UCS properties in classical conditioning of the Albino rabbit's nictitating membrand response.

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Abstract
The effects of light onset and corneal puff as UCSs [unconditioned stimuli] were investigated. In Experiment I a group receiving 100% light UCS trials failed to condition, contrary to contiguity theory expectations, since UCRs [unconditioned responses] were reliably elicited, while a 100% puff group showed clear conditioning. Another groups, receiving 50% puff and 50% light UCSs (50 50-PL), was superior to a conventional 50% puff group (50-P), the light apparently mediating puff effectiveness. In Experiment II a group receiving 50% puff and 50% vibrotactile UCSs performed midway between Groups 50/50-PL and 50-P asymptotically. Light onset was not reinforcing, but instead depressed responding below the normal extinction level in a group switched from 100% puff to 100% light UCS trials. All 50% groups exhibited within-session decrements and between-session recovery.