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Fast Periodic Visual Stimulation EEG as a Measure for Perceptual Categorization and Discrimination

Jaana Van Overwalle1,3, Charlotte Buhre1, Stephanie Van der Donck2,3,

Sander Van de Cruys1,3, Bart Boets2,3 & Johan Wagemans1,3

1 Brain & Cognition Unit, KU Leuven, Belgium; 2 Center for Developmental Psychiatry, KU Leuven, Belgium;

3 Leuven Autism Research (LAuRes), KU Leuven, Belgiuim

• Oddball paradigm: Objects (O) are presented at 6 Hzbase rate and give neural responses at 6 Hz. Faces (F) are inserted at 1.2 Hz oddball rate. When these faces (F) are perceived as different from the objects (O), they elicit responses at 1.2 Hz and additional oddball harmonics (n x 1.2 Hz).

• Sweep paradigm: Extension of the oddball paradigm. The oddball is presented at a specific frequency while it is being parametrically varied (‘‘swept’’).

• Advantages: The response can thus be measured implicitly (i.e. without an explicit behavioral task) and objectively (since it occurs at a predefined frequency).

• Inanimate-Inanimate switch (1)

• Animate-Animate switch (1)

• Inanimate-Animate switch (3)

EEG FFT

Candle-Bottle (CB)

Penguin-Child (PC)

Peacock-Truck (PT)

Watch-Seahorse

(WS)

Church-Duck (CD)

5 sequences of black-and-white stimuli morphed from one entity to another in 10 equally spaced steps 11 morph levels per morph sequence (Hartendorp et al., 2010)

• Study 1: Categorization• Participants: 8 healthy adults• Sweep paradigm across the 11 morph levels• Implicit versus explicit EEG• 2-AFC categorization task

• Study 2: Discrimination• Participants: 18 healthy adults• Comparing 7 pairs (small steps e.g. L1-L3) and 6 pairs

(big steps e.g. L1-L4) across the morph sequence• Oddball versus sweep paradigm • 2-AFC discrimination task

Liu-Shuang et al., 2015

Study 1: Categorization

Part 1: FPVS EEG (n=18) Part 2: Behavior (n=17) Part 3: Consistency of the FPVS EEG

Study 2: Discrimination

Every day we receive plenty of visual information. We react efficiently on this input via categorization. Categorization is an automatic and implicit process, which enables us to respond adaptively to similar exemplars of a category. Although this is an implicit process, research has mainly investigated categorization explicitly. Therefore, using Fast Periodic Visual Stimulation (FPVS) EEG we want to develop an implicit measure to investigate this process and its neural correlates.

Main Goal: developing an implicit measure for categorization• Taking into account complementary processes such as discrimination• Correlating to explicit behavior

Secondary Goal: further investigating…• Differences between the naturally categorically perceived stimuli• The robustness of the FPVS EEG technique: repeated measures and individual differences

Part 1: Sweep FPVS EEG (n=8) Part 2: Behavior (n=8) Part 3: Consistency of the FPVS EEG

Oddball FPVS (n=10) Sweep FPVS (n=8)

Small

Big

Oddball FPVS: different measures

Sweep FPVS: different measures

Background

Stimuli

Oddball & Sweep FPVS Paradigm

Experimental Paradigm

European Conference on Visual Perception 2018Email: jaana.van.overwalle@gmail.com

Conclusions

Main Goal: developing an implicit measure for categorization

The implicit EEG and explicit behavior measures for categorization and discrimination seem to correlate well. However, responses should be quantified further to make any conclusions.

Secondary Goal: further investigating robustness and inter-stimulus differences

The results show a difference in amplitude and consistency of the EEG signal for the different stimuli. In future research comparing responses between patients and healthy individuals, only the stimuli eliciting robust responses will be used.

Different measures (ep1-ep3 implicit + ep4 explicit)

Different individuals