Trends in Cognitive Sciences
Neuronal representations of cognitive state: reward or attention?
Section snippets
Effects of reward expectation on neuronal activity
Several studies have examined how a monkey's expectations about reward can influence the activity of individual neurons. In most such experiments, expectations are varied by having the animal do blocks of trials in which reward conditions are kept constant within blocks (allowing stable expectations to develop) but varied between blocks (allowing comparison of the effects of different expectations). Rewards are typically manipulated by changing either the amount of reward delivered for a
Reward expectation or attention?
The effect of attention on neuronal responses has been studied extensively (reviewed in 18, 19, 20, 21). Single unit studies in visual cortex have shown that increased attention to a stimulus typically increases the responses of neurons that represent that stimulus [22]. Many such studies have examined the effect of attending to a particular stimulus or location in space, but it has been shown that attention to a particular visual feature, such as a direction of motion, can also selectively
Favoring one interpretation
Most studies of attention or reward expectations have not addressed the potential for confusion between them, and have interpreted neuronal signals as either attention-related or reward-related without considering alternatives. However, a few reports did consider the problem and argued specifically for one interpretation. Although such views might be correct, the data do not provide strong support.
Kawagoe and colleagues [15] sought to distinguish their reward-related neuronal modulations from
Distinguishing reward and attention
Recent experiments do not distinguish whether neuronal signals are related to attention or to expectations about reward. Can changes in neuronal activity be assigned unequivocally to one or the other? A complete treatment of the issues involved in defining and distinguishing cognitive signals such as these is beyond the scope of this article. Nevertheless, is it helpful to consider the range of possibilities for signals related to attention and reward, and to suggest approaches that might serve
Conclusion
In summary, I have argued that some experiments examining neuronal representations of attention or reward expectation might in fact have been measuring either of those parameters. Given our limited understanding of the organization of the neuronal representations that support cognition, clarifying our terminologies and descriptions of neuronal activity is crucial for identifying the signals that are most important for different cognitive functions. Efforts to distinguish the relative
Acknowledgments
I thank John A. Assad, William H. Bosking, Raika Pancaroglu and David L. Sparks insightful discussions and helpful comments on earlier versions of this manuscript. Supported by NIH R01 EY05911. J.H.R.M. is an Investigator with the Howard Hughes Medical Institute.
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