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CHANGE BLINDNESS
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Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com) for Millisecond Software, LLC
Date: 09-13-2013
last updated: 04-10-2023 by K. Borchert (katjab@millisecond.com) for Millisecond Software, LLC
Script Copyright © 04-10-2023 Millisecond Software
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BACKGROUND INFO
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This script implements the change blindness paradigm as described in:
Beck, M.R. & Levin, D.T (2003). The role of representational volatility in recognizing pre- and postchange objects.
Perception & Psychophysics, 65, 458-468.
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TASK DESCRIPTION
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Participants are presented a 'before' and an 'after' picture for 2s. Each picture consists of 3-16 different objects that
are arranged in a 4x4 matrix. One object is changed from the 'before' to the 'after' picture. In two recognition tasks
participants are asked to select a) the prechange object and b) the postchange objects out of 4 possible choices.
The order of the tasks is counterbalanced between participants.
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DURATION
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the default set-up of the script takes appr. 15-20 minutes
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DATA FILE INFORMATION
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The default data stored in the data files are:
(1) Raw data file: 'changeblindness_raw*.iqdat' (a separate file for each participant)
build: The specific Inquisit version used (the 'build') that was run
computer.platform: the platform the script was run on (win/mac/ios/android)
date, time: date and time script was run
subject, group: with the current subject/groupnumber
session: with the current session id
blockcode, blocknum: the name and number of the current block (built-in Inquisit variable)
trialcode, trialnum: the name and number of the currently recorded trial (built-in Inquisit variable)
Note: trialnum is a built-in Inquisit variable; it counts all trials run; even those
that do not store data to the data file such as feedback trials. Thus, trialnum
may not reflect the number of main trials run per block.
expcondition: 1 = prechange Forced Choice Task before postchange Forced Choice Task
2 = postchange Forced Choice Task before prechange Forced Choice Task
shift: 1 = right shift of coordinates for postchange presentation;
2 = left shift of coordinates for postchange presentation
numberofobjects: stores the current number of objects in the array
arraypresentationtime: current arraypresentation time
stimulusitems: the presented stimuli in order of trial presentation
response: the participant's response (scancode of response buttons)
correct: accuracy of response: 1 = correct response; 0 = otherwise
latency: the response latency (in ms); measured from: onset of trial
array_itemnumbers: string variable that stores all the itemnumbers of the selected array objects
prechangeobject: contains the itemnumber of the prechanged object (= same as object1)
postchangeobject: contains the itemnumber of the postchanged object
prefoilobject: contains the itemnumber of the prefoil object (= same as object2) in prechange lineup
postfoilobject: contains the itemnumber of the postfoil object (= same as object3) in postchange lineup
pre_unrelatedobject1: contains the itemnumber of a totally new object in prechange lineup
post_unrelatedobject1: contains the itemnumber of a totally new object in postchange lineup
pre_unrelatedobject2: contains the itemnumber of a totally new object in prechange lineup
Post Unrelatedobject2: contains the itemnumber of a totally new object in postchange lineup
object1-
object16: stores the itemnumber of object1 to object16 (screen locations randomly determined)
(2) Summary data file: 'changeblindness_summary*.iqdat' (a separate file for each participant)
inquisit.version: Inquisit version run
computer.platform: the platform the script was run on (win/mac/ios/android)
startDate: date script was run
startTime: time script was started
subjectid: assigned subject id number
groupid: assigned group id number
sessionid: assigned session id number
elapsedTime: time it took to run script (in ms); measured from onset to offset of script
completed: 0 = script was not completed (prematurely aborted);
1 = script was completed (all conditions run)
expcondition: 1 = prechange Forced Choice Task before postchange Forced Choice Task
2 = postchange Forced Choice Task before prechange Forced Choice Task
practice_arraypresentationtime: sets the object array presentation time during practice (default: 3000ms)
Note: a practice session wasn't mentioned in the original article
test_arraypresentationtime: sets the object array presentation time during testing (default: 2000ms)
Note: could also be declared as a list in case different test_arraypresentationtimes = IV
array_ISI: (interstimulus) time between offset of 'before' array and onset of 'after' array (default: 350ms) in ms
4AFC_ISI: time between the two recognition tasks (default: 500ms) in ms
ITI: (intertrial) time between end of 2nd recognition task and onset of next 'before' array (default: 1000ms) in ms
prechange3_hits-
postchange3_fass: sums up hits/False Alarms (FAs) for prechange and postchange recognition
prechange3_diff: difference in values.prechange_hits - values.prechange_FAs for array number = 3 (same for all array numbers)
postchange3_diff: difference in values.postchange_hits - values.postchange_FAs for array number = 3 (same for all array numbers)
the same for all array numbers 3-16
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EXPERIMENTAL SET-UP
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* 'before' and 'after' picture: consist of 3-16 objects, randomly arranged in a 4x4 matrix ('after' picture is slightly
shifted to the left or right by default) => one object changes from the 'before' to the 'after' picture
* order of recognition tasks (prechange picture -> postchange picture) is counterbalanced by groupnumber
* recognition tasks present: one foil (a different one for each task), the target item (prechange object or postchange
object, 2 unrelated objects (different ones for each task); the order of the objects is randomly determined
* by default half the 'after' pictures are shifted to the left, the other half to the 'right' (randomly determined)
* Test Block: 14 different array objects (3-16) * 4 repetitions = 56 trial sequences
*optional practice block: 10 practice trials with number of array objects = 4 and with error feedback (it is run by default);
array presentation times can be set independently from testing session under section Editable Parameters.
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STIMULI
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The images provided with this script are digitalized versions (300px x 300px) of the pictures presented by:
Snodgrass, J. G., & Vanderwart, M. (1980). A standardized set of 260 pictures: Norms for name agreement,
image agreement, familiarity, and visual complexity. Journal of Experimental Psychology:
Human Learning & Memory, 6, 174-215.
The images were created in Paint.NET by Millisecond Software LLC.
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INSTRUCTIONS
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not original; can be edited under section EDITABLE INSTRUCTIONS
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EDITABLE CODE
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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:
Durations:
/runpracticeblock: true = runs a practice block (see block.practice under BLOCKS) - default option
false = skips the practice block (!!!Instructions need to be updated accordingly)
/practice_arraypresentationtime: sets the object array presentation time during practice in ms (default: 3000ms)
Note: a practice session wasn't mentioned in the original article
/test_arraypresentationtime: sets the object array presentation time during testing in ms (default: 2000ms)
Note: could also be declared as a list in case different test_arraypresentationtimes = IV
/array_ISI: (interstimulus) time in ms between offset of 'before' array and onset of 'after' array (default: 350ms)
/4AFC_ISI: time between the two recognition tasks (default: 500ms)
/ITI: (intertrial) time in ms between end of 2nd recognition task and onset of next 'before' array (default: 1000ms)
4x4 Matrix Presentation:
/pictureheight: sets the picture size in canvas height percentages
/column1_x -
/row4_y: sets the picture center (in %) for the 4columns/4rows for 'before' picture
/shiftpercent: determines how much the after picture should be shifted to right/left (default: 10% = 1/2 column width)
