Extra-retinal and perspective cues cause the small range of the induced effect

Area of Science:

• Visual perception
• Stereopsis
• Geometric optics

Background:

• A horizontal magnifier induces a geometric effect where a surface appears rotated.
• A vertical magnifier induces an opposite effect, requiring surface rotation to restore frontoparallelism.
• The induced effect is significant as vertical disparities were previously underestimated in surface perception.

Purpose of the Study:

• To investigate the underlying mechanisms of the induced effect in visual surface perception.
• To explain the plateau observed in the induced effect at higher magnifications.
• To elucidate the roles of retinal and extra-retinal signals in slant perception.

Main Methods:

• Participants viewed a frontoparallel surface with a vertical magnifier before one eye.
• The required surface rotation to perceive frontoparallelism was measured at varying magnifications.
• Perspective cues were manipulated, and eye position sense was considered.

Main Results:

• The induced effect showed a linear increase up to 4% magnification, followed by a plateau around 8%.
• The plateau was demonstrated to result from the integration of diverse slant estimates from different visual cues.
• When perspective cues were minimized or eye position sense aligned with vertical size ratios (VSRs), the induced and geometric effects showed similar magnitudes.

Conclusions:

• Vertical size ratios (VSRs) play a crucial role in compensating for horizontal size ratio (HSR) changes during eccentric gaze, influencing perceived slant.
• The plateau in the induced effect is attributed to the brain's use of multiple, sometimes conflicting, visual signals for slant estimation.
• Understanding these visual cues enhances our knowledge of how the brain constructs 3D surface perception from 2D retinal input.