Abstract
In some phenomena of visual perception, the motion direction of visual stimuli can affect perception. In particular, asymmetries between oblique directions and cardinal (horizontal and vertical) directions have been reported and are known as oblique effects (e.g., contrast sensitivity and motion threshold). In this study, we investigated how vection strength depends on motion direction. Participants observed random-dot optical flow in a circular field and rated the perceived vection strength. Dot movement was systematically controlled using the following angles: 0° (up), 30°, 45°, 60°, 90°, 120°, 135°, 150°, and 180° (down). We found that vection strength depended on motion direction and was weaker in the oblique directions than cardinal directions. Thus, the effect of motion direction on vection strength was variable, as seen in the shape of the oblique effect.
Highlights
Stationary observers perceive self-motion when a moving visual stimulus is presented in their visual fields
We investigated whether the effect of motion direction on vection is caused by the intensity of the motion signal (Experiment 2)
We examined the effect of motion direction on vection strength
Summary
Stationary observers perceive self-motion when a moving visual stimulus is presented in their visual fields. This illusory self-motion is termed vection, and the visual stimuli are termed optical flow. For vection, the direction of gravity is an important factor. Several studies have shown that vection is closely related to and depends on the posture of the observer in relation to the direction of gravity, such as sitting, lying down (Kano, 1991), tilting (Nakamura & Shimojo, 1998), upside down, or right side up (Mori & Seno, 2017). We investigated the effect of motion direction on vection
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