Explicit value cues and response caution in value-based decisions

All else being equal, preference-based choices become faster as the values of the alternatives increase, a phenomenon we refer to as the overall-value effect. There are many competing explanations for the overall-value effect, with normative, mechanistic, and artefactual origins. Here, we examined these potential explanations, applying diffusion modeling to choice and response-time (RT) data from three difference choice domains (snack foods, abstract art, and conditioned stimuli). Within each experiment, we manipulated whether subjects knew the range of overall values in the upcoming block of trials. In each experiment, when subjects did not know the value of the upcoming trials, we observed the overall-value effect. The presence of the overall-value effect in the conditioned-stimulus experiment indicates that it is not due to artefacts from how we measure value, nor from familiarity with high-value items. Moreover, in most cases we also observed accuracy increasing with overall value, which rules out many of the mechanistic, noise-based explanations. When subjects knew the value of the upcoming trials, their response caution (i.e., boundary separation in the diffusion model) increased for high-value trials compared to middle-value trials, reflecting longer RT. This indicates that the overall-value effect is not normative since value-informed subjects display a reverse overall-value effect. Our results indicate that the overall-value effect is a robust phenomenon and is best explained as stronger evidence (i.e. higher drift rates) for higher value items.