Auditory imprinting in domestic chicks during tonic immobility

In present study we attempted to determine whether the characteristic unresponsiveness of animals during tonic immobility is due to sensory or motor inhibition. Specifically, we exposed domestic chicks to an auditory imprinting stimulus during tonic immobility. Seventy-five White Leghorn chicks were tested in 1 of 5 conditions: (1) immobilized and imprinted; (2) restrained but not immobilized, and imprinted; (3) imprinted only; (4) immobilized but not imprinted; and (5) neither immobilized nor imprinted. Chicks in the 1st 3 groups all imprinted to the same degree in that they did not differ in median run times in a straight alley with the imprinting stimulus. These results demonstrate that chicks do process auditory stimuli during tonic immobility and the reduced responsiveness observed during tonic immobility is due mainly to motor inhibition.