According to a new study published in PNAS on June 30, our brains constantly shift attention from one object or location to another, allowing us to efficiently explore the visual world. The study, led by Prof. HE Sheng's group from the Institute of Biophysics of the Chinese Academy of Sciences, has revealed that these shifts are accompanied by a brief suppression of visual processing.

Interactions between the brain and the external world are not limited to overt physical movements. They also occur within the brain's internal cognitive space through covert shifts of attention. Do these internal attention shifts also trigger active modulation of perceptual sensitivity?

Addressing this question first requires identifying the precise moments when these attention shifts occur, despite the absence of any observable movement.

To overcome this challenge, the researchers took advantage of rhythmic attentional oscillations. By densely sampling attentional states over time and characterizing the periodic spatial dynamics of attention, they were able to predict the timing of attention shifts with millisecond precision.

A second challenge was measuring visual sensitivity without disrupting the attentional process itself. Any probe used to assess visual sensitivity could potentially interfere with the ongoing allocation of attention.

To avoid this problem, the researchers presented task-irrelevant visual probes at various points throughout the attention cycle. They then recorded the resulting pupil responses and neural activity using pupillometry and magnetoencephalography (MEG). This passive measurement strategy enabled the researchers to track changes in visual sensitivity without altering the natural dynamics of attention.

The researchers discovered that the brain temporarily suppresses visual sensitivity during attention shifts. This suppression primarily occurs in higher-order cortical regions, particularly the parietal cortex. This suggests that suppression is an integral component of the brain's attentional network.

These results also imply that the active regulation of perception is a common feature of neural systems at various levels of cognition. This enables the brain to maintain stable and efficient processing during interactions with the external world and internal shifts in cognitive states.