The best way to have "seamless" stimuli is to put everything you want to display for that DirectRT session onto a single row of a .csv input file.
The short flash you see is a normal part of DirectRT. For any .csv input file that has multiple trials (rows), DirectRT needs time in between trials to compile and prepare all of the stimuli for the next upcoming trial. The flash is that period of time DirectRT needs to prepare everything before starting that trial.
As such, you will genearlly need to use a nonzero value in the Trial Interval section of the styles.drt file. DirectRT functions as intended when using a value in the Trial Interval section that gives DirectRT enough time to compile the stimuli for each trial; generally a value between 350-2000 works.
You can find more information on the Trial Interval here in the DirectRT manual: http://www.empirisoft.com/directrt/h...l_interval.htm
Jason Reed
Empirisoft Software Support Specialist