In a recent trip to San Francisco over spring break I was confronted with a common psychological problem, a problem of perception. While roaming the rolling hills of the iconic California city, it was hard to establish my bearings. Once reaching the summit of one hill, I looked to find a ridge to follow only to find a series of other large hills and troughs extended before me. The illusion of a horizon was all around me. This experience of an illusionary horizon can be explained through the use of the psychological perception principle of middle vision.
Middle vision is a proposed theory for visual processing following basic feature extraction and object recognition and contextual understanding. A large roll in middle vision is the perception of edges to determine objects. This leads right into another perceptual theory of figure and ground. Terminology indicative of Gestalt psychology, in which “the whole is greater than the sum of the parts”, a figure is the object which is distinguished from the surrounding ground. However, the two can be competing creating dual images depending upon the recognized figure versus ground.
Changes in horizon perception.
Along with object recognition, the Gestalt grouping rule of good continuation in which two elements will tend to group together if they lie on the same contour helps explain my difficulty distinguishing my horizon. Additionally, the city’s architecture and landmark structures created occlusion to the real contour of the city’s hills. When dealing with occlusion that disrupts perception like this the relatability, also known as the degree to which two line segments appear to be part of the same, is used to distinguish curvature.
Further examples of this perceptual problem can be discovered on the Internet through popular anti-gravity videos. These videos “show” a car that defies gravity and rolls up hill while in neutral without any source of energy or operation by a driver. Pop-culture frenzy circulated around these videos as they provide “evidence” against the Newtonian physics that our modern world is built on. Investigation into these videos by trained scientists however revealed the fundamental perception issue. The bottom of the hill that represented the ground was actually the top of the hill and the true horizon of the landscape providing the gravitational force. As stated in a recent Forbes article, “ the position of trees and slopes of nearby scenery, or a curvy horizon line, can blend to trick the eye so that what looks uphill is actually downhill,” thus creating an optical illusion by the landscape (1).
1. Berezow, Alex. "European Journalist Blame "Anti-Gravity" Spot on Magic, Not Physics." Forbes. 11 Nov 201311 Nov 2013: n. page. Web. <http://www.forbes.com/sites/alexberezow/2013/11/19/european-journalists-blame-anti-gravity-spot-on-magic-not-physics/>.
Photo Sources:
http://www.woohome.com/photograph/steep-hills-of-san-francisco
http://boingboing.net/2010/11/30/san-franciscos-steep.html
http://boingboing.net/2010/11/30/san-franciscos-steep.html
I lived in the Bay Area for a few years before I came to Penn State!
I still remember when I first went to SF, I was amazed by the hills and the crooked roads.
This is a remarkably common illusion found everywhere in the city. Trees, walls and cars leaning slightly instead of truly vertical. This creates an optical illusion, making the hill look like a slope.
Our visual cues play an important role in this situation, if the horizon cannot be seen or is not level, we may not be able to see the objects the right way that we expect to be vertical but that really are not. Standing on the hill in downtown SF, I was able to tell which tree is further away from me and which is nearer by the their sizes with the Gestalt principles’ figure and ground. The larger trees are likely to be the figure, closer to me, and the smaller trees appear to be in the background. Our sense of perspective tells us when we see the line of trees gets larger or smaller with distance away.