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GLOBAL LOCAL TASK - NAVON TASK
Script Author: Katja Borchert, Ph.D. (email@example.com) for Millisecond Software, LLC
last updated: 09-21-2021 by K. Borchert (firstname.lastname@example.org) for Millisecond Software, LLC
Script Copyright © 09-21-2021 Millisecond Software
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)
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).
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.
DATA FILE INFORMATION
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
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
-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
- 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.)
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.
- The letter stimuli used in this script were generated by Millisecond Software with the help of PowerPoint and
=> 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"
-Size of the Letters: the size of the letter stimuli can be fine-tuned for a particular display under
section Editable Parameters -> parameters.picturesize
the beep was produced in Audacity
This script provides html instruction pages that are not original to the task.
Change instructions in the provided html documents.
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
/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%