Learned helplessness and immunization: sensitivity to response-reinforcer independence in immunized rats

In experiments 1 and 2, we examined the learned helplessness and immunization effects using a test in which appetitive responding was extinguished by delivering noncontingent reinforcers. Contrary to learned helplessness theory, "immunized" animals showed performance virtually identical to that of animals exposed only to inescapable shock, and different from nonshocked controls. Experiment 2 suggests that the helplessness effect and the lack of immunization are not due to direct response suppression resulting from shock. In Experiment 3, where the immunization effect was assessed by measuring the acquisition of a response to obtain food when there was a positive response-reinforcer contingency, immunization was observed. These results cannot be explained on the basis of proactive interference, but suggest that animals exposed to the immunization procedure acquire an expectancy of response-reinforcer independence during inescapable shock. Thus, immunization effects may reflect the differential expression of expectancies, rather than their differential acquisition as learned helplessness theory postulates.     

Lever-contact responses in rats: automaintenance with and without a negative response-reinforcer dependency

Pairing the presentations of one lever (cueing lever) with food led to the acquisition and persistence of lever contacts by rats. This behavior did not occur with a second lever, which was presented randomly with regard to food delivery. This finding obtained whether food delivery was independent of cueing-lever contacts (positive automaintenance) or dependent on the absence of cueing-lever contacts (negative automaintenance). The general findings were: (1) cueing-lever contacts on the positive automaintenance procedure occurred on a higher proportion of trials and at higher rates when contacts occurred than on the negative automaintenance procedure; (2) instances of the cueing lever's failure to support responding were more frequent on the negative than the positive automaintenance procedure; and (3) the topography and median contact duration of positively automaintained responding differed from negatively automaintained responding. These findings agree substantially with the automaintenance literature on pigeons, suggesting that similar processes may characterize automaintained responding in both pigeons and rats.     

Affective learning increases sensitivity to graded emotional faces

How does the affective significance of emotional faces affect perceptual decisions? We manipulated affective significance by pairing 100% fearful faces with aversive electrical stimulation and hypothesized that increasing the significance of a stimulus via its prior history would lead to enhanced processing. After fear conditioning, participants viewed graded emotional faces that ranged from neutral to fearful. Faces were shown either in a color that was previously paired with shock or a color not paired with shock during conditioning. Increases in the frequency of "fearful" responses for faces shown in the shock-paired color were most robust for faces at intermediate intensity levels (40-60% fearful). Psychometric fits to the data revealed significant increased sensitivity for shock-paired relative to unpaired faces. Thus, despite identical physical features for shock-paired and unpaired stimuli (aside from the color, which was counterbalanced), more frequent (and faster) "fearful" responses were made when participants viewed affectively significant stimuli.     

Stimulus- and response-reinforcer contingencies in autoshaping, operant, classical, and omission training procedures in rats

Separate groups of rats received 500 trials of lever-press training under autoshaping (food delivery followed 10-second lever presentations, or occurred immediately following a response); operant conditioning (responding was necessary for food delivery); and classical conditioning (food followed lever presentations regardless of responding). Each group then received 500 trials on an omission procedure in which food was omitted on trials with a response. Another group received 1000 trials on the omission procedure, and a fifth group, random control, received 1000 uncorrelated presentations of lever and food. The autoshaping, operant, and classical groups reached high response levels by the end of initial training. Acquisition was fastest in the autoshaping group. Responding remained consistently low in the control group. The omission group responded at a level between the control group and the other three groups. During omission training, responding in these three groups declined to the omission-group level. During omission training, the rats continued contacting the lever frequently after lever pressing had declined. Response maintenance under omission training seems not to require topographic similarity between the response and reinforcer-elicited consummatory behaviors.     

An acute stressor enhances sensitivity to a chemical irritant and increases51CrEDTA permeability of the colon in adult rats

We investigated the effect of prior acute stress on colonic permeability induced by a chemical irritant known to induce symptoms similar to inflammatory bowel disease in rodents. Adult male rats (n=12) were stressed by a single session of ten unpredictable, uncontrollable foot shocks, and half were home cage controls (n=12). Twenty-nine days later, half of each treatment group was exposed to 4% DSS (dextran sulphate sodium) solution in their drinking water for 48 hours while half received pure water over two periods separated by 17 days. After food deprivation overnight and light isoflurane anaesthesia the following morning, the animals were given a colonic infusion of 2000 nCi (nanocurie)⁵¹CrEDTA (⁵¹Cr-labelled ethylenediaminetetraacetic acid) and then placed individually in metabolic cages for a six hours continuous urine collection. Radioactivity in urine was measured by a gamma counter and percentage recovery of⁵¹CrEDTA calculated as an indicator of colonic mucosal permeability. Results concluded that pre-shocked animals exposed to DSS showed significantly higher mucosal permeability than the pre-shocked animals given water, and the non-shocked animals given either DSS or water. Pre-shock in combination with two exposures to a chemical irritant separated by 17 days had a pronounced effect on colonic permeability, indicating that stress should be considered a possible initiating or contributory factor to increased intestinal permeability related to a mucosal challenge.     

Biting attack by rats in response to aversive shock

Paired rats are known to behave aggressively when given painful electric shocks. The present study developed a procedure whereby individual rats given shocks might bite an inanimate target object. Unavoidable shock was delivered to the rat while it was restrained in a position close to, and facing a target object. Biting of the target was recorded automatically. Shock caused the rat to bite metal, wood, or rubber targets. Biting was most frequent immediately after shock and decreased as a direct function of time since the shock. Almost every shock produced biting and the behavior continued as long as the shocks were delivered. Biting ceased within and between sessions when shocks were discontinued. These results show how the pain-aggression relation can be studied objectively with rats.     

