Backward masking and skin conductance responses after conditioning to nonfeared but fear-relevant stimuli in fearful subjects

The present study examined two issues. Are skin conductance responses conditioned to fear-relevant stimuli, as contrasted with responses conditioned to fear-irrelevant stimuli, elicited after merely an automatic, nonconscious analysis of the stimulus content? Do fearful subjects show better conditioning to nonfeared but fear-relevant stimuli (e.g., conditioning to spiders in snake-fearing subjects) than do nonfearful subjects? Subjects afraid of snakes, but not of spiders, or vice versa (n= 32) and nonfearful subjects (n= 32) were shown either fear-relevant stimuli (snakes or spiders and rats) or fear-irrelevant stimuli (flowers and mushrooms) in a differential conditioning paradigm, where one of the stimuli was followed by an electric shock. During a subsequent extinction phase, the conditioned stimuli were presented under backward masking conditions, preventing their conscious recognition. Consistent with our hypothesis, during the masked extinction of the conditioned stimuli, differential skin conductance responses to conditioning and control stimuli remained only for subjects conditioned to fear-relevant stimuli. Both fearful and nonfearful control subjects had significantly larger differential electrodermal responses to fear-relevant than to fear-irrelevant stimuli. However, contrary to our hypothesis, fearful subjects did not show enhanced conditionability to their nonfeared but fear-relevant stimuli as compared with nonfearful control subjects.     

Nonconscious associative learning: Pavlovian conditioning of skin conductance responses to masked fear-relevant facial stimuli

We examined the possibility of nonconscious associative learning in a context of skin conductance conditioning, using emotional facial expressions as stimuli. In the first experiment, subjects were conditioned to a backwardly masked angry face that was followed by electric shock, with a masked happy face as the nonreinforced stimulus. In spite of the effectively masked conditioned stimuli, differential conditioned skin conductance responses were observed in a subsequent nonmasked extinction phase. This effect could not be attributed to differential sensitization or pseudo-conditioning. In the second experiment, the differential responding during extinction was replicated with angry but not with happy faces as conditioned stimuli. It was concluded that with fear-relevant facial expressions as the conditioned stimulus, associative learning was possible even in conditions where the subjects remained unaware of the conditioned stimulus and its relationship to the unconditioned stimulus.     

Orienting and Defensive Reactions to Phobic and Conditioned Fear Stimuli in Phobics and Normals

The aim of this study was to compare cardiovascular and electrodermal responses from subjects conditioned to fear-relevant stimuli with responses from phobics selected to fear the same stimuli. In the first session of the conditioning group slides of either a snake or a spider were presented. One of these served as a CS+ reinforced by an electrical shock and the other as a CS-, which was never followed by shock. In addition the conditioning group was exposed to two neutral pictures (flowers and mushrooms). The phobic group viewed the same type of stimuli and were administered some electrical shocks uncorrelated with the slides. In the second session, randomly formed halves of each group were shown (a) slides of a spider and a snake, or (b) two neutral ones. There were reliable acquisition effects in the conditioning group with the CS+ evoking larger palmar than dorsal skin conductance responses (SCRs) whereas the reverse was true for the CS-. During extinction differential responding to CS+ and CS- was maintained but palmar/dorsal differentiation disappeared. In the phobic group, feared and non-feared cues elicited differential responding with larger palmar SCRs for the feared cue only. The conditioning group failed to evidence heart rate differentiation during acquisition when all heart rate responses (HRRs) were collapsed into a single trial block (TB). When HRRs were grouped into 2 TBs, responses shifted from deceleration to CS+ on TB1 to acceleration on TB2 whereas responses to CS- were unaffected. During extinction, HR exhibited deceleration to both cues but more to CS+ than to CS-. The phobic group's heart rate accelerated to the feared cue and decelerated to the unfeared cues in both sessions. There was no difference between groups' responses to neutral cues during the second session. The results partially validate a conditioning analogue for specific phobias and the inconsistent aspects are discussed in terms of different coping strategies.     

Skin Conductance Conditioning to Potentially Phobic Stimuli as a Function of Interstimulus Interval and Delay Versus Trace Paradigm

Because prepared learning has been defined in terms of response acquisition in spite of degraded input, it was expected that differences in resistance to extinction between skin conductance responses conditioned to potentially phobic and neutral stimuli would increase with increased interstimulus interval (ISI) and be larger with a trace than with a delay conditioning paradigm. Twelve groups with 10 subjects each were observed in a differential conditioning experiment manipulating ISI (2, 8, or 16 sec), paradigm (delay versus trace), and fear-relevance of the conditioned stimulus (potentially phobic versus neutral). The results showed highly reliable resistance to extinction of first-interval anticipatory responses to phobic stimuli, and no resistance to extinction of the corresponding responses to the neutral stimuli. This difference did not interact either with the ISI or the paradigm factor. Thus, although underscoring the reliability of the difference in conditioning to potentially phobic and neutral stimuli, the results did not support the specific hypothesis of conditioning to phobic stimuli as being less dependent on the ISI parameters than conditioning to neutral stimuli.     

