Millisecond Forums

Example based on the previous ones I gave you in another thread:

<values>
/ aclickcount = 0
/ arequiredcount = 1
/ ahpos = 0%
/ bhpos = 0%
/ asize = 40%
</values>

<expt>
/ blocks = [1-4=choiceblock]
</expt>

<block choiceblock>
/ onblockbegin = [if (block.choiceblock.totalcount > 0) values.arequiredcount = 2 * values.arequiredcount; ]
/ trials = [1-10=choice]
</block>

<trial choice>
/ ontrialbegin = [if (values.aclickcount <= 0) {values.ahpos=list.indicehposition.nextvalue; values.bhpos=list.indicehposition.nextvalue; values.asize=40%}; ]
/ ontrialend = [if (trial.choice.response=="astim") {values.aclickcount+=1; values.asize=values.asize*0.5; }; ]
/ stimulusframes = [1=astim, bstim, debug]
/ validresponse = (astim, bstim)
/ inputdevice = mouse
/ branch = [if (trial.choice.response=="bstim") trial.b]
/ branch = [if (trial.choice.response=="astim" && values.aclickcount>=values.arequiredcount) trial.a else trial.choice]
</trial>

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

<trial a>
/ ontrialend = [values.aclickcount=0]
/ stimulusframes = [1=mytext, debug]
/ validresponse = (57)
</trial>

<trial b>
/ ontrialend = [values.aclickcount=0]
/ stimulusframes = [1=mytext, debug]
/ validresponse = (57)
</trial>

<text astim>
/ items = ("A")
/ txbgcolor = (blue)
/ vposition = 50%
/ hposition = values.ahpos
/ size = (values.asize, values.asize)
</text>

<text bstim>
/ items = ("B")
/ txbgcolor = (green)
/ vposition = 50%
/ hposition = values.bhpos
/ size = (40%, 40%)
</text>

<text mytext>
/ items = ("<%script.currenttrial%>")
</text>

<text debug>
/ items = ("A clicks required: <%values.arequiredcount%> | A clicks made: <%values.aclickcount%>")
/ position = (50%, 10%)
/ erase = false
</text>

The /size attribute accepts variables (<values> entries), i.e. you can simply set those to the desired value after each click using /ontrialend logic.