Trial Interval

QuickInfo

Sets the inter-trial interval in milliseconds.

Value

Any integer, typically in the range of 350-2000ms

Details

As soon as DirectRT finishes a trial it determines the background color of the next trial, and immediately flips to a screen of that color and begins the Trial Interval. This is the amount of time that must pass before your first stimulus of that next trial is displayed. During this time, DirectRT begins building all of the screens that will be required for the trial. This requires TIME--hopefully, less time than you have requested as the Trial Interval! If so, DirectRT will return with all the screens prepared, and wait for the Trial Interval to expire. 1000ms is usually safe.

More Detail if You're Interested

The time DirectRT requires to prepare the trials will depend on the number of screens needed for a trial, the media being used, and the power of the computer. Because DirectRT does all of this construction in the background WHILE the trial interval is occurring, the construction process has NO effect on timing so long as you set a Trial Interval that is greater than the time it takes to load everything. Usually an interval of 1000ms is sufficient for most computers, although some computers my need as little as 10-100ms even for complex trials.

You can experiment with this. In the Log file that DirectRT creates, it records the number of milliseconds it takes to load each of your trials. You'll see in every case where the load times were less than your Trial Interval, the Trial Interval was maintained. If there is ever a case where it takes LONGER than the interval to load the trials, then the interval will be extended for as long as it takes to finish preparing the trials.

If you requested a sequence of 10 full screen full color images to flash during a single trial, then a trial interval of 200ms would not likely give the system enough time to prepare. In such a case, the trial would begin as soon as possible and the extra time required would be recorded in the log file so you could adjust your Trial Interval accordingly.