EXPERIMENT DESIGN: Stage 4: Add Blocks and Block Conditions [37331]

The goal of this stage is to add a block procedure to run the trials. This will enable multiple blocks to be run during the session. We will also add a new display to the start and end of the experiment, to first welcome the participant and then thank them for their participation.

Stage 4, Step 1: Verify setup of the Block Manipulation

Add a Block List and Procedure.
To setup the block level, we would need to add a block level to the experiment. This involves adding a List object (e.g., named BlockList) and a Procedure object (e.g., named BlockProc). For more information on Lists and Procedures in E-Studio, refer to E-STUDIO: List Object [22700] and E-STUDIO: Procedure Object [22699].

Move the trial stimuli from the session level to the block level

The outline of our experiment needs to change with the addition of the block manipulation. We want to sample all of the trial stimuli randomly, without replacement, for each block of the experiment. At the session level, the order of events has now expanded to the following:

We need to move the trials one level deeper in the experiment. We now want the TrialList to occur in the BlockProc rather than the SessionProc, because the sampling of the trial stimuli as specified on the TrialList object needs to occur at the start of each new block, not once at the start of the experimental session. Specifically, we need to move the TrialList to the BlockProc, and then delete it from the SessionProc.

Stage 4, Step 2: Add Block Instructions

The block procedure should be modified to first present a block introduction screen to the participant. For example, the following information can be shown to the participant:

For the next block, the duration of the Prime will be 500 milliseconds long.

Press the spacebar to begin.

These type of instructions can be added to the experiment by dragging a TextDisplay object to the Block Procedure as the first event in the procedure. Additionally, the participant is instructed to press the spacebar to begin the block. If you were to specify the spacebar as an input key, you would have to make the following settings on the Duration/Input tab of the Block Instructions TextDisplay:

1. Set the Duration equal to “infinite” (i.e., wait until a response is entered)
2. Set the Input Mask to allow keyboard input
3. Set the “Allowable” field to the spacebar (i.e., {SPACE}). The End Action should be already set to “Terminate”.

Stage 4, Step 3: Add Introduction and Goodbye displays

It is important to both instruct the participant as to the task at the beginning of the experiment and to inform the participant when the experiment is completed. We recommend adding introductory text to the experiment similar to the following:

Welcome to the experiment.

Press the spacebar to continue.

When the experiment has completed, the participant should be informed as well. We recommend adding closing text to the experiment similar to the following:

Thank you for participating.

Please leave the room quietly.

It is important to instruct the participant as to what they should do at the end of the experiment. If your laboratory has multiple participant running stations, it is good practice to remind the participant to not disturb the other participants as they leave the lab.

Stage 4, Step 4: Special Notes: Multiple Methods to Divide a Design Between Levels

There are a large variety of ways in which experimental design components are varied between blocks within a single session. The current example varies one of the display characteristics, the duration of the Prime. There are other block manipulations that are commonly used and which are readily supported in E-Prime. Such block manipulations are mentioned briefly here:

Select exemplars from different lists

You may find it useful to select stimuli from different lists of exemplars per block. For example, you could run one block of trials in which all of the words are from the Animal category, and a second block in which all of the words are from the Fruits category. This type of design utilizes a block attribute that defines the master list of exemplars to be used for the current block of trials.

Run different trial procedures

You may want to run different trial procedures in different blocks. For example, in a priming study you may want to run some blocks where the Prime Display is masked prior to the Probe Display and other blocks where the display is not masked. This type of manipulation is readily supported in E-Studio.

Colon Syntax – Sampling multiple stimuli per trial using nested lists
When a design requires multiple stimuli (rows) to be sampled from a List during a single trial, a colon syntax is used to indicate the number of exemplars to be sampled. The colon syntax places a colon and a number after the attribute name within the bracket notation (e.g., [AttrName:1]). When the colon syntax is not used, a single exemplar is sampled by default (i.e., not using the colon syntax is equivalent to [AttrName:0]). When a colon and a number are placed after the attribute name within the bracket notation, the number used indicates the number of stimuli being sampled during the same trial in addition to the default. For example, the use of [AttrName:2]would result in the sampling of three exemplars from the List during the same trial: the default exemplar plus two additional exemplars.

For example, perhaps an experiment might be modified to present two words or non-word strings at the same time instead of just one. If the stimuli are to be sampled from the same List, the colon syntax must be used. By changing the Stimulus attribute values to use the colon syntax (Figure 1 below), two stimuli will be chosen per trial from the List named in the Nested column, and assigned as the value of the Stimulus attribute (i.e., two stimuli will be displayed on the same line). Alternatively, a second attribute could be created and used to display the second exemplar (Figure 2), which would allow for more flexibility in the display (e.g., displaying Stimulus2 on the line below Stimulus).

Refer to Colon Syntax [29966] for more information and a sample experiment utilizing colon syntax.

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