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Magnetic Navigation in Animals, Visual Contrast Sensitivity and the Weber–Fechner Law

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Some animals are known to be able to react to very small changes in the magnetic field (a thousand times smaller than the geomagnetic field) and to use this ability to navigate the Earth’s magnetic landscape. However, the nature of the molecular sensor of the magnetic field remains uncertain, though it has been established that the magnetic sense is associated with vision. A magnetochemical reaction is believed to underlie the functioning of the magnetic sensor. The cryptochromes of photoreceptors lining the retina contain photoinduced spin-correlated pairs of radicals which are involved in forming nerve impulses and are sensitive to magnetic fields. On this basis, animals may sense the magnetic field as changes in brightness over large visual fields, and orient themselves in terms of the contrast of these fields. However, the sensitivity of individual sensors – radical pairs – is very low. It has previously been supposed that this difficulty is overcome by a statistical increase in contrast sensitivity due to the parallel processing by the brain of the primary signals of millions of photoreceptors. We report here testing of this hypothesis. The threshold sensation of brightness contrast was found to depend almost linearly on the logarithm of the angular size of the contrasting stimulus, which is typical for the physiology of sensations obeying the Weber–Fechner law. Contrast sensitivity increases with increases in the number of photoreceptors involved in stimulus recognition, though this increase is quantitatively insufficient to provide a confident explanation of magnetic navigation in animals.

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Correspondence to V. N. Binhi.

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Translated from Sensornye Sistemy, Vol. 37, No. 1, pp. 35–48, January–March, 2023.

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Binhi, V.N. Magnetic Navigation in Animals, Visual Contrast Sensitivity and the Weber–Fechner Law. Neurosci Behav Physi 53, 1036–1046 (2023).

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