Retinal inhomogeneity I Spatiotemporal contrast sensitivity

Spatiotemporal sine-wave contrast thresholds were measured at four retinal eccentricities: 0 degrees, 3 degrees, 6 degrees, and 12 degrees. Threshold functions of spatial frequency were determined for each eccentricity at two selected temporal frequencies, and functions of temporal frequency at two selected spatial frequencies. Fixation was controlled by stabilizing the retinal image. The stimulus patterns were circular cosine targets confined to annular zones, so that stimulation occurred in all meridians simultaneously. In spite of these unusual conditions, our results were in good agreement with unstabilized, single-meridian data from other laboratories. The spatial-frequency functions obtained at both high and low flicker rates scaled with eccentricity in the same way. For the bandpass functions obtained at 0.5 Hz, the reciprocal of the peak spatial frequency varied linearly with eccentricity. Measured with spatial patterns chosen in accord with this scaling relation, both sets of temporal-frequency functions were essentially independent of eccentricity. Threshold functions at constant velocity were also consistent with the same scaling relation.