Abstract

Peripheral contrast thresholds have been measured in many stimulus conditions, and the effect of the cortical magnification factor on sine wave grating detection thresholds is well known. Very little, however, has been done to determine the behavior of suprathreshold contrast perception in the periphery. In the experiments described here, perceived contrast functions were determined for 2° sine wave grating patches of 2,4, 8, and 16 cycles-/deg at the fovea and at four peripheral locations using the method of magnitude estimation. The peripheral locations were distributed over the range of eccentricities for which each stimulus was visible (e.g., 0-40° at 4 cycles/deg and 0-10° at 16 cycles/deg). Experimental results demonstrate two main points: (1) When perceived contrast values at a given spatial frequency are combined across eccentricities, the data are well fitted (R² ≃ 0.9) by a single power function of contrast minus threshold with an exponent near 0.5. This same equation describes the data, at all spatial frequencies studied, implying that similar mechanisms mediate contrast perception in fovea and periphery at both low and high spatial frequencies. (2) While suprathreshold behavior of the 2° grating patches remains remarkably uniform in the fovea and periphery, thresholds increase dramatically with eccentricity. This implies that contrast perception and contrast detection may be mediated by different mechanisms.

© 1985 Optical Society of America