This is Pavlov's term for a response to novelty. Pavlov would often refer to it as the "What is it?" reflex. In Pavlov's (translated) words, this reflex:

"brings about the immediate response in man and animals to ... changes in the world around them, so that they immediately orientate their appropriate receptor organ in accordance with the perceptible quality in the agent bringing about the change..."


For Pavlov's immediate studies, this reflex was considered an obstacle. That is, it tended to get in the way of his ability to objectively observe other reflexes and responses. None the less, he clearly recognized the significance, and importance of this behavior, and the need to further study it.



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Resources

• Visual Cortex Reacts In Response to Novelty (but not to this study)