RDK Dot size in degrees (rather than pixels)?

Builder
1

OS: Win10
PsychoPy version: 2020.1.3
Standard Standalone? (y/n): Y

What are you trying to achieve?:
I’m trying to convert RDK-dot size from pixels to degrees so when my task is run on other computers/monitors (i.e. a participant’s computer) they appear the same size consistently. Under the builder/dot size option it only allows me to input a pixel unit. Other properties such as RDK field size are in degrees and scale appropriately across computers.

(This is the result on two different laptops with the same task)

win_2496x1664
win_2496x16641485×837 39.6 KB

Mac_1440x900
Mac_1440x9002492×1310 111 KB

Is there someway to do a pixel to degree conversion that gives me consistent dot sizes across different screens?

What did you try to make it work?:
I’ve entered the monitor info with the same viewing distance with their respective monitor width and resolution on different laptops. I assume that due to different monitor’s pixel-properties dot sizes appear differently. If there’s no easy way to do a conversion, I’m thinking of using a code snippet that lets me scale dot size based on the monitor’s information (i.e. pixel count and screen width) but not sure how I’d do this

Thanks in advance!

2

Hi, there are some functions built into PsychoPy that allow conversions like this:

https://www.psychopy.org/api/tools/monitorunittools.html#psychopy.tools.monitorunittools.deg2pix

e.g. import this function like this:

from psychopy.tools.monitorunittools import deg2pix

Then you can calculate a value in pixels corresponding to an angle on the local monitor (assuming you have called it win, and that it has a valid entry defined in the Monitor Centre, giving its size and distance):

dot_size = deg2pix(degrees = 0.1, monitor = win.monitor))
3

Thanks for your help Michael! In a code snippet under begin routine I’ve entered this:
My monitor is called ‘M’ and my RDK stimuli is ‘RDK_Prac’

RDK_Prac.dotSize  = deg2pix(degrees = 0.186, monitor ='M')

But I get this error:

image
image1051×1022 193 KB

If I try monitor = M.monitor I get a: ‘NameError: name ‘M’ is not defined’
I’m not the best at coding so I’m probably missing something.

Cheers

4

Please show the line where you create your visual.Window()

5

Under the coder view:

win = visual.Window(
    size=[1997, 1331], fullscr=True, screen=0, 
    winType='pyglet', allowGUI=False, allowStencil=False,
    monitor='M', color=[0.506,0.506,0.506], colorSpace='rgb',
    blendMode='avg', useFBO=True, 
    units='pix')
6

OK, so your code should be like this, rather than trying to directly refer to the monitor name as 'M':

RDK_Prac.dotSize  = deg2pix(degrees = 0.186, monitor = win.monitor)
7

Thanks Michael, that’s fixed it!