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				DIFFERENCE THRESHOLD: Interweaved Staircase Method (Example: determine difference threshold for a red)
SCRIPT INFO

Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com) for Millisecond Software, LLC
Date: 03-26-2014
last updated: 01-08-2016 by K.Borchert (katjab@millisecond.com) for Millisecond Software LLC

Copyright © 01-08-2016 Millisecond Software


BACKGROUND INFO

											*Purpose*
This script implements the interweaved STAIRCASE METHOD to estimate the difference threshold for a particular color red

Reference: 
Ehrenstein, W.H. & and Addie Ehrenstein, A. (1999). Psychophysical Methods. In U. Windhorst & H. Johansson, Hakan (Eds.), 
Modern Techniques in Neuroscience Research (pp.1211-1241). Heidelberg: Springer.
(->http://uni-leipzig.de/~isp/isp/history/texts/PSYPHY-M.PDF)


											  *Task*
In the staircase procedure, participants are asked repeatedly whether a red Target color is lighter or darker than 
a red base color.
 
For example: the red component of the target color is lighter. As long as participants say the target 
red is lighter than the base red, the target red gets adjusted down by a preestablished step size (editable
value). Once participants reverse their answer (and say it's darker), the adjustment reverses and the 
the target color is turned up lighter by the preestablished step size. The reversal threshold = average of the 
last two target red values before reversal (e.g. one perceived lighter and one perceived darker than baseline) gets
noted. Once a predetermined number of reversals has taken place (parameters.max_reversals) the difference
threshold is calculated as the mean of all the obtained reversal thresholds.

Interweaved staircase method: two staircases are run at the same time. One staircase starts with a lighter
red target (= staircase DOWN), the other staircase starts with a darker red target (= staircase UP)
The individual trials of each staircase are either called in a random or in an alternate fashion (-> parameters.staircase_order).
The purpose of the interweaved staircase method is to somewhat obscure the nature of the procedure.

In general, the staircase procedure is considered a variant of the Method of Limits with the difference that once a participant
changes the response (e.g. from "it's lighter" to "it's darker") the threshold estimation isn't over but the
adjustments are reversed and a predetermined number of reveral thresholds are noted => the thresholds gets
crossed several times.

By default, this script runs one cycle: one up and one down staircase interweaved


DATA FILE INFORMATION: 
The default data stored in the data files are:

(1) Raw data file: 'StaircaseMethod_raw*.iqdat' (a separate file for each participant)

build:							Inquisit build
computer.platform:				the platform the script was run on
date, time, subject, group:		date and time script was run with the current subject/groupnumber 
blockcode, blocknum:			the name and number of the current block
trialcode, trialnum: 			the name and number of the currently recorded trial
									(Note: not all trials that are run might record data; by default data is collected unless /recorddata = false is set for a particular trial/block) 
/staircase:						1 = staircase DOWN; 2 = staircase UP
/direction_down:				1 = target lighter; 2 = target darker for staircase DOWN
/direction_up:					1 = target lighter; 2 = target darker for staircase UP
/baseline_value:				stores the red color target tone of the current base
/targetvalue_down:				stores the red color target tone of the current target Color in the DOWN staircase
/targetvalue_up:				stores the red color target tone of the current target Color in the UP staircase
response:						the participant's response
latency: 						the response latency
/countreversals_down:			count number of direction reversal for staircase DOWN
/countreversals_up:				count number of direction reversal for staircase UP
/ReversalThreshold:				estimated Threshold at Reversal point (midpoint between last two target values)
/DiffThreshold_up:				mean reversal thresholds for current UP Staircase 
								(thresholds: midpoint between the last two target values before reversal response)
/DiffThreshold_down:			mean reversal thresholds for current DOWN Staircase 
								(thresholds: midpoint between the last two target values before reversal response)
/DiffThreshold:					mean threshold (based on current DiffThreshold_up and DiffThreshold_Down) for the current cycle

(2) Summary data file: 'StaircaseMethod_summary*.iqdat' (a separate file for each participant)

script.startdate:				date script was run
script.starttime:				time script was started
script.subjectid:				subject id number
script.groupid:					group id number
script.elapsedtime:				time it took to run script (in ms)
computer.platform:				the platform the script was run on
/completed:						0 = script was not completed; 1 = script was completed (all conditions run)

/cycles:						stores the number of staircase cycles run
/staircase_order:				select from "alternate" (default) or "random"
								alternate: staircase up and staircase alternate (until one of the staircases has reached the max. number of reversals)
								random: staircases are selected randomly (until one of the staircases has reached the max. number of reversals)

/step:							the stepsize with which the target color increases/decreases (default: 2)
/initialdifference:				initial difference in the red component of target and base (default: 50+1 = 51)
									Note: in this script the initial difference is selected in such a way that the
									  adjusted targetvalues are always either above or below baseline.
/baselinevalue1:				the baseline_value for cycle 1
/DiffThreshold1:				mean threshold based on DiffThreshold_up and DiffThreshold_Down for cycle 1


INSTRUCTIONS
see section Editable Instructions

EDITABLE CODE:
check below for (relatively) easily editable parameters, stimuli, instructions etc. 
Keep in mind that you can use this script as a template and therefore always "mess" with the entire code to further customize your experiment.

The parameters you can change are:

/responsekey_lighter -
/responsekey_darker_label:			the response key assignments (scancodes and labels)

/baselinevalue1:					the baseline value (0 -> black, 255 -> brightest red)
									Note: to add further staircase cycles with different basevalues
									add a value for each new baseline value you want to test and go to
									BLOCKS for further instructions.

/step:								the stepsize with which the target color increases/decreases (default: 2)

/initialdifference:					initial difference in the red component of target and base (default: 50+1 = 51)
										Note: in this script the initial difference is selected in such a way that the
												targetvalues are always either above or below baseline.

/max_reversals:						the maximum number of reversals per staircase

/staircase_order:					select from "alternate" (default) or "random"
									alternate: staircase up and staircase alternate (until one of the staircases has reached the max. number of reversals)
									random: staircases are selected randomly (until one of the staircases has reached the max. number of reversals)

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