Abstract
We investigated the effects of reference frame on the perception of stimulus orientation in infancy. The human-body figure was used as the stimulus, because the human-body is an ecologically important stimulus. This result was compared with the results of previous studies using a grating as the stimulus (Jouen, 1985; Tsuruhara et al. 2007). We used the preferential looking technique. The stimuli were vertical and oblique human-body silhouette. The infants' looking times for each stimulus were measured. In Experiment 1, only human-body figures were presented. In Experiment 2, each human-body figure was surrounded by a vertical square, and in Experiment 3, the surrounding square was oblique. Additionally, control experiments were conducted. In the control experiments, the stimuli in each experiments were inverted. These inverted human-body figures didn't seem to be human-bodies. The results showed that, in Experiment 2 and 3, the results using the human-body figure were similar to the previous results using a grating stimulus. Vertical surrounding squares induced the preference to the oblique human-body figure and the grating over the vertical human-body figure and the grating. Oblique surrounding squares induced no preference. In the control experiments, the inverted human-body figure produced the same results. On the other hand, in Experiment 1, the results using the human-body figure differed from the previous results using a grating stimulus. Previous studies showed that infants preferred the vertical grating over the oblique grating. By contrast, in our experiment, infants preferred the oblique human-body figure over the vertical human-body figure. In the control experiments, the inverted human-body figure produced no preference. The results of this study suggest that, in infancy, the perception of human-body orientation differs from the perception of grating orientation, although the reference frame have the similar effects on these two stimuli.
This study was supported by PRESTO, JST and a Grant-in-Aid for scientific research(18000090) from JSPS.