Table 2. Experimental design.

Familiarization	Acquisition*	Generalization	Extinction
$$\left(\begin{array}{c}1\times \mathrm{C}\mathrm{S}+\\ 1\times \mathrm{G}\mathrm{S}3\\ 1\times \mathrm{C}\mathrm{S}-\end{array}\right)$$	$$4\times \left(\begin{array}{c}4\times \mathrm{C}\mathrm{S}+\\ \\ 4\times \mathrm{C}\mathrm{S}-\end{array}\right)$$	$$2\times \left(\begin{array}{c}1\times \mathrm{C}\mathrm{S}+\\ 1\times \mathrm{G}\mathrm{S}1\mathrm{-}5\\ 1\times \mathrm{C}\mathrm{S}-\end{array}\right)$$	$$5\times \left(\begin{array}{c}4\times \mathrm{C}\mathrm{S}+\\ \\ 4\times \mathrm{C}\mathrm{S}-\end{array}\right)$$

Notes:

^*75% reinforcement rate of CS+.

CS+, conditioned stimulus paired with “PAIN”; CS−, conditioned stimulus paired with “NO PAIN”; GS, generalization stimulus. Stimuli were presented in semi-random fashion within each block (denoted by brackets) with the condition that no stimulus would be presented more than twice consecutively.