Changing image on keypress

jbrand

Hi,

I am trying to program a test trial where participants can change the image that is displayed on the screen.

To choose the image I would really like for them to scroll through a set of images by pressing a button (e.g. press 'a' to show img_x and press 'l' to show img_y) and then when they decide press 'enter' to move on.

I am trying to do something similar to the BART experiment, i.e. where a participant presses a button such as 'spacebar' and the image increases in size. But instead of increasing in size, during a trial the actual image changes. Once the participant has decided on which image they want, they then press 'enter' and the specific image choice is logged. I have 10 images, named 1.png, 2.png etc.

I know this will require some in-line coding, with if statements, but I just can't figure out how to do it, my programming skills are beginner only.

Any help would be much appreciated!

Thanks,

James

eduard

Hi James,

Sounds like fun. Here my implementation. Let me know if it does what you want.

import random

cv = canvas() # create an empty canvas
kb = keyboard(timeout = 20,keylist = ['a','l','return']) # create a keyboard item that allows for 3 different keys

letters = [1,2,3,4,5,6,7,8] # my stimuli, I don't have your images.

random.shuffle(letters) # randomize images

for i in range(len(letters)-1): # loop over each comparison, I don't knwo whether this is what you had in mind, if not you can remove this for loop 
    var.selected_item = None # initliaze the item that will be selected
    while True: # stay in the loop until a selection was done
        cv.text(letters[i],x = -200) # draw one stimulus to a canvas
        cv.text(letters[i+1],x = 200) # draw the other to the canvas
        cv.show() # shwo the canvas
        if var.selected_item == True:
            cv.clear() # clear the canvas, if no selection has been made yet
        k,t=kb.get_key() # sample a key response
        if k == 'a': # if a was pressed (left stimulus)
            cv.clear() # clear the canvas and...
            cv.rect(-250,-50,100,100) # draw a rectangle around the stimulus to mark it as selected
            var.selected_item = letters[i] # store selection in variable
        elif k == 'l': # same for the right stimulus
            cv.clear()
            cv.rect(150,-50,100,100)
            var.selected_item = letters[i+1]
        elif k == 'return': # if return pressed, break the loop and clear the canvas
            cv.clear()
            break

I made it with letters because I haven't had images, but it should be doable to adjust. Basically get the path for each image like so: path = exp.pool[u'image_in_pool.png'], and store all the paths in a list. And later draw the images with my_canvas.image(path,x=x) instead of with canvas.text(). See also here: http://osdoc.cogsci.nl/3.1/manual/python/canvas/#function-canvas46image40fname-centertrue-xnone-ynone-scalenone41

Good luck.

Eduard