A) Flat Reflection

B) Slant Reflection

C) Flat Random

D) Slant Random

E Reflection – Random scalp maps (300 to 1000 ms)

F) Discriminate Color G) Discriminate Regularity

B) Oddball DetectionA) Explicit Discrimination

A B

C D

480-520 1500-2000

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lar

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480-520 1500-2000

Regu

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Experiment 1

Experiment 2

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C

100-130 ms 170-200 ms 300-1000 ms

Experiment 1

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Experiment 2

Using EEG to investigate visual symmetry perceptionMarco Bertamini, Giulia Rampone and Alexis Makin

In a number of recent studies we have explored the nature of visual symmetry processing by measuring event related potentials and neural oscillatory activity. Here we summarize the answers that we can now provide to seven different questions.

1. There is sustained posterior negativity (SPN) related to the presence of symmetry (Hofel & Jacobsen, 2007). Is the SPN affected by attention? Answer: No, this supports a pre--attentive symmetry processing.

2. Is the SPN generated by the extrastriate visual cortex, and is it therefore the electrophysiological correlate of the fMRI activations (Sasaki et al. 2005)? Answer: Yes.

3. Is the SPN unique to reflection? What about other regularities? Answer: Greatest for Reflection but present for other regularities.

4. Does it matter whether symmetry is present in an object, as opposed to a ground region? Answer: No. 5. Is the SPN generated by symmetry independent of view angle? Answer: Present for slanted symmetry, but slant compensation

is not automatic. 6. Does symmetry perception produce alpha desynchronization? Answer: Symmetry processing (rather than presence) is linked to

more alpha desynchronization in the right hemisphere.7. Does symmetry processing produce an automatic emotional response? Answer: No, but discovering symmetry is affectively

positive.

ReferencesHöfel , L., & Jacobsen, T. (2007a). Electrophysiological indices of processing aesthetics: Spontaneous or intentional processes? International Journal of Psychophysiology, 65, 20-31Makin A.D.J., Rampone, G. Pecchinenda, A. & Bertamini, M. (2013). Electrophysiological responses to visuospatial regularity. Psychophysiology, in press. Makin, A.D.J., Wilton, M.M., Pecchinenda, A. & Bertamini, M. (2012). Symmetry perception and affective responses. A combined EEG/EMG study. Neuropsychologia, 50, 3250-3261Sasaki, Y., W. Vanduffel, T. Knutsen, C. Tyler,R. Tootell, (2005). Symmetry activates extrastriate visual cortex in human and nonhuman primates. Proceedings of the National Academy of Sciences of the United States of America, 102: 3159-3163.

Email: alexis.makin@liverpool.ac.uk

ZM R

espo

nse

(Z)

Time (ms from stimulus onset)

Yes

No

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Reflection

Random

Reflection Rotation Translation Random

Unconstrained Constrained

3 Se

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nse

NORMAL ODDBALL REFLECTION ROTATION RANDOM TRANSLATION

ODDBALL DETECTION

EXPLICIT DISCRIMINATION

Unconstrained OddConstrained Odd Unconstrained ExConstrained Ex

Reflection One Object

Reflection Two Objects

Translation One Object

Translation Two Objects

Discriminate regularity

Left

Right

Left

Right

Discriminate number

*

0

-0.5

Pow

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hang

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)

A B

C D

ERPs from PO7 PO8

Translation - Reflection One - Two

A B

C

D

Sustained Posterior Negativity

N1

Study 1 Makin, Wilton,Pecchinenda and Bertamini (Neuropsychologia, 2012). Participants discriminated reflection and random patterns. In Experiment 1, they pressed different buttons for each pattern. In Experiment 2, they had ‘yes’ and ‘no’ buttons, where were differently assigned in different groups. The SPN was replicated. LORETA source localization estimated sources in the extrastriate visual cortex. Alpha Desynchronization was found all conditions, this was right lateralized. Activation of the Zygomaticus Major (ZM) was greater for reflection than random in Experiment 1, but this response was linked to target category in Experiment 2.

ERPs Alpha ERD

ZM

Study 2. Makin, Rampone and Bertamini (Psychophysiology, 2013). Participants observed three regular patterns (reflection, rotation or translation) and random patterns (with constrained or unconstrained configurations). In one Experiment, participants discriminated regularity, in another, the searched for rare oddballs. The SPN was present for all regularities, but greatest for reflection. The SPN was similar in active and passive viewing conditions. ERD was greater during explicit discrimination, and right lateralization was only present when random patterns were constrained.

Study 3 Makin, Rampone, Wright Martinovic and Bertamini. Participants observed reflection or random patterns, comprising figure or ground regions. In one experiment they discriminated regularity, in another they discriminated number of objects. The SPN was comparable in both experiments. Alpha ERD was only right lateralized in the discriminate regularity task.

Study 4. Makin, Rampone and Bertamini. Participants observed reflection or random patterns, from either a flat or slanted angle. In one experiment they discriminated color, in another they discriminated regularity. During regularity discrimination, the SPN was view-invariant. During color discrimination, the SPN was larger for flat patterns, which produced a symmetrical retinal projection.