Slope illusion
Outdoor tilt illusion where an ascending slope appears to descend or a descending slope appear to ascend
Call for pictures of the slope illusion
e.g. Magnetic Hill in Canada; Wikipedia
since August 30, 2004
"Antigravity hill illusion in Yashima"
The nearer slope appears to descend, though it ascends actually. This antigravity hill illusion (gravity hill illusion, magnetic hill illusion or spook hill illusion) can be observed in the Yashima Drive Way, Mt. Yashima, Takamatsu City, Japan.
Copyright Akiyoshi Kitaoka 2008 (May 7)
Photos taken on May 6, 2008
References
Seiichi's slope illusion pages
Bressan, P., Garlaschelli, L. and Barracano, M. (2003) Antigravity hills are visual illusions. Psychological Science, 14, 441-449.
Imai, S. (1971) Visual illusion of vertical gradient of road. Journal of Social Science and Humanities (Tokyo Metropolitan University), 83, 13-28 (in Japanese).
When viewed from upside, the farther slope appears to ascend slightly, though it actually descend.
For the observed values and some explanation, see "Visual illusions"published by Newton Press (pp. 138-139).
@
@An explanation of the antigravity hill illusion by Akiyoshi
<May 10, 2008>
It might be an important factor whether the vanishing point of a road is above or below the perceived horizontal.
The road appears to ascend in the left panel, while it appears to descend in the right one.
Copyright Akiyoshi Kitaoka 2008 (May 12)
The nearer slope appears to descend in the left panel, while it appears to ascend in the right one.
Copyright Akiyoshi Kitaoka 2008 (May 12)
Moreover, at a road of concave shape as shown above, if there are no more
cues, the nearer slope might tend to be perceived as a descending slope
while the farther one as an ascending slope.On the other hand, at a road
of convex shape as shown below, if there are no more cues, the nearer slope
might tend to be perceived as an ascending slope while the farther one
as a descending slope.
Someone might have already proposed these explanations. If so, let me know.
"Skewed staircase illusion in Shigaraki"
The steps of this staircase appear to tilt in the gravity direction.
Copyright Akiyoshi Kitaoka 2008 (April 21)
"Antigravity hill illusion near the Kyoto International Conference Center"
This slope physically ascends, while it appears to descend sometimes.
Copyright Akiyoshi Kitaoka 2004 (August 30)
When we turn back, the slope appears to descend as it does (the picture
shown below).
The homepage of a researcher of the slope illusion (Seiichi Tsuinashi's page)
Thanks to Dave <May 12, 2008>