Stereoscopic Stimuli

To produce stereopsis it is necessary to generate two images and present them separately to each eye. This can be achieved with a single monitor by interleaving images for the left and right eye in alternate frames. Shutters are used to block alternate eyes in synchrony with these frames, so that each eye sees only one of the interleaved images.

Although the principle appears simple, when designing such a system you should consider:

• Crosstalk
• Frame rate
• Luminance

Crosstalk is the effect where one image will persist into the next. Consequently the shutters should switch from open to close, and the phosphor decay completely during the monitor's frame blanking period.

When interleaving two images, the effective frame rate of each presentation is halved. Therefore the monitor should have a high refresh rate to remove visible flicker.

To maximise the transmitted luminance when open but minimise when closed, the shutters should have both a high open shutter transmission and a large open:close contrast ratio. And since some light is always adsorbed in the shutters, a high luminance display is an advantage.

FE-1 Goggles

Our FE-1 shutter goggle design utilises ferroelectric liquid crystal (FLC) technology from DisplayTech. This provides:

• 100 µs switching times
• 3-log unit contrast ratio
• 25% open shutter transmission

The performance of LCD-type shutters, particularly the closed state transmission, is affected by temperature. Our shutters are specially manufactured by DisplayTech to operate at 24°C for optimum performance. Most off-the-shelf FLC devices are quite small. Therefore our custom shutters have an extra large aperture to provide a good field of view. The adjustable goggle mounting can be worn over normal spectacles, and is electrically isolated for subject safety.

The FE-1 goggles are driven directly by the ViSaGe in synchrony with its monitor configuration. A digital output is concurrently available to trigger a data acquisition system or other external equipment. The CRS MATLAB Toolbox includes full support to control the individual shutter states for complete experiment control. A secondary output allows you to observe the test using a pair of low-cost LCD or similar shutters.

FE-1 Specification

Shutters

• 44 mm clear apertures, set up at 24°C for visible light
• Open shutter transmission: 25% minimum (typically 30%)
• Open:close contrast ratio 500:1 minimum (typically 1000:1)
• 0-90% switching time: 50 µs (typically 35 µs)

Goggles

• Adjustable one-piece moulded goggles with air vents. Can be worn over normal spectacles
• Flexible cable approximately 3 m long, terminated in miniature 3 pin DIN connector for connection to isolation unit

Isolation Unit

• Two miniature output connectors to drive FE-1 goggles and secondary goggles like the LC-1 glasses
• Connected directly to the ViSaGe via a 500 mm lead terminated in 25 way male D connector

Fast-phosphor Monitors

Colour monitors are often not suitable for alternate frame, stereoscopic presentations. Each of the three phosphor components has an individual decay characteristic and none may decay sufficiently between consecutive frames (therefore producing crosstalk). The solution is a monochrome monitor with short persistence phosphor.

The monochrome monitors manufacured by Clinton Electronics and Joyce Electronics both use a DP104 CRT. The graph below compares the decay of DP104 with the RGB P22 phosphor components found in most colour monitors and a monochrome white phosphor. The measurements are normalised with respect to light output and show that the energy remaining in the DP104 display after 400 µs (a typical frame blanking period) is near zero.

Multisync Clinton Monoray Monitor

The Multisync Clinton Monoray monitor is a modified MR2000HB-MED display that features:

• 20" flat profile CRT
• Multi-frequency scanning (V: 50-150 Hz, H: 31-105 kHz)
• SVGA resolution at 150 Hz
• 200 cd.m^-2 calibrated luminance
• CIE chromaticity coordinates (0.430, 0.540)
• On-screen controls like size, position, brightness and contrast

Fixed-Frequency Clinton Monoray Monitor

The Fixed-Frequency Clinton Monoray monitor is an optimised MR2000HB-MED display, which supports VGA resolution at 200 Hz:

• 20" flat profile CRT
• Fixed-frequency scanning (V: 200 Hz, H: 105 kHz)
• VGA resolution at 200 Hz
• 200 cd.m^-2 calibrated luminance
• CIE chromaticity coordinates (0.430, 0.540)
• Configuration of size, position, brightness and contrast via RS-232 port (no on-screen display). Dedicated Windows software provided

Joyce Scope DM5

The Joyce Scope DM5 is a custom monitor that supports ultra-high vertical scan rates. It features:

• 15" flat profile CRT
• Multi-frequency scanning (V: 80-350 Hz, H: 90-110 kHz)
• VGA resolution at 200 Hz
• 350 cd.m^-2 calibrated luminance
• A range of other phosphors for different vision science applications

Contact Cambridge Research Systems for more details and complete technical specifications on the Clinton Monoray and Joyce Scope DM5 monitors.

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