Abstract
We know that adults' contrast sensitivity and spatial resolution are better along the horizontal than vertical meridian -a.k.a. horizontal vertical anisotropy (HVA)- and better in the lower than upper vertical meridian -a.k.a. vertical meridian asymmetry (VMA; Carrasco et al., Spatial Vision 2000, JOV 2002). We also know that for adults the speed of information accrual follows the same pattern, i.e. it is faster along the horizontal meridian and slowest at the North locations (Carrasco et al., VSS 2002). In this study, we investigated the developmental course of these asymmetries with children ages 5–12, by using stimuli of different levels of familiarity, such as shapes, letters and numbers.
We used a 4AFC character identification task to determine the presence and extent of the HVA and VMA. Each trial consisted of a central fixation point followed by a 1 stimulus, presented for 50 ms. The stimulus appeared at one of 10 possible eccentricities, ranging from 4 to 13 , along each of the 8 principal meridians. The brief display duration precluded eye movements, allowing us to equate field and retinal eccentricities.
Results indicate that the HVA was present at all ages for all stimuli tested. Anatomical and physiological findings in macaque monkey provide a possible neural correlate for the visual constraints underlying the HVA. Surprisingly, the VMA did not emerge consistently in either adults or children for the different stimuli tested. This finding suggests that the visual constraints underlying the VMA reported before may play less of a role in our identification of more familiar stimuli. Studying the developmental course of visual field asymmetries helps elucidate the role that the environment plays in perceptual performance, and may have implications for human factors.