Tick Tick
Pavlov conditioned his dogs to salivate in response to auditory stimuli, such as bells and ticking metronomes. A metronome is a device that musicians often use to maintain tempo. This “old-fashioned” metronome has a wind-up knob and a pendulum that ticks at various speed settings. Modern metronomes are digital and often come with additional features such as adjustable volume. Perhaps Pavlov could have used these features to test different aspects of classical conditioning.

Galina Ermolaeva/Dreamstime.com