SuperLab + Cedrus Synchronization: Perfecting fMRI Timing

A common and critical requirement in neuroimaging research is synchronizing the presentation of a behavioral trial with the start of an fMRI scan. Without perfect alignment, cumulative timing errors can render the functional data misaligned with the behavioral events. There are two primary methods to achieve this in SuperLab : direct hardware interfacing and software-based trial pacing. Method 1: Hardware Synchronization (The Gold Standard). Interfacing directly with the scanner is the preferred method. MRI scanners generate a trigger signal just prior to the start of a scan. The goal is to route this trigger so SuperLab recognizes it as a participant input. The Lumina Solution: The easiest and most reliable method uses Cedrus Lumina fMRI response pads. The Lumina 3G controller features built-in inputs specifically designed to accept scanner triggers (via custom cables for GE or fiber optic cables for Siemens)., SuperLab Setup: Once connected, the researcher simply selects "Lumina MRI Pads" as the input device in SuperLab, creates an event that looks for the "Scanner Trigger" as a correct response, and links this event to the beginning of the trials. Method 2: Software-Only Trial Pacing. If hardware interfacing is not possible, SuperLab 5 offers a "Trial Pacing" option. How it Works: Instead of waiting for a physical trigger, you set the pacing interval to match the scanner's TR (e.g., 5,000 ms). SuperLab will run the trial and then actively wait for the remainder of that 5,000 ms interval before starting the next trial., Crucial Requirement: The trial must be designed to end before the interval expires (e.g., ending at 4,800 ms), allowing SuperLab a brief waiting period to snap the next trial perfectly onto the 5,000 ms mark. The "Housekeeping" Pitfall: Why Simple Time Limits Fail. A common mistake is using fixed time limits in the Event Editor (e.g., setting a cue for 500ms and a stimulus for 2,500ms, expecting a perfect 3,000ms trial). This approach fails due to housekeeping overhead. During an experiment, the computer's CPU must perform background tasks:. Allocating and freeing memory., Loading stimuli from the hard disk., Decompressing images before presentation., Drawing elements on the screen. While these tasks take only milliseconds, these tiny delays accumulate over hundreds of trials (timing drift), causing the presentation to fall out of sync with the scanner. Hardware triggers or the Trial Pacing feature are essential to override these internal system delays.