The Effect of context luminance on contrast perception

Pamir, Zahide
The present study has employed psychophysics and functional magnetic resonance imaging (fMRI) methodologies. The aim of the study is to investigate the role of bottom-up and top-down processing of luminance in contrast perception. In particular, since it is thought that visual illusions occur as a result of top-down processing by means of visual context, the present study investigates how luminance in context affects contrast perception by using brightness illusion. In other words, the purpose of the study is to understand whether physical or perceived properties of luminance dictate contrast perception. An illusory stimulus which was especially created for the present study was used in the experiments. Two psychophysical experiment series and one fMRI experiment series was conducted. In the first experimental series, brightness value of the illusory stimulus was measured with several methods and experimental designs to be sure that illusion is strong enough. In the second experiment series, contrast perception was measured by locating a rectified square-wave grating on the illusory stimulus. In the fMRI experiment series, neuronal correlates of psychophysical results were investigated. Results show that perceived properties of luminance has an effect on contrast perception. Furthermore, fMRI findings showed complicated results both favouring physical and perceptual properties in different conditions.


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Citation Formats
Z. Pamir, “The Effect of context luminance on contrast perception,” M.S. - Master of Science, Middle East Technical University, 2014.