ResearchBlogging.org

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

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