Unforgettable ultimatums? Expectation violations promote enhanced social memory following economic bargaining

Abstract

Recent work in the field of neuroeconomics has examined how people make decisions in interactive settings. However, less is currently known about how these social decisions influence subsequent memory for these interactions. We investigated this question by using functional magnetic resonance imaging to scan participants as they viewed photographs of people they had either recently played an Ultimatum Game with in the role of Responder, or that they had never seen before. Based on previous work that has investigated "cheater detection", we were interested in whether participants demonstrated a relative enhanced memory for partners that made either fair or unfair proposals. We found no evidence, either behaviorally or neurally, supporting enhanced memory based on the amount of money offered by the Proposer. However, we did find that participants' initial expectations about the offers they would experience in the game influenced their memory. Participants demonstrated relatively enhanced subjective memory for partners that made proposals that were contradictory to their initial expectations. In addition, we observed two distinct brain systems that were associated with partners that either offered more or less than the participants' expectations. Viewing pictures of partners that exceeded initial expectations was associated with the bilateral anterior insula, anterior cingulate cortex/premotor area, striatum, and bilateral posterior hippocampi, while viewing partners that offered less than initial expectations was associated with bilateral temporal-parietal junction, right STS, bilateral posterior insula, and precuneus. These results suggest that memory for social interaction may not be guided by a specific cheater detection system, but rather a more general expectation violation system.

Keywords: cheater detection; decision-making; expectation; memory; neural; neuroeconomics; social; ultimatum game.

Figure 1

Timeline of memory experiment. Participants first viewed a jittered fixation that was on average 6 s long before seeing each face. Participants saw 24 photographs of previous partners in the Ultimatum Game and 24 new people for 4 s. Participants were then asked to rate their level of confidence that the face was either new or old on a 5 point rating scale.

Figure 2

Behavioral results. (A) The effect of offer amount on D′ plotted in orange. The individual regression lines plotted in blue reveal considerable variability in discriminability by offer amount. Positive slopes indicate enhanced memory for partners that made fair offers, while negative slopes indicate enhanced memory for partners that made unfair offers. (B) The effect of initial expectation on individual memory parameter [i.e. the slopes from (A)]. The individual variability in memory for offer amounts is related to initial expectations. High initial expectations are associated with negative slopes (i.e. enhanced memory for partners that made unfair offers), while low initial expectations are associated with positive slopes (i.e. enhanced memory for partners that made fair offers). (C) The effect of expectation error on subjective confidence ratings, split by initial expectations (groupings are only for plotting, not analysis). High initial expectations (orange) demonstrated enhanced memory for offers that were less than their initial expectation. Low initial expectations (dark blue) were associated with enhanced memory for partners that made offers that exceeded their expectations. No relationship was found for medium initial expectations (light blue).

Figure 3

Brain regions associated with expectation violation. These results are a linear contrast of standardized expectation error (SEE) when participants are viewing pictures of their partners during the memory task. Yellow values are associated with partners that offered more than the participant's initial expectation. Blue values are associated with viewing partners that offered less than the participant's initial expectation. (A) Axial section shows bilateral insula, ventral striatum, bilateral posterior hippocampi, visual cortex associated with positive SEE, while right superior temporal sulcus and bilateral posterior insula are associated with negative SEE. (B) Coronal section shows bilateral anterior insula, ventral striatum, right dorsolateral prefrontal cortex, and pre-supplementary motor area/dorsal anterior cingulate. (C) Coronal section shows bilateral posterior hippocampus. (D) Right lateral section shows DLPFC, VLPFC, and TPJ and STS. (E) Sagittal section shows preSMA/DACC. (F) Sagittal section shows posterior hippocampus/parahippocampus. All clusters survive whole brain correction using cluster correction, Z > 2.3, p < 0.05 and are displayed on the group average T1 image using the radiological convention (left = right).