“Prepared” fear or socio-cultural learning? Fear conditioned to guns,snakes, and spiders is eliminated by instructed extinction in a within-participant differential fear conditioning paradigm

Across three experiments, we investigated whether electrodermal responses conditioned to ontogenetic fear-relevant (pointed guns) and phylogenetic fear-relevant stimuli (snakes and spiders) would resist instructed extinction in a within-participant differential fear conditioning paradigm. Instructed extinction involves informing participants before extinction that the unconditional stimulus (US) will no longer be presented. This manipulation has been shown to abolish fear conditioned to fear-irrelevant conditional stimuli, but is said to leave fear conditioned to images of snakes and spiders intact. The latter finding, however, has only been demonstrated when fear-relevance is manipulated between-groups. It is also not known whether instructed extinction affects fear conditioned to ontogenetic fear-relevant stimuli, such as pointed guns. In Experiment 1, we demonstrated that fear conditioned to images of pointed guns does not resist instructed extinction. In Experiment 2, we detected some evidence to suggest that fear conditioned to images of snakes and spiders survives instructed extinction but this evidence was not conclusive. In Experiment 3, we directly compared the effects of instructed extinction on fear conditioned to snakes and spiders and to guns and provide strong evidence that fear conditioned to both classes of stimuli is reduced after instructed extinction with no differences between ontogenetic and phylogenetic stimuli. The current results suggest that when fear relevance is manipulated within-participants fear conditioned to both phylogenetic and ontogenetic, fear-relevant stimuli responds to instructed extinction providing evidence in favor of a socio-cultural explanation for “preparedness” effects.     

Some Characteristics of Digital Vasomotor Activity

Size and latency of responses to a series of tones, spontaneous fluctuations, and habituation in finger volume and pulse volume were studied in 19 healthy young soldiers by means of pneumoplethysmography. The results indicate that relationships among vasomotor measures differ from those reported for skin conductance measures. Thus, in contrast to what has been shown for skin conductance, no correlation was found between habituation and number of spontaneous fluctuations, and the variability of the first response to the tones did not differ from the variability of the following responses. Auditory stimulation did not increase the number of spontaneous fluctuations. There were highly significant correlations between spontaneous fluctuations during rest and stimulation periods. No significant correlations were obtained between pulse volume responses to an arithmetic task and responses to tone stimuli. Some differences in pattern of relationships were obtained between finger and pulse volume measures. Initial responses in finger volume were related to other response size measures, whereas this was not the case for pulse volume. Response latency increased during the auditory stimulation for pulse volume, but not for finger volume.     

Orienting in Schizophrenia: Habituation to Auditory Stimuli of Constant and Varying Intensity in Patients High and Low in Skin Conductance Responsivity

Groups of schizophrenics and normal controls were exposed to different series of tones of constant (80dB) and variable intensity (60, 80, and 100 dB). Measurements included bilateral skin conductance, finger pulse volume, and heart rate. Both groups were split on the common median in skin conductance response to constant intensity tones to form matched patient and control groups of low and high responsivity. The low and high responsive schizophrenic groups were more clearly separated than the two control groups in rate of spontaneous skin conductance fluctuations, skin conductance magnitudes, and skin conductance levels, primarily because of generalized hyperactivity in high responsive patients. This pattern was clearest for the most intense tone and left hand recordings. High responsive schizophrenics also showed larger response amplitudes, shorter rise and recovery times, and a smaller ratio of elicited to spontaneous responses, than high responsive controls. Finger pulse volume responses recorded from the left hand were smaller in the patient groups, whereas patients and controls did not differ in right hand recordings. High skin conductance responsive subjects showed more heart rate deceleration than low responsive subjects, and schizophrenics had more decelerative responses than controls.     

