The smell of the land

The sense of smell is intriguing. It is not as readily conscious as sight, hearing, touch and taste; so it is often discounted. However, humans do have the ability is smell quite well and can learn to do so in sophisticated and conscious ways. Perfumers are an example of this. We also know that a particular smell can bring back the memory of a place in a flash that seems quite miraculous. It is the most important sense for many mammals – used to identify objects and places, track and navigate, and communicate emotional signals. There is no reason to think that we are that much different; we probably use smell as a background (largely unconscious) canvas on which to perceive the world.

Recent research (citation below) has indicated such a canvas. Jacobs and others experimented with human subjects to see if they could map their surroundings using odour gradients. They used a large room with two distinct sources of different odours. The subjects were disoriented, placed in a spot and asked to remember its smell. They were disoriented again and asked to find the spot using their memory of the odour. This was done first with sight and hearing blocked and only the sense of smell available, then repeated with sight as the only sense available, and finally with all three senses blocked. The subjects could come close to the target spot with scent alone, compared to the control of none of the three senses being available.

This is a distinct ability and not the same a tracking a smell or identifying an object or place. This is the formation of a map based on odour gradients. Spatial maps are created in the hippocampus and the olfactory bulb is strongly connected to the hippocampus. The authors address the relationship between the odour map, the sound map (echo location), and the visual map etc. “The ability to navigate accurately is critical to survival for most species. Perhaps for this reason, it is a general property of navigation that locations are encoded redundantly, using multiple orientation mechanisms, often from multiple sensory systems. Encoding the location with independent systems is also necessary to correct and calibrate the accuracy of any one system. As a general principle, then, navigational accuracy and robustness should increase with the number of unique properties exhibited by redundant orientation systems.

Abstract: “Although predicted by theory, there is no direct evidence that an animal can define an arbitrary location in space as a coordinate location on an odor grid. Here we show that humans can do so. Using a spatial match-to-sample procedure, humans were led to a random location within a room diffused with two odors. After brief sampling and spatial disorientation, they had to return to this location. Over three conditions, participants had access to different sensory stimuli: olfactory only, visual only, and a final control condition with no olfactory, visual, or auditory stimuli. Humans located the target with higher accuracy in the olfaction-only condition than in the control condition and showed higher accuracy than chance. Thus a mechanism long proposed for the homing pigeon, the ability to define a location on a map constructed from chemical stimuli, may also be a navigational mechanism used by humans.”

Citation: Jacobs LF, Arter J, Cook A, Sulloway FJ (2015) Olfactory Orientation and Navigation in Humans. PLoS ONE 10(6): e0129387. Doi:10.1371/ journal.pone.0129387

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