25  Lab 5 exercises

Please save each exercise in its own folder.

25.1 Exercise 1

Start by creating a new experiment. To do so, click on the “Create a new experiment file” icon in the toolbar. This will open a new Builder window with an empty routine called trial.

Make PsychoPy display the text “Hello world!” for 3 seconds. Once this works, change the background colour of the screen to black.

How do I present “Hello world!”?

Use a Text component.

How do I make the trial stop after 3 s?

Pay attention to the “Stop” property of the Text component.

How do I change the background colour?

Check “Experiment Settings” → “Screen”.

You can watch a video of the solution here (to watch the video, make sure you are logged into Office 365):

25.2 Exercise 2

Please don’t forget to create a new folder for this exercise. You can copy your experiment from Exercise 1 to this folder, and modify it.

Make PsychoPy display the text “Hello world!” 1 second after the start of the experiment. Present the text for an infinite amount of time. End the presentation only when the key “y” or the key “n” is pressed on the keyboard (but not another key).

The timing isn’t right.

Pay attention to the “Start” and the “Stop” properties of the Text component.

The trial stops for other keys than “y” or “n”.

Check “Allowed keys” in your Keyboard component.

The trial does not stop.

The trial will only end if “Force end of routine” is ticked and a key that is an “Allowed key” is pressed.

You can watch a video of the solution here:

25.3 Exercise 3

Download the supporting material for this exercise. This is a zip file containing an image of a cat and a dog. Unzip the file and place the images in your exercise3 folder.

Present the cat in the left half of the screen for 5 seconds. Two seconds after the presentation of the cat started, present the dog for three seconds in the right half of the screen. Both animals should be on screen together for 3 seconds. Present the pictures using their original size. (Make sure to open them in Preview so you know what they should look like.)

Once this works, rotate the images so they are presented upside down.

The experiment does not run.

Are you sure the images are in the same folder as your PsychoPy experiment? Are the file names in your image components identical to the file names in your folder (including capitalisation)?

How do I change the location of the pictures on the screen?

You will need to change the x variable of the Position property. If you use norm units, a sensible setting for the cat would be [-0.5, 0]. If you use pixel units, appropriate settings depend on your screen resolution. A sensible setting for a full HD screen (i.e., 1920 x 1080 pixels) would be [-480, 0]. In fact, this would be exactly the same location as [-0.5, 0] in norm units.

The pictures are squashed or stretched.

Simply leave the Size field of the Image component empty. This will present the image in its original size.

The rotation does not work.

Note that the Orientation field of an image component requires the number of degrees you would like to rotate the image by.

You can watch a video of the solution here:

25.4 Challenge exercises

Exercises 1 and 2

Change the text colour to deep pink. Set the colour using the colour name.

Then present the text at 1/3 of the height of your screen:

Try height units as well as norm units for setting the text location. Note that the idea is to calculate the correct position, not to eyeball it!

How do I do this using height units?

Using height units, the total height of the screen is 1. So, the text must be placed 0.33 height units from the bottom of the screen. Using height units, the bottom of the screen is -0.5. So, the text must be placed at \(-0.5 + 0.33 = -0.17\).

How do I do this using norm units?

Using norm units, the total height of the screen is 2. So, the text must be placed 0.66 norm units from the bottom of the screen. Using height units, the bottom of the screen is -1. So, the text must be placed at \(-1 + 0.66 = -0.33\).

Exercise 3

Present the cat in the upper left-hand corner and the dog in the lower right-hand corner of the screen:

Note that the red outlines are only there to indicate where the images should be located. These do not need to be present when running the experiment.

How do I place the images in the corners?

The easiest way to achieve this is to use the “Anchor” image layout property.