Archive for March 3rd, 2011

March 3, 2011

Bridget Riley

Movement in Squares

Bridget Riley (b. 1931) is an English painter who is one of the foremost proponents of op art. She was born in London and studied at the Royal College of Art, where her fellow students included artists Peter Blake and Frank Auerbach. Her early work was figurative with a semi-impressionist style. Around 1960 she began to develop her signature style consisting of black and white geometric patterns that explore the dynamism of sight and produce a disorienting effect on the eye.

They present a great variety of geometric forms that produce sensations of movement or color. Visually, these works relate to many concerns of the period: a perceived need for audience participation (this relates them to the ‘Happenings,’ for which the period is famous), challenges to the notion of the mind-body duality which led some people to experiment with hallucinogenic drugs; concerns with a tension between a scientific future which might be very beneficial or might lead to a nuclear war; and fears about the loss of genuine individual experience in a Brave New World.

March 3, 2011

C. Allan Gilbert


C. Allan Gilbert (1873 – 1929) was a prominent American illustrator. He is especially remembered for a widely published drawing (a memento mori) titled ‘All Is Vanity.’ The drawing employs a double image (or visual pun) in which the scene of a woman admiring herself in a mirror, when viewed from a distance, appears to be a human skull.

It is less widely known that Gilbert was an early contributor to animation, and a camouflage artist (or camoufleur) for the U.S. Shipping Board during World War I.

March 3, 2011

Motion Aftereffect


The motion after-effect is a visual illusion experienced after viewing a moving visual stimulus for a time (seconds to minutes) with stationary eyes, and then fixating a stationary stimulus. The stationary stimulus appears to move in the opposite direction to the original (physically moving) stimulus. The illusion is believed to be the result of motion adaptation.

For example, if one looks at a waterfall for about a minute and then looks at the stationary rocks at the side of the waterfall, these rocks appear to be moving upwards slightly. The illusory upwards movement is the motion aftereffect. This particular motion aftereffect is also known as the waterfall illusion. Another example can be seen when one looks at the center of a rotating spiral for several seconds. The spiral can exhibit outward or inward motion. When one then looks at any stationary pattern, it appears to be moving in the opposite direction. This form of the motion aftereffect is known as the spiral aftereffect.

March 3, 2011



An afterimage or ghost image is an optical illusion that refers to an image continuing to appear in one’s vision after the exposure to the original image has ceased. One of the most common afterimages is the bright glow that seems to float before one’s eyes after looking into a light source for a few seconds. The phenomenon of afterimages may be closely related to persistence of vision, which allows a rapid series of pictures to portray motion, which is the basis of animation and cinema.

Closing the eye can help achieve a better sense of the color in its own aspect. Afterimages come in two forms, negative (inverted) and positive (retaining original color). The process behind positive afterimages is unknown, though thought to be related to neural adaptation. On the other hand, negative afterimages are a retinal phenomenon and are well understood.

March 3, 2011

Illusory Contours

kanizsa triangle

ehrenstein illusion

Illusory contours or subjective contours are a form of visual illusion where contours are perceived without a luminance or color change across the contour. A classic example of illusory contours is the Kanizsa triangle. This figure comprises three black circles with equal wedges cut out of them facing the center point and three black angles on a white background.

But many observers see a white triangle on top of three black disks and an outline triangle. The white triangle appears brighter than the white background and shows a contour even in regions where there is no luminance change in the image. The Ehrenstein illusion is another common form of illusory contours. It is thought that early visual cortical regions such as V2 are responsible for forming illusory contours.

March 3, 2011

Illusory Motion


The term illusory motion is used to define the appearance of movement in a static image. This is an optical illusion in which a static image appears to be moving due to the cognitive effects of interacting color contrasts and shape position.

Another type of motion illusion that causes an optical illusion is when a moving object appears to be moving in a path other than what is perceived by the brain. An example of this can be demonstrated by placing a colored filter over ones eye of the observer, and swinging a ball back and forth in front of them. To the observer the ball appears to be swinging in a circular motion.

