Pavlovian, Observational and Instructed Fear Learning:Emotional Responses to Unmasked and Masked StimuliAndreas Olsson, Kristen Stedenfeld & Elizabeth A. Phelps, New York University

INTRODUCTION The flexibility of human biology and culture allows for a variety of ways to form associations between objects or events (conditioned stimuli, CS) and naturally aversive outcomes (unconditional stimuli, UCS). Among the ways to learn to predict the aversive outcome of a stimulus are:

(1) Pavlovian conditioning: Associations are acquired through direct experience of the UCS paired with the CS. (2) Observational learning: Knowledge of the properties of the UCS and the CS-UCS contingency is acquired through observing another individual having a first-hand experience of the CS in combination with the UCS.

(3) Instructed learning: Information about the UCS and its association with the CS is transferred solely through symbolic means, such as language.

Earlier studies have shown that expectancies resulting from Pavlovian conditioning1 observational2 and instructed learning3,4 produces similar emotional responses, as indicated by a differential skin conductance response (SCR) to the predictive stimulus (CS+) vs. a control stimulus (CS-) when the CSs are presented to subjects’ full awareness.

When fear-learning is acquired through Pavlovian conditioning, subjects also display a differential SCR to subsequent exposures of CSs that are presented briefly and followed by a mask to prevent explicit awareness5.

However, it is still unknown to what degree fear acquired through observation or verbal instruction, produces learning that modulates emotional responses without explicit awareness of the CSs.

METHODSubjects: 126 paid participants were randomly assigned to one of the three learning groups. Twelve subjects were excluded from further analysis after having reported to have seen the masked CSs. Subjects that did not display any SCR (non-responders, N=14) or showed no signs of learning in the unmasked condition (N=33) were also excluded. The final sample consisted of 67 participants.

Materials: Two angry faces served as CS+ (associated with shock) and CS- (control). A neutral face was used as a mask. All images were taken from the Ekman & Friesen6 set of emotional faces. Electric shocks were delivered to the right wrist and SCR were measured on two fingers on the left hand.

Procedure: Each experimental session consisted of three phases: (1) Habituation (baseline SCR was estimated), (2) Acquisition (learning was measured when shocks were expected) and (3) Extinction (rate of extinction was sampled as shocks were no longer expected). Differential SCR to CS+ vs. CS- served as the dependent variable. Here, only the acquisition phase is discussed.

The acquisition phase consisted of 24 trials, equally divided into four types: unmasked (CS+ and CS-) and masked (CS+ and CS-). In all groups, trial duration was 6 seconds and the inter trial interval varied between 7 to 15 seconds. In masked trials, the target was exposed for 30 ms and immediately followed by the mask.

In the Pavlovian conditioning group, the CS+ was associated with the shock through direct experience of an uncomfortable, but not painful, electric shock that co-terminated with the unmasked CS+ (fig.1).

In the observational learning group, participants watched a movie (before the experiment) of a confederate participating in the Pavlovian conditioning group (fig.2). No shocks were administered.

The instructed learning group only received verbal information about the UCS and its association with the CS+ (fig.3). No shocks were given.

DISCUSSION

SELECTED REFERENCES1. Lang, P. J., Ohman, A. & Simons R. F. (1978). The psychophysiology of anticipation. In J. Requin (Ed.), Attention and performance VII (pp. 469-485). Hillsdale, NJ:Erlbaum.2. Hygge S, Ohman A. (1978). Modeling processes in the acquisition of fears: vicarious electrodermal conditioning to fear-relevant stimuli. Journal of Personality and Social Psychology, 36, 271-9.3. Hugdahl, K. & Ohman, A. (1977). Effects of instruction acquisition and extinction of electrodermal responses to fear-relevant stimuli. Journal of Experimental Psychology; Human Learning and Memory, 3, 608-618.4. Phelps, E. A., O’Connor, K. J., Gateby, J. J., Grillon, C., Gore, J. C., & Davis, M. (2001). Activation of the amygdala by cognitive representations of fear. Nature Neuroscience, 4, 437-441.5. Esteves, F., Dimberg, U. & Ohman, A. (1994). Automatically elicited fear: Conditioned skin conductance responses to masked facial stimuli. Cognition and Emotion, 8, 5, 393-413.6. Ekman, P., Friesen, W. (1976). Pictures of facial affect. Palo Alto: Consulting Psychologists Press.

GOALSThis study investigates the relation between emotional and cognitive processes in fear-learning, specifically to what degree a learned fear response is modulated by (1) type of learning (Pavlovian vs. observational vs. instructed) and (2) explicit awareness of the conditioned stimuli (unmasked vs. masked).

RESULTSDifferential Skin Conductance Responses to Unmasked

vs. Masked Stimuli (Acquisition Phase)

Pavlovian conditioning (N=24)

Unmasked CS+ elicited a greater SCR than unmasked CS-, t(23) = 6.43, p<.001 (M=.41, SD=.31).

Also on masked trials, there was a significant differential response, t(23)=2.28, p<.05 (M=.12, SD=.26).

Observational learning (N=16)

SCR to unmasked CS+ was greater than to unmasked CS-, t(15) =6.277, p<.0001 (M=.45, SD=.29).

On masked trials, there was a trend towards a greater SCR to CS+ vs. CS-, t(15)=1.86, p=.83 (M=.07, SD=.12).

Instructed learning (N=27)

Unmasked CS+ elicited a significantly greater SCR than unmasked CS-, t(26)=9.9, p<.0001 (M=.38, SD=20).

There was no significant difference between CS+ and CS- in the masked condition.

Fig.1. In the Pavlovian group, participants received a shock paired with unmasked CS+.

Fig.2. In the observational group, participants watched a movie of a confederate submitted to the same experimental conditions as in the Pavlovian group. Subjects received no shocks.

Fig.3. In the instructed group, learning was acquired through verbal instructions given by the experimenter. No shocks were administered.

Our results confirm earlier findings that shock expectancies acquired with and without direct experience of the shock elicit similar emotional responses when the target stimuli allows for explicit awareness.

In accordance with earlier data, we also found that CSs which were presented without explicit awareness resulted in a differential SCR in the Pavlovian learning group. No such effect was found in the instructed group.

Interestingly, although not significant, the observational group displayed a trend towards a differential SCR to masked CSs. This indicates that observing emotional reactions in another person might provide a more efficient route to emotional fear-learning than that by way of symbolic representations only.

Taken together, these results indicate that emotional responses to stimuli are dependent on how the stimuli acquired their emotional value and whether they are presented to allow for explicit awareness or not.

A 3 (learning group) x 2 (masking condition) ANOVA showed a significant effect for masking condition F(1, 64) = 68.15. No other effects were significant.

T-tests of the differential SCR of both unmasked and masked trials in each individual group revealed the following:

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

PAVLOVIAN OBSERVATIONAL INSTRUCTED

SCR

UNMASKED MASKED

* * p < 0.01

* p < 0.05

* * p < 0.01

(*) p = .085

* * p < 0.01

n.s.

Acknowledgements: We want to thank Laura Thomas for her assistance with programming. This research was supported by the National Institute of Health, MH62104 to EAP and a Fulbrigh Fellowship to the first author.