Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com), Millisecond
Created: January 30, 2013
Last Modified: January 20, 2023 by K. Borchert (katjab@millisecond.com), Millisecond
Script Copyright © Millisecond Software, LLC
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)
35 minutes
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).
-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.
A)Letter Stimuli
- The letter stimuli used in this script were generated by Millisecond 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
Instructions provided by Millisecond. They can be edited under
section Editable Instructionst.
File Name: globallocaltask_summary*.iqdat
| Name | Description |
|---|---|
| inquisit.version | Inquisit version number |
| computer.platform | Device platform: win | mac |ios | android |
| startDate | Date the session was run |
| startTime | Time the session was run |
| subjectId | Participant ID |
| groupId | Group number |
| sessionId | Session number |
| elapsedTime | Session duration in ms |
| completed | 0 = Test was not completed 1 = Test was completed |
| propCorrect | Overall proportion correct responses |
| meanRT | Overall mean latency (in ms) of correct responses |
| propCorrectConsistentGlobal | Proportion correct responses in the consistent global condition |
| meanRTConsistentGlobal | Mean latency (in ms) of correct responses in the consistent global condition same for the remaining conditions |
File Name: globallocaltask_raw*.iqdat
| Name | Description |
|---|---|
| build | Inquisit version number |
| computer.platform | Device platform: win | mac |ios | android |
| date | Date the session was run |
| time | Time the session was run |
| subject | Participant ID |
| group | Group number |
| session | Session number |
| blockCode | Name of the current block |
| blockNum | Number of the current block |
| trialCode | Name of the current trial |
| trialNum | Number of the current trial |
| phase | "practice" vs. "test" 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) |
| xPos | The horizontal x-coordinate (in canvas %) depending on values.quadrant |
| yPos | The vertical y-coordinate (in canvas %) depending on values.quadrant |
The procedure can be adjusted by setting the following parameters.
| Name | Description | Default |
|---|---|---|
| responseKey1 | First response key | "H" |
| responseKey2 | Second response key | "S" |
| pictureSize | Height of the targets in screen height percentages 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) | 20% |
| fontSizeFixation | Fontsize of the fixation mark in screen height percentages | 10% |
| stimulusDuration | Presentation duration of the targets 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 | 500ms |
| iti | Intertrialinterval | 3000ms |
| restDuration | Duration of the resttrial after each block | 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% | |