Processing visually degraded stimuli is a common experience. We struggle to find house keys on dim front porches, to decipher slides projected in overly bright seminar rooms, or to read poor photocopies. This research focuses specifically on stimuli that are degraded via reduction of stimulus contrast and addresses two questions. First, why is it difficult to process low-contrast compared to high-contrast stimuli? Second, is the effect of contrast fundamental in that its effect is independent of the stimulus being processed and the reason for processing the stimulus? We formally address and answer these questions within the context of a series of nested theories, each providing a successively stronger definition of what it means for contrast to affect perception and memory. To evaluate the theories, we carried out six experiments. Experiments 1 and 2 involved simple stimuli (randomly generated forms and digit strings) while Experiments 3-6 involved naturalistic pictures (faces, houses, and cityscapes). Stimuli were presented at two contrast levels at varying exposure durations. We conclude that contrast has what we term a "fundamental effect" which means that it affects processing at some stage prior to when the nature of the stimulus or the reason for processing it to begin with are determined.