Avoidance of 20% carbon dioxide-enriched air with humans.

Four college students were exposed to a Sidman avoidance procedure to determine if an avoidance contingency involving 20% carbon dioxide-enriched air (CO2) would produce and maintain responding. In Phase 1, two conditions (contingent and noncontingent) were conducted each day. These conditions were distinguished by the presence or absence of a blue or green box on a computer screen. In the contingent condition, CO2 presentation were delivered every 3 s unless a subject pulled a plunger. Each plunger pull postponed CO2 presentations for 10 s. In the noncontingent condition, CO2 presentations occurred on the average of every 5 min independent of responding. Following stable responding in Phase 1, condition-correlated stimuli were reversed. In both conditions, plunger response rate was high during the contingent condition and low or zero during the noncontingent condition. Furthermore, subjects avoided most CO2 presentations. However, CO2 presentations did not increase verbal reports of fear. Overall, the results from the present study suggest that CO2 can be used effectively in basic studies of aversive control and in laboratory analogues of response patterns commonly referred to as anxiety.     

Fearing shades of grey: individual differences in fear responding towards generalisation stimuli

Individual differences in fear generalisation have been proposed to play a role in the aetiology and/or maintenance of anxiety disorders, but few data are available to directly support that claim. The research that is available has focused mostly on generalisation of peripheral and central physiological fear responses. Far less is known about the generalisation of avoidance, the behavioural component of fear. In two experiments, we evaluated how neuroticism, a known vulnerability factor for anxiety, modulates an array of fear responses, including avoidance tendencies, towards generalisation stimuli (GS). Participants underwent differential fear conditioning, in which one conditioned stimulus (CS+) was repeatedly paired with an aversive outcome (shock; unconditioned stimulus, US), whereas another was not (CS?). Fear generalisation was observed across measures in Experiment 1 (US expectancy and evaluative ratings) and Experiment 2 (US expectancy, evaluative ratings, skin conductance, startle responses, safety behaviours), with overall highest responding to the CS+, lowest to the CS? and intermediate responding to the GSs. Neuroticism had very little impact on fear generalisation (but did affect GS recognition rates in Experiment 1), in line with the idea that fear generalisation is largely an adaptive process.     

Suppression of visual observing by rhesus monkeys produced by conditioned aversive visual stimuli.

Nine rhesus monkeys were tested in a visual observing situation to determine the influence of conditioned aversive visual stimulation. A set of meaningless visual stimuli was selected on the basis of cumulative frequency and cumulative duration of observing during a pretest phase of the experiment. Three subsets of stimuli (low, medium, high) were formed indicating level of observing during pretesting. A portion of the "medium" category of slides then served as conditioned stimuli in a classical conditioning procedure by being paired with electric shock. Following conditioning the entire set of stimuli was again presented in a visual observing situation. The results showed a significant decrease in both frequency and duration of observing of the slides with conditioned aversive qualities, relative to non-shock control slides. These findings support an aversion-produced suppression of observing relatively unconfounded by methodological, procedural, and other differences existing among previous reports on the role of fear or anxiety in this context.     

A cognitive neuropsychological and psychophysiological investigation of a patient who exhibited an acute exacerbated behavioural response during innocuous somatosensory stimulation and movement

We report findings from a cognitive neuropsychological and psychophysiological investigation of a patient who displayed an exacerbated acute emotional expression during movement, innocuous, and aversive somatosensory stimulation. The condition developed in the context of non-specific white matter ischaemia along with abnormalities in the cortical white matter of the left anterior parietal lobe, and subcortical white matter of the left Sylvian cortex. Cognitive neuropsychological assessment revealed a pronounced deficiency in executive function, relative to IQ, memory, attention, language and visual processing. Compared to a normal control group, the patient [EQ] displayed a significantly elevated skin conductance level during both innocuous and aversive somatosensory stimulation. His pain tolerance was also significantly reduced. Despite this, EQ remained able to accurately describe the form of stimulation taking place, and to rate the levels of pain intensity and pain affect. These results suggest that EQ's exaggerated behavioural response and reduced pain tolerance to somatosensory stimulation may be linked to cognitive changes, possibly related to increased apprehension and fear, rather than altered pain intensity or pain affect per se.     

