It's value reflects attention given to a conditioned stimulus or how effectively the stimlus is precieved. In this demonstration, the salience of the light and tone should be set much higher that that of the context, to which little attention is paid. Set the stength of the unconditioned stimulus. Trials continue until a substantial CR is produced to the tone. Trials consist of tone followed by shock until a substantial CR is produced.
Trials consist of a tone and light, then shock.
Note the difference in CRs to the tone and light. Same as blocking, except that in Phase 2, the shock is not administered at all. Again, note the difference in CR's to the tone and light. Notice how slow the tone acquires a CR compared to a situation in which the shock was never presented alone. You have five seconds to administer a combination of tone, light, and shock.