Cumulative probability

# Generated by OpenSesame 0.27.2 (Frisky Freud)
# Thu Jun 13 14:44:02 2013 (posix)
# <http://www.cogsci.nl/opensesame>

set foreground "white"
set subject_parity "even"
set description "A template containing a practice and an experimental phase"
set title "Extended template"
set compensation "0"
set coordinates "relative"
set height "768"
set mouse_backend "xpyriment"
set width "1024"
set sampler_backend "legacy"
set keyboard_backend "legacy"
set background "black"
set subject_nr "0"
set canvas_backend "xpyriment"
set start "experiment"
set synth_backend "legacy"

define inline_script set_prop
	set _run ""
	___prepare__
	# Set the initial probability
	exp.set('prob', .5)
	__end__
	set description "Executes Python code"

define sequence trial_sequence
	set flush_keyboard "yes"
	set description "A single trial"
	run cumulative_probability "always"
	run sketchpad "always"

define loop block_loop
	set repeat "10"
	set description "A single block of trials"
	set item "trial_sequence"
	set column_order ""
	set cycles "1"
	set order "random"
	run trial_sequence

define sequence experiment
	set flush_keyboard "yes"
	set description "The main sequence of the experiment"
	run set_prop "always"
	run block_loop "always"

define sketchpad sketchpad
	set duration "keypress"
	set description "Displays stimuli"
	set start_response_interval "no"
	draw textline 0 0 "event_occurs = [event_occurs]" center=1 color=white font_family="mono" font_size=18 font_italic=no font_bold=no show_if="always"
	draw textline 0.0 64.0 "prob = [prob]" center=1 color=white font_family="mono" font_size=18 font_italic=no font_bold=no show_if="always"

define inline_script cumulative_probability
	set _run ""
	___prepare__
	from random import random

	# random() returns a number between 0 and 1
	# so this sets `event_occurs` to True or False
	# with a probability of [prob].
	prob = self.get('prob')
	event_occurs = random() < prob

	# If the event does not occur, increase the
	# probability for the next time, but not
	# higher than 1.
	if not event_occurs:
		prob += .1
		if prob > 1:
			prob = 1
	# If the event does occur, decrease the probability,
	# but not below 0.
	else:
		prob -= .1
		if prob < 0:
			prob = 0

	# Store [prob] and [event_occurs]
	exp.set('prob', prob)
	exp.set('event_occurs', event_occurs)
	__end__
	set description "Executes Python code"