Optical implementation of a three-dimensional (3-D) Fourier transform is proposed and demonstrated. A spatial 3-D object, as seen from the paraxial zone, is transformed to the 3-D spatial frequency space. Based on the new procedure, a 3-D joint transform correlator is described that is capable of recognizing targets in the 3-D space.

We study the reaction time (RT) to the appearance of a stimulus composed of a sinusoidal grating of spatial frequency. Five subjects participated in the experiment: 3 young emmetropic subjects, an older presbyopic subject (with optic corrections) and an albino subject (M). The data show that the RT varies according to the product of contrast (C) by the period (P) of the gratings. The CxP is the...

It is a matter of common sense that a person is easier to recognize when close than when far away. A possible explanation for why this happens begins with two observations. First, the human visual system, like many image-processing devices, can be viewed as a spatial filter that passes higher spatial frequencies, expressed in terms of cycles/degree, progressively more poorly. Second, as a face ...

Humans can recognize a complex natural scene even when it appears only briefly. The rapid recognition of natural scenes is accomplished by parallel processing of information based on multiple spatial frequencies and integration of this information. Previous studies have revealed the time course of integration of frequency-based information. However, it is still unclear how frequency-based infor...

Timing is critical for the effectiveness of a modulating surround signal. In this study, the optimal timing of a suppressing surround signal was measured psychophysically in human subjects. The perceived contrast of a fixated 1-deg circular patch of vertical sinusoidal grating (the target: 4 cpd, Michelson contrast 0.2) was measured as a function of the onset asynchrony between the target and a...

The type of visual information needed for categorizing faces and nonface objects was investigated by manipulating spatial frequency scales available in the image during a category verification task addressing basic and subordinate levels. Spatial filtering had opposite effects on faces and airplanes that were modulated by categorization level. The absence of low frequencies impaired the categor...

We study induced modulation instability in a nematic liquid crystal cell. Two broad elliptical beams along one direction are launched into the cell. The two beams have slightly different angle in order to create a sinusoidally varying intensity at the entrance of the cell. In this way, the gain of perturbations with different spatial frequency is investigated. The evolution of the optical patte...

Motion-defined contours are ecologically important cues to object boundaries in complex fields of optic flow. We designed a novel stimulus in which the velocities of randomly positioned dots are defined by a 2D Gabor function, resulting in a motion-defined pattern with a clear orientation. We found that the number of correct responses in a vertical/horizontal orientation discrimination task inc...

The ability of younger and older adults to perceive the 3-D shape, depth, and curvature of smooth surfaces defined by differential motion and binocular disparity was evaluated in six experiments. The number of points defining the surfaces and their spatial and temporal correspondences were manipulated. For stereoscopic sinusoidal surfaces, the spatial frequency of the corrugations was also vari...