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FEEDBACK RECEIVED 16.09.2012: Here's my non PD impression - It kind of made me nauseated & headachey - I just used the default setting. I had to stop after 20-30 seconds. The center back of my head still feels a bit strange.


This page allows you to create flashing images with pulsating, metronomic-like sounds. You can control the frequency and phase of the flashing and beeping. You can increase the impact by using a piece of card, running from your face to near the screen. This will make the left eye see a different image from the right eye. Similarly, the sound effect is enhanced if you use headphones to separate the stereo channels.

WARNING: flashing lights are dangerous for some people. Do not use if you think you may be affected.

WARNING: most of the images you can create here will make your tremor worse.

WARNING: the images you create may make you sleepy.


Duration (sec): delay starting (sec): acceleration ratio: background color (#rrggbb): beat interval (msec): random color difference (#rrggbb):
width (%): movement (%): Markovian fraction: horizontal probability: adaptive minimum (moves): adaptive color change (#rrggbb):
Left: frequency (hz): phase (degrees): color on fraction: primary color (#rrggbb): secondary color (#rrggbb): secondary color probability:
Right: frequency (hz): phase (degrees): color on fraction: primary color (#rrggbb): secondary color (#rrggbb): secondary color probability:

Input meanings

At the end of each field's explanation a range of sensible values is given. [x, y] denotes "from x to y".

Duration: the time of the run in seconds. [10, 10000].

Delay: the delay in seconds between pressing the start button and the run starting. This allows you time to get ready for the tremor measurement to begin: you need to put a finger on the pressure pad. [0,10].

Acceleration ratio: the increase(>1) or decrease(<1) of frequency of successive flashes. For instance, if the frequency is initially 10 and the acceleration ratio is 1.1, the frequency goes from 10, to 11, to 12.1, etc.. Acceleration happens very quickly, so a ratio of no more than 1.001 is advised. [0.9, 1.001].

Background color: the color of the background color in the format #rrggbb, where r, g and b are hexadecimal (base 16) numbers, with r standing for red, g for green, b for blue. For example, #000000 gives black, #ff0000 gives red, #ffffff gives white. [#000000,#ffffff].

Beat interval: the period of time in msec at which the left and right sides are asked what is their color. This value limits the frequencies that can be used: the frequency of the beat must be more than the frequency of the flashes. The other factor that needs to be taken into account is whether the browser is able to refresh the page at this rate. [10,100].

Random color difference: the maximum size of a random change to the color. This is decided for each color character pair using hexadecimal arithmetic. For instance, if the original color is #777777, the random color difference is #010101 and a trace of 3 random numbers is 0.9, 0.8, 0.1, the new color generated is #787877. How this is applied will depend on the Markovian factor, see below. [#000000,#ffffff].

Width: the width of each vertical, color column as a percentage of the screen size. [0,30].

Movement: the movement of the columns per cycle, as a percentage of total screen size. [0,30].

Markovian: a measure of the correlation between successive random colors. This field takes a value from 0 to 1: 0 gives pure random; 1 gives, in effect, turns off the random changes, you are left with the original values; intermediate values give a weighted mixture of the two. [0,1].

Horizontal probability: the chance that the color blocks are drawn horizontally. [0,1].

Adaptive minimum: the number of finger movements detected by the pressure pad required to fire the adaptive response (e.g. change the orientation of the color blocks). Further adaptive responses occur each time this number of movements are detected. [0,1000000].

Adaptive color change: the magnitude of the color reduction per adaptation. Each color is controlled seperately. For example, #010000 will take 1 from just the red value. [#000000,#ffffff].

Separate left side and right side control over::

Frequency: the frequency of the color changes. [0.01,20]

Phase: the amount that the left and right sides are out of step. 180 degrees represents opposite. [0,180]

Color on fraction: the fraction of the cycle that the column is colored. For the rest of the time the background color is used. [0,1].

Primary color: the default color of the column. [#000000,#ffffff].

Secondary color: an alternative color for the column which is fired randomly. [#000000,#ffffff].

Secondary color probability: the probability that the alternative color is used. [0,1].

Physical options:

Screen divider: a piece of cardboard can be placed on the keyboard, between the screen and your nose. This causes each eye to see a different image.

Pressure pad: putting your finger on the pressure pad can detect the tremor. Whether this works depends on the size of the tremor, the stickyness of the pad and the lightness of the touch. To gauge whether it is working, place a finger lightly on the pad. Any tremor should cause the finger to move on the pad, making the cursor to move around the screen.


On pressing the PRESS TO START button:
1. A new window is created.
2. A message saying get ready is written.
3. Flashing images are produced. These should match the input specification. However, for high frequencies, more than 10 hz, say, the refresh rate will be too slow to keep pace. The maximum frequency depends mainly on the browser.
4. The new window is closed.
5. The original window is opened.
6. A summary of errors is produced:
- late errors mean that a color change did not occur at the earliest possible beat. If the number of on lates is similar to the number of off lates, this is not usually serious.
- missed errors mean cases where a whole block of color has been missed. These are serious: you can get output that is not nearly to spec. They occur because the previous timer event was called before the color block was required, while the next one occurred after the block was due to close. In short, the browser is unable to keep up. The program tries to fix the problem by generating new next times, but once it happens it is likely to reoccur.