Participants were 48 infants, 24 6- to 7-month-olds (12 females) and 24 9- to 10-month-olds (12 females). For the 6- to 7-month-olds, mean age of the females was 193.83 days, SD = 16.99, and mean age of the males
was 186.08 days, SD = 12.56, a difference that was not see more significant, t(22) = 1.27, p > .20, two-tailed. Likewise, for the 9- to 10-month-olds, mean age of the females was 280.58 days, SD = 13.03, and mean age of the males was 277.25 days, SD = 8.74, a difference that was again not reliable, t(22) = 0.73, p > .20, two-tailed. Three additional 6- to 7-month-olds were tested (one female), but one did not complete the procedure due to fussiness and two were excluded from analyses because of failure to compare the test stimuli. Two additional 9- to 10-month-olds were tested (both female), but one did not complete
the procedure due to fussiness, and the other was excluded from analyses because of side preference. Familiarization included seven 15-s familiarization trials, Bcr-Abl inhibitor each presenting the number 1 (or its mirror image) in a different degree of rotation. Two identical copies of each stimulus were presented on each trial. The seven values of rotation and their order of presentation were randomly chosen for each female and a corresponding male participant. There were two 10-s preference test trials, each of which paired the rotation of the number 1 (or its mirror image) not experienced during familiarization with its mirror image. Left-right positioning of the two test stimuli was counterbalanced across both females and males on the first test trial and reversed on the second test trial. Interobserver agreement was calculated for the preference test trials of six infants (three female) in each
age group. Average level of agreement was 98.48% (SD = 0.71) for the 6- to 7-month-olds, Acetophenone and 97.60% (SD = 2.19) for the 9- to 10-month-olds. As in Experiment 1, preliminary analyses indicated that left versus right orientation of the familiar stimulus (i.e., number 1 versus mirror image) did not impact looking time during familiarization or novelty preference for either gender. Individual looking times were summed over left and right copies of the stimulus presented on each trial and then averaged across the first three trials and last three trials. Mean looking times are shown in Table 2. An analysis of variance (ANOVA), Sex of Participant (female versus male), Age of Participant (6–7 months versus 9–10 months) × Trial Block (1–3 versus 5–7), performed on the looking times revealed only a significant effect of trial block, F(1, 44) = 4.96, p < .03. The trial block effect indicates that infants displayed a reliable decrement in looking time from the first to last half of familiarization that is consistent with the presence of habituation (Cohen & Gelber, 1975). Each infant’s looking time to the mirror image stimulus was divided by looking time to both test stimuli and converted to a percentage score.