Theories that ascribe the congruity effect in mental comparisons to an encoding stage predict an interaction of congruity with stimulus quality.  In Experiments 1 through 7, stimuli were degraded by being combined with dot masks of varying densities.  Experiments 1, 6, and 7 examined potential effects of attentional load on degraded and intact finite-set stimuli;  Experiments 2-5 examined attentional load and stimulus quality effects in an infinite-set paradigm.  Experiment 8 allowed a comparison of dot with luminosity degradation to assess potential cascade-model interpretations of additivity of dot degradation with congruity.  Effective manipulations of stimulus quality in these experiments were additive with congruity, regardless of attentional load.  Thus, within the framework of either a cascade model or a discrete stage model, congruity appears to involve processes separate from encoding.