Getting Started

Kelpy experiments follow a basic structure:

  1. Create the kelpy window via initialize_kelpy.
  2. Load the stimuli (images, sounds) and add images to the OrderedUpdates list.
  3. Add animations to the DisplayQueue.
  4. Run the kelpy_standard_event_loop and check for task/user events.

You should always include the following kelpy modules:

  • kelpy.OrderedUpdates
  • kelpy.DisplayQueue
  • kelpy.EventHandler

Key Components


This sets up the kelpy screen based on the given dimensions and background color. All the stimuli are displayed within this window. For example, this function can be called like so:

screen, spots = initialize_kelpy( dimensions=(1024,768), bg=(250,250,250) )

Where screen is the reference to the screen object and spots is a reference to the StandardLocations object (see StandardLocations ).

Alternatively, you can also set the kelpy screen to fullscreen:

screen, spots = initialize_kelpy( fullscreen=True, bg=(250,250,250) )


OrderedUpdates takes a list of kelpy sprites (e.g., CommandableImageSprite) and uses the list order as the order to draw/update the sprites. This order is important when stimuli overlap, such as when needing an occluder to hide an image:

# create your kelpy sprites
occluder = CommandableImageSprite(screen, start_position, image_paths[0])
reward = CommandableImageSprite(screen, start_position, image_paths[1])

# add sprites to a list
stimuli = [reward, occluder]

# store the order that we will draw and update things in this variable 'dos'
dos = OrderedUpdates(stimuli)

In this example, reward is drawn first since it is at [0]. occluder is then drawn second – since the two sprites share the same location (start_position), occluder is drawn on top of reward.

For the kelpy screen to recognize this OrderedUpdates list, the dos object must be passed to the kelpy_standard_event_loop (see kelpy_standard_event_loop()).


The DisplayQueue stores the order of stimulus events that will occur during the kelpy_standard_event_loop. Kelpy sprites have certain actions they can perform, such as moving or rotating, which can be executed in the order specified in the DisplayQueue:

# create the DisplayQueue
Q = DisplayQueue()

# add the sprite events to the queue:
# first the occluder moves to the north position off-screen (taking 1.5 seconds)
Q.append(obj=occluder, action='move', pos=spots.north, duration=1.5)
# once the occluder is finished, the the reward sprite wiggles for 2 seconds
Q.append(obj=reward, action='wiggle', duration=2, amount=45, cycles=5)

You can also set actions to occur simultaneously by using append_simultaneous():

# create the DisplayQueue
Q = DisplayQueue()

# have the occluder move while the reward wiggles
Q.append(obj=occluder, action='move', pos=spots.north, duration=1.5)
Q.append_simultaneous(obj=reward, action='wiggle', duration=2, amount=45, cycles=5)

Like OrderedUpdates, a DisplayQueue must be passed to the kelpy_standard_event_loop. For a list of specific actions for the different types of kelpy sprites, see Stimulus Types.


With your kelpy screen, OrderedUpdates object, and DisplayQueue object, you can now run an event loop:

# pass your 3 objects to the event loop.
# the loop will run indefinitely while processing interactions,
# unless you tell it otherwise within the for loop.
for event in kelpy_standard_event_loop(screen, Q, dos):
# in this example, once the reward is clicked, a sound is played
# and then it breaks out of the event loop
        if is_click(event):
                # check what was clicked
                who = who_was_clicked(dos)
                if who is reward:
                        play_sound(sound_file, wait=True, volume=0.7)

Within the for loop, you can detect user events (such as clicking on objects, dragging objects), add additional sprite actions to the DisplayQueue, play sounds, and whatever else necessary for the flow of your experiment.

Other Useful Classes/Functions


Once a kelpy screen is created, a StandardLocations object is returned along with a reference to the screen object itself. StandardLocations has several pre-defined properties that refer to spots both on and off the screen, based on the dimensions of the kelpy window. These spots can be used for image placement. Description of available positions:

Off-screen locations

  • north
  • northeast
  • east
  • southeast
  • south
  • southwest
  • west
  • northwest

On-screen locations

Default on-screen locations are based on a 4x4 grid pattern, with rows as letters a-d and columns as numbers 1-4. For example, a1 is the top left corner, while d1 is the bottom left corner. There is also a row of 4 positions at the middle height of the screen (midrow1, midrow2, etc.) and a column of 4 positions at the middle width (midcol1, midcol2, etc.). The center position of the screen is center.


During the kelpy_standard_event_loop, if you make a call to who_was_clicked() and pass your DisplayQueue as an argument, the function will return what kelpy sprite was clicked on, if any.

who = who_was_clicked(dos)
if who is correct_sprite:
        #return something positive
elif who is wrong_sprite:
        #return something negative?
        #possibly do nothing since no sprite was clicked


This function simplifies calling stimuli files that are included with kelpy, located in the kelpy/stimuli directory. For example, if you wanted to use the Beep.wav sound file:

beep = kstimulus('sounds/Beep.wav')

There are many images and sounds in the stimuli library, so take some time to browse through them!


As the function name implies, this returns just the filename (e.g., image.png) of the filepath that is passed to it (e.g., /home/user/kelpy-master/kelpy/stimuli/image.png). This is useful when outputting either to the command window or to a data file what stimuli were displayed/played.


This is a call to the DisplayQueue to check if it still has anything in its queue. If it does, it returns False. Otherwise, it returns True. This is potentially useful when determining when to move on during a task.

Code Reference