Visual transient phenomenon: its polarity and a paradox.

Luminance stimuli modulated at frequencies above flicker fusion create perceptible visual transient responses when the frequency is changed abruptly. The polarity of these transients, as directly perceived and objectively confirmed, is shown enough by itself to yield a powerful criterion for visual models. An apparent paradox when light flashes are superposed on the frequency discontinuity has further implications for models and suggests a possible non-conservation of polarity in the brightness perception process.