Figure 1.
Experimental design and results. (A) Offer pairs were presented sequentially. The first offer was presented in red and remained on screen for 1.5 s. After a 6 s delay, a second reward was presented in green. In half of trials the first offer presented a smaller and more immediate reward. The other half presented a larger but more delayed reward. The probability of choosing the larger reward was estimated to be 0.1, 0,4, 0.6, or 0.9, using decision parameters obtained from a staircase procedure completed outside the fMRI scanner. (B) Choice probabilities during the fMRI experiment were symmetrically distributed around indifference (i.e., ), and varied systematically with valuation. (C) Response times decrease with increases in valuation differences demonstrating that response times become faster as choice difficulty is reduced.