WEBVTT

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Hi. My name's John Pierce.

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I'm a lecturer at the University of Nottingham.

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I'm the inventor of PsychoPy.

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In this demo, I'll show you how to

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create a simple experiment in PsychoPy.

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We're going to use the Stroop effect.

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When you first start up PsychoPy,

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you'll find two windows come open:

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One is the builder view, which allows you to

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construct your experiments graphically.

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And the other is the coder view, which allows you to

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create your experiments using Python scripts

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if you prefer to write code directly.

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Today we're going to be using the builder view.

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The builder view has three panels.

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It's got components. It's got one or more routines.

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Here we've got a single routine called the "trial".

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And it's got a flow which allows you to

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combine multiple routines together.

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In the case of the Stroop task, we'll need a

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a text object as part of our trial

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because we need to present a word to the subjects.

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So, let's create a text object.

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We'll call it "target". We'll have it start at

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maybe naught point five seconds,

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and it will last for five seconds.

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Notice that each of these parameters,

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as I hover my mouse over them, it gives me a tip to

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inform me about what I would be expected to include.

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There's also a help button. If I click on that,

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I'll go to the PsychoPy web site where it will tell me

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more detailed information about how to use

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this particular component.

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For now, we're not going to set color and the text

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of this text object. We'll come back to that

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later on.

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Having hit "OK", we can see the text object

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appearing in our routine and if we want to edit

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that, we can click on the icon again and we

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can get back and change our stimulus.

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Maybe we want it to be for four seconds, instead of for five.

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So it's now changed that representation.

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We also, for the Stroop task, need for the

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subjects to respond. So let's add a keyboard

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to this routine. We'll call it "response".

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We'll also start that at naught point five seconds.

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We don't want subjects to respond before

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the target was presented.

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I'm going to set this to have an infinite duration.

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If we set that to be blank, then the keyboard

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will be available forever.

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We're going to leave the allowed keys for now.

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I'll come back and change those later on,

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once we've set up our trials.

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OK, now we that the response is going to

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last forever.

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So, that's roughly what one trial is going to look like

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in the Stroop task. But we need to run more

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than one trial and right now we've got that

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routine appearing just once on our flow.

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Let's insert a loop around the trial,

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so that we can repeat it.

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If I click on "Insert loop" just once,

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and select, again with a single click,

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where we want our loop to start and stop.

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It brings up a dialog box, asking me

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what do I want to call this loop.

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We'll call it "trials". That's fine.

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Should it be random or sequential in choosing the next condition?

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Random is fine.

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We'll have five repeats, and we need to

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go and specify our conditions file.

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Now, you'll notice here it's asking for a trial

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a file that's CSV or XLSX. We need to go off

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to Excel in order to create our file.

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And click "OK". You'll see it insert the

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loop around the trial.

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Let's go and save that experiment now,

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so that we don't lose it.

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Save. I'm going to create a new folder on

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my desktop called "Stroop" and maybe I'll

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call the file "Stroop Experiment".

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Okay.

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The easiest way to define the conditions for

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your experiment is to use a spreadsheet package

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like Excel.

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We can create a number of parameters for

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our experiment, such as the word that we're

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going to present, or the color that it will

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be presented in, and we can create a number

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of different conditions. We specify one on each row.

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So, for the Stroop task, we might use the word "red"

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written in red. We might have the word "red" written

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in green. We might have the word "green"

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written in green, etc.

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"Green" in blue. "Blue" blue. "Blue" and red.

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I'm going to keep track of whether or not

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those are congruent. We don't really need to do this.

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We could always work it out later, but it's

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kind of convenient to have that stored as well.

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So, congruent and I'm going to say "1";

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that means "true"; and "0" for "false".

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That's just going to help us later on.

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Now we also need to specify what's the

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correct answer, cause PsychoPy will want to know

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whether or not the subject got it right or wrong.

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I'm going to call that "corrAns".

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These parameters can't use any punctuation

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or spaces in their names. So, I'm going to

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take away the space and give it a capital letter

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for, uh, to specify the correct answer.

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In this case, we're going to use the left,

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down, and right cursor keys from the keyboard.

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So, I'm going to specify that red -- and remember

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in the Stroop task that the subjects are asked

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to report the color of the text rather than

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the word itself. So, when the color is red, I'm

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going to ask the subjects to press "left".

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That's the left cursor key.

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When it's green they should press "down".

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"Down" again.

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When the color's blue they should press "right".

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"Right".

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And now I've got red again, so they should

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press "left".

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Okay, that defines six different conditions

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for our experiment with four different parameters.

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Okay, let's save that file.

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I'm going to put it in the same folder as my

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experiment, although you don't have to.

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And I'm going to call it "conditions.xlsx".

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It's very important that you save it

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in the XLSX format. PsychoPy can't use the old

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XLS style spreadsheets.

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Click "Save" and we're done.

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So now we need to show PsychoPy where that file

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is, and how to use it during the trials.

