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Updated: May 7, 2026
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Simultaneous Transcranial Alternating Current Stimulation and Functional Magnetic Resonance Imaging
Published on: June 5, 2017
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Individual alpha frequency tACS modifies the detection of space-time optical illusion
Francesco Neri1,2, Vincenzo Catrambone3, Alessandra Cinti4
1Siena Brain Investigation and Neuromodulation Lab (Si-BIN Lab), Department of Medicine, Surgery and Neuroscience, Neurology and Clinical Neurophysiology Section, University of Siena, Siena, Italy. francesco.neri3@unisi.it.
Experimental Brain Research
|September 9, 2025
Summary
Postdiction, influenced by later stimuli, involves attention, not just perception. Longer intervals and alpha frequency brain stimulation enhanced illusion detection, suggesting attentional roles in this phenomenon.
Area of Science:
- Cognitive Neuroscience
- Visual Perception
Background:
- Postdiction describes how later stimuli alter the perception of earlier ones.
- The 'rabbit illusion' demonstrates postdiction, with stimuli appearing equidistant.
- Previous studies used short intervals (100-200 ms), neglecting longer intervals and attention.
Purpose of the Study:
- To investigate if postdiction involves attentional mechanisms alongside perceptual ones.
- To explore the effect of extended inter-stimulus intervals on postdiction.
- To examine the impact of alpha frequency brain stimulation on postdiction.
Main Methods:
- 33 participants were divided into 250 ms and 500 ms inter-flash interval (IFI) groups.
- Active transcranial electrical stimulation (tES) protocols (IAF-tACS, Alpha-tRNS) and a placebo (Sham) were applied to the left precuneus/inferior parietal gyrus.
- Participants performed a rabbit illusion task to assess postdiction phenomenon.
Main Results:
- The postdiction phenomenon was observed in both 250-IFI and 500-IFI groups.
- Participants in the 500-IFI group showed improved illusion detection with IAF-tACS.
- Behavioral data indicated enhanced performance with longer intervals and specific brain stimulation.
Conclusions:
- Postdiction is influenced by attentional processes, not solely perceptual ones.
- Extended inter-stimulus intervals and targeted brain stimulation can modulate postdiction.
- Findings highlight the interplay between attention and perception in temporal visual processing.
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