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Bin Zhang, Ye Wang, Xiaofeng Tao, Guofu Shen, Earl L Smith, Izumi Ohzawa, Yuzo M Chino; Adultlike Sensitivity to Curvatures of V2 Neurons in Infant Monkeys. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3825.
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© ARVO (1962-2015); The Authors (2016-present)
Non-human primates can discriminate texture-defined form as early as 6–8 weeks of age despite their relatively low visual acuity. The neuronal mechanisms underlying this remarkable visual capacity have not been extensively studied. Based on the findings that the receptive-field subunits of V2 neurons is as complex as in adults and the ability of V2 neurons to compare local features of neighboring stimulus elements is nearly adult like, our previous study implied that V2 neurons in infant monkeys could encode angles or curvatures. In this study we tested this idea more directly by using two-dimensional dynamic noise stimuli and a new analytical method called “Transform Domain Reverse Correlation (TDRC)”.
Unit recordings were made in V2 of anesthetized infant macaque monkeys (4 and 8weeks) and adult monkeys. In TDRC analysis, two neighboring regions in the 2D noises are filtered by Gaussian windows and transformed into the spatial frequency domain. For each region, the amplitude spectra within certain frequency band was integrated along all orientations, and the joint distribution of orientations of the two regions were computed as the product the amplitudes for all pairs of orientations. A further coordinate transformation mapped the data from the double orientation domain into the curvature-direction domain. Finally, the spike-triggered analysis is performed between the spikes and transformed stimuli in curvature-direction domain. The resulting map reveals the stimulus selectivity of individual neurons for angled or curved contours.
As early as 4 weeks of age, about 40% of V2 neurons in non-human primates were sensitive to angled or curved contours in image sub-regions. The percentage of neurons that were sensitive to curvatures was similar in infants and adults. Moreover, there was no bias in optimal curvature direction in any age groups. The optimal curvature tuning width, the signal strength, and reliability (Zmax) for infant neurons were not significantly different from that for adults. Only the variance of curvatures of subunits for infant monkeys was lower in infants than in adults.
Our results provide a physiological substrate for the aforementioned perceptual finding that infant monkeys are capable of discriminating texture-defined visual borders as early as 6 weeks of age.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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