Visual Search Task - Divided Attention with Eye Tracking

Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com), Millisecond

Created: January 19, 2017

Last Modified: January 31, 2023 by K. Borchert (katjab@millisecond.com), Millisecond

Script Copyright © Millisecond Software, LLC

Background

This script implements a basic visual search paradigm based on:

Motter,B.C., & Simoni, D.A. (2008). Changes in the functional visual field during search with and without eye movements. Vision Research 48 (2008) 2382–2393.

Duration

25 minutes

Description

Participants are asked to check letter arrays of green and red L's and T's (in 6 different spatial rotations) of varying array sizes (6, 12, 24, 48) for a target letter. The target letter shares one feature with each distractor letter ("conjunction style search array"). For example, if the target letter is a red L, the distractor letters are red T's and green L's. Half the arrays contain the target.

Procedure

Practice: default
- 24 practice trials (6 per target category, e.g. 'green L', order is randomized)
- each possible target is used once per target category - random selection)
- 2 different array sizes per target category (4 stims vs. 16 stims), random selection
- half the trials (12) have the target present (order of 'target present' vs. 'target absent' randomized)
- provides performance feedback


Test: default
2 target colors (green vs. red) x 2 target letters (L vs. T) x 4 array sizes (6, 12, 24, 48) x 2 target condition (present vs. absent)
x 6 reps = 192 trials,
tested in a full, mixed design

- the 4 target categories (color x letter) are selected in random order
- in each of the 4 target conditions (color x letter, e.g. 'green L'):
- equal frequency of the 4 possible array sizes (array size is randomly determined)
- half the targets are present, half the targets are absent (randomly selected)
=> balanced across the 4 different set sizes (6 targets present/6 targets absent for each of the 4 set sizes)
Motter & Simoni (2008) ran sessions of 240 trials.

- Target Selection:
- The target stimulus is selected randomly from the 6 possible rotations (see under STIMULI) for the given target condition)
- each rotation is selected equally often
=> each target rotation is run 8 times per target condition

- Distractor Selection:
- half the distractors are selected from the opposite color (but same letter)
-> the appropriate item numbers are selected randomly without replacement (repetitions are possible, once all 6 possible stims were selected)
- the remaining distractors are selected from the same color (but different letter)
-> the appropriate item numbers are selected randomly without replacement (repetitions are possible, once all 6 possible stims were selected)

- Stim Locations:
- 48 possible stim locations (7x7 matrix, with fixation cross in the center)
- stim locations are randomly (without replacement) assigned to each of the stims (including target)
- stim locations reset before each new trial


Canvas:
By default, the canvas (=part of the screen used by this script) is the biggest square (width = height) that can be
established on the current monitor. The canvas can be further manipulated by explicitly forcing
a specific canvas size and/or by forcing a specific windowsize (see section DEFAULTS for more info)


Trial Sequence:
Fixation Cross (until Spacebar press) -> Cue (default: 1000ms)->Array (max: 7000ms)

Stimuli

provided by Millisecond - can be edited under section Editable Stimuli


each target category (green L, red L, green T, red T) can be represented by 1 of 6 orientations:
the letter was rotated 6 times by increments of 60deg

Instructions

Instructions are not original to the task. They are provided by Millisecond
as htm/html pages and can be edited by changing the provided htm/html files.
To edit htm/html-files: open the respective documents in simple Text Editors such as TextEdit (Mac)
or Notepad (Windows).

Summary Data

File Name: visualsearch_letter_et_summary*.iqdat

Data Fields

Raw Data

File Name: visualsearch_letters_raw*.iqdat

Data Fields

Parameters

The procedure can be adjusted by setting the following parameters.