Left hemisphere advantage for classical conditioning to auditory verbal CSs: Effects of nonattended extinction

The effects of brain laterality, or hemispheric asymmetry, on electrodermal classical conditioning during both attended and nonattended stimulus conditions were studied. Participants were conditioned to consonant-vowel (CV) syllables during an acquisition, or learning, phase of the experiment. During a subsequent extinction phase, the conditioned stimuli (CS) were presented in a dichotic mode of presentation. Half of the participants attended to the left car (right hemisphere) during the extinction phase and the other half of the participants attended to the right ear (left hemisphere). The results showed effects of conditioning for all participants during the acquisition phase. During dichotic extinction, the left hemisphere group showed remaining learning effects in both the attended and nonattended conditions, whereas the right hemisphere group demonstrated conditioning only in the attended condition.     

Hemispheric Asymmetry in Conditioning to Facial Emotional Expressions

In the present experiment, we report a right hemisphere advantage for autonomic conditioning to facial emotional expressions. Specifically, angry, but not happy, facial expressions showed significantly more resistance to extinction when presented initially to the right as compared to the left hemisphere. Slides of happy and angry faces were used as conditioned stimuli (CS+ and CS-) with shock as the unconditioned stimulus (UCS). Half of the subjects (n = 15) had the angry face as CS+ (and the happy face as CS-), the other half had the happy face as CS+ (and the angry face as CS-). During acquisition, the CSs were presented foveally. During extinction, using the Visual Half-Field (VHF) technique, half of the CS+ and CS- trials were randomly presented in the right visual half-field (initially to the left hemisphere), and half of the trials were presented in the left half-field (initially to the right hemisphere). Stimuli were presented for 210 ms during acquisition, and for 30 ms during extinction. Bilateral skin conductance responses (SCRs) were recorded. The results showed effects of acquisition only for the angry CS+ group. During extinction, there was a significant Conditioning X Half-field interaction which was due to greater SCRs to the CS+ angry face when it was presented in the left half-field. It is concluded that the present results reveal hemisphere asymmetry effects in facial emotional conditioning.     

Greater Resistance to Extinction of Electrodermal Responses Conditioned to Potentially Phobic CSs: A Noncognitive Process?

Previous results have suggested that electrodermal responses classically conditioned to potentially phobic CSs (e.g., pictures of snakes or spiders) are highly resistant to extinction and occur largely independently of cognitive expectancies. In order to test stringently for these possibilities, 144 college student subjects were administered differential classical conditioning acquisition and extinction paradigms while expectancies of the shock UCS were closely monitored. Half the subjects had potentially phobic CSs, whereas the other half had neutral CSs. Regardless of type of CS, during acquisition no evidence of electrodermal conditioning was found among subjects unaware of the CS?UCS contingency, nor was conditioning found on the pre-aware trials of subjects who became aware. During extinction, there was significantly greater resistance to extinction of electrodermal responses conditioned to potentially phobic CSs as well as a similar trend with expectancies of the UCS. However, when expectancies were equated, there was no greater resistance to extinction of electrodermal responses conditioned to potentially phobic CSs. Thus, while electrodermal responses conditioned to potentially phobic CSs did exhibit greater resistance to extinction, this conditioning was no more independent of expectancies than is conditioning with neutral CSs.     

Hemispheric Asymmetry and Human Classical Conditioning to Verbal and Non-Verbal Visual CSs

A new paradigm called “the dichoplic acquisition paradigm” was developed to study Ihc effects of hemispheric asymmetry on classical etcctrodcrmal conditioning. The paradigm involves three phases: 1) A habituation phase where two different color-words written in two incongruent colors are tachistoscopically displayed bilaterally to the visual half-fields left and right of center fixation; 2) An acquisition phase, wherein the display is followed by a 105dB white noise on each trial; and 3) An extinction phase, where each of the four CS cues (two color-words and two colors) are separately presented bilaterally for simultaneous input to both hemispheres. Here the color-words are now presented in grey against a black background, and the colors as color-bars against the same background. A control group had no UCS presentations. Bilateral skin conductance responses (SCRs) of right-handed males were used to evaluate conditioning. Conditioning to the CS color-word previously presented in the right half-field (i.e. initial left-hemisphere input) during acquisition led to larger SCRs during extinction, than the color-word previously presented in the left half-held (i.e. initial right-hemisphere input). In contrast, the CS color cue previously presented in the left half-field during acquisition resulted in larger SCRs during the first extinction trial, than the CS color cue previously presented in the right half-field. Thus, the present experiment revealed effects of hemispheric asymmetry on human electrodermal conditioning.     

