Visual Search Task help

CJones20

Hi all,

I am hoping to receive some direction/ guidance on a task I'm trying to create. I'm new to OpenSesame (and coding more generally). I'm trying to create a visual search task, where a target letter (T) can be presented at either 90 or 270 degrees (i.e on its side, pointing left or right), surrounded by distractors (L) which can appear at 0, 90, 180, and 270 degrees. I would like the display to be randomly generated, with a variable set size of 4, 8, 12, 16, and 20 items. In half the trials, the target is present, and in the other half it is absent.

I've scoured what I could find from the forums, but haven't been able to make much of some of the previous code as it was written in (much) older versions of OpenSesame. I have also tried to reverse engineer the written Visual Search tutorial, but to no avail (I have also tried the video tutorial on youtube, but that uses fixed position and orientation stimuli).

My current workaround is to manually create a pseudo-random stimulus array in powerpoint, but this is sub-optimal for a number of reasons.

I'm hoping someone can point me in the direction of some help with this, or suggestions on how to modify the written tutorial script, as this creates a randomly generated field, with a varying set size, and present/ absent targets.

Any help would be gratefully received,

Many thanks!

sebastiaan

Hi,

The easiest way to do this is to use the xy_random() function to get a random set of coordinates, and then add the target and distractors as Image elements to a Canvas with a script like the one below. This assumes that, in the file pool, you have two images (t.png and l.png) for the T's and L's.

See also:

• https://osdoc.cogsci.nl/3.2/manual/python/common/
• https://osdoc.cogsci.nl/3.2/manual/python/canvas/

Does that make sense?

Cheers!

Sebastiaan

TsandLs.osexp

import random

search_display = Canvas()
for i, (x, y) in enumerate(xy_random(
        n=var.set_size,
        width=400,
        height=400,
        min_dist=50
)):
    if i == 0:  # The first stimulus is always the target
        search_display += Image(
            pool['t.png'],
            rotation=var.target_rotation,
            x=x,
            y=y     
        )
    else:
        search_display += Image(
            pool['l.png'],
            rotation=random.choice([0, 90, 180, 270]),
            x=x,
            y=y     
        )
search_display.show()

CJones20

Hi Sebastiaan,

Thank you so much for your help! Yes, this makes sense.

I added in a (likely inelegant) addition to the script, as for half the trials, the target is absent. For this to run, I added another column to block_loop ('target_condition', which was either 'present', or 'absent'). This seems to produce the desired effect.

Thank you again for your help!

import random
search_display = Canvas()
for i, (x, y) in enumerate(xy_random(
		n=var.set_size,
		width=400,
		height=400,
		min_dist=50
)):
	if var.target_condition == 'present':
		if i == 0: # The first stimulus is always the target
			search_display += Image(
				pool['t.png'],
				rotation=var.target_rotation,
				x=x,
				y=y   
			)
		else:
			search_display += Image(
				pool['l.png'],
				rotation=random.choice([0, 90, 180, 270]),
				x=x,
				y=y   
			)
	elif var.target_condition == 'absent':
		search_display += Image(
				pool['l.png'],
				rotation=random.choice([0, 90, 180, 270]),
				x=x,
				y=y   
			)
search_display.show()