple schedules and in choice situations. Development of negative discriminative stimuli as punishers of operant behavior could provide an effective approach to behavioral treatments for problem behavior and subverting suboptimal choices involved in addictions.

RELATIONS AMONG EQUIVALENCE, NAMING, AND CONFLICTING BASELINE CONTROL

Three studies were conducted with different groups of 6 students each to explore the effects of training class-inconsistent relations and naming on demonstrations of emergent arbitrary stimulus relations. In all studies, two three-member equivalence classes of Greek symbols (A1B1C1 and A2B2C2) emerged as a result of training in conditional discriminations. Two new symbols were introduced (X and Y), and additional conditional discriminations were trained, whereby X was designated as the positive discriminative stimulus (S+) and Y was designated as the negative discriminative stimulus (S-) for A1 and B2. Conversely, Y was designated as the S+ and X as the S- for B1 and A2. This introduced conflicting sources of control within and between classes. In Study 1, subjects were not provided with names for the stimuli. In Study 2, the experimenter provided common names for the stimuli within each class. In Study 3, the subjects were required to use the common names during conditional discrimination training and test-trial blocks. In all experiments, equivalence responding with respect to the original classes was disrupted for some subjects subsequent to learning the new relations. Furthermore, in Studies 2 and 3, there were frequent examples of noncorrespondence between observed (listener or speaker) naming patterns and derived relations. These results support the view that demonstrations of equivalence are subject to control from a variety of sources rather than being fundamentally dependent on naming.

Categorical discrimination and generalization in pigeons: All negative stimuli are not created equal.

Three experiments investigated categorical discrimination and generalization in pigeons. Multiple fixed interval-extinction training was conducted with a pool of 48 different negative discriminative stimuli (12 slides each of people, flowers, cars, and chairs). The most errors were committed to negative stimuli (S−s) from the same category as the 12 positive stimulus (S+) slides

REAL‐TIME DETECTION OF ORIENTATION DURING NEGATIVE BEHAVIORAL CONTRAST WITH KEY PECKING AND A TURNING RESPONSE

We developed a video system for real-time detection of a pigeon's orientation and for reinforcement of a "turning response." Using this system, negative behavioral contrast was found across key-peck and turning responses. In addition, turning away from the pecking key was detected by the system just after presentation of the negative discriminative stimulus on the key. The results suggest that avoidance of the discriminative stimulus in the constant component, which has been regarded as a causal factor for negative contrast (additivity theory), is not the primary factor for negative behavioral contrast of pigeons' key pecking, but may account for negative local contrast.

Negative discriminative stimuli provide information about the identity of omitted response-contingent outcomes

Three experiments using rats examined whether a signal for the nonreinforcement of an instrumental response (S-) provided information about the identity of the omitted outcome. In all three experiments, one stimulus was established as a signal for the nonreinforcement of a response that earned food pellets and another stimulus signaled the nonreinforcement of a response that earned liquid sucrose. Experiment 1 found that each S-suppressed another instrumental response trained with the same outcome significantly more than a response trained with a different outcome. Using a variant of this transfer design, Experiment 2 demonstrated that an S- was slower to develop discriminative control over a new response reinforced in its presence with the same outcome compared with an outcome different from the one whose omission-the S- had previously signaled. Experiment 3 examined transfer of the S- stimuli to a response trained with two outcomes, one of which had subsequently been devalued. Performance of this response significantly increased in the presence of a signal for the omission of the devalued outcome, but decreased in the presence of a signal for the omission of the valued outcome. These results suggest that S-s do provide information about the identity of omitted response-contingent outcomes.

Discrimination between the odours of fresh oestrous and non-oestrous ewe urine by rams

Four sexually experienced adult rams were trained using operant conditioning techniques to discriminate between oestrous and non-oestrous ewe urine odours. Fresh oestrous and non-oestrous urine was collected from different ewes within 1 h prior to each experiment. Oestrous urine odour was the positive discriminative stimulus (S+) and non-oestrous urine odour was the negative discriminative stimulus (S−). The rams performed 22 olfactory discrimination experiments and on each test day urine from various pairs of ewes and from various oestrous cycles was used. The only consistent feature of S+ therefore was the oestrous state of the donor ewe and the only consistent feature of S− was the non-oestrous state of the donor ewe. All rams could discriminate between fresh oestrous and non-oestrous urine odours on every occasion. During the first 12 experiments, the rams learnt to respond to the consistent difference in odour between the two urine types. In the last 10 experiments, they were able to choose the new oestrous urine odour consistently in the initial trial. These results demonstrate that rams are able to differentiate between sexually receptive and non-receptive ewes on the basis of differences in urine odour. The implications of these findings and suggestions for further experimental work are discussed.