Personality and extinction of a conditioned electrodermal response

This study investigated personality differences in extinction of a conditioned EDR. The subjects were selected on the basis of EPI neuroticism and impulsivity scores. Subjects with scores on, or near, the sample means were excluded. Fifty-one subjects underwent an aversive discrimination conditioning procedure. The reinforcement was 75 per cent, the UCS was 100 dB white noise for 1 sec, while the CS was one of five different coloured lights of 2 sec duration. The UCS was presented at CS termination. Subjects were informed of the CS--UCS contingency before the acquisition phase and informed of the onset of the extinction phase. Subjects high on impulsivity showed significantly (P less than 0.01) greater extinction of the discrimination than subjects low on impulsivity.     

Awareness of the CS-UCS contingency and classical conditioning of skin conductance responses with olfactory CSs

The possibility of demonstrating acquisition of classically conditioned responses without awareness of the conditioned stimulus-unconditioned stimulus (CS-UCS) contingency using olfactory stimuli with 58 college student subjects was tested. A classical discrimination delay conditioning paradigm was employed, with electric shock as the UCS and two pleasant odors (perfumes) as the conditioned stimuli (CS+ and CS-). Trial-by-trial measures of skin conductance conditioned responses served as dependent variables. A masking task in the form of an olfactory memory task was employed for the purpose of delaying the onset of awareness of the conditioning contingency. Awareness of the conditioning contingency was assessed by a concurrent and a post hoc measure, and subjects who satisfied both criteria were considered aware of the CS-UCS contingency. Conditioning was observed only in the aware subjects, and only after the onset of awareness of the CS+-UCS contingency. Respiratory activity, measured as a check against possible artifacts, had no effect on the SCR measures. It was concluded that the awareness of the CS-UCS contingency is necessary for acquisition of discriminative conditioned responses in humans, regardless of the sensory modality in which CSs are presented. Sex differences in skin conductance measures and performance on the olfactory memory task were observed.     

Vulnerability and conditioning in relation to the human menstrual cycle

An experiment aimed at testing some implications of a model of symptom acquisition is reported. In particular, the effect conditioning and extinction is examined. Sixteen female phobic patients were tested either immediately pre-menstrually or inter-menstrually. Using white noise as the UCS and a blue light as the CS, conditioned GSR responses were readily established in members of the pre-menstrual group, who also showed resistance to extinction. Subjects tested inter-menstrually were less susceptible to these effects. Those subjects taking the contraceptive pill showed increased sensitivity to the acquisition of conditioned responses.     

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.     

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.     

Conditioned diminution of the unconditioned skin conductance response

During Pavlovian conditioning the expression of a conditioned response typically serves as evidence that an association between a conditioned stimulus (CS) and an unconditioned stimulus (UCS) has been learned. However, learning-related changes in the unconditioned response (UCR) produced by a predictable UCS can also develop. In the present study, we investigated learning-related reductions in the magnitude of the unconditioned skin conductance response (SCR). Healthy volunteers participated in a differential conditioning study in which one tone (CS+) was paired with a loud white-noise UCS and a second tone (CS-) was presented alone. In addition, probe trials that consisted of UCS presentations paired with the CS+ (CS + UCS) and CS- (CS - UCS), as well as presentations of the UCS alone were included to assess UCR diminution. SCR and participants' expectations of UCS presentation were monitored during conditioning. Greater diminution of the UCR was observed to the UCS when it followed the CS+ compared to when it followed the CS- or was presented alone. Further, UCR amplitude showed an inverse relationship with the participants' ratings of UCS expectancy. However, conditioned UCR diminution was also observed independent of differential UCS expectancies. Our findings demonstrate conditioned diminution of the unconditioned SCR. Further, these findings suggest that although UCR amplitude is modified by conscious expectations of the UCS, conditioned diminution of the UCR can be expressed independent of learning-related changes in these expectations.     

