Millisecond Forums

+x

 

Francesca Miti - 2/15/2021

Hi,
I modified a script for a visual search paradigm where 6 pictures are displayed in a circle around the fixation cross. The size of the circle is now based on the height and width of the display (I think).
How can I choose  the size of the circle despite the monitor size? I'd like to try with a fixed size of the circle because the experiment will run online and I cannot control for the display of the participant. 

If there is a specific reason why I should NOT keep the circle size constant, please tell me.

This is a part of the code that should be relevant, more or less, I can provide more if needed.

Thanks,
Francesca

--some of the parameters--
<parameters>
/ trialnumber = 120
/ practicetrials = 12
/ fontsize = 10%
/ fontsize_fixation = 5%
/ pictureheight = 15%
/ radiusscreenproportion = 0.4
/ readyduration = 100
/ blankduration = 200
</parameters>

-- an example of picture selection  --
<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (100%, parameters.pictureheight)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

----------------------------------------------------
Calculate circle coordinates
----------------------------------------------------

<expressions>
/ xcenter = 0.5 * display.canvaswidth
/ ycenter = 0.5 * display.canvasheight

/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
/ Radians_Circle_angle0 = rad(0)
/ Radians_Circle_angle60 = rad(60)
/ Radians_Circle_angle120 = rad(120)


/ heightchange_Circle_angle0 = sin(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ widthchange_Circle_angle0 = cos(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ heightchange_Circle_angle60 = sin(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ widthchange_Circle_angle60 = cos(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ heightchange_Circle_angle120 = sin(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
/ widthchange_Circle_angle120 = cos(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
</expressions>


----------------------------------------------------
Circle coordinates positions
----------------------------------------------------

<list x_coordinates_pictures>
/ items = (expressions.widthchange_Circle_angle0,
expressions.widthchange_Circle_angle60,
expressions.widthchange_Circle_angle120,
-expressions.widthchange_Circle_angle0,
-expressions.widthchange_Circle_angle60,
-expressions.widthchange_Circle_angle120)
/ replace = false
/ selectionrate = always
</list>

<list y_coordinates_pictures>
/ items = (expressions.heightchange_Circle_angle0,
expressions.heightchange_Circle_angle60,
expressions.heightchange_Circle_angle120,
-expressions.heightchange_Circle_angle0,
-expressions.heightchange_Circle_angle60,
-expressions.heightchange_Circle_angle120)
/ selectionmode = list.x_coordinates_pictures.currentindex
/ selectionrate = always
</list>

+x

 

Dave - 2/15/2021

+x

 

Francesca Miti - 2/15/2021

Hi,
I modified a script for a visual search paradigm where 6 pictures are displayed in a circle around the fixation cross. The size of the circle is now based on the height and width of the display (I think).
How can I choose  the size of the circle despite the monitor size? I'd like to try with a fixed size of the circle because the experiment will run online and I cannot control for the display of the participant. 

If there is a specific reason why I should NOT keep the circle size constant, please tell me.

This is a part of the code that should be relevant, more or less, I can provide more if needed.

Thanks,
Francesca

--some of the parameters--
<parameters>
/ trialnumber = 120
/ practicetrials = 12
/ fontsize = 10%
/ fontsize_fixation = 5%
/ pictureheight = 15%
/ radiusscreenproportion = 0.4
/ readyduration = 100
/ blankduration = 200
</parameters>

-- an example of picture selection  --
<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (100%, parameters.pictureheight)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

----------------------------------------------------
Calculate circle coordinates
----------------------------------------------------

<expressions>
/ xcenter = 0.5 * display.canvaswidth
/ ycenter = 0.5 * display.canvasheight

/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
/ Radians_Circle_angle0 = rad(0)
/ Radians_Circle_angle60 = rad(60)
/ Radians_Circle_angle120 = rad(120)


/ heightchange_Circle_angle0 = sin(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ widthchange_Circle_angle0 = cos(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ heightchange_Circle_angle60 = sin(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ widthchange_Circle_angle60 = cos(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ heightchange_Circle_angle120 = sin(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
/ widthchange_Circle_angle120 = cos(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
</expressions>


----------------------------------------------------
Circle coordinates positions
----------------------------------------------------