Positive conditioned suppression: conditioned suppression using positive reinforcers as the unconditioned stimuli

Research has revealed the phenomenon of conditioned suppression in which the rate of responding is reduced during a stimulus that is paired with noncontingent shock. The present study replicated this procedure, but used noncontingent positive reinforcers instead of the aversive shock. The lever-pressing responses of rats were reinforced with food or water. While the rats were responding, a stimulus was occasionally presented and paired with the delivery of a noncontingent positive reinforcer, which was either food, water, or brain stimulation for different rats. The result was a reduction in the rate of responding during the conditioned stimulus. This finding shows that conditioned suppression occurs during a signal for reinforcing as well as aversive stimuli.     

Sensation seeking and the aversive motivational system

Sensation seeking (SS) has traditionally been viewed as a phenomenon of the appetitive motivational system. The limited SS research exploring contributions from the aversive motivational system reveals greater anxious reactivity to dangerous activities among low sensation seekers. The present study extends this line of work by comparing levels of fear and anxiety during anticipation of predictable and unpredictable aversive stimuli across high- and low-SS groups. Low sensation seekers displayed greater fear-potentiated startle (FPS) to predictable aversive stimuli, and only those low on SS showed FPS and skin conductance response effects during experimental contexts in which aversive stimuli were delivered unpredictably. Findings implicate enhanced apprehensive anticipation among those low on SS as a potential deterrent for their participation in intense and threatening stimulus events.     

Is pain-related fear a predictor of somatosensory hypervigilance in chronic low back pain patients?

Pain-related fear has been found to be associated with increased disability and increased pain perception in patients with chronic low back pain. A possible mechanism by which pain-related fear could lead to increased pain perception is heightened attention to somatosensory sensations. In the present study, chronic pain patients reporting either a high or low level of pain related fear and control participants performed an auditory reaction time task, while occasionally non-painful electrical stimuli--accompanied by threatening instructions--were given to the arm or back. In the primary task condition, participants had to perform the auditory task while ignoring the electrical stimuli. Next, the task was presented under dual task conditions in which participants had to respond both to tones as well as to detection of electrical stimuli. It was hypothesized that for the primary task, high fearful patients would show greater disruption of performance on the auditory task than low fearful patients and controls when stimuli were presented to the back. For the dual task, slower reaction times for the auditory task, in combination with faster detection of electrical stimuli was expected. The hypotheses were not confirmed but patients scoring high on pain-related fear did show an overall increase in reaction time for all conditions of the primary task, with or without simultaneous stimulation. Regression analyses demonstrated that high pain-related fear was associated with increased reaction time to tones both in patients and healthy controls, and that within patients pain-related fear was a better predictor of reaction time to tones than present pain intensity. The findings may be interpreted as showing that patients with elevated levels of pain-related fear habitually attend to somatic sensations, giving less priority to other attention-demanding tasks.     

Extinction of avoidance in rats: response availability and stimulus presentation effects

A conditioned a versive stimulus presented in prolonged, continuous fashion is said to be flooded. Using a two-way shuttle avoidance task. Polin (1959) found that animals allowed to respond to flooded stimuli extinguish faster than animals prevented from responding to discrete stimuli of equal total duration. But, as Shearman (1970) noted, the CS presentation and response availability factors were confounded. He arranged them factorially, in a 2 × 2 design, again utilizing two-way avoidance, but found no differences between any of the experimental groups, although all groups extinguished faster than a regular extinction control group, the only group for which CS termination was response-contingent. Since there is evidence from one-way avoidance studies that response prevention facilitates extinction of avoidance with CS exposure held constant (Shipley et al., 1971). we repeated the Shearman design, using a one-way avoidance paradigm, and including a group for whom the aversive CS would be presented in discrete trials at increasing intensities. A separate aspect of the present investigation concerned the measurement of a fear response as well as the avoidance response. Results of several investigations have shown (e.g. Coulter et al. 1969; Linton et al.. 1970) that avoidance behaviour can be extinguished without the extinction of fear. It was thought useful to assess the generality of this result, since in two-factor theory, fear and avoidance are related.Two supplementary experiments replicated important conditions of the initial one, while examining whether response prevention and response non-availability have similar effects (II), and the relation between the fear test and the test for extinction (III).     

