2nd Year Practical Semester 2 2011
Selective attention & the flanker paradigm
2nd year practicals run for 5 week periods. Within these 5 weeks you will be expected to design and run an experiment which you will present both verbally and in written report form.
This practical will examine selective attention and the flanker compatability effect
The flanker paradigm has been used to investigate what factors may affect selective attention and the extent to which processing of irrelevant information occurs. There are lots of variants of the classic flanker paradigm (one is shown above), some of which we will discuss in class.
The classic flanker effect
Flankers are stimuli which are presented spatially close to target stimuli and which have been sometimes shown to interfere with target processing/responses.
The classic flanker effect shows differences in reaction times for compatible and incompatible response mappings on a choice reaction task.
Eriksen and Eriksen (1974) had subjects respond with one hand if a
central target was an H or a K and with the other hand if it was an
S or C. The flanking items were either from the same response set as
the target (compatible, e.g. H flankers with K target), from the other
response set (incompatible, e.g. S flankers when the target was a K),
or neutral (e.g. X flankers when the target was a K). Responses to targets
with compatible flankers are generally faster than responses to targets
with incompatible flankers. This paradigm examines to what extent irrelevant
information is processed in a visual task. You will be manipulating
factors to see what effects they have on the level of interference in
the flanker task.
|Designing and running an experiment using EPrime
Running the software
You were introduced to E-Prime in your 1st year. You will use E-Prime to test your experiments. The best way to learn about E-Prime is to try out an example experiment. An example experiment is available here (classic flanker) and here (colour flanker)
*** It is important that you save any programs to your HARD DISK and not to your network space. Running E-Prime experiments from the network will result in inaccurate timing and other possible problems. ***
The example experiment (classic flanker - FCE-original.es)
In this experiment the task of the subject is to respond to the central letter (known as the target) whilst ignoring the outside letters (distracters) which 'flank' the target. The target stimuli must be responded to by pressing the 1 key if it is an S or C (rounded/curved features), and the 0 key if it is a K or H (straight features). Speed of responses is affected by whether the target is surrounded by response compatible or incompatible flankers (see presentation). We will also manipulate the spatial distance (eccentricity) between the target & distracters, at 2 levels (near flankers & far flankers). This leads to a 2 x 2 design.
To run the experiment, start EStudio (select Start/Programs/E-Prime/E-Studio). You can then select the "Open an existing experiment" option and choose the experiment that you want to modify. You will see a screen that looks like this (this is from the 'FCE-original' example):
Here is a quick reminder of the components that you can see on the screen:
Lets examine the structure window
:The structure window starts with some general instructions and is then followed by a list which runs 2 blocks, a practise procedure and an experimental procedure. Both of these procedures (Practise & Expt) give the sequence of events for the practise and experimental trials respectively. Each of these two procedures has some instructions and a trial list controlling the presentation of stimuli. The actual trial procedure (TrialProc) determines what happens in an idividual trial.
This shows the order for events in the experiment. It runs something like this:
Trial List Section
Lets now take a look at trial list - this is the bit that you will have to modify to adapt the experiment for your designs (you may also need to adapt other components, depending on your design). Double clicking on the TrialList icon in the structure window shows us a window that looks like this:
The buttons on the top allow us to add/delete new columns or rows to our list. Beneath that we are told the total number of trials in this list (64 trials). Beneath this is the list, with the following columns:
You will see that the weightings column assists in presenting equal numbers of compatible and incompatible trials (8 of each) for each of the 2 distance conditions. One complete set of trials would be 32 samples (although this has been doubled to present 64 trials in total!).
You may modify or redesign the e-prime files to test your own hypothesis. Depending on your design/hypothesis, you may need to construct your program in a different way to my example! e.g. you may need to use nested lists or different states of a slide object.
After modifying your experiment, make sure to save your new experiment. You may want to choose "Save as" from the "File" menu to give the program a new name.
If you use any images as stimuli they must be saved as windows bitmaps (.bmp's) and E-Prime files MUST be in the SAME directory on the C: drive of the PC (create a temporary storage space off C:\).
Piloting your study
Before collecting data, it is important to test your design to validate and verify that everything works correctly. Choose "Run" from the "E-Run" menu to start the experiment.
To examine your pilot data, choose "E-Data-Aid" from the "Tools" menu. Then open your data file (it is saved in the same folder as your experiment, and the name shows the subject number).
After you have thoroughly tested your experiment, you are now ready to begin collecting data. For this practical, you will want to test at least 6 people - 12 would be better. Consider whether you can test yourselves. When you run each individual, give them a different subject number so that the old data will not be overwritten.
IMPORTANT: If each member of a group is collecting data, decide before hand what subject number you will each start with! (e.g. person 1 in group uses subject numbers 1-25, person 2 uses 26-50. This is vital to prevent duplicating the same subject number for different subjects! Make sure to keep a backup copy of your data after each subject (copy it to your network drive).
You can analyse data using SPSS for Windows
Summary of time-plan (remember, you should be working on your practical between classes too!):