Economic choices can be made using only stimulus values

Abstract

Decision-making often involves choices between different stimuli, each of which is associated with a different physical action. A growing consensus suggests that the brain makes such decisions by assigning a value to each available option and then comparing them to make a choice. An open question in decision neuroscience is whether the brain computes these choices by comparing the values of stimuli directly in goods space or instead by first assigning values to the associated actions and then making a choice over actions. We used a functional MRI paradigm in which human subjects made choices between different stimuli with and without knowledge of the actions required to obtain the different stimuli. We found neural correlates of the value of the chosen stimulus (a postdecision signal) in ventromedial prefrontal cortex before the actual stimulus-action pairing was revealed. These findings provide support for the hypothesis that the brain is capable of making choices in the space of goods without first transferring values into action space.decision-making | functional MRI | goods space | reinforcement learning | ventromedial prefrontal cortex I magine you are thirsty and walk up to a vending machine that is serving a variety of soft drink beverages. On the machine you see the brand marks of the offered beverages, and because you had previously sampled them, you easily assign values to each drink based on their taste. To get the desired beverage, you press the button that is distinctively associated with the preferred option. This situation exemplifies many of the decisions that humans and animals make in daily life. It is a well-established belief among economists, psychologists, and neuroscientists that the brain solves such choice problems by first computing a value for each alternative and then selecting the one that has the highest value (1-4). Neuroscientists have considered two possible alternative ways for how values might be compared in order to make a choice in these situations.First is the actions-based model, in which choices are embedded in premotor processes of action selection: the values of stimuli are passed as action values to the motor plans required to obtain them, and the decision is then made in action space by comparing action values (5-7). Values are learned through experience and associated with each motor plan, and during choice a single motor act eventually emerges through a winner-takes-all process. Although this action based model of making decisions may seem convoluted, it is in fact the predominant view among many decision neuroscientists who have found value signals in areas of the brain known to be involved in representing and planning movements such as lateral parietal and premotor cortices (8-11). Further evidence for the view that decisions are computed by a comparison between actions comes from the finding of action value signals in several regions of the brain, including the caudate nucleus (5, 6), supplementary motor cortex (12), and action-related value signals in lateral int...

Separate value comparison and learning mechanisms in macaque medial and lateral orbitofrontal cortex

“…S8), as was the case in a recent recording study that focused on the lOFC (34). In contrast, our hypothesis that the mOFC is concerned with value-guided decision-making can account for previous findings; it predicts mOFC signals should correlate with the values of the choice options being considered and then with the value of the choice finally taken (3,4,23). Moreover, an account of the lOFC that focuses on value assignment predicts lOFC activation to errors if the errors occasion reassignment of values to options.…”

“…The precise nature of the mOFC's involvement, however, remains to be specified. Functional MRI studies have reported that ventromedial frontal activity, but not lOFC activity, reflects the value of the option that will be chosen but also the value of options that will go unchosen (3,4,23). In some cases, but not all (23), a value-difference signal suggests a value comparison process within the ventromedial frontal cortex.…”

Double Dissociation of Stimulus-Value and Action-Value Learning in Humans with Orbitofrontal or Anterior Cingulate Cortex Damage

“…These results suggest that decisions can be taken in either stimulus-based or action-based decision space, depending on the context, and that these decisions engage different neural substrates. These findings argue for material-specific contributions of dACC to action selection, and OFC to stimulus selection, based on value (Rushworth et al, 2007a;Buckley et al, 2009;Hayden and Platt, 2010;Wunderlich et al, 2010).…”

“…Further, it is not clear whether decisions proceed stepwise, with choice resting on the transformation of stimulus value to action. Indeed, fMRI evidence argues that action value representations in dACC are not needed for stimulus-based decision making (Wunderlich et al, 2010). An alternative view is that value influences choices between stimuli and between actions through distinct, perhaps parallel, mechanisms.…”

How Embodied Is Perceptual Decision Making? Evidence for Separate Processing of Perceptual and Motor Decisions

“…In addition, different kinds of decisions involve different prefrontal areas. Value-based decision making involves ventromedial PFC (Basten et al, 2010;Philiastides et al, 2010;Wunderlich et al, 2010). Predictive coding of categories also involves mPFC (Summerfield et al, 2006).…”