<list x_coordinates_pictures>
/ items = (expressions.widthchange_Circle_angle0,
expressions.widthchange_Circle_angle60,
expressions.widthchange_Circle_angle120,
-expressions.widthchange_Circle_angle0,
-expressions.widthchange_Circle_angle60,
-expressions.widthchange_Circle_angle120)
/ replace = false
/ selectionrate = always
</list>

<list y_coordinates_pictures>
/ items = (expressions.heightchange_Circle_angle0,
expressions.heightchange_Circle_angle60,
expressions.heightchange_Circle_angle120,
-expressions.heightchange_Circle_angle0,
-expressions.heightchange_Circle_angle60,
-expressions.heightchange_Circle_angle120)
/ selectionmode = list.x_coordinates_pictures.currentindex
/ selectionrate = always
</list>

> If there is a specific reason why I should NOT keep the circle size constant, please tell me.

With a fixed (physical) size you run the risk that stimuli cannot be displayed properly if the fixed size is such that it exceeds the physical dimensions of the given display.

As for specifying a fixed circle size, that question is not answerable based on the code snippets you provided.

+x

 

Dave - 2/15/2021

+x

 

Dave - 2/15/2021

+x

 

Francesca Miti - 2/15/2021

Hi,
I modified a script for a visual search paradigm where 6 pictures are displayed in a circle around the fixation cross. The size of the circle is now based on the height and width of the display (I think).
How can I choose  the size of the circle despite the monitor size? I'd like to try with a fixed size of the circle because the experiment will run online and I cannot control for the display of the participant. 

If there is a specific reason why I should NOT keep the circle size constant, please tell me.

This is a part of the code that should be relevant, more or less, I can provide more if needed.

Thanks,
Francesca

--some of the parameters--
<parameters>
/ trialnumber = 120
/ practicetrials = 12
/ fontsize = 10%
/ fontsize_fixation = 5%
/ pictureheight = 15%
/ radiusscreenproportion = 0.4
/ readyduration = 100
/ blankduration = 200
</parameters>

-- an example of picture selection  --
<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (100%, parameters.pictureheight)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

----------------------------------------------------
Calculate circle coordinates
----------------------------------------------------

<expressions>
/ xcenter = 0.5 * display.canvaswidth
/ ycenter = 0.5 * display.canvasheight

/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
/ Radians_Circle_angle0 = rad(0)
/ Radians_Circle_angle60 = rad(60)
/ Radians_Circle_angle120 = rad(120)


/ heightchange_Circle_angle0 = sin(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ widthchange_Circle_angle0 = cos(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ heightchange_Circle_angle60 = sin(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ widthchange_Circle_angle60 = cos(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ heightchange_Circle_angle120 = sin(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
/ widthchange_Circle_angle120 = cos(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
</expressions>


----------------------------------------------------
Circle coordinates positions
----------------------------------------------------

<list x_coordinates_pictures>
/ items = (expressions.widthchange_Circle_angle0,
expressions.widthchange_Circle_angle60,
expressions.widthchange_Circle_angle120,
-expressions.widthchange_Circle_angle0,
-expressions.widthchange_Circle_angle60,
-expressions.widthchange_Circle_angle120)
/ replace = false
/ selectionrate = always
</list>

<list y_coordinates_pictures>
/ items = (expressions.heightchange_Circle_angle0,
expressions.heightchange_Circle_angle60,
expressions.heightchange_Circle_angle120,
-expressions.heightchange_Circle_angle0,
-expressions.heightchange_Circle_angle60,
-expressions.heightchange_Circle_angle120)
/ selectionmode = list.x_coordinates_pictures.currentindex
/ selectionrate = always
</list>

> If there is a specific reason why I should NOT keep the circle size constant, please tell me.

With a fixed (physical) size you run the risk that stimuli cannot be displayed properly if the fixed size is such that it exceeds the physical dimensions of the given display.

As for specifying a fixed circle size, that question is not answerable based on the code snippets you provided.

Assuming you've not modified any of the deeper guts of the visual search script that would affect sizing and positioning, the following should work to specify a fixed circle size.