Touch noise increases vibrotactile sensitivity in old and young

Stochastic resonance (SR) occurs when the detection of a subthreshold signal is aided by the presence of random energy fluctuations in the signal modality, commonly called noise. SR is counterintuitive because such noise usually worsens performance. Nonetheless, SR has been demonstrated both theoretically and experimentally in human sensory systems. Using a psychophysically sophisticated paradigm, we show that SR aids the detection of vibrating touch stimuli presented to the foot soles of both healthy elderly people with elevated vibrotactile thresholds and healthy young people with normal vibrotactile thresholds. The results also suggest that it is possible to know a priori the amount of noise needed for optimal SR effects given the degree to which the signal is subthreshold. Thus, SR may be practical as a rehabilitative aid for individuals with elevated sensory thresholds.     

Reactions to merit pay increases: a longitudinal test of a signal sensitivity perspective

The relationships among merit pay raises, trait positive affectivity (PA), and reactions to merit pay increases (pay attitudes and behavioral intentions) were explored in a longitudinal study of hospital employees. Drawing on signal sensitivity theory, the authors expected that PA would moderate the relationship between merit pay raise size and reactions to the increase such that pay raise size would be more strongly related to pay attitudes and behavioral intentions among those low in PA. Results strongly supported the predictions in the case of reactions to the raise amount (happiness and effort intentions) but not for pay level satisfaction. Implications of the results and directions for future research are identified.     

Wearable activity schedules to promote independence in young children

Activity schedules consist of a series of visual discriminative stimuli, arranged in booklets or binders, which function as prompts for appropriate behavior. Although activity schedules are useful, their typical presentation in binders can be cumbersome and stigmatizing, placing additional barriers for independence and inclusion. The purpose of the present studies was to evaluate the usefulness of a wearable activity schedule and determine whether prompts provided by it would be sufficient to support completion of a complex chain of behaviors by young children. In Experiment 1, the Octopus watch® provided prompts to children of typical development to complete a morning routine independently. In Experiment 2, the usefulness of the watch was evaluated in children with autism spectrum disorder engaged in play activities in a clinical setting. In both experiments, children reliably displayed a greater proportion of independent engagement in target behaviors when prompts were delivered by the watch compared to control conditions.     

Field-dependence/independence: ability in relation to mobility-fixity

Previous authors have pointed out that, while the classic Rod-and-Frame Test (RFT) yields a measure of ability to perform field-independently, it is unsuitable for identifying stylistic preference, such as mobility-fixity within the field-dependence/independence dimension. To relate mobility-fixity and ability aspects of field-dependence/independence, we compared data obtained from two versions of the test: one with a "free" instruction, on which the subjects were invited to adjust the rod to any position(s) they preferred on each of 10 trials and a process-oriented version (RFT-P), involving 20 trials with the standard instruction but with a constant rod-and-frame configuration, making possible analysis of the process of adaptation. Mobility versus fixity was defined in terms of more or less frequent changes of rod positions and choice of a high or a low proportion of nongeometrical positions in the RFT-Free. 38 female and 23 male university students completed first the RFT-Free and thereafter the RFT-Process. Women were more field-dependent than men throughout the RFT-Process trials; there were no differences between the sexes over trials or in choice of positions in the RFT-Free. Compared with field-dependent subjects, field-independent subjects more often changed rod positions in the RFT-Free and preferred nongeometrical positions somewhat more. Among field-independent subjects, those with consistently low deviations in RFT-Process more often preferred a variety of nongeometrical positions in RFT-Free than did those with gradually increasing deviations. We conclude that field-independence is associated with mobility and field-dependence with fixity, as defined by the RFT-Free variables, and that a prerequisite for high mobility is a relative stability of field-independence as reflected on the RFT-Process. Theoretical implications of this conclusion are discussed.     

Effects of a variable-ratio conditioning history on sensitivity to fixed-interval contingencies in rats.

We investigated the possibility that human-like fixed-interval performances would appear in rats given a variable-ratio history (Wanchisen, Tatham, & Mooney, 1989). Nine rats were trained under single or compound variable-ratio schedules and then under a fixed-interval 30-s schedule. The histories produced high fixed-interval rates that declined slowly over 90 sessions; differences as a function of the particular history were absent. Nine control animals given only fixed-interval training responded at lower levels initially, but rates increased with training. Despite differences in absolute rates, rates within the intervals and postreinforcement pauses indicated equivalent development of the accelerated response patterns suggestive of sensitivity to fixed-interval contingencies. The finding that the histories elevated rates without retarding development of differentiated patterns suggests that the effective response unit was a burst of several lever presses and that the fixed-interval contingencies acted on these units in the same way as for single responses. Regardless of history, the rats did not manifest the persistent, undifferentiated responding reported for humans under comparable schedules. We concluded that the shortcomings of animal models of human fixed-interval performances cannot be easily remedied by including a variable-ratio conditioning history within the model.     

Relationship of field dependence/independence to adaption-innovation in alcoholics

Using alcoholics as subjects, the present study attempted a replication of Kirton's 1978 study in which he demonstrated a relationship between his adaption-innovation theory and Witkin's concept of field dependence/independence. Correlations obtained in the present study paralleled those of Kirton. As a group, alcoholics tended to be field-dependent in orientation. Innovators were less field-dependent than adaptors and "average" individuals. It was suggested that the varied characteristics of alcoholics should be considered when planning therapeutic strategies.