Effects of Potentially Phobic Conditioned Stimuli on Retention, Reconditioning, and Extinction of the Conditioned Skin Conductance Response

Discriminative classical conditioning of skin conductance responses (SCRs) was studied in 163 college students as a function of four variables: CS type (potentially phobic versus neutral conditioned stimuli), Sex of the subject, Interstimulus interval (ISI) during conditioning (.5 versus 8 s), and Retention interval between conditioning and retention assessment (1 versus 6 months). CS type did not affect acquisition, retention, or reconditioning of the differential conditioned responses. The effect of CS type was highly significant during extinction, with differential SCRs to CS+ and CS- being greater with potentially phobic conditioned stimuli. This was true for both sexes, both the .5-s and the 8-s ISI, and after a 1-month or a 6-month retention interval. Moreover, SCRs conditioned to phobic conditioned stimuli with the .5-s ISI persisted even after subjects' cognitive expectancy of the UCS, which was measured on a trial-by-trial basis, had completely extinguished. The results indicate that the effect of potentially phobic conditioned stimuli on the conditioned skin conductance response is unique to resistance to extinction-they affect not learning but unlearning of the autonomic response.     

Effects of conditioned stimulus pre-exposure on human electrodermal conditioning to fear-relevant and fear-irrelevant stimuli

The effects of conditioned stimulus (CS) pre-exposure and fear-relevance of the CS on human Pavlovian electrodermal conditioning were investigated. A differential delayed conditioning paradigm was used with a CS-unconditioned stimulus (US; shock) interval of 8 s. In Experiment 1, 64 subjects were randomized into four groups, two of which received fear-relevant stimuli and the other two fear-irrelevant stimuli. Half of the subjects were pre-exposed to the to-be-CSs and the other half to two not-to-be-CSs, with 15 exposure of each stimulus. During acquisition, subjects received 8 reinforced and 8 nonreinforced CS+ and CS- trials, and during the extinction phase 15 nonreinforced trials of each CS. Pre-exposure to the to-be-CSs retarded conditioning for the first and second interval anticipatory responses (FIRs and SIRs); that is, a latent inhibition effect was demonstrated, although the results for the FIR were inconclusive. The expected effects of fear-relevance were not revealed. Experiment 2 addressed the question whether the long pre-exposure period interfered with the frequently observed "preparedness effect" of higher resistance to extinction to fear-relevant stimuli. The design was similar to that of Experiment 1, but for half of the subjects the acquisition phase was initiated immediately after a short rest period, and for the other half acquisition started after an extended rest period, equal to the duration of the pre-exposure phase in Experiment 1. Twenty extinction trials of each CS were presented. A reliable difference in arousal in terms of spontaneous fluctuations was produced by the rest periods, but although differential conditioning was observed, no effect of fear-relevance was seen during extinction.     

Are two threats worse than one? The effects of face race and emotional expression on fear conditioning

Facial cues of racial outgroup or anger mediate fear learning that is resistant to extinction. Whether this resistance is potentiated if fear is conditioned to angry, other race faces has not been established. Two groups of Caucasian participants were conditioned with two happy and two angry face conditional stimuli (CSs). During acquisition, one happy and one angry face were paired with an aversive unconditional stimulus whereas the second happy and angry faces were presented alone. CS face race (Caucasian, African American) was varied between groups. During habituation, electrodermal responses were larger to angry faces regardless of race and declined less to other race faces. Extinction was immediate for Caucasian happy faces, delayed for angry faces regardless of race, and slowest for happy racial outgroup faces. Combining the facial cues of other race and anger does not enhance resistance to extinction of fear.     

Direction of changes in the cardiac component in a Pavlovian conditioning paradigm with variations in CS- and UCS-contents

The research reported was aimed at examining the direction of heart rate post-stimulus changes in a conditioning paradigm with fear-relevant (snakes and spiders), and fear-irrelevant (circles and triangles) slide-CSs. Furthermore, half of the subjects in each group had electric shocks as the UCS, whereas the other two halves were merely threatened about the shock. Finally, all subjects were informed at the start of the extinction about the removal of the UCS. Thus, a 2 X 2 factorial design was used. The conditioning situation involved a differential paradigm with an interstimulus interval of 8 sec. There were 12 presentations of each cue during acquisition, and 20 during extinction. The results showed reliable effects of decelerative acquisition in the fear-relevant shock group, and the fear-irrelevant threat group. During extinction, only the fear-relevant shock group showed evidence of continuing differential responding, with larger deceleration to the CS+. It is speculated that responses to fear-relevant CSs, together with shock-UCSs, share important similarities with the irrational aspect of phobic behavior, since the instructions about the omission of the UCS during extinction did not eliminate the responses to the CS+ in the fear-relevant shock group.     

