Together, slowly but surely: the role of social interaction and feedback on the build-up of benefit in collective decision-making

Abstract

That objective reference is necessary for formation of reliable beliefs about the external world is almost axiomatic. However, Condorcet (1785) suggested that purely subjective information--if shared and combined via social interaction--is enough for accurate understanding of the external world. We asked if social interaction and objective reference contribute differently to the formation and build-up of collective perceptual beliefs. In three experiments, dyads made individual and collective perceptual decisions in a two-interval, forced-choice, visual search task. In Experiment 1, participants negotiated their collective decisions with each other verbally and received feedback about accuracy at the end of each trial. In Experiment 2, feedback was not given. In Experiment 3, communication was not allowed but feedback was provided. Social interaction (Experiments 1 and 2 vs. 3) resulted in a significant collective benefit in perceptual decisions. When feedback was not available a collective benefit was not initially obtained but emerged through practice to the extent that in the second half of the experiments, collective benefits obtained with (Experiment 1) and without (Experiment 2) feedback were robust and statistically indistinguishable. Taken together, this work demonstrates that social interaction was necessary for build-up of reliable collaborative benefit, whereas objective reference only accelerated the process but--given enough opportunity for practice--was not necessary for building up successful cooperation.

Figure 1. (A) Sequential schema of events in Experiments 1–3. Each trial started with two stimulus intervals. Visual stimuli consisted of six vertically oriented Gabor patches that were displayed equidistantly around an imaginary circle. One (randomly selected) interval contained the target (here indicated by the dashed circle) of higher contrast. Participants then indicated their individual decisions privately. If they disagreed, in Experiments 1 and 2 participants negotiated a joint decision; in Experiment 3, one (randomly assigned) participant made a joint decision on behalf of the group without any interaction. Feedback about accuracy was provided in Experiments 1 and 3 but not in Experiment 2. (B) Testing setup. (C) Group average psychometric functions relating the individual and group choice to stimulus strength in Experiment 1. The X axis shows the contrast difference at the oddball location (i.e., contrast in the second interval minus contrast in the first). The Y axis shows the proportion of trials in which the target was reported to be in the second interval. Circles: average performance of the less sensitive dyad members; squares: average performance of the more sensitive dyad members; diamonds: average performance of the dyads. The curves are the best fit to a cumulative Gaussian function.

Figure 2. Average sensitivity (i.e., the slope of the psychometric function—see Figure 1C) is plotted for the best performing member of each group (S_max) and the dyads (S_dyad). Interacting dyads (Experiments 1 and 2) exceeded their own best performing individual. Without interaction, providing feedback (Experiment 3) did not afford any group benefit.

Figure 3. Sliding window analysis shows that collective benefit was gradually accumulated in the absence of feedback. Collective benefit (Y axis) is plotted against the trial number at the center of the sampling window. Error bars represent one standard error of the mean.

Figure 4. Average collective benefit accrued from joint decision making is plotted for the two sessions of the experiments. Error bars represent one standard error of the mean.