Millisecond Forums

In essence, you do something along the following lines:

<block myblock>
/ trials = [1-3=matchtrial]
</block>

<trial matchtrial>
/ ontrialend = [list.nomatch.reset(); ]
/ stimulusframes = [1=a, b_match, b_nomatch1, b_nomatch2]
/ inputdevice = mouse
/ validresponse = (b_match, b_nomatch1, b_nomatch2)
/ correctresponse = (b_match)
</trial>

<text a>
/ items = aitems
/ position = (50%, 10%)
</text>

<item aitems>
/ 1 = "RED"
/ 2 = "GREEN"
/ 3 = "BLUE"
</item>

<text b_match>
/ items = aitems
/ select = text.a.currentindex
/ hposition = list.randomhpos.nextvalue
/ vposition = 60%
</text>

<text b_nomatch1>
/ items = aitems
/ select = list.nomatch.nextvalue
/ hposition = list.randomhpos.nextvalue
/ vposition = 60%
</text>

<text b_nomatch2>
/ items = aitems
/ select = list.nomatch.nextvalue
/ hposition = list.randomhpos.nextvalue
/ vposition = 60%
</text>

<list randomhpos>
/ items = (25%, 50%, 75%)
/ selectionrate = always
</list>

<list nomatch>
/ items = (1,2,3)
/ selectionrate = always
/ not = (text.a.currentindex)
</list>