The influence of gonadal hormones on conditioned fear extinction in healthy humans

Recent rodent studies suggest that gonadal hormones influence extinction of conditioned fear. Here we investigated sex differences in, and the influence of estradiol and progesterone on, fear extinction in healthy humans. Men and women underwent a two-day paradigm in which fear conditioning and extinction learning took place on day 1 and extinction recall was tested on day 2. Visual cues were used as the conditioned stimuli and a mild electric shock was used as the unconditioned stimulus. Skin conductance was recorded throughout the experiment and used to measure conditioned responses (CRs). Blood samples were obtained from all women to measure estradiol and progesterone levels. We found that higher estradiol during extinction learning enhanced subsequent extinction recall but had no effects on fear acquisition or extinction learning itself. Sex differences were only observed during acquisition, with men exhibiting significantly higher CRs. After dividing women into low- and high-estradiol groups, men showed comparable extinction recall to high-estradiol women, and both of these groups showed higher extinction recall than low-estradiol women. Therefore, sex differences in extinction memory emerged only after taking into account women's estradiol levels. Lower estradiol may impair extinction consolidation in women. These findings could have practical applications in the treatment of anxiety disorders through cognitive and behavioral therapies.     

Fear conditioning, preparedness, and the contingent negative variation

Psychophysiological research on preparedness has previously focused on autonomic nervous system parameters. The present study used electrocortical indices of fear conditioning. Subjects (n= 10) were tested under fear-relevant and fear-irrelevant conditions (1 week apart, order of conditions counterbalanced). Each condition comprised acquisition and extinction sessions. The contingent negative variation (CNV) was elicited in anticipation of forewarned slides (fear relevant: small animals; fear irrelevant: landscapes). In acquisition, reinforced conditioned stimulus (CS+) (but not nonreinforced conditioned stimulus [CS-]) slides were followed by white noise as an unconditioned stimulus (UCS). In extinction, the UCS was omitted. In the fear-relevant condition, CNV amplitude was significantly larger for CS+ than CS- in both acquisition and extinction. In the fear-irrelevant condition, CNV differentiation between CS+ and CS- was weak in both sessions. CNV was significantly larger in the fear-relevant than in the fear-irrelevant condition, for CS+ but not CS-. The findings are consistent with a preparedness interpretation and suggest that CNV under such circumstances may represent an automatic affective response to fear-relevant stimuli. Electrocortical measures could be particularly useful in examining information processing mechanisms in phobia and cognition-affect relationships generally.     

Assessment of female sexual arousal: Response specificity and construct validity

Specificity of vaginal pulse amplitude and vaginal blood volume in reaction to visual sexual stimuli was investigated by comparing responses to sexual, anxiety-inducing, sexually threatening, and neutral film excerpts. Subjective sexual arousal, body sensations, emotional experience, skin conductance, and heart rate were monitored along with the genital measures. Self-report data confirmed the generation of affective states as intended. Results demonstrated response specificity of vaginal vasocongestion to sexual stimuli. In terms of both convergent and divergent validity, vaginal pulse amplitude was the superior genital measure. Skin conductance discriminated among stimuli only to a small degree, whereas heart rate failed to discriminate among stimuli altogether.     

Orienting and Defensive Responding in the Electrodermal System: Palmar-Dorsal Differences and Recovery Rate during Conditioning to Potentially Phobic Stimuli

It was suggested that the effects of fear-relevant pictures as conditioned stimuli (CSs) for electrodermal responses may be explained if it is assumed that they produce conditioned defense responses (DRs), as opposed to the orienting responses (ORs) that are produced by fear-irrelevant stimuli. Some propositions in Edelberg's theory of electrodermal activity were used to differentiate between DRs and ORs in a test of this hypothesis. Groups of subjects were conditioned to fear-relevant (snakes and spiders) or fear-irrelevant (flowers and mushrooms) CSs by means of an aversive (electric shock) or a non-aversive (imperative signal for a reaction time (RT) task) unconditioned stimulus in long interval differential paradigms. The neutral-shock, phobic-RT, and neutral-RT groups showed no palmar-dorsal differences either in magnitude, probability or amplitude, and no conditioning in the recovery rate measure. However, the phobic-shock group showed a peak of dorsal magnitude early in training that subsequently habituated whereas the palmar magnitude data indicated a gradual conditioning effect that lasted throughout the 20 extinction trials. In addition, it showed slower recovery to the reinforced than to the nonreinforced stimulus. These data are taken as support for the hypothesis.     

