Creating Blocks

The next step is to define the different kinds of blocks that will be used in the experiment. Blocks represent sequences of trials that can be in random or fixed order. For this experiment, two block elements will be defined, one for practice trials and one for data collection.

First, let's define the practice block element for the task.

<block practice>
/ trials = [1-20 = noreplace(pleasant, pleasant, unpleasant, unpleasant, pleasanttargettop, pleasanttargetbottom, unpleasanttargettop, unpleasanttargetbottom)]
/ bgstim = (taskreminder)
</block>

This block element is named "practice". The trials attribute specifies that the block runs 20 trials randomly selected without replacement from a set of 8 different trials. You may have noticed that 2 of the trials, "pleasant" and "unpleasant", are listed twice. The reason is that we wanted exactly half of the trials in the block to be followed up with a target '!', and the other half not to have a follow up. As the trials attribute is specified, 2 of every 8 trials in the block will be "pleasant", 2 will be "unpleasant", 1 will be "pleasanttargettop", 1 will be pleasanttargetbottom, 1 will be unpleasanttargettop, and 1 will be unpleasanttargetbottom.

The bgstim attribute specifies that the "taskreminder" instruction text stimulus is presented on the screen as background.

The nonpractice block below (named "critical") is quite similar:

<block critical>
/ preinstructions = (taskreminder)
/ trials = [1-36 = noreplace(pleasant, pleasant, pleasant, pleasant, unpleasant, unpleasant, unpleasant, unpleasant, pleasanttargettop, pleasanttargetbottom, unpleasanttargettop, unpleasanttargetbottom)]
</block>

One difference is that the critical block presents the "taskreminder" instruction page at the beginning of the block as specified by the "preinstructions" attribute. The other difference is that there are 4 "pleasant" and 4 "unpleasant" trials in the selection pool rather than 2 of each. The proportion of trials with follow up trials is now 4 out of 12, or 33%.

Creating Trials

Creating an Expt