In physiological studies, tones
are mainly used as stimuli. Here frequency discrimination of pure
sinusoidal sounds is compared with the frequency-resolving ability
for sinusoidally frequency-modulated tones. The question is raised
if the resolving power is improved by the latter stimulus procedure.
The method used was heartrate conditioning. With the help of this
classical conditioning technique, an associative connection between
a conditioned (acoustic) stimulus ( = test tone) and a following
unconditioned stimulus (a weak electric shock) is developed. In
addition, a randomized number of reference tones which are not followed
by a shock is played to the bird. The heart-beat rate recorded during
the reference tones is compared with the heart-beat rate during
the test tone, using the Student's t-test. The threshold criterion
was determined at a onetailed error probability of 2.5%.