ON CONDITIONED REINFORCING EFFECTS OF NEGATIVE DISCRIMINATIVE STIMULI

Observing responses by pigeons were studied during sessions in which a food key and an observing key were available continuously. A variable-interval schedule and extinction alternated randomly on the food key. In one condition, food-key pecking during extinction decreased reinforcement frequency during the next variable-interval component, and in the other condition such pecking did not affect reinforcement frequency. Observing responses either changed both keylight colors from white to green (S+) or to red (S-) depending on the condition on the food key, or the observing responses never produced the S+ but produced the S- when extinction was in effect on the food key. Observing responses that produced only S- were maintained only when food-key pecking during extinction decreased reinforcement frequency in the subsequent variable-interval component. The red light conformed to conventional definitions of a negative discriminative stimulus, rendering results counter to previous findings that production of S- alone does not maintain observing. Rather than offering support for an informational account of conditioned reinforcement, the results are discussed in terms of a molar analysis to account for how stimuli acquire response-maintaining properties.

Transformation of a waiting schedule into a temporal regulation schedule (DRRD) by addition of external stimuli in the dog

Waiting schedules do not impose temporal regulation but condition the animal to give the operant response during a given time. At the end of the required delay, a positive discriminative stimulus is presented. The suspension of the response while the discriminative stimulus is being given suspension of the response while the discriminative stimulus is being given is accompanied by reinforcement. The transformation of a waiting schedule into a temporal regulation schedule is generally achieved by suppressing the external facilitating factors or by physically modifying them. Our study reveals that a similar transformation can be achieved in the dog by the addition of a further stimulus. This stimulus, which is physically exactly the same as the excitatory stimulus and which punctuates the waiting period, is randomly introduced into the temporal delay. The absence of reinforcement in response to the added stimulus should force the animal to regulate its behavior in time and the additional negative discriminative stimulus favours the expression of the active nature of the inhibation. The results show that subjects can differentiate their response durations according to stimuli that only differ according to temporal location. Thus this pattern resembles a DRRD schedule. The peak of responses at the time of the inhibition stimulus reveals considerable behavioral conflict : either the response must be maintained or the inhibition suppressed. The positive or negative resolution of this conflict reveals noteworthy aspects of the behavioural inhibition process.

The role of observing and attention in establishing stimulus control.

Early theorists (Skinner, Spence) interpreted discrimination learning in terms of the strengthening of the response to one stimulus and its weakening to the other. But this analysis does not account for the increasing independence of the two performances as training continues or for increases in control by dimensions of a stimulus other than the one used in training. Correlation of stimuli with different densities of reinforcement produces an increase in the behavior necessary to observe them, and greater observing of and attending to the relevant stimuli may account for the increase in control by these stimuli. The observing analysis also encompasses errorless training, and the selective nature of observing explains the feature-positive effect and the relatively shallow gradients of generalization generated by negative discriminative stimuli. The effectiveness of the observing analysis in handling these special cases adds to the converging lines of evidence supporting its integrative power and thus its validity.

SEPARATING THE EFFECTS OF SALIENCE AND DISPARITY ON THE RATE OF OBSERVING

Pigeons producing deliveries of grain on a mixed variable-interval, extinction schedule by pecking a center key could also produce discriminative stimuli on concurrent variable-interval schedules by pecking the left or right observing key. The stimuli produced by each observing key were varied independently. In the first experiment, the negative discriminative stimulus was at the far end of the spectrum from the key illumination accompanying the mixed schedule and from the positive discriminative stimulus. When the magnitude of the difference between the latter two stimuli (salience) was varied, more pecks occurred on the observing key producing the larger of the two differences than on the key producing the smaller difference. In the second experiment, the stimulus accompanying the mixed schedule was at the far end of the spectrum, and the magnitude of the difference between the two discriminative stimuli (disparity) was varied. The proportion of pecks occurring on each observing key shifted systematically in the direction of the key producing the larger difference. The salience of the discriminative stimuli and their disparity each has an independent influence on the frequency of observing when the other is controlled, but the effect of the salience appears to be the more substantial.

