Introduction

Bistable perception occurs when stimuli present ambiguous sensory information that can be interpreted in two different ways, spontaneously changing in aware experience, and is widely used as an experimental approach in consciousness research. In the present study, we compared the neural activity induced by dynamic bistable stimuli that create illusory directional flips with that of rotating patterns changing direction.

Methods

Stimuli were spiral glass patterns of similar appearance. Six of them included a sequence of 1,000 different patterns, while the other six contained patterns rotating either clockwise or counterclockwise, changing direction unpredictably.

Thirty-six subjects participated in this study and had to press a joystick button whenever they perceived a change in the stimulus motion direction.

EEG was recorded at 26 positions. Epochs taken 1,000 msec before button presses were classified in two categories: illusory and real rotation directional flips. Representational similarity analysis (RSA) was applied using Pearson correlation. We examined the overall similarity within and across categories, its time course, and its spatiotemporal distribution (searchlight analysis).

Results

No significant differences in the overall neuronal similarity and its time course were found within or across categories, although real rotations showed the highest correlation. Category-specific information appeared earlier for illusory reversals than for real directional flips.

The searchlight analysis indicated differences in average correlation among brain regions and time windows for both types of directional flips’ categories. Illusory flips induce lower similarity of neural activity but involved more brain regions than the real flips. Both types of flips displayed significant neural similarity across all electrodes approximately 250 milliseconds before the button press.

Conclusions

Directional transitions in bistable stimuli elicit neural activity that resembles real directional changes. However, illusory reversals recruit more widespread cortical regions and show distinct temporal dynamics, consistent with evidence that bistable perception engages distributed brain networks.