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				DIFFERENCE THRESHOLD: METHOD OF CONSTANT STIMULI (Example: determine difference threshold for a red)
SCRIPT INFO

Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com) for Millisecond Software, LLC
Date: 01-21-2014
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 METHOD OF CONSTANT STIMULI to estimates 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*
Participants are asked repeatedly whether a red Target color is lighter or darker than a red base color. 
By default, 7 targetvalues (3 lighter, 3 darker, 1 the same) are presented 10 times each in a random
order.

At the end a difference threshold is estimated = hypothetical targetvalue at which point participant
says the red is lighter 50% of the times.
=> Underlying idea: Difference threshold is at the point where participant says "lighter" 50% of the times.
The algorithm estimates the targetvalue at "50% lighter responses" by linear interpolation.


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

(1) Raw data file: 'ConstantStimuliMethod_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) 
/taskcount:					counts how many adjustment tasks have been run	
/baseline_value:			stores the color of the current base 
/target_value:				stores the color of the current target Color
response:					the participant's response
latency: 					the response latency

(2) Summary data file: 'ConstantStimuliMethod_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)

/step:						the stepsize used to calculate the target red color values

/baseline_value:			the default baseline_value
/targetvalue1_baseline-
/targetvalue7_baseline:		calculates the targetvalues (here: the red color components of the target stimuli) depending on parameters.step

/percentUP_targetvalue1-
/percentUP_targetvalue7:	calculates the percentage of "lighter" responses for each targetvalue
/NoNegativeSlope:			determines whether the percentage of "lighter" response for a given targetvalue are greater or the same
							as the percentage of "lighter" responses for the preceding targetvalue
								Note: the number of lighter reponses should NOT DEcrease for lighter targetvalues (they can, however,
								stay the same)
								!!!If expressions.nonegativeslope is evaluated to being false, the threshold is not determined
								by the script algorithm. The raw data might need to be re-evaluated manually.
/DiffThreshold:				determines the Difference Threshold (if for some reason the implemented algorithm cannot calculate
							a threshold, the data will read "not determined". The raw data might need to be re-evaluated manually).
							Implemented Algorithm: 
							Underlying idea: Difference threshold is at the point where participant says "lighter" 50% of the times.
							The algorithm estimates the targetvalue at "50% lighter responses" by linear interpolation.


EXPERIMENTAL SET-UP
By default, 7 targetvalues (3 lighter, 3 darker, 1 the same) are presented 10 times each in a random
order.

At the end a difference threshold is estimated = hypothetical targetvalue at which point participant
says the red is lighter 50% of the times.
=> Underlying idea: Difference threshold is at the point where participant says "lighter" 50% of the times.
The algorithm estimates the targetvalue at "50% lighter responses" by linear interpolation.

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_up-
/responsekey_down_label:		Response Key assignments
								up -> 'lighter'
								down -> 'darker'

/baselinevalue:					the baselinevalue (0 -> black, 255 -> brightest red)

/step:							the stepsize used to calculate the target red color values

/debug_displaytargetvalue:		false: debug information is not displayed on screen (default)
								true: debug information is displayed on screen


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