Morton Fleshler

Startle Reaction: Modification by Background Acoustic Stimulation

Six rats were exposed to a sequence of gunshot-like acoustical bursts during silence, during steady noise, and during pulsed noise. Assessment of their startle reactions to the bursts revealed that a background of steady noise enhanced the response, whereas a background of pulsed noise produced suppression of response. It is hypothesized that pulsed noise causes a relative refractory state in the mechanisms responsible for startle and that steady noise may enhance startle by masking uncontrolled punctiform acoustic stimuli.

Stimulus Generalization of Conditioned Suppression

A tone ending in unavoidable electric shock was periodically presented to pigeons while they pecked a key for food. When pecking was completely disrupted by tone, shock was disconnected, and the training tone and tones having new frequencies were presented. Initially the gradient of generalization was broad; as testing proceeded, however, the gradient narrowed severely.

Aversive Training: Long-Term Effects

Three years ago a tone ending in unavoidable electric shock was periodically presented to pigeons while they pecked a key for food. When pecking was disrupted by tone, shock was disconnected and the training tone and tones of different frequencies were presented. At first all tones caused a reduction in the rate of pecking, but as testing proceeded the gradient narrowed. In our study, testing was resumed after a 2�-year interruption. Despite the interruption the tones still suppress behavior.