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Imagine the scenario. My friend and I are playing a game of chess near a highway. Initially, I notice the sound of the highway. While I'm playing chess, however, I do not notice it. After the game my friend asks me if I can hear the highway, and I regain my ability to notice it. This seems to be different for smells. If we were playing chess in a room filled with garbage, the smell would gradually fade away. If my friend asked me if I could smell the garbage, I would not be able to smell the garbage as severely. What is the cause of this difference? It seems that visual and touch follows the same pattern as hearing. What makes smell unique?

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Adaptation occurs in every sensory system. For example in vision there is the motion after effect that occurs through adaptation of visual neurons in the cortex. Also, the visual system strongly adapts to low and high lighting conditions through light and dark adaptation. The tactile system also shows substantial adaptation, as touch receptors in the skin fail to convey information after prolonged stimulation (you won't feel a watch/ring/band aid etc after wearing it for a while). For example, mechanoreceptors in the skin such as the Pacinian corpuscles fail to transmit tactile stimuli when activated for a prolonged time. The auditory system also adapts to loud sounds by cortical mechanisms as well as peripheral mechanisms through the middle ear muscles. Lastly, as you correctly identified, the olfactory system adapts to stimulation as well through metabolic mechanisms that decrease the responsiveness of chemical receptors. The list of adaptational mechanisms provided is not comprehensive, but I just used some obvious examples to show that adaptation occurs in all the senses in a variety of ways. In fact, one of the hallmarks of any physiological intact sensory system is the capability to operate over a wide range of stimulus levels. For example, vision operates over a range of intensities differing 8 orders of magnitude, while hearing operates in an intensity range of 1013. To maintain such an impressive range of input intensities sensory systems have to adapt at various levels. As an analogy, the same applies to your photo camera in which the exposure time has to be regulated in order to take pictures under different lighting conditions.

So to come back to your suggestion that smell cannot be revived after continued stimulation while it can be revived with other senses is not true I think. The attentional revival you are talking about is not so much adaptation but has more to do with the attentional shift, which may occur with any sensory modality.

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    $\begingroup$ I do believe that it is true that you cannot revive the smell to a certain degree. For example, when my toilet was broken and it got very smelly, while I was cleaning up in there, it smell was more bearable than initially. I would try to detect the smell again, but it did not seem too bad, and it was bad initially. $\endgroup$ – CognisMantis Nov 25 '14 at 0:40
  • $\begingroup$ @CognisMantis - I agree with you. You need to step outside and 'clear the smell from your nose' to smell it as well again. It's not so much a central effect as a peripheral exhaustion. $\endgroup$ – anongoodnurse Nov 25 '14 at 2:43
  • $\begingroup$ To revive the tactile sense you also have to 'reset' it. That's adaptation. It may well be that continued acoustic stimulation results in less pronounced adaptation. Good point $\endgroup$ – AliceD Nov 25 '14 at 2:47

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