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GLOBAL LOCAL TASK - NAVON TASK
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Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com) for Millisecond Software, LLC
Date: 10-30-2013
last updated: 09-21-2021 by K. Borchert (katjab@millisecond.com) for Millisecond Software, LLC
Script Copyright © 09-21-2021 Millisecond Software
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BACKGROUND INFO
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This script implements the Navon Global Local Task; a test of perceptual processing of global
and local features of stimuli.
The implemented procedure is based on:
Navon, D. (1977). Forest Before Trees: The Precedence of Global Features in Visual Perception.
COGNITIVE PSYCHOLOGY, 9, 353-383.(Experiment3)
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TASK DESCRIPTION
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Participants are briefly presented with letter shapes (e.g. H or S) that are made up of little
letter shapes (e.g. H or S). Some of these letters have the same global (overall shape) and
local (individual building shapes) letters (e.g. an H that consists of Hs), and some have
different global and local letters (e.g. an H that consists of Ss). In the global condition
participants are asked to respond to the global shape of the letter (e.g. press key H if the
global shape of the letter is an H regardless of individual building blocks);
in the local condition participants are asked to respond to the local shapes of the letter
(e.g. press H if the local building elements are Hs regardless of overall shape).
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DURATION
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the default set-up of the script takes appr. 35 minutes to complete
Note: the task duration can be shortened by running fewer blocks. Go to section Experiment and
change the number of blocks run if needed.
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DATA FILE INFORMATION
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The default data stored in the data files are:
(1) Raw data file: 'globallocaltask_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
script.sessionid: 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.
phase: "practice" vs. "test"
Note: by default 2 (parameters.numberpracticeblocks) blocks in each condition are
practice blocks
condition: 1 = Global; 2 = Local
quadrant: stores the currently selected quadrant the stimulus is presented in
consistency: "consistent": global and local shapes are consistent (e.g. an H made of little Hs)
"conflicting": global and local shapes are conflicting (e.g. an H made of little Ss)
"neutral": global and local shapes are inconsistent but not conflicting as one element
stimulus: stores the name of the current stimulus picture
stimulusitem: presented stimuli in order of implementation
target: 'S' or 'H'
response: the participant's response (scancode of response button)
35 = H
31 = S
("O") has no response button attached to it (e.g. an H made of little "Os")
correct: the correctness of the response (1 = correct; 0 = otherwise)
latency: the response latency (measured from onset of stimuli; in ms)
x_pos: the horizontal x-coordinate (in canvas %) depending on values.quadrant
y_pos: the vertical y-coordinate (in canvas %) depending on values.quadrant
(2) Summary data file: 'globallocaltask_summary*.iqdat' (a separate file for each participant)
computer.platform: the platform the script was run on (win/mac/ios/android)
script.startdate: date script was run
script.starttime: time script was started
script.subjectid: assigned subject id number
script.groupid: assigned group id number
script.sessionid: assigned session id number
script.elapsedtime: time it took to run script (in ms); measured from onset to offset of script
script.completed: 0 = script was not completed (prematurely aborted);
1 = script was completed (all conditions run)
PropCorrect: overall proportion correct responses
meanRT: overall mean latency (in ms) of correct responses
PropCorrect_consistent_global: proportion correct responses in the consistent global condition
meanRT_consistent_global: mean latency (in ms) of correct responses in the consistent global condition
same for the remaining conditions
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EXPERIMENTAL SET-UP
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-2 conditions (global vs. local) tested within. Order is counterbalanced by groupnumber.
-3 consistencies (consistent vs. neutral vs. conflicting):
global and local shapes the same (congruent);
global and local shapes different (incongruent)
neutral = control condition
*Blocks:
- per condition: 6 blocks of 36 trials
=> by default, the first 2 blocks of each condition are considered practice blocks
=> altogether 8 test blocks of 36 trials = 288 trials total
- the 6 stimuli per condition (global: overall shapes S and H only; local: building elements S and H only) are presented
6 times (random selection)
- the stimuli can be either presented randomly in any of the 4 screen quadrants (default) or in the center of the screen
(if random; the four different screen quadrants that the stimuli can be presented in are randomly selected 9 times each.)
*Trial Sequence:
Beep (50ms) + Fixation Cross (500ms) -> Stimulus (parameters.stimulusduration) -> mask until response -> ITI: 3s
Latencies are measure from onset of stimulus. Participants are instructed to press either S or H.
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STIMULI
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A)Letter Stimuli
- The letter stimuli used in this script were generated by Millisecond Software with the help of PowerPoint and
Paint.Net.
=> The height of the global shape = 7* the height of the individual local shapes
=> The width of the global shape = 6* the width of the individual local shapes
There are 9 different stimuli: 3 global shapes (H, S, "O"*) and 3 local shapes (H, S, "O").
You are welcome to use these stimuli or substitute your own under
section Editable Stimuli -> item.stims
* the actual shape was supposed to be a rectangle but Navon (1977) notes that it was referred to as an "O"
by participants
-Size of the Letters: the size of the letter stimuli can be fine-tuned for a particular display under
section Editable Parameters -> parameters.picturesize
B) Beep:
the beep was produced in Audacity
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INSTRUCTIONS
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This script provides html instruction pages that are not original to the task.
Change instructions in the provided html documents.
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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:
/responsekey1: first response key (default: "H")
/responsekey2: second response key (default: "S")
/picturesize: height of the targets in screen height percentages (default: 20%)
Notes: - Stimuli used in Experiment 3 were the same as in Experiment 2 - small size condition (Navon, 1977, p.369)
- 'The size of the whole stimulus was the same as in Experiment 1' - small size condition (Navon, 1977, p.365)
- 'The longest vertical diameter of each of the visual stimuli was 28 mm'
(50cm viewing distance) (Navon, 1977, p.362)
/fontsize_fixation: fontsize of the fixation mark in screen height percentages (default: 10%)
/stimulusduration: presentation duration of the targets
Note: the original study (Navon, 1977) used an oscilloscope with a presentation time of 40ms.
This script adapts the procedure to the computer and increases the presentation time
(default: 100ms)
/fixationduration: presentation duration of the fixation stimulus (default: 500ms)
/iti: intertrialinterval (default: 3000ms)
/restduration: duration of the resttrial after each block (default: 20000ms)
/numberofpracticeblocks: the number of blocks in each condition that count as practice.
Navon (1977) used the first 2 blocks in each condition as practice blocks.
/randomtargetlocation: true = target is presented randomly in any of the four screen quadrants;
the four different screen quadrants that the stimuli can be presented in are randomly selected 9 times each. (default)
false = target is presented in the center of the screen
Quadrant screen coordinates: Navon (1977, p.369): "The distance between the center of any of the stimuli and the fixation point was 24 mm."
/xpos1 = 25%
/xpos2 = 75%
/ypos1 = 25%
/ypos2 = 75%