The responses people give to stimuli depend on prior events. In psychophysical judgment tasks, responses are positively correlated with the just previous stimulus or response or feedback. Too, those responses are either positively or negatively correlated with earlier events in the sequence. Which occurs depends, predictably, on details of the experiment. It is suggested here that these independent variables (prior stimuli, prior responses, and prior feedback) are not the source of the observed sequential effects. Instead, these variables are all correlated with one another and all seem to reflect an underlying memory scale for prior events. It is suggested that the manner in which people use and maintain this memory scale produces the persistent sequential effects. A model based on this possibility, which requires two assumptions, is shown to account reasonably well for the various observed contextual effects.