Valuation of opportunity costs by rats working for rewarding electrical brain stimulation - Fig 1

<p><b>A: Objective-price function.</b> Subjective prices are equal to objective prices, as assumed in early studies using the reward-mountain model [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182120#pone.0182120.ref014" target="_blank">14</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182120#pone.0182120.ref017" target="_blank">17</a>]. <b>B: Sigmoidal-slope function.</b> The functional form resembles a hockey stick. The flat “blade” of the function denotes the range over which costs are subjectively invariant. That portion merges with an upward-bending segment over which the costs are discriminable, but do not yet rise at the same rate as the objective price. The final “handle” portion denotes the range over which the relationship between objective and subjective costs is scalar. Changing the value of the parameter shifts the curve vertically, whereas changing the value of the parameter alters the abruptness of the transition between the blade and the handle. <b>C: Linear-price function.</b> This is the subjective-price function derived from Mazur’s [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182120#pone.0182120.ref032" target="_blank">32</a>] hyperbolic-discounting equation. The greater the value of <i>K</i>_<i>h</i>, the faster the function rises. In order for the terminal slope to approach unity, <i>K</i>_<i>h</i> must equal 1. (The lines look curved because they are plotted in double logarithmic coordinates; in linear coordinates, they would be straight.) <b>D: Exponential-price function.</b> This is the subjective-price function derived from exponential discounting. The larger the <i>K</i>_<i>x</i> value, the more rapidly the function rises. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182120#pone.0182120.s001" target="_blank">S1 File</a> for a discussion of units.