Influence of Biases in Numerical Magnitude allocation on Human Pro-Social Decision Making

Over the past decade neuroscientific research has attempted to probe the neurobiological underpinnings of human pro-social decision-making. Such research has almost ubiquitously employed tasks such as the dictator game or similar variations (i.e. ultimatum game). Considering the explicit numerical nature of such tasks, it is surprising that the influence of numerical cognition upon decision-making during task performance remains unknown. Whilst performing these tasks, participants typically tend to anchor upon a 50:50 split that necessitates an explicit numerical judgement (i.e. number-pair bisection). Accordingly, we hypothesise that the decision-making process during the dictator game recruits overlapping cognitive processes to those known to be engaged during number-pair bisection. We observed that biases in numerical magnitude allocation correlated with the formulation of decisions during the dictator game. That is, intrinsic biases towards smaller numerical magnitudes were associated with the formulation of less favourable decisions, whereas biases towards larger magnitudes were associated with more favourable choices. We proceeded to corroborate this relationship by subliminally and systematically inducing biases in numerical magnitude towards either higher or lower numbers using a visuo-vestibular stimulation paradigm. Such subliminal alterations in numerical magnitude allocation led to proportional and corresponding changes to an individual's decision-making during the dictator game. Critically, no relationship was observed between neither intrinsic nor induced biases in numerical magnitude on decision-making when assessed using a non-numerical based pro-social questionnaire. Our findings demonstrate numerical influences upon decisions formulated during the dictator game and highlight the necessity to control for confounds associated with numerical cognition in human decision-making paradigms.

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