Circular ROIs for mouse responses (inline JavaScript)

Comments

• Fab

  January 26

  Hi @CarlaC,

  I'm not sure how you display your circles, whether you somehow draw then using coding or whether you're using pictures (most probably you're doing the latter). Regions of interest are indeed related to the objects and pictures are rectangular.

  Let's assume that you're using a picture containign a circle with a radius of 100 pixels.

  

  If you want to restrict responses to mouse clicks that are within a circle, you'll need to do some programming in Javascript to implement the following logic:

  (1) Establish the (x,y) coordinate of your picture's center. In Open Sesame, that would simply be the x and y of your picture as pasted on your sketchpad.

  (2) read out the (x,y) coordinates of the mouse click (cursor_x, cursor_y, whihc in Javascript gets accessed using vars.cursor_x, vars.cursos_y).

  (3) dig into your memories from school to apply the Pythagorean theorem in order to establish whether the distance between the mouse click and the center of the circle is smaller or equal to the radius (in whihc case the subject clicked within the circle) or greater than the radius (in which case the subject clicked outside the circle).

  Let's imagine that the subject clicked where you see the yellow dot here.

  

  You know the radius of the circle (100 pixels), you know the coordinates of the center of your picture (x,y), and you can get the coordinates of the mouse click (cursor_x, cursor_y).

  You want to know whether how c compares the radius.

  All you have to do now is to apply the Pythagorean theorem:

  

  You can calculate a by taking the absolute value of the difference between y and cursos_y (I say absolute valoue because that way you get a measure that is not dependent upon whether the subject clicks above or below the circle's center.

  a = | y - cursos_y |

  Apply a similar logic to b:

  b = | x - cursos_x |

  Now you just have to calculate the square root of (a2 + b2) to get c:

  

  Then you'll just have to compare c to the radius.

  You'll need to implement this in a loop that goes on for many cycles and use the "break if" parameter to interrupt it when a valid response has been registered (without doing this, your task will just take one mouse click and move on to the next bit of your task irrespective of whether the subject actually clicked on the circle).

  Hope this helps,

  Fabrice.

  
• CarlaC

  February 9

  Hi Fabrice, 

  thank you very much for your thorough response, that was very helpful!

  Best,

  Carla