The influence of stimulus salience on over-selective responding was investigated in the context of a comparator theory of over-selectivity. In Experiments 1 and 2, participants were presented with two cards, each displaying two colors. In comparison to matched control participants, participants with Autistic Spectrum Disorder (ASD) demonstrated more over-selectivity, which increased when the stimuli differed in salience. In Experiment 3, the over-selected color was extinguished, and the previously under-selected color emerged to control behavior. The results suggest that stimuli of different salience may trigger over-selectivity in individuals with ASD, and provide preliminary support that this may be due to the action of an over-sensitive comparator mechanism functioning at the retrieval level of processing.