Infant temporal contrast sensitivity functions (tCSFs) mature earlier for luminance than for chromatic stimuli: evidence for precocious magnocellulardevelopment?

In order to investigate the development of luminance and chromatic temporal contrast sensitivity functions (tCSFs), we obtained chromatic and luminanc e contrast thresholds from individual 3- and 4-month old infants, and compa red them to previously obtained functions in adults. Stimuli were moving si nusoidal gratings of 0.27 cyc/deg, presented at one of five temporal freque ncies: 1.0, 2.1, 4.2, 9.4 or 19 Hz (corresponding speeds: 3.8, 7.7, 15, 34, 69 deg/s). Previous studies, including our own, have shown that adult tCSF s are bandpass for luminance stimuli (peaking at 5-10 Hz), yet lowpass for chromatic stimuli (sensitivity falling at >2 Hz), and that the two function s cross one another near 4-5 Hz when plotted in terms of cone contrast. In the present study, we find that the shapes and peaks of the luminance tCSF in both 3- and 4-months-olds appear quite similar to those of adults. By co ntrast, chromatic tCSFs in infants are markedly different from those of adu lts. In agreement with our earlier report (Dobkins, K. R., Lia, B., & Telle r, D. Y. (1997). Vision Research, 37(19), 2699-2716), the chromatic functio n in 3-month-olds is rather flat, lacking the sharp high temporal frequency fall-off characteristic of the adult function. In addition, the luminance tCSF in 3-month-olds is elevated above the chromatic tCSF, and the two func tions do not exhibit an adult-like cross-over within the range of temporal frequencies tested. By 4 months of age, substantial development of chromati c contrast sensitivity takes place at the lowest temporal frequencies. Alth ough still immature, the 4-month-old chromatic tCSF has begun to adopt a mo re adult-like shape. In addition, similar to adults, luminance and chromati c tCSFs in 4-month-olds cross one another near 5 Hz. In adults, magnocellul ar (M) and parvocellular (P) pathways are thought to underlie the bandpass luminance and lowpass chromatic tCSF, respectively (e.g. Lee, B. B., Pokorn y, J., Smith, V. C., Martin, P. R., & Valberg, A. (1990). Journal of the Op tical Society of America (a), 7(12), 2223-2236). Based on this corresponden ce between psychophysical and neural responses in adults, our results sugge st that the relatively slow development of the chromatic tCSF in infants ma y reflect immature chromatic responses in the P pathway and/or reliance on chromatic responses originating in the M pathway. (C) 1999 Elsevier Science Ltd. All rights reserved.