Change

<expressions>
...
/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
...
</expressions>

to something along the lines of

<expressions>
...
/ radius_Circle_px = 55/display.getmmx(100,1)*100
...
</expressions>

What this does:
55 is the physical radius size in mm you want for the circle, so 11cm diameter in this case. Change the radius according to your preferences.
display.getmmx(100,1) just figures out how many mm 100 pixels equate to on the given display ( see https://www.millisecond.com/support/docs/v6/html/language/functions/getmmx.htm ), and then we just calculate how many pixels we need on that display to get (close to) our desired radius.

+x

 

Dave - 2/15/2021

+x

 

Dave - 2/15/2021

+x

 

Francesca Miti - 2/15/2021

Hi,
I modified a script for a visual search paradigm where 6 pictures are displayed in a circle around the fixation cross. The size of the circle is now based on the height and width of the display (I think).
How can I choose  the size of the circle despite the monitor size? I'd like to try with a fixed size of the circle because the experiment will run online and I cannot control for the display of the participant. 

If there is a specific reason why I should NOT keep the circle size constant, please tell me.

This is a part of the code that should be relevant, more or less, I can provide more if needed.

Thanks,
Francesca

--some of the parameters--
<parameters>
/ trialnumber = 120
/ practicetrials = 12
/ fontsize = 10%
/ fontsize_fixation = 5%
/ pictureheight = 15%
/ radiusscreenproportion = 0.4
/ readyduration = 100
/ blankduration = 200
</parameters>

-- an example of picture selection  --
<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (100%, parameters.pictureheight)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

----------------------------------------------------
Calculate circle coordinates
----------------------------------------------------

<expressions>
/ xcenter = 0.5 * display.canvaswidth
/ ycenter = 0.5 * display.canvasheight

/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
/ Radians_Circle_angle0 = rad(0)
/ Radians_Circle_angle60 = rad(60)
/ Radians_Circle_angle120 = rad(120)


/ heightchange_Circle_angle0 = sin(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ widthchange_Circle_angle0 = cos(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ heightchange_Circle_angle60 = sin(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ widthchange_Circle_angle60 = cos(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ heightchange_Circle_angle120 = sin(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
/ widthchange_Circle_angle120 = cos(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
</expressions>


----------------------------------------------------
Circle coordinates positions
----------------------------------------------------

<list x_coordinates_pictures>
/ items = (expressions.widthchange_Circle_angle0,
expressions.widthchange_Circle_angle60,
expressions.widthchange_Circle_angle120,
-expressions.widthchange_Circle_angle0,
-expressions.widthchange_Circle_angle60,
-expressions.widthchange_Circle_angle120)
/ replace = false
/ selectionrate = always
</list>

<list y_coordinates_pictures>
/ items = (expressions.heightchange_Circle_angle0,
expressions.heightchange_Circle_angle60,
expressions.heightchange_Circle_angle120,
-expressions.heightchange_Circle_angle0,
-expressions.heightchange_Circle_angle60,
-expressions.heightchange_Circle_angle120)
/ selectionmode = list.x_coordinates_pictures.currentindex
/ selectionrate = always
</list>

> If there is a specific reason why I should NOT keep the circle size constant, please tell me.

With a fixed (physical) size you run the risk that stimuli cannot be displayed properly if the fixed size is such that it exceeds the physical dimensions of the given display.

As for specifying a fixed circle size, that question is not answerable based on the code snippets you provided.

Assuming you've not modified any of the deeper guts of the visual search script that would affect sizing and positioning, the following should work to specify a fixed circle size.

Change

<expressions>
...
/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
...
</expressions>

to something along the lines of

<expressions>
...
/ radius_Circle_px = 55/display.getmmx(100,1)*100
...
</expressions>

What this does:
55 is the physical radius size in mm you want for the circle, so 11cm diameter in this case. Change the radius according to your preferences.
display.getmmx(100,1) just figures out how many mm 100 pixels equate to on the given display ( see https://www.millisecond.com/support/docs/v6/html/language/functions/getmmx.htm ), and then we just calculate how many pixels we need on that display to get (close to) our desired radius.

