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T. Rowan Candy, Thomas J. Baker, Anthony M. Norcia; Orientation tuning in the visual cortex of human infants. Journal of Vision 2008;8(6):423. doi: https://doi.org/10.1167/8.6.423.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Behavioral studies have determined that infants are sensitive to Gabor-patch contour configurations by 3 months of age (Baker, Tse, Gerhardstein, & Adler, in press; Gerhardstein, Kovács, Ditre, Feher, 2004). Completion of this task depends on the orientation tuning of cortical neurons and their interactions across space. The present study sought to determine the orientation tuning of neurons in primary visual cortex in human infants, using a nonlinear steady-state VEP paradigm. Methods: Three month-old infants and adults were presented with two overlapping 1cpd, 40% contrast spatial sinusoids, subtending 12 degs (Regan & Regan, 1987; Candy, Skoczenski & Norcia, 2001). One, the reference, counterphase reversed at 3.27 Hz, while the other was presented at 5.14 Hz at orientation offsets of 0, 3, 7, 10, 15 & 30 deg to the reference across conditions. A steady-state VEP was recorded from O1, Oz & O2 for 6, 21 sec trials in each condition. Results: The response amplitudes at the second harmonics of the stimulus frequencies and their intermodulation frequencies were derived, and normalized to the aligned, 0 deg offset, value. The amplitude of the reference second harmonic (6.54 Hz) remained above 80% of the aligned value at all orientation offsets in adults and infants, while the amplitude at the sum frequency (8.24 Hz) fell to less than 50% of the aligned value by 7 deg in adults and 15 deg in infants. Conclusions: The presence of an intermodulation response indicates processing of the two stimuli by a common nonlinear process. The decrease in intermodulation as a function of relative orientation suggests that the orientation tuning of neurons contributing to this population response is within a factor of two of the adult value by three months of age.
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