Economic approaches to decision making assume that people attach values to prospective goods and act in order to maximise their obtained value. Neuroeconomics strives to observe these values directly in the brain. A widely used valuation term in formal learning and decision-making models is the reward prediction error: the value of an outcome relative to its expected value. An influential theory (Holroyd and Coles, 2002) claims that an electrophysiological component, the feedback related negativity (FRN), codes a reward prediction error in the human brain. Such a component should be sensitive to both the prior likelihood of reward and its magnitude on receipt. A number of studies have found the FRN to be insensitive to reward magnitude, thus questioning the Holroyd and Coles account.However, because of marked inconsistencies in how the FRN is measured, a meaningful synthesis of this evidence is highly problematic. We conducted a meta-analysis of the FRN's response to both reward magnitude and likelihood using a novel method in which published effect sizes were disregarded in favour of direct measurement of the published waveforms themselves, with these waveforms then averaged to produce "great-grand averages". Under this standardised measure, the meta-analysis revealed strong effects of magnitude and likelihood on the FRN consistent with it encoding a reward prediction error. In addition, it revealed strong main effects of reward magnitude and likelihood across much of the waveform, indicating sensitivity to unsigned prediction errors or "salience". The great grand average technique is proposed as a general method for meta-analysis of ERPs.Keywords: Feedback related negativity (FRN); Event-related potential (ERP); Reward prediction error (RPE); Unsigned prediction error; Meta-analysis; Great grand average Masked Manuscript without Author Information 2 Explaining human behavior under choice requires understanding how humans assign value to goods and actions. This valuation occurs at a nexus of psychological influences running from high level processes such as framing effects and counterfactual comparisons down to basic physiological influences such as satiation. It is likely to be dependent on an individual's knowledge both through conscious extrapolation from experience and simple reinforcement learning.Early attempts to explain human valuation were aimed at demonstrating that choice was entirely rational, and embodied key axioms of neoclassical economics such as expected utility. This approach employed a black box methodology, observing the "revealed preferences" of outward behavior in favor of the underlying apparatus of valuation, and treating humans only "as if" they computed utilities (Friedman, 1953;Samuelson, 1937).These assumptions have come under attack from the field of behavioral economics, which has succeeded in documenting widespread and consistent deviations from rational choice. A fully psychological approach, behavioral economics has endeavored to open the black box and consider a more va...