a new principle of neural action is [thus] introduced". This is the Pavlov "second-signal system" principle that distinguishes verbal conditioning, or language acquisition, in man from first-signal conditioning in men and animals. This view is different from most American behaviorists, who claim language is either a mediator, operating principally according to the laws of the reactions that it mediates, or is simply a conditioned vocal reaction.
The text introduces Pavlov's "second-signal system" principle, which distinguishes verbal conditioning in humans from first-signal conditioning in animals and men. This contrasts with the prevailing view among American behaviorists who believe language either mediates reactions or functions as a conditioned vocal response.