Autonomic reactions to social and neutral stimuli in subjects high and low in public speaking fear

People with specific animal phobias react with increased autonomic activity when exposed to fear-relevant stimuli. The present study examined whether individuals having a less circumscribed fear (public speaking fear) also react with increased autonomic responses when exposed to fear-relevant i.e. social stimuli. A High-fear and a Low-fear group, as indicated by the PRCS questionnaire, were exposed to pictures of faces (social stimuli) and mushrooms (neutral stimuli) while heart rate (HR) and skin conductance responses (SCRs) were measured. It was found that: Social stimuli evoked larger SCRs as compared to neutral stimuli only in the High-fear group; SCR magnitude to social stimuli was positively correlated with self-reported fear in the High-fear group; the High-fear group showed larger overall SCRs compared with the Low-fear group; the High-fear group showed slower SCR habituation to social stimuli as compared to the Low-fear group; the High-fear group displayed more nonspecific electrodermal fluctuations than did the Low-fear group. Both the High-fear and the Low-fear group displayed HR deceleration to social but not to neutral stimuli. Thus, subjects high in public speaking fear reacted with increased skin conductance activity when exposed to social stimuli compared to low-fear subjects. The two groups did not differ in heart rate responses. These results are discussed in terms of orienting, defense and species-specific response patterns.     

Reconsolidation in a human fear conditioning study: A test of extinction as updating mechanism

Disrupting reconsolidation seems to be a promising approach to dampen the expression of fear memory. Recently, we demonstrated that disrupting reconsolidation by a pharmacological manipulation specifically targeted the emotional expression of memory (i.e., startle response). Here we test in a human differential fear-conditioning paradigm with fear-relevant stimuli whether the spacing of a single unreinforced retrieval trial relative to extinction learning allows for “rewriting” the original fear association, thereby preventing the return of fear. In contrast to previous findings reported by Schiller et al. (2010), who used a single-method for indexing fear (skin conductance response) and fear-irrelevant stimuli, we found that extinction learning within the reconsolidation window did not prevent the recovery of fear on multiple indices of conditioned responding (startle response, skin conductance response and US-expectancy). These conflicting results ask for further critical testing given the potential impact on the field of emotional memory and its application to clinical practice.     

Measuring the conditioned response: A comparison of pupillometry,skin conductance,and startle electromyography

In human fear conditioning studies, different physiological readouts can be used to track conditioned responding during fear learning. Commonly employed readouts such as skin conductance responses (SCR) or startle responses have in recent years been complemented by pupillary readouts, but to date it is unknown how pupillary readouts relate to other measures of the conditioned response. To examine differences and communalities among pupil responses, SCR, and startle responses, we simultaneously recorded pupil diameter, skin conductance, and startle electromyography in 47 healthy subjects during fear acquisition, extinction, and a recall test on 2 consecutive days. The different measures correlated only weakly, displaying most prominent differences in their response patterns during fear acquisition. Whereas SCR and startle responses habituated, pupillary measures did not. Instead, they increased in response to fear conditioned stimuli and most closely followed ratings of unconditioned stimulus (US) expectancy. Moreover, we observed that startle‐induced pupil responses showed stimulus discrimination during fear acquisition, suggesting a fear potentiation of the auditory pupil reflex. We conclude that different physiological outcome measures of the conditioned response inform about different cognitive‐affective processes during fear learning, with pupil responses being least affected by physiological habituation and most closely following US expectancy.     

Facial reactions to fear-relevant and fear-irrelevant stimuli

Earlier research has shown that subjects exposed to different facial expressions react spontaneously with different facial electromyographic (EMG) response patterns. In the present study subjects were exposed to fear-relevant (snakes/spiders) and fear-irrelevant (flowers/mushrooms) stimuli, while facial EMG activity, skin conductance responses (SCRs) and heart rate (HR) were measured. The stimuli evoked different response patterns. Fear-relevant stimuli elicited increased corrugator muscle activity, whereas fear-irrelevant stimuli evoked increased zygomatic muscle activity. Fear-relevant stimuli also evoked HR deceleration and larger SCR magnitudes. The present data are consistent with the theory that the face constitutes an emotional 'readout/output-system'.     

Reinstatement of conditioned fear in humans is context dependent and impaired in amnesia

A contextual reinstatement procedure was developed to assess the contributions of environmental cues and hippocampal function in the recovery of conditioned fear following extinction in humans. Experiment 1 showed context specificity in the recovery of extinguished skin conductance responses after presentations of an auditory unconditioned stimulus. Experiment 2 demonstrated that fear recovery did not generalize to an explicitly unpaired conditioned stimulus. Experiment 3 replicated the context dependency of fear recovery with a shock as an unconditioned stimulus. Two amnesic patients failed to recover fear responses following reinstatement in the same context, despite showing initial fear acquisition. These results extend the known functions of the human hippocampus and highlight the importance of environmental contexts in regulating the expression of latent fear associations.