stimulus presentation problem

Partenope
Very experienced

Hi everybody!

Posts: 63

stimulus presentation problem Jan 19, 2022 12:53:31 GMT

Quote

Post by Partenope on Jan 19, 2022 12:53:31 GMT

Hi everyone!

I have to create a task in which tere are 4 stimuli in total and in each trial it could appear one of the 4 stimuli randomly selected by the software. This stimulus could appear each time on 4 different locations on the screen. My first problem is this one: 1. How I can randomize the position on the screen for each trial?
Moreover, after the presentation of this stimulus, it has to appear a smiling face 50% half the time, and another face for the other half of the time. So, my problem is: 2. How can I tell to the software to show this smiling face precisely half the time, and the other face precisely for the other 50% of the times?

Thank you in advance, this is my script at the moment, I will appreciate any suggetion

options

fullscreen

bitmaps

child1
child2
child3
child4
fixpoint
smilingface
otherface

table selection
child1
child2
child3
child4

task selection
table selection
show bitmap fixpoint
delay 500

clear -1

delay 500

show bitmap @1 #this one has to appear in 4 different locations on the screen and not just at the centre
readmouse l 1 3000
set $number_of_bitmap UNDER_MOUSE
clear -1
delay 500
show bitmap smilingface #this one has to appear half of the time (and only if child1 has appeared)
delay 1000

clear -1
delay 500

save TASKNAME BLOCKNAME RT $number_of_bitmap

block MyBlock

tasklist

selection 10

end

silk
Experienced

Posts: 32

stimulus presentation problem Jan 29, 2022 17:52:35 GMT matia likes this

Quote

Post by silk on Jan 29, 2022 17:52:35 GMT

Hi there,

I don't know if it is too late or not but here is an answer using arrays.

First, what you can do is define arbitrary x and y coordinates using arrays to generate all the possible locations of the picture. See the code below:

set &&possible_x 100 -100                   # Create an array with all possible x (horizontal) positions.
set &&possible_y 100 -100                   # Create an array with all possible y (vertical) positions.
set $coord_x &&possible_x use random        # Store a possible x coordinate (from the x array) in a local variable.
set $coord_y &&possible_y use random      # Store a possible y coordinate (from the y array) in a local variable.
show bitmap my_picture $coord_x $coord_y    # Use the previously defined local variables as coordinates for the picture.

By doing so, the picture will always appear in one of the 4 possible locations. However it will be entirely random and you might want to control that. For instance you might want the current location of the picture be different from the previous one. This can be done by remembering the coordinates from the previous trial and using some while and if statements:

set $valid 0                                      # Set a value that we will reset at the beginning of each trial.
set &&possible_x 100 -100                          # This value is for controlling the while loop.
set &&possible_y 100 -100
while $valid == 0                                  # Beginning of the while loop: endlessly select a possible location until it is
set $coord_x &&possible_x use random              # different from the previous one.
set $coord_y &&possible_y use random
if $coord_x != &old_x || $coord_y != &old_y # Check if at least 1 of the 2 previous coordinates is different
set $valid 1                                  # from the current ones.
fi                                              # If so, the current location is not repeated, we can exit the while loop.
while-end
set &old_x $coord_x # Remember the current x coordinate for the next trial.
set &old_y $coord_y # Remember the current y coordinate for the next trial.
show bitmap my_picture $coord_x $coord_y

Note that this code does not balance the number of times the picture appears on each location. In other words there is a (very very low) chance that a location is never chosen. It is hard to fix with total randomization and would certainly need a more complex code.

For the second question, I would create an array with two types of values (for instance, 0 and 1). The size of this array (= the sum of the number of 0 and 1) should be equal to the number of trials for which you want to show a face. Then, for each of those trial we select and remove 1 of the 2 values from this array to decide which face to show.

task myArrays
set &&smile 1 times 5                          # Array with five 1 --> change the number after "times" to change the ratio of
set &&sad 0 times 5                              # Array with five 0 --> happy/sad face in the &&face array.
set &&face append &&smile                      # Create a &&face array and insert all the values from the previous arrays.
set &&face append &&sad                          #

task myTask
set $my_face &&face remove random              # Store 1 of the 2 possible values and remove it from the &&face array.
if $my_face == 1 # If it is the happy face value, show the corresponding picture...
show bitmap happy_face $coord_x $coord_y       #
else                                          # ...otherwise, show the other.
show bitmap sad_face $coord_x $coord_y
fi

Note that there are more straightforward ways of doing that, but this way of doing is clear and you don't have to make a lot of edits if you want to make changes to your experiment (for instance 60/40% instead of 50/50%).

Last Edit: Jan 29, 2022 17:53:59 GMT by silk

Partenope Very experienced Hi everybody! Posts: 63	stimulus presentation problem Jun 6, 2022 11:13:11 GMT Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by Partenope on Jun 6, 2022 11:13:11 GMT Thank you very much! Very helpful, I've really appreciated it! Have a good day

stimulus presentation problem

Post by Partenope on Jan 19, 2022 12:53:31 GMT

Post by silk on Jan 29, 2022 17:52:35 GMT

Post by Partenope on Jun 6, 2022 11:13:11 GMT