Date Published: May 20, 2019
Publisher: Public Library of Science
Author(s): Agnes Moors, Chiara Fini, Tom Everaert, Lara Bardi, Evelien Bossuyt, Peter Kuppens, Marcel Brass, Alessio Avenanti.
This study examines two contrasting explanations for early tendencies to fight and flee. According to a stimulus-driven explanation, goal-incompatible stimuli that are easy/difficult to control lead to the tendency to fight/flee. According to a goal-directed explanation, on the other hand, the tendency to fight/flee occurs when the expected utility of fighting/fleeing is the highest. Participants did a computer task in which they were confronted with goal-incompatible stimuli that were (a) easy to control and fighting had the highest expected utility, (b) easy to control and fleeing had the highest expected utility, and (c) difficult to control and fleeing and fighting had zero expected utility. After participants were trained to use one hand to fight and another hand to flee, they either had to choose a response or merely observe the stimuli. During the observation trials, single-pulse Transcranial Magnetic Stimulation (TMS) was applied to the primary motor cortex 450 ms post-stimulus onset and motor-evoked potentials (MEPs) were measured from the hand muscles. Results showed that participants chose to fight/flee when the expected utility of fighting/fleeing was the highest, and that they responded late when the expected utility of both responses was low. They also showed larger MEPs for the right/left hand when the expected utility of fighting/fleeing was the highest. This result can be interpreted as support for the goal-directed account, but only if it is assumed that we were unable to override the presumed natural mapping between hand (right/left) and response (fight/flight).
Many (aversive) emotional encounters are characterized by behaviors that qualify as fighting (i.e., aggressive or offensive behavior) or fleeing (i.e., avoidant, defensive, or safety seeking behavior), or at least by the tendencies to engage in these behaviors. A barking dog makes us want to flee. A demeaning offense makes us want to fight. Many existing accounts of emotional behavior follow a dual process logic. They explain this behavior by the interplay of stimulus-driven and goal-directed processes, two types of processes that have been defined in terms of the content of their mediating representations [1–3] (see Fig 1).
We restricted our analyses to the measurements taken during the experimental trials for the three thieves in the three conditions: easy-fight, easy-flee, and difficult. The condition with the giver was not considered in the analyses. In fact, this condition was only inserted to allow participants to gain money and thus to keep their motivation high during the task. We first report the results for the manipulation checks from (a) the post-experimental questionnaires and (b) the frequency proportions of the fight and flee responses in the response trials. Next, we report the neurophysiological results: the MEP amplitudes for the fight and flee responses in the observation trials.
In the current study, we pitted two mechanisms against each other that have been invoked to explain the early action tendencies to fight and flee. According to one stimulus-driven mechanism, high/low control over a goal-incompatible or negative stimulus activates the tendency to fight/flee. According to the goal-directed mechanism, the tendency to fight/flee is activated when fighting/fleeing has the highest expected utility. In typical cases, such as a competition in the animal world or between children on a playground, both mechanisms predict the same action tendency. This is because in these cases, fighting has the highest expected utility when control is high and fleeing when control is low. To pit the two mechanisms against each other, we created atypical cases in which both mechanisms predicted different action tendencies. Participants encountered three thieves (goal-incompatible stimuli) of which one could never be defeated (difficult to control and zero expected utility for fighting and fleeing), another could be defeated by fighting (easy to control and highest expected utility for fighting), and still another could be defeated by fleeing (easy to control and highest expected utility for fleeing). The said stimulus-driven process predicts a tendency to flee in the difficult condition and a tendency to fight in the two easy conditions. The goal-directed process predicts a tendency to be passive in the difficult condition, a tendency to fight in the easy-fight condition, and a tendency to flee in the easy-flee condition.