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Microsaccades strongly modulate but do not directly cause the EEG N2pc marker of spatial attention
Baiwei Liu1, Siyang Kong1, Freek van Ede1
1Department of Experimental and Applied Psychology, Institute for Brain and Behavior Amsterdam, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
Abstract:
The N2pc is a popular human-neuroscience marker of covert and internal spatial attention that occurs 200-300 ms after being prompted to shift attention-a time window also characterized by the spatial biasing of small fixational eye movements known as microsaccades. Here, we show how co-occurring microsaccades profoundly modulate N2pc amplitude during top-down shifts of spatial attention in both perception and working memory. At the same time, we show that a significant-albeit severely weakened-N2pc can still be established in the absence of co-occurring microsaccades. Moreover, despite the strong modulation of the N2pc by microsaccade presence and direction, the N2pc does not align to the precise timing of microsaccades, ruling out that the observed N2pc modulations by microsaccades are a direct artifact of microsaccade-related eye-muscle activity, corneo-retinal dipole movement, or visual inputs moving over the retina. Thus, while microsaccades strongly modulate N2pc amplitude, microsaccades themselves are not a prerequisite for, nor a direct cause of, the N2pc.
Insights
Microsaccades significantly influence the N2pc brain signal during spatial attention shifts. However, microsaccades are not essential for the N2pc
Area of Science:
- Human Neuroscience
- Cognitive Neuroscience
- Visual Attention
Background:
- The N2pc component is a key electrophysiological marker for covert and internal spatial attention.
- The N2pc occurs within a specific time window (200-300 ms) post-stimulus.
- This time window also coincides with the occurrence of microsaccades, small fixational eye movements.
Purpose of the Study:
- To investigate the modulatory effect of microsaccades on the N2pc component.
- To determine if microsaccades are a prerequisite for the N2pc.
- To explore the relationship between microsaccade timing and N2pc generation.
Main Methods:
- Electrophysiological recordings (EEG) to measure the N2pc.
- Behavioral tasks involving shifts in spatial attention in perception and working memory.
- Analysis of the co-occurrence and directionality of microsaccades relative to the N2pc.
Main Results:
- Microsaccades profoundly modulate N2pc amplitude during top-down attention shifts.
- A detectable N2pc can still be observed even in the absence of microsaccades.
- N2pc modulation by microsaccades is not explained by eye-muscle activity or retinal image motion.
Conclusions:
- Microsaccades significantly influence, but do not cause, the N2pc.
- The N2pc is not an artifact of microsaccade-related neural or visual processes.
- Spatial attention mechanisms can operate independently of, yet be modulated by, microsaccades.
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