Young (18-30 years) and elderly (63-88 years) human subjects received
70 trials of single-cue classical eyeblink conditioning (paired group)
, or 70 explicitly unpaired presentations of the tone conditioned stim
ulus (CS) and airpuff unconditioned stimulus (unpaired group). Before
and after conditioning, reflex-eliciting white noise and corneal airpu
ff stimuli were presented alone or paired with the CS to investigate t
he effects of conditioning on eyeblink reflex amplitude. The results s
howed increased conditioned responses in the paired group compared to
the unpaired group for the young but not the elderly subjects. There w
as, however, evidence of conditioned facilitation of noise-elicited re
flexes in both young and elderly subjects. These data indicate that co
nditioned facilitation of the startle reflex may be a sensitive indica
tor of classical conditioning processes in human subjects.