The function of the tectum for attention to auditory stimuli in the cat.

Cats were trained to avoid a shock by moving from one to the other compartment of a double grill box at the onset of a compound signal which consisted of a soft low tone and a bright flashing light. After training on the compound signal unreinforced test trials were givcn on the tone alone and the light alone. By this procedure the relative potency of sound and light was established for normal cats and cats deprived of various structures in their auditory system. On the basis of this and other subsidiary experiments also reported here, several conclusions seem warranted: 1. In normal cats sound is a prepotent stimulus over light. 2. The prepotency of sound does not depend on the intensities of the competing stimuli. 3. Even with approximately 90% of the second order auditory fibers destroyed, sound is still prepotent over light. 4. Bilateral removal of auditory cortex does not affect the prepotency of sound. 5. Deep bilateral section of the brachia of the inferior colliculus and small bilateral lesions in the apices of the inferior colliculi abolish the prepotency of sound. 6. The loss of the prepotency of sound after midbrain lesions is not the result of a change i n absolute threshold for the sound. ' I. .. It is not usual for the organism to be exposed to the action of only one stimulus at a time. It is more usual for the organism to be acted on by many stimuli concurrently, and to be driven re-flexly by some group of stimuli which is at any particular moment prepotcnt.. . " (Sherrington, '47). A significant portion of Sherrington's inquiry into the integra-tive action of the central nervous system is devoted to demonstrating the way in which the spinal cord resolves the competition between concurrent stimuli for the control of the motor system. To be sure, concurrent stimuli do not necessarily compete but may reinforce each other. The condition for competition is met when each of the two stimuli applied separately tends ". .. to evoke reflex action that for its end-effect employs the same final common path but employs it in a different way from the other.. . " (Sherrington, '47). For example , when a noxious injurious stimulus and a harmless tactual stimulus are simultaneously applied to the planta of a dog's foot the withdrawal reflex is prepotent, and as a rule the noci-ceptive reflexes …