PsychoPy-Scene

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This repo is a lightweight experiment framework for PsychoPy, source code <300 lines.

Features

• Lightweight: Only 1 file, no extra dependencies
• Type-safe: All parameters are type annotated
• Newcomer-friendly: Only the concepts of Context and Scene are required to get started.

Install

pip install psychopy-scene

Usage

Context

Experiment context Context means this experiment's global settings, including environment parameters, task parameters, and so on. The first step to writing an experiment is to create an experiment context.

from psychopy_scene import Context
from psychopy.visual import Window
from psychopy.monitors import Monitor

# create monitor
monitor = Monitor(
    name="testMonitor",
    width=52.65,
    distance=57,
)
monitor.setSizePix((1920, 1080))

# create window
win = Window(
    monitor=monitor,
    units="deg",
    fullscr=False,
    size=(800, 600),
)

# create experiment context
ctx = Context(win)

Scene

The experiment can be seen as a composition of a series of scenes Scene, only 2 steps are required to write an experiment program:

1. create scene
2. write scene presentation logic

we can pass several stimuli to be drawn directly into the Scene method, and these stimuli will be drawn automatically:

from psychopy.visual import TextStim

# create stimulus
stim_1 = TextStim(win, text="Hello")
stim_2 = TextStim(win, text="World")
# create scene
scene = ctx.Scene(stim_1, stim_2)
# show scene
scene.show()

The scene has 2 configuration methods, each method should be called once. duration method sets the duration of the scene, close_on method sets the keys to close the scene,

scene = ctx.Scene(stim).duration(1).close_on("f", 'j')

The duration of some scenes isn't fixed, so we can set its duration dynamically by state management:

scene = ctx.Scene(stim).duration()
scene.show(duration=1)

Caution

error example of configuring scene:

scene = ctx.Scene(stim).duration(1).duration(2)

scene_1 = ctx.Scene(stim).duration(1)
scene_2 = scene_1.close_on("f", 'j')

Different scenes may draw the same type of stimulus, such as guide and end scenes need to draw text stimulus. In this case, we only need to create 1 text stimulus, then use the hook method to add a custom function to a specific stage of the scene, this function is named lifecycle hook. In the following example, the guide and end scenes will show different text, but they use the same stimulus. Because the hook is added to the setup stage will be called before the first draw.

# this is equivalent to:
# guide = ctx.Scene(stim).hook('setup')(lambda: stim.text = "Welcome to the experiment")
@(ctx.Scene(stim).hook('setup'))
def guide():
    # change stimulus parameters before first drawing
    stim.text = "Welcome to the experiment"

@(ctx.Scene(stim).hook('setup'))
def end():
    # change stimulus parameters again, becasue this scene will show another text
    stim.text = "Thanks for your participation"

guide.show()
end.show()

In this way, we can draw stimlus flexibly. if we want to draw dynamic stimuli, just add a lifecycle hook to the frame stage:

from psychopy import core

@(ctx.Scene(stim).hook('frame'))
def scene():
    stim.text = f"Current time is {core.getTime()}"

scene.show()

State Management

Always, we need to show a series of scenes with the same type of stimulus but different content. In this case, we can use these kinds of parameters that will be changed in each show as the state of the scene:

@(ctx.Scene(stim).duration(0.1).hook('setup'))
def scene():
    stim.text = scene.get("text") # get `text` state

for instensity in ['A', 'B', 'C']:
    scene.show(text=instensity) # set `text` state and show

Note

the show method will reset state during its initialization phase at each call. See lifecycle for details.

Built-in State

Some states will be set automatically by the configured method of the scene.

State	Description	Which method
show_time	timestamp of the start of the display	show
close_time	timestamp of the end of the display	show
duration	duration	duration
keys	pressed keys	close_on
response_time	timestamp of key press	close_on

Handle Interaction

In most cases, using close_on method to configure the keys to close the scene is enough. However, if we want to do other things when the keys are pressed, we can use the on method to add custom functions for different keys. These functions are named event listeners, ref wiki:

# add listener for keys, listener will be executed when the corresponding key is pressed
ctx.Scene().on(
    space=lambda e: print(f"space key was pressed, this event is: {e}"),
    mouse_left=lambda e: print(f"left mouse button was pressed, this event is: {e}"),
)

Note that one key with one listener, the last listener will cover the previous listeners:

# only the last listener will be emitted when multiple listeners are added for the same key
ctx.Scene().on(
    space=lambda e: print("this listener won't be executed")
).on(
    space=lambda e: print("this listener will be executed")
)

# when `f` is pressed, the scene won't be closed
ctx.Scene().close_on("f", "j").on(
    f=lambda e: print("this listener will cover `close_on` listener")
)

Every listener function should accept an event object as parameter e, which includes the scene that emits the event and the pressed keys

ctx.Scene().on(
    space=lambda e: print(f"this scene is: {e.target}; pressed keys are: {e.keys}")
)

Keys

• keyboard: same as the return value of keyboard.getKeys()
• mouse: mouse_left、mouse_right、mouse_middle

Data Collection

PsychoPy's recommended way of collecting experimental data is to use ExperimentHandler. Now we can use ctx.addLine for data collection, and access the ExperimentHandler object via ctx.expHandler.

