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C. M. Anderson, C. L. Wu, K. R. Dobkins; Tuning of infant directional mechanisms. Journal of Vision 2001;1(3):23. doi: https://doi.org/10.1167/1.3.23.
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© ARVO (1962-2015); The Authors (2016-present)
Previous psychophysical studies in adults have shown that directionally selective mechanisms have a tuning bandwidth of approximately 60‖ (e.g., Levinson & Sekuler, 1976; Ball & Sekuler, 1979). To date, little is known about the tuning of directional mechanisms in infants. Recent evidence has shown that directions differing by 180 degrees are detected by independent mechanisms in infants (Dobkins & Teller, 1996), however, the issue of independence is unknown for directions differing by less than 180 degrees. In the present study, we investigated infant directional tuning by measuring contrast thresholds for two superimposed fields of dots moving either in the same or different directions. In 3-month-old infants, we used the FPL technique to obtain thresholds for three different angular differences between the two fields: 0 (both fields move in same direction), 90 degrees and 180 degrees. In adults, we used standard 2-AFC techniques to test six different angular differences: 0 degrees, 22.5 degrees, 45 degrees, 67.5 degrees, 90 degrees and 180 degrees. (Dot speed = 3.5 degrees/second, mean luminance = 20 cd/m2). For adults, contrast thresholds rose in comparison to the 0 degrees condition as the angular difference between the two moving dot fields increased, with a significant increase at 90 degrees (1.20-fold) and 180 degrees (1.12-fold). Thus, the tuning of directional mechanisms in our adult subjects is roughly in line with that reported in previous studies. In infants, we similarly found elevated thresholds for angular differences of both 90 degrees (1.29-fold) and 180 degrees (1.13-fold). Control experiments in adults tested with single moving dot fields showed that these effects could not be accounted for by directional anisotropies, since comparable thresholds were observed across different directions. In sum, these results suggest that directional tuning develops fairly quickly in infants.
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