Video Display

XYScope display settings

• • D, W, H : These settings describe the display geometry for the particular X-Y vector oscilloscope installed in the experiment rig. All are expressed in millimeters and restricted to integer values in [50 .. 5000]. The display geometry is crucial, since Maestro uses it to convert all coordinates expressed in "visual degrees subtended at the eye" to physical display device coordinates. Users should be aware of these basic assumptions behind the coordinate transformations: The display screen is flat (definitely an approximation!) and is oriented such that the line-of-sight vector from the eye intersects the screen plane at a right angle, passing through the screen's center. The origin (0 deg, 0 deg) lies at this central point, and the distance to the eye, D, is measured along the line-of-sight vector.

  • FOV (Field of View) : This static readout indicates the current visual field of view (in degrees subtended at the eye) spanned by the display screen -- calculated in accordance with the display geometry. The readout is updated whenever one of the parameters D, W, or H is changed.

  • Dot draw timing : The XYScope controller is a DSP device that drives a custom-designed video output circuitry which, in turn, drives the X, Y and trigger inputs of the oscilloscope. To draw each dot in an XYScope target, the controller must change the X and Y drive voltages to “move” to the dot’s screen location while the electron beam is off, then raise the trigger input to turn on the beam. Each dot draw cycle is thus characterized by a "delay" phase, which gives the updated drive voltages time to settle (otherwise, the dots will have “tails” because the beam is still moving when it is turned on!), and an "on" phase, during which the trigger pulse gates on the beam. The user can adjust the durations of these two phases to some extent to get the best possible performance from the particular oscilloscope in use. The draw cycle Delay can range from [1..15] ticks, and the beam-ON Duration can range from [1..254], so long as the total cycle time does not exceed 255 ticks. Maestro will automatically correct invalid entries. The video output box runs at one of two possible clock speeds, 1MHz or 10MHz, which is selected by an external switch. The slower clock speed may be necessary to drive oscilloscopes with relatively long settling times for the X/Y drive voltages. The clock speed determines the duration of a "tick", 1µs or 100ns. On the Video Display tab the units are not listed – so be aware of what the XYScope video output clock speed is in your rig!

  • Dot pattern random seed : The XYScope controller uses a simple pseudo-random generator to create the random dot patterns of most XYScope target types. Here the user specifies the seed for that generator. If the Auto-generate radio button is selected, Maestro generates the seed at the beginning of each trial or stimulus run; in this case, since the seed will be different each time, we are guaranteed that the random patterns will be different each time. On the other hand, if the Fixed radio button is chosen, the seed entered in the accompanying numeric edit control will be used every time – which means the random patterns generated will be the same for each repetition of a trial or stimulus run. The edit control admits any nonnegative integer value up to 8 digits long.

RMVideo display settings

• • Video Mode : This combo box selects the video mode (screen resolution plus vertical refresh rate) for the RMVideo monitor. The current mode is displayed in the combo box field, and all alternative modes are shown in the dropdown list. Only video modes with a minimum screen resolution of 1024x768 pixels and a minimum vertical refresh of 75Hz are offered. Switching modes can take up to 10 seconds because RMVideo must perform an accurate frame period measurement after the mode switch. An hourglass cursor will appear and input to the application frame window is disabled until RMVideo completes the measurment. Video mode switching is enabled only in Idle mode. Also, the video mode is NOT saved in the user's experiment document. Maestro queries RMVideo at startup to obtain the list of available modes and the currently selected mode.

  • Gamma RGB : These three numeric text fields display/edit the red, green and blue (in order from left to right after the label) gamma-correction factors for the RMVideo monitor. Gamma correction is an important consideration when displaying stimuli on a color CRT. The color specification of most RMVideo target types assumes that actual monitor luminance varies linearly with the pixel value applied (separately for R, G and B axes). The luminance-vs-pixel value curve is more like a gamma function in reality, so gamma correction is needed to achieve a linear relationship. A typical correction factor is 2.2, but it is a good idea to perform some measurements with a photometer and fine-tune the correction for your particular setup. This is a lot easier now that the gamma-correction factors can be set directly from Maestro. As with the video mode, the R/G/B gamma-correction factors are NOT saved in the user's experiment document but are retrieved from RMVideo at startup. The fields are enabled only in Idle mode; the allowed range for each correction factor is [0.800 .. 3.000].

  • Geometry - D,W,H,FOV : The display geometry and effective field of view for the CRT monitor controlled by RMVideo. See above discussion of XYScope display geometry.

  • Background Color : These parameters determine the color and luminance of the uniform background on the RMVideo display. Maestro only supports a uniform background set to the specified RGB (red, green, blue) color. Each axis of the RGB triplet is specified with 8-bit resolution: [0..255], where 0 corresponds to minimum luminance and 255 to maximum luminance. If the framebuffer display has been properly gamma-corrected, this range will translate into a roughly linear variation of luminance along each coordinate. Note the Use grayscale checkbox. When color is not required, the user can check this box to simplify data entry. When checked, the green and blue axis controls are grayed out, and the user simply enters the desired grayscale luminance in the red control. Any change in background color will be reflected immediately on the framebuffer display, even in Idle mode.

  • Sync Flash : This feature is new in Maestro 4.0.0. It addresses the problem that video frame updates on the RMVideo display occur less frequently than Maestro's 1-millisecond time resolution in Trial mode. As a consequence, if you define a trial segment to begin at T=600ms, the first display frame for that segment will actually start some time after that, up to a whole frame period. To get a more exact reading on when the stimulus changes associated with the start of a trial segment actually appear on the display, Maestro can instruct RMVideo to "flash" (from black to white) a small square-shaped region at the top-left corner of the screen starting on the first video frame for that segment. (The top-left corner was chosen because a video display is refreshed from top to bottom and left to right, so the top-left corner is updated very early during a single refresh.) Then a photodiode assembly can be permanently affixed to that corner of the display; the circuit should generate a TTL pulse for each luminance flash, and that pulse is routed to one of the digital input channels for time-stamping by Maestro. Here you set the size of the spot in millimeters and the duration of the flash in #frames -- which should provide enough flexibility to present a flash that is large enough and long enough to adequately stimulate the photodiode. Spot size is restricted to [0..50] mm, where 0 disables the feature altogether. Flash duration can be anywhere from 1 to 9 frames. Note that, when this feature is enabled, the flash spot will be black (RGB = 0,0,0) when the flash is not on (including in Idle mode), regardless the current RMVideo background color. Naturally, you should be careful to design your trials so that targets do not approach the top-left corner. [Currently, the feature is not available in Continuous mode operation. If the spot size is non-zero, the square region occupied by the flash will be black, but there is no mechanism to "turn on" the flash at particular times.]