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S-S theory S-R theory Test
redrawn after Lieberman (2000), page 162 or Lieberman (1993) page 167.

A very simple test of whether the S-S or the S-R theory is most accurate is to weaken the link between the US and the UR.

According to the S-S theory the conditioned response itself depends on the US-UR link, because the learned association is just between the CS and the US, but for the S-R theory the conditioned response is independent of this US-UR link because of the direct assocation between the CS and the CR (in this case the same as the UR). Generally, weaking the US-UR link, by prefeeding or taste-aversion training for a food US, weakens the CR (conditioned response), and this supports the orginal Pavlovian S-S interpretation.