Flow

In the Flow panel a number of Routines can be combined to form an experiment. For instance, your study may have a Routine that presented initial instructions and waited for a key to be pressed, followed by a Routine that presented one trial which should be repeated 5 times with various different parameters set. All of this is achieved in the Flow panel.

Adding Routines

The Routines that the Flow will use should be generated first (although their contents can be added or altered at any time). To insert a Routine into the Flow click the appropriate button in the left of the Flow panel or use the Experiment menu. A dialog box will appear asking which of your Routines you wish to add and where to add it. To select the location choose the number (being shown in small black disks on the timeline) that corresponds to the location for your Routine. Note that the numbers do not represent physical units of time (e.g. seconds), merely an ordering.

Loops

Loops control the repetition of Routines and the choice of stimulus parameters for each. PsychoPy can generate the next trial based on the method of constants or using an adaptive staircase. To insert a loop use the button on the left of the Flow panel, or the item in the Experiment menu of the Builder. The start and end of a loop is set in the same way as the location of a Routine (see above) using numbers to indicate the entry points on the time line. Loops can encompass one or more Routines and other loops (i.e. they can be nested).

As with components in Routines, the loop must be given a name, which must be unique and made up of only alpha-numeric characters (underscores are allowed). I would normally use a plural name, since the loop represents multiple repeats of something. For example, `trials`, `blocks` or `epochs` would be good names for your loops.

Method of Constants

Selecting a loop type of random or sequential will result in a method of constants experiment, whereby the types of trials that can occur are predetermined. In this case, a file must be provided that describes the parameters for the repeats. This should be a csv file in which columns refer to parameters that are needed to describe stimuli etc and rows one for each type of trial. These can easily be generated from a spreadsheet package like excel. The top row should give headers; text labels describing the contents of that column (which must also not include spaces or other characters other than letters, numbers or underscores). For example a csv file containing the following table:

ori   text    corrAns
0     aaa     left
90    aaa     left
0     bbb     right
90    bbb     right

would represent 4 different conditions (trial types) with parameters ori, text and corrAns. It’s really useful to include a column called corrAns that shows what the correct key press is going to be for this trial (if there is one).

If the loop type is sequential then, on each iteration of the Routines, the next row will be selected in order, whereas under the random type the next row will be selected randomly. nReps determines how many repeats will be performed (for all conditions). All conditions will be presented once before the second repeat etc.

Staircase methods

The loop type staircase allows the implementation of simple up-down staircases where an intensity value is varied trial-by-trial according to certain parameters. For this type of loop a ‘correct answer’ must be provided from something like a Keyboard Component. Various parameters for the staircase can be set to govern how many trials will be conducted and how many correct or incorrect answers make the staircase go up or down.

Accessing loop parameters from components

The parameters from your loops are accessible to any component enclosed within that loop. PsychoPy creates a variable name that represents the current iteration of your loop by making it singular and capital and prepending ‘this’. Example scenarios:

1. You want to loop randomly over some conditions in a loop called trials. Your conditions are stored in a csv file with headings ‘ori’, ‘text’, ‘corrAns’ which you provide to this loop. You can then access these values from any component using $thisTrial.ori, $thisTrial.text, and $thisTrial.corrAns
2. You create a random loop called blocks and give it a csv file with a single column called movie. On each repeat you can access this with $thisBlock.movie
3. You create a staircase loop called stairs. On each trial you can access the current value in the staircase with $thisStair

When you set a component to use a value from your loop, e.g. you set the colour of your text to $thisTrial.rgb you should remember to change the component parameter from `constant` to `set every repeat` or `set every frame` or it won’t have any effect!