A) Flat Reflection

1. Discriminate regularity ERPs from PO7 PO8 A) Flat Reflection Using EEG to investigate visual symmetry perception Marco Bertamini, Giulia Rampone and Alexis Makin Translation - Reflection One - Two A B Left Reflection One Object Translation One Object Right 0 ZM Response (Z) E Reflection – Random scalp maps (300 to 1000 ms) B) Slant Reflection Reflection Rotation Translation Random * F) Discriminate Color G) Discriminate Regularity Reflection Random A B Sustained Posterior Negativity 3 Seconds Time (ms from stimulus onset) 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. 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. 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. Is the SPN unique to reflection? What about other regularities? Answer: Greatest for Reflection but present for other regularities. Does it matter whether symmetry is present in an object, as opposed to a ground region? Answer: No. Is the SPN generated by symmetry independent of view angle? Answer: Present for slanted symmetry, but slant compensation is not automatic. Does symmetry perception produce alpha desynchronization? Answer: Symmetry processing (rather than presence) is linked to more alpha desynchronization in the right hemisphere. Does symmetry processing produce an automatic emotional response? Answer: No, but discovering symmetry is affectively positive.   Power change (p) Discriminate number Reflection Two Objects Translation Two Objects C) Flat Random D C Unconstrained Constrained N1 Left Right EXPLICIT DISCRIMINATION ODDBALL DETECTION ZM Response (Z) -0.5 D)SlantRandom Until response Yes No D NORMAL ODDBALL REFLECTION ROTATION RANDOM TRANSLATION C Time (ms from stimulus onset) 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. 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. ERPs Alpha ERD Experiment 1 Experiment 1 480-520 1500-2000 A B B A P1 Amplitude (+/-2V) Regular 170-200 ms 100-130 ms 300-1000 ms C N1 Random Experiment 2 Experiment 2 480-520 1500-2000 C D E D Regular F Random 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. B) Oddball Detection A) Explicit Discrimination Constrained Odd Unconstrained Odd Constrained Ex Unconstrained Ex 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. References Höfel , L., & Jacobsen, T. (2007a). Electrophysiological indices of processing aesthetics: Spontaneous or intentional processes? International Journal of Psychophysiology, 65, 20-31 Makin 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, 3250-3261 Sasaki, 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