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The olfactory hypothesis of salmon imprinting ..
The latter hypothesis (of biogenetic magnetite) is most likely in Chinook salmon, as studies have found chains of single-domain magnetite particles in the dermethmoid tissue of the skull. (Kirschvink, )
An image of magnetite chains is shown below from sockeye salmon
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As shown by , visual acuity increases with the level of illumination (as previously said) and with the increase of object-background contrast (Adrian 1993). This effect is particularly marked in young people. A large light background and a dark object thus provides the best efficiency. However, in real life, contrast will never reach unity. For example, when a black letter is printed on a white sheet of paper, the object-background contrast reaches a value of only around 90%.
imprinting hypothesis, the proportion of sockeye salmon ..
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When the visual task requires alternative far and near vision, bifocal, trifocal or even progressive lenses are recommended. However, it should be kept in mind that the use of multifocal lenses can create important modifications to the posture of an operator. For example, VDU operators with presbyopia corrected by the means of bifocal lenses tend to extend the neck and may suffer cervical and shoulder pain. Spectacles manufacturers will then propose progressive lenses of different kinds. Another cue is the ergonomic improvement of VDU workplaces, to avoid placing the screen too high.
Older workers are at a double disadvantage in conditions of weak contrast and weak luminosity of the environment; first, they need more light to see an object, but at the same time they benefit less from increased luminosity because they are dazzled more quickly by glare sources. This handicap is due to changes in the transparent media which allow less light to pass and increase its diffusion (the veil effect described above). Their visual discomfort is aggravated by too sudden changes between strongly and weakly lighted areas (slowed pupil reaction, more difficult local adaptation). All these defects have a particular impact in VDU work, and it is very difficult, indeed, to provide good illumination of workplaces for both young and older operators; it can be observed, for example, that older operators will reduce by all possible means the luminosity of the surrounding light, although dim light tends to decrease their visual acuity.
Olfactory Imprinting and Homing Salmon - ResearchGate
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Perception of chemicals can be altered by previous encounters. Tolerance develops when exposure reduces the response to subsequent exposures. Adaptation occurs when a constant or rapidly repeated stimulus elicits a diminishing response. For example, short-term solvent exposure markedly, but temporarily, reduces solvent detection ability (Gagnon, Mergler and Lapare 1994). Adaptation can also occur when there has been prolonged exposure at low concentrations or rapidly, with some chemicals, when extremely high concentrations are present. The latter can lead to rapid and reversible olfactory "paralysis". Nasal pungency typically shows less adaptation and development of tolerance than olfactory sensations. Mixtures of chemicals can also alter perceived intensities. Generally, when odorants are mixed, perceived odorant intensity is less than would be expected from adding the two intensities together (hypoadditivity). Nasal pungency, however, generally shows additivity with exposure to multiple chemicals, and summation of irritation over time (Cometto-Muñiz and Cain 1994). With odorants and irritants in the same mixture, the odour is always perceived as less intense. Because of tolerance, adaptation, and hypoadditivity, one must be careful to avoid relying on these sensory systems to gauge the concentration of chemicals in the environment.
Individuals with olfactory disturbance must first be assessed for rhinitis, nasal polyps and sinusitis. It is estimated that 20% of the United States population, for example, has upper airway allergies. Environmental exposures can be unrelated, cause inflammation or exacerbate an underlying disorder. Rhinitis is associated with olfactory loss in occupational settings (Welch, Birchall and Stafford 1995). Some chemicals, such as isocyanates, acid anhydrides, platinum salts and reactive dyes (Coleman, Holliday and Dearman 1994), and metals (Nemery 1990) can be allergenic. There is also considerable evidence that chemicals and particles increase sensitivity to nonchemical allergens (Rusznak, Devalia and Davies 1994). Toxic agents alter the permeability of the nasal mucosa and allow greater penetration of allergens and enhanced symptoms, making it difficult to discriminate between rhinitis due to allergies and that due to exposure to toxic or particulate substances. If inflammation and/or obstruction in the nose or sinuses is demonstrated, return of normal olfactory function is possible with treatment. Options include topical corticosteroid sprays, systemic antihistamines and decongestants, antibiotics and polypectomy/sinus surgery. If inflammation or obstruction is not present or treatment does not secure improvement in olfactory function, olfactory tissue may have sustained permanent damage. Irrespective of cause, the individual must be protected from future contact with the offending substance or further injury to the olfactory system could occur.
