An ANOVA, Sex of Participant (female versus male) × Age of Participant (6–7 months versus 9–10 months), revealed only a significant effect of sex, C646 mouse F(1, 44) = 18.25, p < .001, indicating that the mean novelty preference for males was reliably higher than

that for females. In addition, as shown in Table 2, t-tests comparing preference scores to 50% (chance responding) revealed that in both age groups, males preferred the mirror image significantly above chance, whereas as a group, females showed no preference. Examined from the perspective of individual infants, at 6–7 months of age, 10 of 12 males displayed novelty preference scores above 50%, p < .04, whereas only 5 of 12 females did so, p = .77. Similarly, at 9–10 months of age, 11 of 12 males displayed novelty preference scores above 50%, p < .01, whereas only 6 of 12 females did, p = 1.0. For the high throughput screening compounds two age groups combined, the proportion of infants preferring the mirror image was greater for males than females, Fisher’s exact test, p < .005. Both the group and individual data show that males, more strongly than females, generalized familiarization to the novel rotation of the familiar stimulus and preferred the novel mirror

image stimulus. Quinn and Liben (2008) familiarized 3- to 4-month-olds with varying rotations of the number one (or its mirror image) and then tested with a novel rotation of the familiar stimulus paired with its mirror image. Males were more likely to prefer selleck chemical the mirror image, whereas females were more likely to divide attention between the test stimuli. This performance difference suggested that a sex difference in mental rotation ability is present as early as 3 months of age (see also Moore & Johnson, 2008, 2011, for additional evidence that the difference is manifested in the initial months of life). In Experiment 1, we investigated an alternative explanation for the Quinn and Liben (2008) result, one in which the performance difference between females and males can

be attributed to females being more sensitive than males to the various rotations of the familiarized stimulus. The 3- to 4-month-olds in the current study were presented with a discrimination task in which each female and a corresponding male were tested with randomly selected familiarization and novel test rotations of the number one (or its mirror image) from the Quinn and Liben study. Both females and males discriminated between the different rotations at equivalent levels of above-chance performance. This finding suggests that the performance difference in the Quinn and Liben task is unlikely to be attributable to females being more sensitive to the angular rotations than males. In Experiment 2, we used the Quinn and Liben (2008) procedure to determine whether a sex difference in mental rotation is also present in 6- to 7-month-olds and 9- to 10-month-olds.