Fearlessness in juvenile offenders is associated with offending rate

Poor fear conditioning is a correlate of violent offending in adults, but there is no evidence concerning juvenile offenders. Our aim was to compare emotional learning in juvenile offenders and controls and establish whether crime rate is related to seriousness of emotional learning problems. To this end, emotional learning was assessed in 42 juvenile offenders by measuring skin conductance responding (SCR) during fear conditioning. Compared to controls, juvenile offenders showed lower conditioned SCRs to visual stimuli associated with a subsequent aversive stimulus and the magnitude of the SCR during fear acquisition was inversely associated with the number of their recorded offences. These findings suggest that juvenile offenders have impairments in the neural systems that subserve emotional learning. The implication is that using punitive measures to control persistent offenders is unlikely to be effective in an identifiable group of juvenile offenders.     

The effects of incorrect pain expectations on acquired fear and pain responses

Previous experimental research on the effects of incorrect intensity expectations of aversive events can be criticized because intensity expectations were not manipulated independently from changes in objective intensity. The present study aims at investigating the effects of incorrect intensity expectations on the immediate and later responses to a painful stimulus, and on the acquisition of anticipatory responses, with proper experimental control. Subjects (n = 62) received 20 painful stimuli of varying intensity. In the control group intensities were correctly signalled on all trials by an analogue signal. On 3 trials the signal was too large in the overprediction condition, and too small in the underestimation condition. Underpredicted painful experiences were related to subsequent higher pain responses on the physiological level, but not on the subjective level; and to increased anticipatory responses (increased pain expectations, uncertainty, subjective fear, skin conductance responses). Skin conductance level also indicated increased fear after underpredicted experiences. Overpredicted painful experiences were related to a faster decrease in subjective fear compared to the control group, but did not influence other variables. The findings support the notion that underpredictions contribute to the acquistion of fear and disrupt habituation processes. The asymmetrical processing of the two kinds of incorrectly predicted experiences is discussed.     

Reversibility of single-incentive selective associations.

Rats were trained to press a lever in the presence of a tone-light compound stimulus and not to press in its absence. In each of two experiments, schedules were designed to make the compound a conditioned punisher for one group and a conditioned reinforcer for the other. In Experiment 1, one group's responding produced food in the presence of the compound but not in its absence. The other group's responding terminated the compound stimulus, and food was presented only in its absence. When tone and light were later presented separately, light controlled more responding than did tone in the former group, but tone gained substantial control in the latter. The same effects were also observed within subjects when the training schedules were switched over groups. In Experiment 2, two groups avoided shock in the presence of the compound stimulus. In the absence of the compound, one group was not shocked, and the other received both response-independent and response-produced shock. When tone and light were presented separately, the former group's responding was mainly controlled by tone, but the latter group's responding was almost exclusively controlled by light. These effects were also observed within subjects when the training schedules were switched over groups. Thus, these single-incentive selective association effects (appetitive in Experiment 1 and aversive in Experiment 2) were completely reversible. The schedules in which the compound should have been a conditioned reinforcer consistently produced visual control, and auditory control increased when the compound should have become a conditioned punisher. Currently accepted accounts of selective associations based on affinities between shock and auditory stimuli and between food and visual stimuli (i.e., stimulus-reinforcer interactions) do not adequately address these results. The contingencies of reinforcement most recently associated with the compound and with its absence, rather than the nature of the reinforcer, determined whether auditory or visual stimulus control developed.     

