Classical avoidance without a warning stimulus.

SIDMAN (1962) removed every warning light or buzzer from a shuttle box. Rats had to press a lever to avoid shock, but the only cue was the time since their last response.

The experiment asked: can avoidance live on pure internal clock, or do animals need an outside signal?

The rats learned to press on a steady rhythm and kept shocks away. After a while, some animals started waiting longer and longer until shocks finally slipped through.

The study showed that a silent internal timer can run avoidance, but the same timer can later pull the behavior apart.

Edwards et al. (1970) repeated the setup with pigeons and saw the same pattern: birds pecked on a clock they could not see, and some later fell into post-shock bursts. The finding extends the rat result to a new species and response.

Zeiler (1968) looks like a contradiction at first: his rats mastered a hold-release lever move when a single light told them when to act. The difference is cue: D gave one, M gave none. The papers together prove that adding even a minimal signal can protect against the drift that ruins pure temporal avoidance.

Sachs et al. (1969) tested humans and also saw responding bunch up just before an expected shock. Across rats, pigeons, and people, the internal clock keeps showing up, but only the animal studies reveal how it can later spoil the avoidance pattern.

If you run avoidance programs for head-banging or elopement, do not assume a warning stimulus is required. A silent fixed-time schedule can work, but watch for longer and longer response gaps. When you see drift, add a brief visual or auditory cue; the later literature shows that tiny signal can restabilize the whole chain.