Overview
The first step in building an experiment is to create the experimental stimuli and specify how they should be presented. Stimuli will typically consist of text or pictures presented during a trial, instruction text that remains on the screen throughout a block of trials, and feedback messages that indicate when to respond and whether or not a response was correct.
First, let's create a text element that defines the pleasant prime words:
<text pleasantprime> / items = pleasant </text>
The text element's name is "pleasantprime". The element could be named anything we wish, but it's a good idea to picks a simple, descriptive name. It has a single attribute called "items" that specifies where the actual items are located. In this case, we have specified that the items are located in an item element called "pleasant" that we will create a bit later.
The text element allows us to define other attributes including color and screen lcoation. In this element, we will use the default values. (The default color is black, and the default position is the center of the screen.) Later, we'll demonstrate how to change these values.
In the example above, we defined pleasant prime stimuli. Next, we'll define pleasant target stimuli:
<text pleasanttarget> / items = pleasant </text>
With the exception of it's name, this text element is identical to the pleasantprime element. Note that the items attribute is set to the same item list (that we'll create in a moment) named "pleasant". This element will use those same items as targets.
Now, lets define the items used by both the pleasantprime and pleasanttarget text elements:
<item pleasant> / 1 = " HONOR " / 2 = " LUCKY " / 3 = " DIAMOND " / 4 = " LOYAL " / 5 = " FREEDOM " / 6 = " RAINBOW " / 7 = " LOVE " / 8 = " HONEST " / 9 = " PEACE " /10 = " HEAVEN " </item>
Pretty simple isn't it? Notice the opening and closing lines: <item pleasant> and </item> The name of this element is pleasant. Notice that there are 8 spaces on either side of the items (words). This is done to center the words in the presentation box during a given trial.
Now, lets define the unpleasant primes and targets:
<text unpleasantprime> / items = unpleasant </text>
<text unpleasanttarget> / items = unpleasant </text>
These text elements similar to the previous ones, except that they use "unpleasant" items. Let's create the unpleasant items:
<item unpleasant> / 1 = " EVIL " / 2 = " CANCER " / 3 = " SICKNESS " / 4 = " DISASTER " / 5 = " POVERTY " / 6 = " VOMIT " / 7 = " BOMB " / 8 = " ROTTEN " / 9 = " ABUSE " /10 = " MURDER " </item>
Let's review what we've covered so far.
We aren't done with the stimuli yet. We still need to define the forward and backward, the error messages, and create background messages. Here is the text element that will serve as the forward masks of the primes, called "forwardmask":
<text forwardmask>
/ items = (" KQHYTPDQFPBYL ", " PYLDQFBYTQKPH ")
</text>
This text element consists of two items, "KQHYTPDQFPBYL" and "PYLDQFBYTQKPH". Note that the items in this case are defined directly inside the forwardmask text element. You can define items this way or by using an items element as was done previously. A good rule of thumb is to use the items element for large item sets, or for item sets that will be shared by multiple text elements (for example, the pleasant items were used by both pleasantprime and pleasanttarget). For small item sets such as the two forward masks, or for items sets that are only used by one text element, it is usually more convenient to define such items directly inline.
Here is the text element that will define the stimuli that will serve as backward masks of the primes. Let's call it "backwardmask". The backward mask is very similar to the forward mask:
<text backwardmask>
/ items = (" PYLDQFBYTQKPH ", " KQHYTPDQFPBYL ")
/ select = current (forwardmask)
</text>
Note the addition of the select attribute set to the current option. By default, the select attribute is set to noreplace and items are selected without replacement on each trial. The current setting links the selection of the backwardmask item on each to that of the forwardmask item. Thus, for trials on which both a forward and backward mask are presented, if the first forward mask item is selected and presented on that trial, then the first backward mask item will also be presented. If the second forward mask was selected and presented, then the second backward mask will also be presented. Thus, each forward mask item has a complimentary backward mask item that always appears in conjunction with it. By linking these two stimuli, the forward and backward masks on a given trial will never be identical since the order of the two items is reversed.
Now, lets create stimuli (text) to be shown in the background throughout an entire block of trials. These stimuli will serve as reminders to the subject to press the "a" key for unpleasant and the "5" key for pleasant.
<text pleasantreminder>
/ items = ("5 = pleasant")
/ position = (75, 25)
</text>
This stimulus is similar to the previous stimuli, except the position attribute is no longer set to the default (center). Inquisit specifies screen position using a coordinates system ranging from 0 to 100 on both the horizontal and vertical axes. The upper left corner of the screen is (0, 0), and the lower right corner of the screen is (100, 100). The center of the screen is (50, 50). So, the coordinates of (75, 25) used above in pleasantreminder will place the stimuli above and to the right of the center of the screen.
Now, lets define the unpleasant reminder, which will be displayed on the upper left region of the screen.
<text unpleasantreminder>
/ items = ("a = unpleasant")
/ position = (25, 25)
</text>
Finally, lets define a stimulus to show subjects whenever they incorrectly classify a target stimulus:
<text errormessage>
/ items = (" ERROR ")
/ color = (255, 0, 0)
</text>
The errormessage text element uses the color attribute. The color attribute takes three integers between 0 and 255 that define the intensity of the red, green, blue components of the color respectively. The red component is the maximum intensity, 255, whereas the green and blue components are 0. This combination produces a rich red color.
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