# it will call `ctx.expHandler.addData` and `ctx.expHandler.nextEntry` automatically
ctx.addLine(correct=..., rt=...)

As stated in the State Management section, some interaction data are automatically collected by close_on. If we use the close_on method, we can access these states after the show method is executed:

scene = ctx.Scene().close_on("f", "j")
scene.show()

keys = scene.get("keys") # KeyPress or str
response_time = scene.get("response_time") # float

Of course, we can also add listeners manually as in the Handle Interaction section:

scene = ctx.Scene().on(space=lambda e: scene.set(rt=core.getTime() - scene.get("show_time")))
scene.show()

rt = scene.get("rt") # float

Lifecycle

There are a series of steps involved in drawing a picture to the screen using the show method: Resetting and initializing the state, clearing the event buffer, drawing the stimulus, recording the start of the display time, and so on, this entire process is named the lifecycle of the scene. During this process, lifecycle hooks are executed at the same time, allowing us to perform some custom actions at specific stages of the screen showing process.

Stage	Execution Timing	Common Usage
setup	before first draw	set stimulus parameters
drawn	after first draw	execute time-consuming tasks
frame	every frame	update stimulus parameters

Illustration of the lifecycle:

graph TD
Initialize --> setup-stage --> First-draw --> drawn-stage --> c{should it show ?}
c -->|no| Close
c -->|yes| frame-stage --> Redraw --> Listen-interaction --> c

Loading

Best Practices

Separation of context and task

It is recommended to write the task as a function, pass the experimental context as the first parameter, the task-specific parameters as the rest of the parameters, and return the experimental data.

from psychopy_scene import Context

def task(ctx: Context, duration: float):
    from psychopy.visual import TextStim

    stim = TextStim(ctx.win, text="")
    scene = ctx.Scene(stim).duration(duration)
    scene.show()
    return ctx.expHandler.getAllEntries()

Focus only on task-related logic

Task functions should not contain any logic that is not related to the task itself, for example:

• Introductory and closing statements
• Number of blocks
• Data processing, analysis, presentation of results

If there are no data dependencies between blocks, it is recommended to write the task function as a single block. For experiments that require the presentation of multiple blocks, consider the following example.

from psychopy_scene import Context
from psychopy.visual import Window

def task(ctx: Context):
    from psychopy.visual import TextStim

    stim = TextStim(ctx.win, text="")
    scene = ctx.Scene(stim).duration(0.2)
    scene.show()
    return ctx.expHandler.getAllEntries()

win = Window()
data = []
for block_index in range(10):
    ctx = Context(win)
    ctx.expHandler.extraInfo['block_index'] = block_index
    block_data = task(ctx)
    data.extends(block_data)

Separate of TrialHandler and task

Thanks to PsychoPy's encapsulation, we can easily control the next trial.

from psychopy.data import TrialHandler

handler = TrialHandler(trialsList=['A', 'B', 'C'], nReps=1, nTrials=10)
for trial in handler:
    trial # except: 'A" or 'B' or 'C'

For the separation of the trial iterator from the task function, the library provides the ctx.handler property. It can be used to control the next trial and collect trial-related data into ctx.expHandler. All we need to do is set the handler parameter when creating the context.

from psychopy_scene import Context
from psychopy.visual import Window
from psychopy.data import TrialHandler

def task(ctx: Context):
    from psychopy.visual import TextStim

    stim = TextStim(ctx.win, text="")
    @(ctx.Scene(stim).duration(0.2).hook('setup'))
    def scene():
        stim.text = scene.get("text")
    for instensity in ctx.handler:
        scene.show(text=instensity)
    return ctx.expHandler.getAllEntries()

ctx = Context(
    Window(),
    handler=TrialHandler(trialsList=['A', 'B', 'C'], nReps=1, nTrials=10),
)
data = task(ctx)

However, when we intend to use StairHandler and access ctx.handler.addResponse, the Pylance type checker will report an error, even though ctx.handler is a StairHandler object. This is because ctx.handler does not have an addResponse method of type ctx.handler. To work around this, we can use ctx.responseHandler instead of ctx.handler.

Warning

If the ctx.handler does not have an addResponse method at runtime, accessing ctx.responseHandler will throw an exception. So make sure the handler parameter passed in has an addResponse method when using ctx.responseHandler.