The Active Process of Non-Perception

This piece, by Onno Berkan, was published on 10/29/24. The original text, by Wagener & Nieder, was published by the Journal of Cognitive Neuroscience on 03/01/24.

This University of Tübingen study investigated how crows process and become consciously aware of visual information. The researchers trained crows to report whether they saw or didn't see brief visual stimuli that were presented at different intensities.

The experimental setup had crows position their heads in front of a touchscreen and maintain that position while various visual stimuli were shown. In half the trials, they were shown a visual stimulus of varying intensity, while in the other half, no stimulus was shown at all.

What made this study particularly interesting was how the crows had to report their experience. After seeing (or not seeing) the stimulus, they had to wait for a colored rule cue that told them how to respond. A red cue meant they should nod their head to report seeing the stimulus, while a blue cue meant they should stay still to report seeing it. The opposite rules applied when they didn't see a stimulus.

The researchers recorded activity from neurons in a brain region called the NCL (nidopallium caudolaterale) while the crows performed this task. They discovered two distinct groups of neurons– "yes" neurons that became active when crows reported seeing the stimulus, and "no" neurons that fired when crows reported not seeing anything.

The study revealed a fascinating two-stage process of conscious perception. Initially, these neurons primarily encoded the physical intensity of the stimulus. Later in the trial, they shifted to representing the crow's subjective experience of whether they saw something or not. This matches with a theory called "global neuronal workspace theory" which suggests that consciousness emerges when sensory information is broadcast and maintained across brain networks.

This research provides important insights into how consciousness might work across different species. The findings suggest that both the experience of seeing something and the experience of seeing nothing are actively encoded in the brain, rather than the absence of perception being simply a lack of neural activity.

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