Measuring the role of conditioning and stimulus generalisation in common fears and worries

Common and persistent fears may emerge through learning mechanisms such as fear conditioning and generalisation. Although there have been extensive studies of these learning processes in healthy but also psychiatric samples, many of the tasks used to produce conditioning and assess generalisation either use painful and aversive stimuli as the unconditioned stimuli (UCS), or suffer from poor belongingness between the conditioned stimuli and the UCS. Here, we present novel data from a paradigm designed to examine fear conditioning and generalisation in healthy individuals. Two female faces served as conditioned threat cue (CS+) and conditioned safety cue (CS?) respectively. The CS+ was paired repeatedly with a fearful, screaming face (unconditioned stimulus). Generalisation included intermediate faces which varied in their similarity to the CS+ and CS?. We measured eyeblink startle reflex and self-reported ratings. Acquired fear of the CS+ generalised to intermediate stimuli in proportion to their perceptual similarity to the CS+. Our findings demonstrate how fears of new individuals may develop based on resemblance to others with whom an individual has had negative experiences. The paradigm offers new opportunities for probing the role of generalisation in the emergence of common and persistent fears.     

Integration of noxious stimulation across separate somatosensory communications systems: a functional theory of pain

Functional measurement analyses and psychophysical techniques were used to assess how separate, cross-modal, aversive events are integrated in judgements of pain. Subjects made magnitude estimations of noxious stimuli produced by a 6 X 6 factorial design of electric shocks and loud tones. Group data and most of the individual results were consistent with a model of linear pain summation: The estimates of pain approximated the linear sum of the pain estimates of the individual electrocutaneous and auditory components. The relation between painful sensation and current intensity could be described by a mildly expansive power function with an exponent of about 1.1. Auditorily produced painful sensation related to sound pressure level by a mildly compressive power function with an exponent of about 0.90 as a representative figure. Results are interpreted in terms of a functional theory of pain. Noxious events are first transformed to psychological scale values via stimulus-specific psychophysical transfer functions. The outputs of these functions are then combined with other pain-related internal representations of either sensory or cognitive origin, according to simple algebraic models.     

The Malicious Serpent: Snakes as a prototypical stimulus for an evolved module of fear

As reptiles, snakes may have signified deadly threats in the environment of early mammals. We review findings suggesting that snakes remain special stimuli for humans. Intense snake fear is prevalent in both humans and other primates. Humans and monkeys learn snake fear more easily than fear of most other stimuli through direct or vicarious conditioning. Neither the elicitation nor the conditioning of snake fear in humans requires that snakes be consciously perceived; rather, both processes can occur with masked stimuli. Humans tend to perceive illusory correlations between snakes and aversive stimuli, and their attention is automatically captured by snakes in complex visual displays. Together, these and other findings delineate an evolved fear module in the brain. This module is selectively and automatically activated by once-threatening stimuli, is relatively encapsulated from cognition, and derives from specialized neural circuitry.     

Effects of differentially modeled stimuli on vicarious autonomic arousal

The present study examined effects of variations in modeled pain cues on level of vicarious arousal, using heart rate and blood-volume amplitude as psychophysiological measures. Students were assigned randomly to one of four groups in which they either (a) underwent directly the cold-pressor test, (b) observed a model exposed to the cold-pressor test and expressing pain by facial and bodily movements, (c) heard only the modeled verbal expressions of pain, or (4) observed the model express neither verbal expressions nor physical movements while undergoing the painful stimulation. The results show aversive stimulation increases heart rate whereas vicarious aversive stimulation produces reductions in heart rate. The deceleration of heart rate was not found in response to all three forms of modeling. Both direct and vicarious aversive stimulation produced decreases in the amplitude of vasomotor responses. The size of the decrement between direct stimulation and the minimal modeling condition of vicarious arousal showed significant differences, but differences between direct stimulation and the maximal modeling condition were not significant. The vasoconstriction was found in response to two forms of modeling.     

Conditioned fear-induced opiate analgesia on the Formalin test: Evidence for two aversive motivational systems

Fear, conditioned to apparatus cues associated with electric shock, was measured by recording freezing. Pain reactivity was simultaneously measured by recording the paw-licking and paw-lifting response to Formalin injected into a paw. Stimuli associated with shock produced freezing and inhibited the responses to Formalin; whereas various control stimuli did neither. These results indicate that one of the responses to fear is analgesia. The opiate antagonist naltrexone reversed this analgesia, suggesting that the analgesia has an opiate nature. The results were interpreted in terms of a two-aversive-motivational-systems model. One system, the pain system, is instigated by tissue-damaging stimuli and produces recuperative behavior that functions to promote healing. The other system, the fear system, is triggered by conditioned fear stimuli. It produces species-specific defensive reactions and also inhibits the pain system via analgesia.     

