O efeito do ruído espacial de cor sobre a discriminação limiar de luminância: investigação básica e aplicada em populações expostas ao mercúrio
Natural images are a complex set of color and luminance contrast that when combined in visual scene helps to create the discrimination of objects from the surrounding visual environment. A series of neural streams transmits the color and luminance information from the retina to the higher cortical c...
| Autor principal: | FARIAS, Letícia Miquilini de Arruda |
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| Grau: | Tese |
| Idioma: | por |
| Publicado em: |
Universidade Federal do Pará
2018
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| Assuntos: | |
| Acesso em linha: |
http://repositorio.ufpa.br/jspui/handle/2011/10006 |
| Resumo: |
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Natural images are a complex set of color and luminance contrast that when combined in visual scene helps to create the discrimination of objects from the surrounding visual environment. A series of neural streams transmits the color and luminance information from the retina to the higher cortical centers. Several proposals have been made to study how the visual system processes the stimuli that combining color and luminance contrasts. This thesis has as main proposal to introduce a new stimulus to be used luminance discrimination task under chromatic noise masking. Thus, five experiments were carried out with focus this new paradigm to explore basic and applied questions about its use. Study 1 investigated the effect of color noise saturation on the threshold discrimination of luminance contrast. Study 2 investigated how the mosaic arrangement contributed to the contrast values of luminance contrast thresholds under the chromatic noise masking. Study 3 investigated the influence of the color content of the noise on the threshold discrimination of the luminance contrast. Study 4 investigated the influence of the polarity of the luminance contrast under the chromatic noise masking on the estimated threshold contrasts. Study 5 compared the values of threshold luminance contrasts under chromatic noise masking of two riverine populations of different Amazonian regions of the Pará State and exposed to different levels of mercury by feeding. The main finding of this thesis was that the luminance contrast thresholds varied as a function of the vector length of the chromatic noise values. The higher chromatic noise length, the higher luminance contrast threshold. The contrast threshold estimated by the non-mosaic stimulus exhibited significantly lower values than those estimated with mosaic stimuli (p <0.01). No statistical difference was observed between the contrasts threshold estimated around the five reference chromaticities at different saturation conditions (p> 0.05). The luminance contrasts thresholds estimated in the luminance decrement protocol were xiii significantly lower at all saturation levels than those estimated using the luminance increase protocol (p <0.05). There is no statistical difference between the thresholds of estimated luminance discrimination among riverine communities that were differently exposed to mercury (p> 0.05). The luminance contrasts threshold estimated by the new stimulus, described in this thesis, were influenced by chromatic and spatial noise, and by the polarity of the stimulus of luminance contrast. However, the different chromatic noise
compositions did not exhibit any influence on the luminance discrimination. The presence of one or more color-sensitive visual pathways and luminance may be the physiological substrate of the mechanism underlying the luminance contrast perception of this new stimulus. |