Maybe group A always gets faces first, then houses, and group B always gets houses first, then faces. In a counterbalanced design you want to control the order explicitly and you want to provide a different order for different groups of participants. At the moment we also only have one repeat of each block, but we could also present more than one repeat of each block by controlling the number of rows assigned to each block in our ‘chooseBlocks’ file. Until now, we have a randomised block design, where the order of blocks is set to random. ![]() In this case, of course, the values in the outer loop are changing less often than the values in the inner loop.Ĭounterbalancing is simply an extension of blocking. ![]() Variables that are defined in the loops are available anywhere within those. In this demo you could add a value readyText that says “Ready for some houses”, and “Ready for some faces” and use this in your get ready Routine. Your chooseBlocks.xlsx can contain other values as well, such as useful identifiers. Now, when PsychoPy ® starts this loop it will find the current value of condsFile and insert the appropriate thing, which will be the name of an conditions file and we’re away! Then, in the inner (trials) loop you set the conditions file not to be any file directly but simply $condsFile. In the outer (blocks) loop you set up the conditions file to be chooseBlocks.xlsx which creates a variable condsFile. In the chooseBlocks.xlsx file you set up a variable called something like condsFile and that has values of facesBlock.xlsx and housesBlock.xlsx. So, how to switch between these files? That’s the trick and that’s what the other file is used for. In a real experiment you’d probably also have response keys andsuchlike as well. In this example we can just use a variable stimFile with values like stims/face01.jpg and stims/face02.jpg while the housesBlock file has stims/house01.jpg and stims/house02.jpg. The facesBlock, and housesBlock, files look more like your usual conditions files. So, how do you get the block to change from one set of images to another? To do this create three spreadsheets, one for each block, determining the filenames within that block, and then another to control which block is being used: You can also have additional Routines like something to inform participants that the next block is about to start. randomly selecting a number of images) but then you will have a second loop around this to define how the blocks change. You can add a loop around your trials, as normal, to control the trials within a block (e.g. ![]() This example is included in the Builder demos, as of PsychoPy ® 1.85, as “images_blocks”. It would be tempting to create a Routine called presentFace and another called presentHouse but you actually want just one called presentStim (or just trial) and then set that to differ as needed across different stimuli. For instance, let’s imagine you’re trying to create an experiment that presents a block of pictures of houses or a block of faces. Try to define your trials with a single Routine. ![]() The key thing to understand is that you should not create different Routines for different trials in your blocks (if at all possible).
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