This paper discusses three studies which examined the interaction of dimensional dominance with the attentional components of alertness and encoding. In Study I, twenty 6- and 7-year-olds observed thirty 3-second exposures of a color, then participated in a 40-trial choice reaction time task in which the familiarized color and a novel color served as warning signals. Results supported the hypothesis that the stimulus familiarization effect (familiar stimuli elicit slower responses than do novel stimuli) is a result of a decrease in the alerting value of that stimulus. In Study II, 20 first graders were familiarized to a color and then given 40 choice reaction time trials in which the familiar color and novel color served as response cues. An unrelated warning signal was also used just prior to each response cue to insure maximum alertness, regardless of the stimulus that followed. Results showed that a positive encoding effect could be observed when the alertness decrement was by-passed. In Study III, 22 kindergarteners were familiarized to a colored shape and were then given 36 straight reaction time trials with one of two shapes of one of two colors. A color-form preference test was also given to determine dimensional dominance. The results indicated that the familiarized stimulus was responded to more slowly than the completely different stimulus and that response speeds to partially different stimuli varied as a function of dimensional dominance. Findings from these studies are discussed in terms of the relationship between perception and cognition. (JMB)