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.     

Aversive learning in patients with unilateral lesions of the amygdala and hippocampus

The present study applied a visual half field paradigm with emotional facial expressions in patients with selective unilateral amygdalo-hippocampectomy (AHE) to elucidate the contributions of the left and right medial temporal lobe and amygdala to emotional learning. Electrodermal indicators of aversive learning were studied in 14 left AHE and 12 right AHE patients, as well as 13 controls matched in sex and age. In a differential conditioning paradigm with negative (CS+) and positive (CS-) facial expressions, CS+ were associated with an aversive vocalization (US, 95 dB, 3 s). During extinction, stimuli were presented laterally and preattentively using backward masking. Appropriate CS durations yielding preattentive presentation were individually determined prior to conditioning. In contrast to controls, both left and right AHE patients failed to show an autonomic conditioning effect following left visual field presentations of masked negative CS+ during extinction. AHE patients also showed no clear differential acquisition. Moreover, right AHE patients poorly recognised that negative valence was an affiliating dimension of the CS-US compound.     

Conditioned suppression, heart rate and pulse volume: effects of instructions on extinction

Two experimental groups of undergraduate volunteers received five classical aversive conditioning trials with a tone conditioned stimulus (CS) and shock unconditioned stimulus (UCS). Control groups received either the CS alone or UCS alone. Subjects from one experimental group were subsequently instructed that they would not receive further shocks, while the other experimental group received no such instructions. The CS alone was then presented once to all four groups while subjects were engaged in a button-pressing task maintained by slide reinforcement. During this latter phase rate of button pressing was measured as well as heart rate and pulse volume. The last two measures being employed as indices of autonomic arousal. The results indicated that while instructions as to the absence of the UCS completely abolished the conditioned suppression of button-pressing, they had no effect upon the pulse volume CR. A heart rate CR was not obtained. These results reflect unfavourably upon theoretical formulations of conditioned suppression that emphasize the causal interdependence of motor and autonomic events or the primacy of either one.     

Differential conditioning to facial emotional expressions: effects of hemispheric asymmetries and CS identification

Previous studies on aversive learning have suggested a right hemispheric advantage for eliciting autonomic reactions to a masked conditioned facial stimulus (CS) depicting anger. The present study investigated the effects of visual field (VF), stimulus awareness, and emotional valence of the CSs on indicators of conditioning (bilateral SCRs, HR) using a differential conditioning paradigm (N = 41). In Group 1, four different negatively valenced facial expressions (CS+) but not four positively valenced CS- were associated with an unconditioned stimulus (US, aversive vocalization, 97 dB, 3 s) during acquisition. Group 2 received a treatment reversal with positive CS+ associated with the US. In a repeated measures design, CSs were presented with or without awareness during extinction (two weeks interval, order counterbalanced). SOAs were adapted for each subject and condition prior to the experiment so that identification performance was approaching chance level. The results revealed that both negative and positive facial expressions could be aversively conditioned providing evidence for a generalization of learning in the valence dimension. During extinction, preattentive negative CS+ presented to the left VF showed a trend towards greater electrodermal and cardiac reactions. However, no such effect emerged under full awareness of the CSs. These results confirm and further specify the nature of hemispheric asymmetries in emotional associative learning.     

Reduced amygdala responsivity during conditioning to trauma‐related stimuli in posttraumatic stress disorder

Exaggerated conditioned fear responses and impaired extinction along with amygdala overactivation have been observed in posttraumatic stress disorder (PTSD). These fear responses might be triggered by cues related to the trauma through higher‐order conditioning, where reminders of the trauma may serve as unconditioned stimuli (US) and could maintain the fear response. We compared arousal, valence, and US expectancy ratings and BOLD brain responses using fMRI in 14 traumatized persons with PTSD and 14 without PTSD (NPTSD) and 13 matched healthy controls (HC) in a differential aversive conditioning paradigm. The US were trauma‐specific pictures for the PTSD and NPTSD group and equally aversive and arousing for the HC; the conditioned stimuli (CS) were graphic displays. During conditioning, the PTSD patients compared to the NPTSD and HC indicated higher arousal to the conditioned stimulus that was paired with the trauma picture (CS+) compared to the unpaired (CS?), increased dissociation during acquisition and extinction, and failure to extinguish the CS/US‐association compared to NPTSD. During early and late acquisition, the PTSD patients showed a significantly lower amygdala activation to CS+ versus CS? and a negative interaction between activation in the amygdala and dorsolateral prefrontal cortex (PFC), while NPTSD and HC displayed a negative interaction between amygdala and medial PFC. These findings suggest maladaptive anticipatory coping with trauma‐related stimuli in patients with PTSD, indicated by enhanced conditioning, with related abnormal amygdala reactivity and connectivity, and delayed extinction.     