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The way to do that is with the loop dialog.

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So, if I just click on that loop again,

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we'll get the properties back for the loop

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and there's a conditions file. If we browse,

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we can select our file that we've just created,

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open that, and it's told me that there are

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six conditions with four different parameters.

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The parameters are color, word, congruent

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and correct answer.

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Ok? If the file had been invalid in some way,

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maybe we had a space in one of our column

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headings, then we would get a warning here to

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say that we couldn't use that file or it

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wouldn't show us the parameters were there.

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Now we can select "OK". It's showing that we've

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got five times six random trials.

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So, five different repeats of six different conditions.

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Okay, so the conditions file is now being set

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here on each repeat through the loop, we use

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a different row.

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We still need to tell the stimulus about the

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parameters that it needs to use.

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We want the color of our stimulus to be set

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by that color parameter. Now, I've typed in

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"$colour" here, spelt with a "u" because that's

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how we spelt it in the Excel file.

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And that "$" is to tell PsychoPy "This isn't a

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literal value. It's a variable."

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Okay? So, it's going to go off and find a

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variable called "colour" and see what the current

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value of that variable is.

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It's going to be red or green or blue.

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I'm also going to set that to change on every repeat

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rather than being constant.

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Okay? We don't want the stimulus just to be

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fixed to one particular color for the entire experiment.

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Similarly, the text of this text stimulus should be

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the word that we've specified in the Excel file

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and it shouldn't be "word" it should be the variable

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"word" in order to go and fetch that variable

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which is going to be red or green or blue.

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And, again, we want that to change on every repeat

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of this routine.

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Okay. We also need to set the response to be

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based on the conditions. So I need to change

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the keys that are going to be allowed for

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the subject to respond with. We don't want them

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to use the "yes" or the "no". We want them to use

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"left", "right" and "down". So, notice that any keys

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I want to put here I separate by commas and

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I have to put inverted commas around the names

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of each of the keys.

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If I leave that blank -- the entire box -- then all keys

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will be available. Okay? So that allows the subject

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to press any key. I've also got "forceEndRoutine"

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checked here. We left the response to be

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infinite but as soon as they press any key,

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it will force the end of that trial.

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So that's a useful thing for us to do.

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We're also going to want to store correct.

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So, if I check that box, we have to tell PsychoPy

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what is the correct answer on this trial,

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and if you remember, that was stored as "corrAns".

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Again, we need to use "$corrAns" to specify

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the fact that this is a variable name not,

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it shouldn't be looking for a key called "corrAns"

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cause it will never find one. It's got to use

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the variable "corrAns". And that's us done. Okay.

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Save. Okay, we're pretty much there.

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That should be a working experiment, but we do also

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want to provide the subject with some instructions.

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I'm going to insert another routine into the flow.

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When I click that button it shows me either "new"

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or "trial". Let's select "new" and I'll call it

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"instructions"... if I can spell it. "Instructions".

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It asks where I want to insert the instructions.

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We don't want it to be here because that would

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repeat the instructions on every trial.

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Let's put it before the loop. And now we can click

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on the instructions routine and we can edit that.

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So, we're going to want another text object.

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We're going to call that, say, "instrText",

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start at time zero. Duration, we'll make it infinite.

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Color white, that's fine. And we'll give it the text

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"Remember choose the color of the letters,

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ignoring the word:

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left = red, down = green, right = blue.

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Okay.

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Now because we've made that text last forever,

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we gave it an infinite duration, we need to make

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sure that the subject can get rid of them.

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So, we'll click on a keyboard, we'll allow any key,

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we'll force the end of the routine, and we won't

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bother storing anything.

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We make that last forever.

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Okay.

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If you do get that wrong, you should always be able

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to hit "escape" and you will still be able to quit

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the experiment without having to

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restart your computer.

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Okay, I'm going to save that again.

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I think we're done.

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Okay, let's just have a quick look at the

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Experiment Settings dialog box.

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In this dialog, you can control things like whether

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or not the mouse is visible during the experiment,

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the color of the background of the screen,

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whether or not it's in a window or in full screen,

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is it "screen 1" or "screen 2" if you've got

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multiple monitors, and what sort of data files

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you want to save out. So, lots of useful things there

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to control your experiment.

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Now, at this point we could construct a script.

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That'll allow you to go off and maybe learn a little

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bit about how Python works. It's about 220 lines

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long, this particular experiment. So, not too

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complicated a script. But we don't need to.

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We could actually go off and run our experiment

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by hitting the green man.

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Often takes a few seconds, especially the first time

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you run. So, be patient with that one.

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There we go. We've got a dialog box come up

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asking for the participant and the session number.

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That was also being controlled in the Experiment

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Settings dialog.

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I'm not actually going to run the experiment.

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I'll leave that to you.

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Okay. Have you found that useful?

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Check out the Demos menu for more ideas

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and I hope you enjoy using PsychoPy!