Observational learning of fear in real time procedure

Abstract

Learning to avoid threats often occurs by observing others. Most previous research on observational fear learning (OFL) in humans has used pre-recorded standardized video of an actor and thus lacked ecological validity. Here, we aimed to enhance ecological validity of the OFL by engaging participants in a real-time observational procedure (35 pairs of healthy male friends, age 18-27). One of the participants watched the other undergo a differential fear conditioning task, in which a conditioned stimulus (CS+) was paired with an aversive electric shock and another stimulus (CS-) was always safe. Subsequently, the CS+ and CS- were presented to the observer to test the OFL. While the friend's reactions to the shock elicited strong skin conductance responses (SCR) in all observers, subsequent differential SCRs (CS+ > CS-) were found only when declarative knowledge of the CS+/US contingency (rated by the participants) was acquired. Contingency-aware observers also showed elevated fear potentiated startle responses during both CS+ and CS- compared to baseline. We conclude that our real-time procedure can be effectively used to study OFL. The procedure allowed for dissecting two components of the OFL: an automatic emotional reaction to the response of the demonstrator and learning about stimulus contingency.

Figure 1

Design of the experiment. (a) In the OFL phase, the observer watched their friend performing a differential fear conditioning task. The conditioned stimuli (blue and yellow squares) were displayed on the demonstrator’s screen in a pseudorandom order. Presentation of one of the squares (CS+, here: blue) was accompanied with an uncomfortable electric shock (unconditioned stimulus, US) to the right forearm of the demonstrator with 50% probability. The other color square served as a stimulus that was never reinforced (CS−, here: yellow). A fixation cross was presented between the stimuli. The observer’s SCR and FPS response were used to assess learning. In order to measure the startle reflex magnitude, the white noise burst was pseudorandomly presented through the headphones in half of all types of trials (in which a blue square, yellow square, or fixation cross was presented). (b) In the DE phase, the observer performed the demonstrator’s task but the USs were not applied. Instructions provided to the observers did not suggest that the electrical stimulation would accompany only one CS in the OFL phase nor that it would be omitted in the DE phase.

Figure 2

(a) SCR magnitudes to stimuli presented in the experiment: obs CS+ and obs CS− (appearance of CS+/CS− in the OFL phase), obs US and no US (observation of a friend receiving/not receiving electric shock during CS+ in the OFL phase), dir CS+ and dir CS− (appearance of CS+/CS− in the DE phase). Substantial differences are marked. N = 32. (b) SCR magnitudes to the appearance of the CS+ and CS− in the DE phase of the experiment for contingency-aware (n = 14) and -unaware (n = 18) participants separately. The stimulus (CS+ vs. CS−) × contingency (aware vs. unaware) interaction was found, F(1, 30) = 12.29, p = 0.001, η_p² = 0.29, and substantial effects of the post-hoc comparisons are marked. Error bars indicate 1.5*IQR beyond the 1st quartile and above the 3rd quartile. The * symbol was used for p < 0.05.

Figure 3

(a) FPS responses measured during different stimuli presented in the experiment: obs CS+, obs CS− and obs fix (presentation of CS+/CS−/fixation cross in the OFL phase), dir CS+, dir CS− and dir fix (presentation of CS+/CS−/fixation cross in the DE phase). Substantial differences are marked. N = 32. (b) FPS magnitudes measured in the DE phase: results of contingency-aware (n = 13) and -unaware (n = 19) participants are grouped separately. A trend toward the stimulus (CS+ vs. CS− vs. fixation cross) × contingency (aware vs. unaware) interaction was found, F(2, 60) = 2.59, p = 0.083, η_p² = 0.08, and substantial effects of the post-hoc comparisons are marked. Error bars indicate 1.5*IQR beyond the 1st quartile and above the 3rd quartile. The * symbol was used for p < 0.05, and # symbol for p < 0.1.