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

Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com) for Millisecond Software, LLC
Date: 01-20-2014
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 LIMITS 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*
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 by a preestablished step size (editable
value). Once participants reverse their answer (and say it's darker), the trial is over and the threshold is
calculated as the mean between the last two red color components for the target (aka the last "lighter" and 
the first "darker" red component).

By default this scripts estimates the Difference Thresholds for 1 red colors (-> editable parameters), 
with 2 trials each, one for a lighter and one for a darker start target. The order is determined randomly
for each participant (-> list.baseline_values)

1 cycle = 1 "up" sequence + 1 "down" sequence



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

(1) Raw data file: 'LimitsMethod_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) 
/cycles:						stores the number of "limits" cycles run (one cycle runs an up and a down sequence)

/baseline_value:				stores the color of the current base
/target_value:					stores the color of the current target
/direction:						1 = Down (sequence starts with targetvalue > baseline value)
								2 = Up (sequence starts with targetvalue < baseline value)

/sequencecount:					counts how many limits sequences have been run in a cycle	
response:						the participant's response
latency: 						the response latency in ms
						
/DiffThreshold_up:				the estimated Difference threshold for the current UP sequence (= starting with
								target value < baseline value)
/DiffThreshold_down:			the estimated Difference threshold for the current DOWN sequence (= starting with
								target value > baseline value)
/TotalDiffThreshold:			mean difference threshold for one adjustment cycle (up and down)

(2) Summary data file: 'LimitsMethod_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 "limit" cycles run
/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 of the first "limits" cycle
/DiffThreshold1:				stores the Difference Threshold of the first cycle


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) for cycle 1
									Note: to add further 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
												adjusted targetvalues are always either above or below baseline.

/interadjustmentpause:				pause after an adjustment sequence in ms (default: 500ms)

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