Previous research (Andersen, 1989) has suggested that the recovery of 3-Dshape from nonsmooth optic flow (motion transparency) can be performed by segregating surfaces according to the distributions of velocities present in the flow field. Five experiments were conducted to examine this hypothesis in a surface detection paradigm and to determine the limitations of human observers to detect 3-D surfaces in the presence of noise. Two display types were examined: a flow field that simulated a surface corrugated in depth and a flow field that simulated a random volume. In addition, two types of noise were examined: a distribution of noise velocities that overlapped or did not overlap the velocity distribution that defined the surface. Corrugation frequency and surface density were also examined. Detection performance increased with decreasing corrugation frequency, decreasing noise density, and decreasing surface density. Overall, the subjects demonstrated remarkable tolerance to the presence of noise and, for some conditions, could discriminate surface from random conditions when noise density was twice the surface density. Discrimination accuracy was greater for the nonoverlapping than for the overlapping noise, providing support for an analysis based on the distribution of velocities.Optic flow, the perspective transformation of visible feature points during motion of the observer or objects in the environment, can be a useful source of information for the the recovery of 3-D shape and the layout of a scene (Gibson, 1950(Gibson, , 1966 Helmholtz, 1867/1%2; von Kries, 1910 von Kries, /1962. Considerable research has examined the ability of human observers to recover the shape and depth of objects in a scene from optic flow. Studies have demonstrated the effectiveness of optic flow in providing the curvature and shape of a surface (Cornilleau-Peres & Drou1ez, 1989;Eby, 1992;Norman & Lappin, 1992;Rogers & Graham, 1979;Todd, 1984), the orientation in depth of a surface (Braunstein & Andersen, 1981), the slant of a surface (Braunstein & Payne, 1969), and the depth order and relative depth between surfaces (Andersen, 1989).An important assumption in this research is that sufficient information is present in the display for the perception of a surface. Although considerable research has examined the minimal conditions for the perception of a surface from binocular disparity (e.g., Uttal, 1975Uttal, , 1983Uttal, , 1985Uttal, , 1987Uttal, , 1988Uttal, Davis, Welke, & Kakarala, 1988), there has been relatively little research examining the minimal conditions for surface detection from optic flow. In a recent study examining the minimal conditions This research was supported by National Science Foundation Grant BNS 9021081. The authors would like to thank Myron L. Braunstein, Jan Koenderink, and Jim Todd for comments on an earlier draft. We would also like to thank Myron L. Braunstein for beneficial discussions regarding the design of Experiment 5. Reprint requests should be sent to G. J. Andersen, Department of Psychol...