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Olfactory Homing of Chum Salmon to Stable …
The site of injury within the olfactory system differs with various agents (Cometto-Muñiz and Cain 1991). For example, ethyl acrylate and nitroethane selectively damage olfactory tissue while the respiratory tissue within the nose is preserved (Miller et al. 1985). Formaldehyde alters the consistency, and sulphuric acid the pH of nasal mucus. Many gases, cadmium salts, dimethylamine and cigarette smoke alter ciliary function. Diethyl ether causes leakage of some molecules from the junctions between cells (Schiffman and Nagle 1992). Solvents, such as toluene, styrene and xylene change olfactory cilia; they also appear to be transmitted into the brain by the olfactory receptor (Hotz et al. 1992). Hydrogen sulphide is not only irritating to mucosa, but highly neurotoxic, effectively depriving cells of oxygen, and inducing rapid olfactory nerve paralysis (Guidotti 1994). Nickel directly damages cell membranes and also interferes with protective enzymes (Evans et al. 1995). Dissolved copper is thought to directly interfere with different stages of transduction at the olfactory receptor level (Winberg et al. 1992). Mercuric chloride selectively distributes to olfactory tissue, and may interfere with neuronal function through alteration of neurotransmitter levels (Lakshmana, Desiraju and Raju 1993). After injection into the bloodstream, pesticides are taken up by nasal mucosa (Brittebo, Hogman and Brandt 1987), and can cause nasal congestion. The garlic odour noted with organophosphorus pesticides is not due to damaged tissue, but to detection of butylmercaptan, however.
Imprinting to Olfactory Cues: The Basis for Home …
The olfactory nerves provide a direct connection to the central nervous system and may serve as a route of entry for a variety of exogenous substances, including viruses, solvents and some metals (Evans and Hastings 1992). This mechanism may contribute to some of the olfactory-related dementias (Monteagudo, Cassidy and Folb 1989; Bonnefoi, Monticello and Morgan 1991) through, for example, transmittal of aluminium centrally. Intranasally, but not intraperitoneally or intracheally, applied cadmium can be detected in the ipsilateral olfactory bulb (Evans and Hastings 1992). There is further evidence that substances may be preferentially taken up by olfactory tissue irrespective of the site of initial exposure (e.g., systemic versus inhalation). Mercury, for example, has been found in high concentrations in the olfactory brain region in subjects with dental amalgams (Siblerud 1990). On electroencephalography, the olfactory bulb demonstrates sensitivity to many atmospheric pollutants, such as acetone, benzene, ammonia, formaldehyde and ozone (Bokina et al. 1976). Because of central nervous system effects of some hydrocarbon solvents, exposed individuals might not readily recognize and distance themselves from the danger, thereby prolonging exposure. Recently, Callender and colleagues (1993) obtained a 94% frequency of abnormal SPECT scans, which assess regional cerebral blood flow, in subjects with neurotoxin exposures and a high frequency of olfactory identification disorders. The location of abnormalities on SPECT scanning was consistent with distribution of toxin through olfactory pathways.
Experimental Evidence for Olfactory Imprinting by …
Although smoking can inflame the lining of the nose and reduce smell ability, it may also confer protection from other damaging agents. Chemicals within the smoke may induce microsomal cytochrome P450 enzyme systems (Gresham, Molgaard and Smith 1993), which would accelerate metabolism of toxic chemicals before they can injure the olfactory neuroepithelium. Conversely, some drugs, for example tricyclic antidepressants and antimalarial drugs, can inhibit cytochrome P450.
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