page_title: Oblique effect
section_title: The phenomenon
hierarchical_section_title: Oblique effect / The phenomenon
caption_attribution_description: English: For orientations around the clock, discrimination of the length of a line is the same, but discrimination of orientation is worse for oblique than horizontal or vertical
context_page_description: Oblique effect is the name given to the relative deficiency in perceptual performance for oblique contours as compared to the performance for horizontal or vertical contours.
context_section_description: The effect is exhibited predominantly in tasks involving discrimination of the angle of tilt of patterns or contours.  People are very good at detecting whether a picture is hung vertical, but are two- to fourfold worse for a 45-degree oblique contour, even when a comparison is available. However there is no oblique deficit in some other tasks, such as judgment of lengths.  Similarly, while it is harder to judge the direction of motion when it is oblique, this is not the case for speed.
  The figure on the right shows the performance when an observer makes judgments about the length (top) and the orientation (bottom)of a line, in eight orientations around the clock.
  Even the immediate appearance of the form of a figure, often called gestalt, changes on a 45-degree rotation—the geometrical congruity of the square and the diamond does not extend to their perception as figures (see left) as was emphasized by Ernst Mach.
caption: Discrimination of length (top) and orientation (bottom) for a line at various orientations around the clock
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