The OCTA Toolbox: A new tool to create flexible and
reproducible stimuli for studying perception and appreciation

Eline Van Geert, Christophe Bossens, & Johan Wagemans
Laboratory of Experimental Psychology, KU Leuven, Belgium

Aim of OCTA

Create reproducible and flexible multi-element displays varying qualitatively and quantitatively in:

ORDER

structure and organization

COMPLEXITY

quantity and variety

available as a free tool for
programmers (as a Python library) and
non-programmers (as an online Shiny app)

Test the OCTA Shiny app & code

Shiny app documentation Python code

1 Create stimulus

Stimulus types

Grid
Outline
Concentric

Stimulus features
➜

2 Add element positions

Position pattern definitions

Create2DGrid

CreateSineGrid

CreateRandomPositions

CreateCircle

CreateShape

CreateCustomPositions

3 Add feature patterns & values

Features (including dynamic feature options!)

shapes

fillcolors

boundingboxes

orientations

borderwidths

bordercolors

opacities

mirrorvalues

additional non-visual features: links, classlabels, idlabels Pattern types

Repeat

ElementRepeat

Mirror

Gradient

Random

TiledGrid

TiledElementGrid

Pattern directions

AcrossElements

AcrossRows

AcrossColumns

AcrossLeftDiagonal

AcrossRightDiagonal

AcrossLayers

4 Add deviations & calculate measures

Position and element deviations

position
jitter

position
deviations

swap
elements

randomize
elements

remove
elements

Feature deviations

swap
features

change
features

randomize
features

jitter
features

Calculate order and complexity measures

ORDER
pattern type congruency
pattern direction congruency
# pattern deviants
# position deviants

COMPLEXITY
# elements
# distinct elements
# distinct values
# non-identical features

Calculate your own measures using the vector or raster image output

5 Render, save, and recreate the stimulus

Output options

stimulus as vector image (SVG)
stimulus as raster image (PNG, JPG, PDF, TIFF)
computer-readable JSON output to recreate the stimulus
in Python with the LoadFromJSON function
in the online Shiny app: download or view the Python code
to create the stimulus in Python

Set a seed to reproduce the exact same random deviations

Scale option to increase quality for raster images

SVG

PNG scale 0.5

PNG scale 1

PNG scale 10

Applications

OCTA stimuli are ideal for online or offline studies on:

aesthetic
appreciation

order and
complexity

grouping
principles

symmetry
detection

local-global processing

creativity

visual
search

and many
more!

easy to use in any kind of task
(rating, ranking, sorting, detection, construction, adjustment, …)

Why use OCTA?

OCTA facilitates reproducible stimulus construction and experimental design in research on aesthetics and visual perception
Use OCTA when you want to create stimuli that are:

varying qualitatively or quantitatively in order and/or complexity
reproducible, adjustable, and open source
easy to create
tailored for online use
static or dynamic
multimodal (adding sound is possible using Javascript)
…

Many opportunities for further development
Subscribe to email updates on OCTA here
Get in touch for questions, feature requests, or collaborations! eline.vangeert@kuleuven.be

Contact

Eline Van Geert - eline.vangeert@kuleuven.be
supported by a Ph.D. fellowship of the Research Foundation - Flanders (FWO)

European Conference on Visual Perception 2021 - August 26^th - Virtual