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Monday Round-Up September 29, 2008

Posted by Emma Byrne in Uncategorized.
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Shape fast – colour slow: spotting changes in rival images

A study published in October’s Vision Research gives more detail about the way colour and orientation information are handled in the visual system [1].

Volunteers were presented with two different images – one to each eye. This results in binocular rivalry: only one of the images is seen at a time and perception flips between the two.

Sandra Veser from Leipzig university, together with colleagues from New Zealand and Cuba looked at the time it took 17 volunteers to spot a change in one of the images. When a change was made to the image that was currently being perceived, the difference was noticed straight away. Otherwise the switch was not seen.

The research team measured the changes in the volunteers’ brain activity (specifically, the event related potentials) when either the orientation or the colour of the bars changed. The response to a change in orientation happened about twice as fast (0.1 second) as the response to a change in colour (0.2sec).

Gene therapy to reduce retinal cell death

Gene therapy may one day help save the sight of patients with detached retinas, according to a study by Mong-Ping Shyong and colleagues in Taiwan [2].

Patients with retinal detachment may still lose their sight, even if the retina is reattached surgically. Previous research suggested that programmed cell death (apoptosis) may be responsible for this loss of vision.

The researchers tested a virus that was modified to express an the enzyme HO-1. This enzyme is known to reduce the rate of apoptosis. They injected the genetically modified virus beneath the retinas of rats with experimentally detached retinas. Compared to rats that had another virus injected into the retina, or that received no treatment at all, the rats treated with the HO-1 producing virus had more photoreceptors and a thicker outer layer of the retina 28 days after treatment.

The researchers suggest that gene therapy may one day lead to better recovery for patients after surgical reattachment of the retina.

Sound strengthens seeing

In a paper in October’s Acta Psychologica, Aleksander Väljamäe and Salvador Soto-Faraco report an experiment that shows that sound strengthens the visual perception of movement [3].

That sound and vision act together to give clues about motion has been known for a long time. The authors give the example of the sliding doors in the film The Empire Strikes Back, which were created using two stills (one of the door open, one of it closed) and a sound effect.

Väljamäe and Soto-Faraco used the motion after effect (similar to the waterfall illusion, where watching water cascade downwards for some time makes the rocks appear to move uphill) to study whether sound reinforces the perception of movement.

Volunteers watched short videos of several flashes in succession. Some of these flashes were made progressively bigger, some were made smaller, so that it looked like the light was approaching or receding. The researchers then measured the motion after effect to see how “strong” the perception of motion had been.

Some flashes were so far apart that they did not give the impression of movement by themselves. ut when they were accompanied by sounds that also seemed to be approaching or receding, the participants experienced motion after effect.

The researchers suggest that fewer frames per second might be needed in videos, as long as the sound effects are closely matched to the images. This could lead to much higher rates of data compression.

[1] S VESER, R OSHEA, E SCHROGER, N TRUJILLOBARRETO, U ROEBER (2008). Early correlates of visual awareness following orientation and colour rivalry Vision Research, 48 (22), 2359-2369 DOI: 10.1016/j.visres.2008.07.024

[2] M SHYONG, F LEE, W HEN, P KUO, A WU, H CHENG, S CHEN, T TUNG, Y TSAO (2008). Viral delivery of heme oxygenase-1 attenuates photoreceptor apoptosis in an experimental model of retinal detachment Vision Research, 48 (22), 2394-2402 DOI: 10.1016/j.visres.2008.07.017

[3]A VALJAMAE, S SOTOFARACO (2008). Filling-in visual motion with sounds Acta Psychologica, 129 (2), 249-254 DOI: 10.1016/j.actpsy.2008.08.004

Lighting in Relation to Public Health September 11, 2008

Posted by David Corney in Uncategorized.
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Browsing in the library just now, I just came across, and dipped into, a rather elderly book entitled “Lighting in Relation to Public Health” by Dr Janet Howell Clark, published in Baltimore by Williams and Wilkins Company, in 1924. The wonderful “old book” smell came at no extra cost. Something that caught my eye was from Chapter 8, Lighting in Schools. “If possible, unilateral light from the left should be used….” And for rooms that are too wide, “lighting from the left and rear being preferable to lighting from the right and left” (p.92).

Why light from the left? Again, a few pages later, there’s a section on “Lighting Legislation in schools” (p.99). Apparently, designs for new schools should be approved by the State Board of Education or some equivalent body, each state having their own legislation. Examples included, “Indiana: light from left only” and “Minnesota: Light from left, except in very large rooms. Light from east best, west next. North and South light to be avoided in regular study rooms.” Many other states are listed as requiring “light from left, or left and rear” in classrooms.

Why this idea about light coming from the left in schools? I couldn’t see any explanation given in the book, nor any mention of left-light for factories or the home. (Though it did suggest that kitchen lighting should be stronger than dining room lighting, so that crockery is “visibly” clean…) And this amongst plenty of sensible-seeming advice about natural vs artificial light, and the importance of sufficient light in the workplace and so on.

So my first thought was that the author was some crank, or being charitable, that this was some outdated idea that seemed perfectly reasonable in the 1920’s. Anyway, I did a quick google, and via “The Biographical Dictionary of Women in Science” found a little more about the author.

Dr Janet Howell Clark (1889-1969) gained a PhD in Physics from Johns Hopkins in 1913, having graduated from Bryn Mawr College, and was later made professor of biological sciences at the University of Rochester, and Dean of the Women’s College there. Some years later, this post was apparently downgraded from being equal to the Dean of Men, to being subordinate to it (in 1952) so she resigned and returned to Johns Hopkins, eventually retiring at 78.

She was an expert in the effect of radiation on eyesight and diseases caused by low or high levels of lighting (such as glassblowers and iron smelters). She investigated the use of ultraviolet light both as an antibiotic and to prevent rickets in children. She was also greatly concerned about women’s education in general, feeling it was a good thing, and was head of Bryn Mawr school for a number of years, in between various university teaching and research posts.

So clearly not a crank. But why light from the left?

So some more googling, and an explanation that I probably should have thought of myself. In “Electric Lighting” , one Olin Jerome Ferguson of the University of Nebraska, writing in 1920, pointed out that when writing at a desk, it’s helpful if the light doesn’t cast a shadow over your work. So if you’re right-handed, then light from the left would help. And Dr Clark had made it clear that light from the rear means that there’s less glare and excessive contrast for the blackboard at the front of the classroom. So it all makes sense, and I guess it’s so obvious to school designers that Dr Janet Clark didn’t feel the need to explain. My bad.

A final quote of Dr Clark from a chapter on Lighting in the Workplace:

“Cigar factories – Cigars are sorted in respect to color and the varieties of shades of brown are distinguished with difficulty if at all, under yellowish artificial light”

Couldn’t agree more!