+x

 

Francesca Miti - 2/16/2021

+x

 

Dave - 2/15/2021

+x

 

Dave - 2/15/2021

+x

 

Francesca Miti - 2/15/2021

Hi,
I modified a script for a visual search paradigm where 6 pictures are displayed in a circle around the fixation cross. The size of the circle is now based on the height and width of the display (I think).
How can I choose  the size of the circle despite the monitor size? I'd like to try with a fixed size of the circle because the experiment will run online and I cannot control for the display of the participant. 

If there is a specific reason why I should NOT keep the circle size constant, please tell me.

This is a part of the code that should be relevant, more or less, I can provide more if needed.

Thanks,
Francesca

--some of the parameters--
<parameters>
/ trialnumber = 120
/ practicetrials = 12
/ fontsize = 10%
/ fontsize_fixation = 5%
/ pictureheight = 15%
/ radiusscreenproportion = 0.4
/ readyduration = 100
/ blankduration = 200
</parameters>

-- an example of picture selection  --
<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (100%, parameters.pictureheight)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

----------------------------------------------------
Calculate circle coordinates
----------------------------------------------------

<expressions>
/ xcenter = 0.5 * display.canvaswidth
/ ycenter = 0.5 * display.canvasheight

/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
/ Radians_Circle_angle0 = rad(0)
/ Radians_Circle_angle60 = rad(60)
/ Radians_Circle_angle120 = rad(120)


/ heightchange_Circle_angle0 = sin(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ widthchange_Circle_angle0 = cos(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ heightchange_Circle_angle60 = sin(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ widthchange_Circle_angle60 = cos(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ heightchange_Circle_angle120 = sin(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
/ widthchange_Circle_angle120 = cos(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
</expressions>


----------------------------------------------------
Circle coordinates positions
----------------------------------------------------

<list x_coordinates_pictures>
/ items = (expressions.widthchange_Circle_angle0,
expressions.widthchange_Circle_angle60,
expressions.widthchange_Circle_angle120,
-expressions.widthchange_Circle_angle0,
-expressions.widthchange_Circle_angle60,
-expressions.widthchange_Circle_angle120)
/ replace = false
/ selectionrate = always
</list>

<list y_coordinates_pictures>
/ items = (expressions.heightchange_Circle_angle0,
expressions.heightchange_Circle_angle60,
expressions.heightchange_Circle_angle120,
-expressions.heightchange_Circle_angle0,
-expressions.heightchange_Circle_angle60,
-expressions.heightchange_Circle_angle120)
/ selectionmode = list.x_coordinates_pictures.currentindex
/ selectionrate = always
</list>

> If there is a specific reason why I should NOT keep the circle size constant, please tell me.

With a fixed (physical) size you run the risk that stimuli cannot be displayed properly if the fixed size is such that it exceeds the physical dimensions of the given display.

As for specifying a fixed circle size, that question is not answerable based on the code snippets you provided.

Assuming you've not modified any of the deeper guts of the visual search script that would affect sizing and positioning, the following should work to specify a fixed circle size.

Change

<expressions>
...
/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
...
</expressions>

to something along the lines of

<expressions>
...
/ radius_Circle_px = 55/display.getmmx(100,1)*100
...
</expressions>

What this does:
55 is the physical radius size in mm you want for the circle, so 11cm diameter in this case. Change the radius according to your preferences.
display.getmmx(100,1) just figures out how many mm 100 pixels equate to on the given display ( see https://www.millisecond.com/support/docs/v6/html/language/functions/getmmx.htm ), and then we just calculate how many pixels we need on that display to get (close to) our desired radius.

I'm sorry, I fixed the circle but I'm struggling with image size. I'd like to have my images presented 3X3 cm despite the monitor size, so I converted and specified 113X113 px.
It works on my big monitor, but on my laptop that is smaller, images are smaller too. How can I prevent this from happening?

<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (113, 113)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

Thank you

+x

 

Dave - 2/16/2021

+x

 

Francesca Miti - 2/16/2021

+x

 

Dave - 2/15/2021

+x

 

Dave - 2/15/2021

+x

 

Francesca Miti - 2/15/2021

Hi,
I modified a script for a visual search paradigm where 6 pictures are displayed in a circle around the fixation cross. The size of the circle is now based on the height and width of the display (I think).
How can I choose  the size of the circle despite the monitor size? I'd like to try with a fixed size of the circle because the experiment will run online and I cannot control for the display of the participant. 