Human orbitofrontal cortex mediates extinction learning while accessing conditioned representations of value

In extinction, an animal learns that a previously conditioned stimulus (CS+) no longer predicts delivery of a salient reinforcer (unconditioned stimulus, UCS). Rodent studies indicate that extinction relies on amygdala-prefrontal interactions and involves formation of memories that inhibit, without actually erasing, the original conditioning trace. Whether extinction learning in humans follows similar neurobiological principles is unknown. We used functional magnetic resonance imaging to measure human brain activity evoked during olfactory aversive conditioning and extinction learning. Neural responses in orbitofrontal cortex and amygdala were preferentially enhanced during extinction, suggesting potential cross-species preservation of learning mechanisms that oppose conditioning. Moreover, by manipulating UCS aversiveness via reinforcer inflation, we showed that a CS+ retains access to representations of UCS value in distinct regions of ventral prefrontal cortex, even as extinction proceeds.     

Endogenous and exogenous control of attention in dichotic listening

Dichotic listening to verbal stimuli results in a right ear advantage (REA), indicating a left hemisphere processing superiority. The magnitude of the REA can be modulated by instructions to direct attention to the left or right ear stimulus. A previous study from our laboratory showed that presenting a prime syllable before the presentation of the dichotic syllables increases reports of the nonprimed syllable, apparently a negative priming effect that inhibits attention to the distracting prime representation. The present study combined attention instruction and priming, making up a 3 x 3 factorial design. The prime stimulus was a single consonant-vowel syllable presented binaurally just before onset of the dichotic consonant-vowel syllables. Results showed that both instructions and priming manipulations had an effect on which dichotic stimulus was selected. There was also a significant interaction between attention instruction and priming manipulation, indicating that the mechanism for instructed attention and the mechanism for negative priming work on the same level of processing.     

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.     

Positron emission tomographic imaging of neural correlates of a fear acquisition and extinction paradigm in women with childhood sexual-abuse-related post-traumatic stress disorder

BACKGROUND: In the conditioned fear paradigm, repeated pairing of an aversive unconditioned stimulus (US) (e.g. electric shock) with a neutral conditioned stimulus (CS) (e.g. bright light) results in a conditioned fear response to the light alone. Animal studies have shown that the amygdala plays a critical role in acquisition of conditioned fear responses, while the medial prefrontal cortex (including anterior cingulate), through inhibition of amygdala responsiveness, has been hypothesized to play a role in extinction of fear responses. No studies have examined neural correlates of fear conditioning and extinction in patients with post-traumatic stress disorder (PTSD). METHOD: Women with early childhood sexual-abuse-related PTSD (n = 8) and women without abuse or PTSD (n = 11) underwent measurement of psychophysiological (skin conductance) responding as well as positron emission tomographic (PET) measurement of cerebral blood flow during habituation, acquisition and extinction conditions. During habituation subjects were repeatedly exposed to a blue square on a screen. During acquisition, exposure to the blue square (CS) was paired with an electric shock to the forearm (US). With extinction, subjects were again exposed to the blue squares without shock. On a different day subjects went through the same procedure with electric shocks administered randomly in the absence of the blue square. RESULTS: Skin conductance responding to the CS was consistent with the development of conditioned responses with this paradigm. PTSD patients had increased left amygdala activation with fear acquisition, and decreased anterior cingulate function during extinction, relative to controls. CONCLUSIONS: These findings implicate amygdala and anterior cingulate in the acquisition and extinction of fear responses, respectively, in PTSD.