Previous research has shown that decisions about odd numbers take longer than decisions about even numbers (the "odd efect"). It has also been shown that females are better at processing linguistic stimuli and males are better at processing spatial stimuli. In the present experiment, male and female subjects made odd versus even the classification judgments on numbers presented visually in three different formats: digits, number words, and dot patterns. Males showed longer decision times for odd numbers only when the numbers were presented in dot pattern format. Females showed this effect only when the stimuli were presented in the word format. These results suggest that differential speed of respose to odd and even numbers is found most strongly when the stimuli are presented in a format which is processing more efficiently by the subjects. This finding may imply that the effect is being produced by some higher order cognitive process, based on higher order representations that do not necessarily involve linguistic or verbal coding.