Abstract
A great deal of studies using different visual tasks (e.g., Vernier acuity tasks, tilt illusion, crowding, etc) have revealed that our perception is strongly influenced by the orientation of the stimulus. Most studies have investigated visual acuity in two-dimensional visual spaces (2D) but little is known about the effect of line orientation in depth perception (3D). In one experiment, Vernier Acuity (VA) in frontoparallel (2D) and medial (3D) planes was investigated. We used a virtual reality setup inducing inter-ocular disparities to simulate a 3D visual space, and a common computer screen to present stimuli in the frontal plane. In the experiment, by using the method of constant stimuli, the observer compared VA in the 2D and 3D visual spaces as a function of the stimulus orientation. Results showed that only judgments in the 3D condition were affected by the well-known 'oblique effect', and some impairment in stereoacuity (lines in depth plane) in comparison to 2D acuity (lines in frontal plane) was observed. We attributed the cause for such deterioration in stereoacuity to changes in vertical disparities.
Highlights
The visual system exhibits several anisotropies, and according to Campbell and Kulikowski (1966) and Maffei and Campbell (1970) such anisotropies have a neural basis
The observer was asked to perform 14 tests, which consisted of two visual conditions, namely, the 2D Vernier acuity and the 3D stereoacuity; in each one of them the lines were presented in seven different orientations
Notice that we use the percentage of constant error (%CE) with respect to the Point of Objective Equality (POE), in order to enable the comparison between the 2D and 3D visual conditions
Summary
The visual system exhibits several anisotropies, and according to Campbell and Kulikowski (1966) and Maffei and Campbell (1970) such anisotropies have a neural basis. One example of them is the inhomogeneous spatial resolution in the visual field (De Valois & De Valois, 1988) Another type of anisotropy is related to the perceived orientation of pictorial elements, such as lines, gratings, and edges. Studies with human beings on orientation of stimuli revealed the well-known oblique effect (see Appelle, 1972 and Howard, 1982 for a review). It refers to the well-established fact that our discriminability of orientation or direction is significantly better around the cardinal (horizontal or vertical) axes compared
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