If there is a specific reason why I should NOT keep the circle size constant, please tell me.

This is a part of the code that should be relevant, more or less, I can provide more if needed.

Thanks,
Francesca

--some of the parameters--
<parameters>
/ trialnumber = 120
/ practicetrials = 12
/ fontsize = 10%
/ fontsize_fixation = 5%
/ pictureheight = 15%
/ radiusscreenproportion = 0.4
/ readyduration = 100
/ blankduration = 200
</parameters>

-- an example of picture selection  --
<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (100%, parameters.pictureheight)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

----------------------------------------------------
Calculate circle coordinates
----------------------------------------------------

<expressions>
/ xcenter = 0.5 * display.canvaswidth
/ ycenter = 0.5 * display.canvasheight

/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
/ Radians_Circle_angle0 = rad(0)
/ Radians_Circle_angle60 = rad(60)
/ Radians_Circle_angle120 = rad(120)


/ heightchange_Circle_angle0 = sin(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ widthchange_Circle_angle0 = cos(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ heightchange_Circle_angle60 = sin(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ widthchange_Circle_angle60 = cos(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ heightchange_Circle_angle120 = sin(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
/ widthchange_Circle_angle120 = cos(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
</expressions>


----------------------------------------------------
Circle coordinates positions
----------------------------------------------------

<list x_coordinates_pictures>
/ items = (expressions.widthchange_Circle_angle0,
expressions.widthchange_Circle_angle60,
expressions.widthchange_Circle_angle120,
-expressions.widthchange_Circle_angle0,
-expressions.widthchange_Circle_angle60,
-expressions.widthchange_Circle_angle120)
/ replace = false
/ selectionrate = always
</list>

<list y_coordinates_pictures>
/ items = (expressions.heightchange_Circle_angle0,
expressions.heightchange_Circle_angle60,
expressions.heightchange_Circle_angle120,
-expressions.heightchange_Circle_angle0,
-expressions.heightchange_Circle_angle60,
-expressions.heightchange_Circle_angle120)
/ selectionmode = list.x_coordinates_pictures.currentindex
/ selectionrate = always
</list>

> If there is a specific reason why I should NOT keep the circle size constant, please tell me.

With a fixed (physical) size you run the risk that stimuli cannot be displayed properly if the fixed size is such that it exceeds the physical dimensions of the given display.

As for specifying a fixed circle size, that question is not answerable based on the code snippets you provided.

Assuming you've not modified any of the deeper guts of the visual search script that would affect sizing and positioning, the following should work to specify a fixed circle size.

Change

<expressions>
...
/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
...
</expressions>

to something along the lines of

<expressions>
...
/ radius_Circle_px = 55/display.getmmx(100,1)*100
...
</expressions>

What this does:
55 is the physical radius size in mm you want for the circle, so 11cm diameter in this case. Change the radius according to your preferences.
display.getmmx(100,1) just figures out how many mm 100 pixels equate to on the given display ( see https://www.millisecond.com/support/docs/v6/html/language/functions/getmmx.htm ), and then we just calculate how many pixels we need on that display to get (close to) our desired radius.

I'm sorry, I fixed the circle but I'm struggling with image size. I'd like to have my images presented 3X3 cm despite the monitor size, so I converted and specified 113X113 px.
It works on my big monitor, but on my laptop that is smaller, images are smaller too. How can I prevent this from happening?

<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (113, 113)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

Thank you

Just specify the physical size you want directly

<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (3cm, 3cm)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture

+x

 

Francesca Miti - 2/18/2021

+x

 

Dave - 2/16/2021

+x

 

Francesca Miti - 2/16/2021

+x

 

Dave - 2/15/2021

+x

 

Dave - 2/15/2021

+x

 

Francesca Miti - 2/15/2021

Hi,
I modified a script for a visual search paradigm where 6 pictures are displayed in a circle around the fixation cross. The size of the circle is now based on the height and width of the display (I think).
How can I choose  the size of the circle despite the monitor size? I'd like to try with a fixed size of the circle because the experiment will run online and I cannot control for the display of the participant. 