All we need is a cue to remember: the effect of an extinction cue on renewal

In the present study, it was investigated by employing a human fear conditioning paradigm whether an extinction retrieval cue can attenuate renewal of conditioned responding after an extinction treatment procedure, and if so, what the precise role of such an extinction cue comprises. It was hypothesized that such a cue can attenuate renewal and would function as a safety signal capable of directly inhibiting the expectancy of an aversive outcome and conditioned skin conductance responding to a conditioned stimulus. The results demonstrated that the extinguished expectancy of an aversive outcome was renewed when the CS was presented outside the extinction context and that an extinction cue attenuated this effect. This extinction cue, however, only transferred its inhibitory properties to other, non-extinguished stimuli when there was no contextual switch. This safety signal function was not observed after a switch in context. Possible functions of the extinction cue and its application in extinction-based exposure treatments are discussed.     

Conditioned suppression as a sensitive baseline for social facilitation

The key pecking of pigeons maintained on a variable-interval schedule of food reinforcement was suppressed during occasional presentations of a warning stimulus paired with electric shock. On alternate sessions, a co-actor pigeon was visible in an adjoining chamber where it emitted the same food-reinforced key peck during the warning stimulus that signalled shock for the subject. With no shock and at low shock intensities, where the subject's responding was not suppressed or suppressed only slightly, the co-actor had little effect. At the higher shock intensities, where the subject's responding was reduced by at least 40%, the response rate during the warning stimulus was consistently higher when the co-actor was present. One explanation of these results assumes a special relationship between social stimuli and aversive stimuli in which the presence of another animal reduces emotional reactions and thereby allows operant responses to increase. This was not the case here because the mere presence of the co-actor did not maintain social facilitation. Rather, the present results, taken in conjunction with previous findings, suggest that changes in social and non-social variables which affect the rate of food-reinforced responding may produce proportionately larger changes in responding when that responding is suppressed by aversive stimulation than when it is not.     

Direction of human motor responses by men and women to aversive stimulation

The frequency of extensions and flexions of the arms of 12 men and 12 women (ages 20-30 years) responding to a neutral tone or to an electric shock was recorded. Subjects had to choose between pushing or pulling a lever upon receipt of an acoustic signal which was paired or unpaired with an electric shock. They were instructed to perform either long duration movements, allowing for on-line control of the execution, or short duration movements with prior specification of amplitude. Regardless of duration of movements, the aversive signal increased the frequency of extensions and intraindividual variability of choices of the men but decreased the frequency of extensions and intraindividual variability of choices of the women. These findings show that stimuli such as pain or fear automatically elicit patterns of terminal motor states corresponding to fight or flight, initiating processes of preparation of spatially oriented movements which are automatic and sex-typed and impair the use of the terminal cues for simultaneous preprogrammed voluntary movements.     

How do social fears in adolescence develop? Fear conditioning shapes attention orienting to social threat cues

Social fears emerging in adolescence can have negative effects on emotional well-being. Yet the mechanisms by which these risks occur are unknown. One possibility is that associative learning results in fears to previously neutral social stimuli. Such conditioned responses may alter subsequent processing of social stimuli. We used a novel conditioning task to examine how associative processes influence social fear and attention orienting in adolescents. Neutral photographs were paired with socially rewarding or aversive stimuli during conditioning; a dot-probe task then assessed biases in attention orienting. The social conditioning task modified subjective ratings of the neutral stimuli. Moreover, for the neutral stimulus that was paired with the aversive stimulus, the strength of conditioning showed a relationship with subsequent attentional vigilance. The findings elucidate mechanisms by which negative peer experiences during adolescence may affect emotional processing.