Suprathreshold stereo-depth matches as a function of contrast and spatial frequency.

Area of Science:

• Visual perception
• Stereopsis
• Spatial frequency processing

Background:

• Stereoscopic depth perception is generally independent of spatial frequency at suprathreshold levels.
• However, at very low spatial frequencies (<0.5 cycles deg-1), perceived depth from crossed disparities decreases.
• The influence of contrast fading on this breakdown of depth invariance at low spatial frequencies was not well understood.

Purpose of the Study:

• To investigate the effects of contrast fading on stereoscopic depth perception at low spatial frequencies.
• To examine how spatial frequency and contrast interact to influence perceived depth and introduce biases.

Main Methods:

• Used spatially filtered vertical bars (difference of Gaussian functions) across a range of spatial frequencies (0.15-9.6 cycles deg-1).
• Adjusted physical contrast (10-100%) and disparity to match perceived depth to a standard.
• Investigated depth perception with pulsed presentations and matched perceived contrast.

Main Results:

• At low spatial frequencies, greater crossed disparity was needed to match perceived depth as contrast decreased.
• A depth bias towards the uncrossed direction was observed, particularly for low-contrast, low-spatial-frequency stimuli.
• This bias, perceived both monocularly and binocularly, was amplified by contrast reduction and was greater binocularly.

Conclusions:

• Contrast fading significantly alters perceived depth at low spatial frequencies, disrupting depth invariance.
• Reduced contrast enhances an uncrossed depth bias, which has both monocular and binocular components.
• These findings highlight the critical role of contrast in maintaining accurate stereoscopic depth perception, especially at lower spatial frequencies.