Touch and the development of trust: tactile stimulation affects decision-making and face perception.

Social touch is necessary for the healthy development of trust. Although casual touch has been assumed to affect emotion and decision-making through a parallel mechanism, this has been challenging to test: How does touch affect learning to associate trust with people? A social version of the Iowa Gambling Task was designed by replacing cards with faces and associating these with tactile stimuli and economic outcomes. We measured how learned associations affected 1) choice preference during the Social Gambling Test (SGT), 2) face preferences in a subsequent oddball EEG task featuring SGT-stimuli; 3) choice adjustment in a final SGT with economic outcomes being reversed. Contrary to predictions, no initial bias toward touch-associated faces was observed. However, event-related potentials during the oddball task showed preferential processing toward disadvantageous/touch-associations, with early P3 component amplification. This effect presaged preference adjustments toward touch-associated faces in the second SGT when reward contingencies were reversed. Touch therefore did not directly produce trust but modified decision-making indirectly. We argue that tactile events and emotional outcomes are integrated within episodic memory and retrieved when risks require adaptation. We relate this interpretation to attachment theory, which likely highlights the relation between stressful uncertainty and tactile behavior.