March 3, 2011

Zöllner Illusion

The Zöllner illusion is a classic optical illusion named after its discoverer, German astrophysicist Johann Karl Friedrich Zöllner. In 1860, Zöllner sent his discovery in a letter to physicist and scholar Johann Christian Poggendorff, who subsequently discovered the related Poggendorff illusion, in the original drawing by Zöllner. In the illusion the black lines seem to be unparallel, but in reality they are parallel. The shorter lines are on an angle to the longer lines. This angle helps to create the impression that one end of the longer lines is nearer to us than the other end.

This is very similar to the way the Wundt illusion appears. It is also is similar to the Hering illusion and the Müller-Lyer illusion. All these illusions demonstrate how lines can seem to be distorted by their background.

March 3, 2011

Optical Illusion

same color illusion

An optical illusion is characterized by visually perceived images that differ from objective reality. An illusion is different from a hallucination; a hallucination is sensing something which is not real, but an illusion is interpreting what we sense wrongly.

The information gathered by the eye is processed in the brain to give a percept that does not tally with a physical measurement of the stimulus source. There are three main types: literal optical illusions that create images that are different from the objects that make them, physiological ones that are the effects on the eyes and brain of excessive stimulation of a specific type (brightness, tilt, color, movement), and cognitive illusions where the eye and brain make unconscious inferences.

March 3, 2011

Seattle Hempfest


Seattle Hempfest is an annual event in Seattle, Washington, the world’s largest annual gathering advocating decriminalization of marijuana. Founded in 1991 as the Washington Hemp Expo (attended by 500 people), it has grown into a 2-day annual political rally, concert, and arts and crafts fair with attendance typically over 250,000. Speakers have included Seattle city council member Nick Licata, actor/activist Woody Harrelson, travel writer and TV host Rick Steves, and former chief of the Seattle Police Department Norm Stamper.

Sixty people were cited for illegal marijuana use at the 1997 Hempfest, and about twenty were arrested the following year. Eventually Hempfest and the police reached a modus vivendi: there was only one arrest in 2001. The political context surrounding marijuana in Seattle and Washington has changed considerably over the years. Washington legalized medical marijuana in 1998. In 2003, Seattle passed an initiative that made adult personal use marijuana offenses the city’s lowest law enforcement priority.

March 3, 2011



The National Organization for the Reform of Marijuana Laws (NORML) is an American non-profit organization based in Washington, DC whose aim is to move public opinion sufficiently to achieve the legalization of non-medical marijuana in the United States so that the responsible use of cannabis by adults is no longer subject to penalty.

The organization was founded in 1970 by Keith Stroup, funded by $5,000 from the Playboy Foundation. Since then, it has played a central role in the cannabis decriminalization movement.

read more »

March 3, 2011

Coronal Mass Ejection


A coronal mass ejection (CME) is a massive burst of solar wind, plasma, and magnetic fields rising above the solar corona or being released into space. CMEs are often associated with other forms of solar activity, most notably solar flares, but a causal relationship has not been established. Most ejections originate from active regions on Sun’s surface, such as groupings of sunspots associated with frequent flares.

March 3, 2011

Solar Prominence


A prominence is a large, bright feature extending outward from the Sun’s surface, often in a loop shape. Prominences are anchored to the Sun’s surface and extend outwards into the Sun’s corona. While the corona consists of extremely hot ionized gases, known as plasma, which do not emit much visible light, prominences contain much cooler plasma. A prominence forms over timescales of about a day, and stable prominences may persist in the corona for several months. Some prominences break apart and give rise to coronal mass ejections.

A typical prominence extends over many thousands of kilometers; the largest on record was observed by the Solar and Heliospheric Observatory (SOHO) in 2010 and is estimated at over 700,000 kilometres (430,000 mi) long – roughly the radius of the Sun.