FrameTracker Tutorial

Let's walk through an example use case for the FrameTracker. Say you want to flash a sequence of images on a screen. You need to know when each image is displayed to the subject. 

Let's set up your FrameTracker to deliver that information, down to the microsecond.

Step 1: Affix light sensors to screen

The easiest way to fix the light sensor to the screen is with mounting putty or tape. Common brand names for mounting putty include Loctite Fun-Tak, Gorilla Mounting Putty, and Bostik Blu Tack. 

 

Step 2: Mark up your stimuli

The FrameTracker detects major changes in brightness of the pixels under its sensors. The easiest way to use it is to add alternating white and black squares to the top and bottom left corners of your images. We will refer to these squares as “sync tiles.”

Tip

Make your sync tiles small, so that the sensors completely cover them. You want your experimental subjects to focus on the contents on the screen, not some flickering tile in the corner. If it is not practical to make the sync tiles small enough, cover the rest with mounting putty, tape, or any other opaque material.

Step 3: Create a stimulus sequence

Different experiments may have different requirements, and the FrameTracker easily adapts to all. Here are a few examples, but you should feel free to use the FrameTracker however it suits you.

Example 1: A single stimulus

If you just need to present a single stimulus at a time, start with the sync tiles black in the time before the stimulus is presented, then present the stimulus with white sync tiles. At the end of the stimulus, switch the sync tiles back to black.

Example 2: A sequence of stimuli with time in between

Again, start with the sync tiles black in the time before the stimulus sequence starts. Make the sync tiles white during each stimulus and black in between. Be sure to end with black at the end of the sequence.

Example 3: A sequence of consecutive stimuli

Again, start with the sync tiles black in the time before the stimulus sequence starts. Make the sync tiles white during the first, third, fifth, etc. stimulus frame and black during the second, fourth, sixth, etc. If the length of the sequence is even, add an extra frame at the end with sync tiles white, so that you can reconstruct the end time of the final real frame of your sequence, then turn to black.

Example 4: A movie

You can treat a movie like a sequence of consecutive stimuli and toggle the sync tiles in every frame. Alternatively, you can toggle them at a reduced rate (for instance, every 5th frame). While this loses some amount of temporal resolution, it is more robust in if your movie player occasionally drops a frame.

Advanced tip for use with movies:

Make the top sync tile toggle every frame, and the bottom sync tile every 5th frame. That way, you have frame-perfect temporal resolution as well as robustness against dropped frames. 

Step 4: Record the sync pulses

To be useful, the output from the FrameTracker has to be recorded and registered to whatever else you're recording in your experiment—be it EEG, extracellular electrophysiology, behavioral output, etc. The FrameTracker is compatible with any data acquisition system. If you don't already own one, we highly recommend ours, the picoDAQ.

And if you need help registering the rest of your data with the FrameTracker output, take a look at our other product, the Barcoder.