The Resistance to Reinforcement Technique for Measuring Inhibition

This experiment investigated use of the resistance to reinforcement procedure to measure the inhibitory properties of a negative discriminative stimulus (S-) following discrimination training. One group of rats initially learned a problem with Cue Light 1 as the positive discriminative stimulus (S + ) and Cue Light 2 as S-; a second group had equal training with house light on as S + and dark as S-. During subsequent testing both groups were reinforced for responding to both dark and Cue Light 2. Thus, inhibitory properties of each S- could be evaluated by both within- and between-subject comparisons, with responding to a novel stimulus as the baseline in both cases. Between- and within-subject comparisons corresponded perfectly with both showing the dark S- to be a strong inhibitor, but neither showing the Cue Light 2 S- to have inhibitory properties. A possible explanation of the latter result is that discrimination learning involves two stages. In the first, excitatory properties of S- are lost, and only then does further training result in the development of true inhibition. The light-dark problem was learned quickly, and training continued well beyond the point where responding to S-was very low. Thus, it is not surprising that strong inhibition was demonstrated. With the more difficult problem, subjects achieved good discrimination performance only near the end of training and responding to S- was still relatively high. Thus, training may not have been sufficient to get beyond the stage of reducing excitation and into the development of true inhibition.

Differential production of positive and negative discriminative stimuli by normal and retarded children

Using an observing procedure similar to Wyckoff's (1969), two normal and two mentally retarded children were studied. The children were initially trained to earn pennies by pressing a rectangular key according to a multiple variable-interval extinction schedule of reinforcement. After discrimination training, the children were allowed to produce the discriminative stimuli by depressing a second or observing key. The retarded children were different from the normal children in that they produced more of the positive discriminative stimulus (S+) than the negative discriminative stimulus (S−). In the case of the retarded children, S+ observing started high and remained high. In the case of the normal children, S+ observing was initially substantial and then rapidly diminished.

Ability of goats and calves to distinguish between conspecific urine samples using olfaction

Goats and calves were trained, using an operant conditioning method, to discriminate between odours from pairs of urine samples collected from two different individuals of their own species. In the discrimination task the animals faced two response panels, and a tube adjacent to one panel emitted an odour used as the positive discriminative stimulus and another tube near the other panel emitted the odour used as the negative discriminative stimulus. Only presses on the panel associated with the positive stimulus were reinforced and both odours were presented simultaneously. After each reinforcement the position of the positive odour was randomly varied. In control tests, in which the same odour was emitted over both panels, the animals were unable to score below chance levels.

The ability of sheep to distinguish between conspecifics by means of olfaction

Sheep have been trained, using an operant conditioning method in which they pressed panels with their muzzles in order to obtain food, to discriminate between odours from a variety of excretory or secretory products obtained from other sheep. They were able to discriminate between odours from pairs of urine samples collected from two different individuals, and also between odours from pairs of samples of wool, faeces, saliva and the secretions from the interdigital pouch, the inguinal pouch and the infraorbital pouch collected from different sheep. In the discrimination task the sheep faced two response panels and a tube adjacent to one panel emitted the odour used as the positive discriminative stimulus and another tube near the other panel emitted the odour used as the negative discriminative stimulus. Only presses on the panel associated with the positive stimulus were reinforced and both odours were presented simultaneously. After each reinforcement the position of the positive odour was randomly varied. Following olfactory bulbectomy the sheep were unable to make the discriminations.

MAINTENANCE OF BEHAVIOR CONTROLLING THE DURATION OF DISCRIMINATIVE STIMULI1

THE MAINTENANCE OF A RESPONSE CONTROLLING THE DURATION OF POSITIVE AND NEGATIVE DISCRIMINATIVE STIMULI IN A MULTIPLE SCHEDULE WAS EXAMINED WITH RESPECT TO THE POSSIBLE CONSEQUENCES OF THE RESPONSE: none, escape from the negative stimulus, production of the positive stimulus, and initiation of the reinforcement schedule associated with the latter. The last two seemed to be the major factors in producing and maintaining the response. Escape from the negative stimulus maintained it in most subjects, but only at a much lower level.

