Graphical representation of the probability of a correct response.

<p>The shaded areas in A and B correspond to the integrals in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074815#pone.0074815.e040" target="_blank">Equations (4</a>) and (5), respectively. The smooth curves trace out the PDF of the noise, <i>f</i>(<i>ε</i>) on the internal difference signal, <i>z</i>. As explained in the text, <i>f</i> has to be even-symmetric, and this means that the two integrals in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074815#pone.0074815.e040" target="_blank">Equations (4</a>) and (5) are equal. The shaded areas correspond to the probability of a correct response. The psychometric function (expressed as a function of <i>z</i>) is the CDF of the noise, increasing from 0.5 to 1 as <i>z</i> increases from 0 to ∞.