Early astigmatism contributes to the oblique effect and creates its Chinese-Caucasian difference.

The Oppel–Kundt Illusion and Its Relation to Horizontal-Vertical and Oblique Effects

Perception ◽

10.1177/03010066211006545 ◽

2021 ◽

pp. 030100662110065

Author(s):

Klaus Landwehr

Keyword(s):

Oblique Effect ◽

The Other ◽

Vertical Orientation ◽

Horizontal Orientation ◽

Full Circle ◽

Original Stimulus ◽

Vertical Part

The Oppel–Kundt illusion consists in the overestimation of the length of filled versus empty extents. Two experiments explored its relation to the horizontal-vertical illusion, which consists in the overestimation of the length of vertical versus horizontal extents, and to the oblique effect, which consists in poorer discriminative sensitivity for obliquely as opposed to horizontally or vertically oriented stimuli. For Experiment 1, Kundt’s (1863) original stimulus was rotated in steps of 45° full circle around 360°. For Experiment 2, one part of the stimulus remained at a horizontal or vertical orientation, whereas the other part was tilted 45° or 90°. The Oppel–Kundt illusion was at its maximum at a horizontal orientation of the stimulus. The illusion was strongly attenuated with L-type figures when the vertical part was empty, but not enhanced when this part was filled, suggesting that the horizontal-vertical illusion only acts on nontextured extents. There was no oblique effect.

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“Motor Oblique Effect”: Perceptual Direction Discrimination and Pointing to Memorized Visual Targets Share the Same Preference for Cardinal Orientations

Journal of Neurophysiology ◽

10.1152/jn.00515.2006 ◽

2007 ◽

Vol 97 (2) ◽

pp. 1068-1077 ◽

Cited By ~ 16

Author(s):

Nikolaos Smyrnis ◽

Asimakis Mantas ◽

Ioannis Evdokimidis

Keyword(s):

Visual Target ◽

Motor Task ◽

Oblique Effect ◽

Quadratic Function ◽

Initial Direction ◽

Direction Discrimination ◽

Pointing Movements ◽

Equivalent Measure ◽

Visual Targets ◽

Target Locations

In previous studies we observed a pattern of systematic directional errors when humans pointed to memorized visual target locations in two-dimensional (2-D) space. This directional error was also observed in the initial direction of slow movements toward visual targets or movements to kinesthetically defined targets in 2-D space. In this study we used a perceptual experiment where subjects decide whether an arrow points in the direction of a visual target in 2-D space and observed a systematic distortion in direction discrimination known as the “oblique effect.” More specifically, direction discrimination was better for cardinal directions than for oblique. We then used an equivalent measure of direction discrimination in a task where subjects pointed to memorized visual target locations and showed the presence of a motor oblique effect. We finally modeled the oblique effect in the perceptual and motor task using a quadratic function. The model successfully predicted the observed direction discrimination differences in both tasks and, furthermore, the parameter of the model that was related to the shape of the function was not different between the motor and the perceptual tasks. We conclude that a similarly distorted representation of target direction is present for memorized pointing movements and perceptual direction discrimination.

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