Ability of the pig to distinguish between conspecific urine samples using olfaction

In two female pigs it has been shown using operant conditioning techniques in which the animals pushed panels with their snouts in order to obtain food, that they could distinguish between the odor from urine samples taken from other pigs. In the discrimination task, the pigs faced two panels and a tube adjacent to one of the panels emitted urine odor used as the positive discriminative stimulus while another tube adjacent to the other panel emitted the negative discriminative stimulus consisting of odor from another urine sample. Only presses on the panel associated with the positive stimulus were reinforced on a fixed ratio shcedule of 6. Both positive and negative discrimination stimuli were presented simultaneously. After each reinforcement the position of the positive and negative odor stimuli was varied according to the Gellerman series. When fully trained, the pigs made very few responses on the incorrect panel.

DIFFERENTIAL AUTOSHAPING TO COMMON AND DISTINCTIVE ELEMENTS OF POSITIVE AND NEGATIVE DISCRIMINATIVE STIMULI1

The learning by hungry pigeons of a discrimination between two successively presented compound visual stimuli was investigated using a two-key autoshaping procedure. Common and distinctive stimulus elements were simultaneously presented on separate keys and either followed by food delivery, S+, or not, S-. The subjects acquired both between-trial and within-trial discriminations. On S+ trials, pigeons pecked the distinctive stimulus more than the common stimulus; before responding ceased on S- trials, they pecked the common stimulus more than the distinctive one. Mastery of the within-display discrimination during S+ trials preceded mastery of the between-trials discrimination. These findings extend the Jenkins-Sainsbury analysis of discriminations based upon a single distinguishing feature to discriminations in which common and distinctive elements are associated with both the positive and negative discriminative stimuli. The similarity of these findings to other effects found in autoshaping-approach to signals that forecast reinforcement and withdrawal from signals that forecast nonreinforcement-is also discussed.

Colour changes of Octopus rubescens during attacks on unconditioned and conditioned stimuli

Octopus rubescens exhibits a sequence of skin colour changes when it attacks and captures prey. These displays were observed during attacks on (1) free-swimming crabs, (2) crabs of different sizes impaled on thin rods, and (3) positive and negative discriminative stimuli. Animals were housed separately in light-blue aquaria which also served as experimental apparatuses. Animals in each condition showed the same typical sequence of colour displays. This sequence is (1) before detection of crab: various colours, (2) on detection and during a free-swimming attack: colours ranging from light orange to grey, (3) on landing: colourless and nearly transparent, (4) on seizing the crab: spotted or mottled, and (5) afterward: various colours. The colour changes may be tied to locomotor acts and postural adjustments.

PUNISHMENT OF OBSERVING BY THE NEGATIVE DISCRIMINATIVE STIMULUS1

To determine the effect of a negative discriminative stimulus on the response producing it, two pigeons were each studied in a three-key conditioning chamber. During alternating periods of unpredictable duration, pecking the center (food) key either was reinforced with grain on a variable-interval schedule or was never reinforced. On equal but independent variable-interval schedules, pecking either of the side (observing) keys changed the color of all keys for 30 sec from yellow to either green or red. When the schedule on the center key was variable-interval reinforcement, the color was green (positive discriminative stimulus); when no reinforcements were scheduled, the color was red (negative discriminative stimulus). Since pecking the side keys did not affect grain deliveries, changes in the rate of pecking could not be ascribed to changes in the frequency of primary reinforcement. In subsequent sessions, red was withheld as one of the possible consequences of pecking a given side key. When red was omitted, the rate on that key increased, and when red was restored, the rate decreased. It was concluded that red illumination of the keys, the negative discriminative stimulus, had a suppressive effect on the response that produced it.

Generalization along the dimension of sound intensity in pigeons

Two groups of four pigeons each were trained on a discrimination between two intensities of white noise. The low-intensity group had a 60-dB intensity as the negative discriminative stimulus (S−) and a 70-dB intensity as the positive discriminative stimulus (S+): the high-intensity group had a 95-dB intensity as S− and an 85-dB intensity as S+. Generalization stimuli were all of higher intensity than S+ for the former group and all of lower intensity than S+ for the latter group. The rate of acquisition of the discrimination was faster for the Ss in the high-intensity group. In both groups, the maximum of the generalization function was shifted toward the middle values of the set of test stimuli, away from the training stimuli. Responding showed a decline at the far end of the range of test stimuli. Responding to the positive training stimulus was initially as great as it had been on the preceding training sessions, but became markedly depressed relative to responding to the other stimuli as the test progressed.