An averaging meter cannot distinguish between a subject of uniform luminance and one that consists of light and dark elements.
2.
These authors presented observers in an fMRI scan with simultaneous contrast stimuli composed of a central circle of uniform luminance and a peripheral region whose luminance was modulated in time ( and also tested other conditions where the modulated and the constant regions were inverted ).
3.
:: The candela is indeed a measure of the intensity of the source ( and not directly comparable to luminance measures ), but the stimulus in the paper is characterized by its luminance given as candela per square metre, which should be comparable to other per-unit-area measures ( the paper used a Ganzfeld-type stimulus, which is basically a surface illuminated such that it has uniform luminance, which is why the surface is characterized by a luminance measure rather than one of luminous intensity ).
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