MODIFICATION OF PIGEONS VISUAL STARTLE REACTION BY SENSORY ENVIRONMENT

A series of 7 experiments related amplitude and latency of the pigeon''s startle response, elicited by an intense visual stimulus, to antecedent auditory and visual events in the sensory environment. Within broad limits the amplitude of the reflex was a positive function of the intensity of the sensory background prevailing at the time of startle elicitation. A change in the sensory environment occurring 15-2000 ms prior to the startle-eliciting stimulus inhibited the amplitude of the response. A change in the sensory environment less than 10 ms prior to the startle-eliciting stimulus reduced the latency of the response. These findings are consistent with previous research on acoustic elicited startle in the rat. A pathway including the reticulospinal tract and the bulbopontine reticular nuclei may be the major mediator of startle. Latency-reduction effects may occur because of partial activation of this pathway, amplitude inhibition may occur because of cerebellar influence, and amplitude facilitation may reflect cerebral or striatal influences.