Two Eyes for an Eye: The Neuroscience of Force Escalation

Physical conflicts tend to escalate. For exam-ple, as tit-for-tat exchanges between two chil-dren escalate, both will often assert that the other hit him or her harder. Here we show that, in such situations, both sides are report-ing their true percept and that the escalation is a natural by-product of neural processing. Six pairs of naı̈ve participants took part in a tit-for-tat experiment. Each member of a pair rested his or her left index finger in a molded support. A force transducer, which was attached to a lightweight lever of a torque motor, was placed on top of this finger (Fig. 1, inset). A trial was started by one torque motor producing a 0.25 N force on one participant’s finger. Partic-