It would seem as though DirectRT would have a much easier time completing this task; however MediaLab is also quite capable of handling the requirements of your experiment.
Randomly selecting an image to display in the manner you've mentioned could be completed in a few ways. The first way would use either the BGR function or the WGR function. If you had 8 images to select from, you would need 8 separate trials to complete the randomization. The questionnaire would have a setup similar to the following example:
Code:
1. Image1 -> WGR = 1 -> Skip1 = Item 9
2. Image2 -> WGR = 1 -> Skip1 = Item 9
3. Image3 -> WGR = 1 -> Skip1 = Item 9
... etc.
The above syntax basically denotes that you would have 8 slots for the 8 potential images. Each slot would have the same randomization value so that they are scrambled among each other. Upon finishing, the displayed stimulus would always exit to the 9th item, which would skip the rest of the stimuli.
Another method you may want to look into would involve utilizing the advanced capabilities of MediaLab with Microsoft Excel. By working with Execl's Int + Rand() (ie. =INT(RAND()*10)+1) functions, you can create a more complex skip method. For more information on the advanced features ML supports, see the following link: http://www.empirisoft.com/medialab/h...d_features.htm
For more information on the WGR function, see this link: http://www.empirisoft.com/medialab/help/querwg.htm
Also be sure to check out the sample library included with MediaLab. A few of the samples included with the software may help point you in the right direction for completing your experiment. Please let me know if you have any additional questions or if I can help in any way.