Why Does the Fridge Hum Fade from Awareness?

When you first enter a quiet kitchen, the refrigerator compressor may sound conspicuously loud. After a while, the hum seems to disappear. The machine has not stopped and your ears have not switched off. This progressive reduction in response to a repeated stimulus is called habituation, a simple form of non-associative learning.

The sound is not erased. Rather, it is steady, predictable and has produced no new consequence. At first it triggers an orienting response: attention turns towards the source while the body prepares to decide whether it matters. With repetition, the system devotes less response to the same input and remains available for change. If the fridge suddenly makes a different click, attention often returns at once. After leaving the kitchen for a while, the original hum may also become noticeable again. Such dishabituation and spontaneous recovery show that reduced responding is not a permanent loss of sensation.

Habituation is not identical to sensory adaptation. Adaptation can involve reduced responsiveness in receptors or sensory systems during sustained stimulation. Habituation is usually identified behaviourally through features such as stimulus specificity and recovery after something novel. Nor is it simply boredom: boredom includes a subjective judgement about monotony, whereas habituation describes a response decreasing with repetition.

The research boundary matters. A person’s failure to respond does not by itself prove habituation. Fatigue, diverted attention, hearing differences or a quieter stimulus can produce the same surface result. The cautious conclusion is that habituation can explain a smaller response when a harmless stimulus repeats, but evidence about recovery, specificity and stimulus strength is needed to rule out alternatives.

https://pmc.ncbi.nlm.nih.gov/articles/PMC2754195/
https://pmc.ncbi.nlm.nih.gov/articles/PMC4288050/