Ho, YX, Mahon, K, & Carrasco,
M (2003). Developmental course of performance fields with familiar stimuli.
Vision Sciences Society. Sarasota, FL.
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.