If there is a specific reason why I should NOT keep the circle size constant, please tell me.

This is a part of the code that should be relevant, more or less, I can provide more if needed.

Thanks,
Francesca

--some of the parameters--
<parameters>
/ trialnumber = 120
/ practicetrials = 12
/ fontsize = 10%
/ fontsize_fixation = 5%
/ pictureheight = 15%
/ radiusscreenproportion = 0.4
/ readyduration = 100
/ blankduration = 200
</parameters>

-- an example of picture selection  --
<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (100%, parameters.pictureheight)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

----------------------------------------------------
Calculate circle coordinates
----------------------------------------------------

<expressions>
/ xcenter = 0.5 * display.canvaswidth
/ ycenter = 0.5 * display.canvasheight

/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
/ Radians_Circle_angle0 = rad(0)
/ Radians_Circle_angle60 = rad(60)
/ Radians_Circle_angle120 = rad(120)


/ heightchange_Circle_angle0 = sin(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ widthchange_Circle_angle0 = cos(expressions.Radians_Circle_angle0) * expressions.radius_Circle_px
/ heightchange_Circle_angle60 = sin(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ widthchange_Circle_angle60 = cos(expressions.Radians_Circle_angle60) * expressions.radius_Circle_px
/ heightchange_Circle_angle120 = sin(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
/ widthchange_Circle_angle120 = cos(expressions.Radians_Circle_angle120) * expressions.radius_Circle_px
</expressions>


----------------------------------------------------
Circle coordinates positions
----------------------------------------------------

<list x_coordinates_pictures>
/ items = (expressions.widthchange_Circle_angle0,
expressions.widthchange_Circle_angle60,
expressions.widthchange_Circle_angle120,
-expressions.widthchange_Circle_angle0,
-expressions.widthchange_Circle_angle60,
-expressions.widthchange_Circle_angle120)
/ replace = false
/ selectionrate = always
</list>

<list y_coordinates_pictures>
/ items = (expressions.heightchange_Circle_angle0,
expressions.heightchange_Circle_angle60,
expressions.heightchange_Circle_angle120,
-expressions.heightchange_Circle_angle0,
-expressions.heightchange_Circle_angle60,
-expressions.heightchange_Circle_angle120)
/ selectionmode = list.x_coordinates_pictures.currentindex
/ selectionrate = always
</list>

> If there is a specific reason why I should NOT keep the circle size constant, please tell me.

With a fixed (physical) size you run the risk that stimuli cannot be displayed properly if the fixed size is such that it exceeds the physical dimensions of the given display.

As for specifying a fixed circle size, that question is not answerable based on the code snippets you provided.

Assuming you've not modified any of the deeper guts of the visual search script that would affect sizing and positioning, the following should work to specify a fixed circle size.

Change

<expressions>
...
/ radius_Circle_px = parameters.radiusscreenproportion * display.canvasheight
...
</expressions>

to something along the lines of

<expressions>
...
/ radius_Circle_px = 55/display.getmmx(100,1)*100
...
</expressions>

What this does:
55 is the physical radius size in mm you want for the circle, so 11cm diameter in this case. Change the radius according to your preferences.
display.getmmx(100,1) just figures out how many mm 100 pixels equate to on the given display ( see https://www.millisecond.com/support/docs/v6/html/language/functions/getmmx.htm ), and then we just calculate how many pixels we need on that display to get (close to) our desired radius.

I'm sorry, I fixed the circle but I'm struggling with image size. I'd like to have my images presented 3X3 cm despite the monitor size, so I converted and specified 113X113 px.
It works on my big monitor, but on my laptop that is smaller, images are smaller too. How can I prevent this from happening?

<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (113, 113)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture>

Thank you

Just specify the physical size you want directly

<picture target>
/ items = targets
/ selectionrate = always
/ select = values.target
/ size = (3cm, 3cm)
/ position = ( 1px * values.target_x, 1px * values.target_y)
</picture

I'm sorry but this is not working since I need to keep the absolut sizes of the images constant, despite the size of the monitor used.
Anyway I found this topic

https://www.millisecond.com/forums/Topic14608.aspx

I'll work on this.
Thank you!