The timescale and functional form of context-dependence during human value-learning

Abstract

AbstractContrary to the predictions of normative theories, choices between two high-value alternatives can be biased by the introduction of a third low-value alternative (dubbed the distractor effect). Normalization-based theories, like divisive and range normalization, explain different forms of the distractor effect by suggesting that the value of each alternative is normalized by a summary statistic of the values encountered in a particular decision context. The decision context can include alternatives encountered over an extended timeframe (temporal context); and alternatives that are available for choice on a given instance (immediate context). To date, the extent to which the immediate and temporal context (co-) shape context-dependent value representations remains unclear. To investigate this, we designed a task in which participants learned the values associated with three different alternatives and provided explicit value estimates before making a series of choices among ternary and binary combinations of those alternatives. We show that context-dependence already emerges in the pre-choice value estimates and is equally present in binary and ternary choice trials. Based on these findings, we conclude that the temporal (and not the immediate) context modulates subjective value representations. Interestingly, the functional form of context-dependence we report runs against both divisive and range normalization theories. Instead, our data are best explained by a stochastic rank-based model, according to which the value of an alternative is distorted by a series of memory-based binary comparisons with previously encountered alternatives.