Summary: A groundbreaking study delves into the intriguing concept of visual masking, a phenomenon where rapid sequential images cause the initial image to go unnoticed.
The study succeeded in demonstrating visual masking in mice, mirroring human perception, indicating a shared neurological process. By training the mice to respond to visual stimuli, the researchers identified specific brain regions crucial for this illusion, shedding light on the formation of conscious perception.
The findings suggest that the generation of awareness may occur in the visual cortex or higher cortical areas.
Key Facts:
- Visual masking involves the failure to perceive an initial image when quickly followed by another, a phenomenon proven to occur in both humans and mice by this study.
- The research identifies brain regions responsible for this phenomenon, suggesting that conscious perception originates in the visual cortex or downstream cortical areas.
- The similarity in human and mouse perception of visual masking challenges existing understanding of how conscious awareness is generated in the brain.
Source: Allen Institute
A remarkable new study published today in Nature Neuroscience on visual masking sheds light on how we unsee things and offers insights into the generation of conscious perception in the brain.
In a phenomenon known as visual masking, individuals are unable to consciously perceive an image if another image is shown rapidly after. The timing of these images is crucial – the initial image must flash on and off quickly, and the second image must follow rapidly (approximately 50 milliseconds) to create the masking effect.
Shawn Olsen, Ph.D., an investigator at the Allen Institute, and his colleagues delved into the science behind this optical illusion and demonstrated for the first time that it occurs in mice as well. By training mice to report on what they saw, the team also pinpointed a specific brain region necessary for the visual masking illusion.
“This is an intriguing observation, where what is present in the world is not accurately reflected in your perception,” said Olsen. “Like other visual illusions, we believe that it provides insight into the workings of the visual system and ultimately about the neural circuits underlying visual awareness.”
Scientists first identified this strange phenomenon in the 19th century, but the reasons why and how the human brain does this remain a mystery.
The study narrows down the parts of the brain responsible for awareness of the world around us, explained Christof Koch, Ph.D., a meritorious investigator at the Allen Institute, who led the study with Olsen and Sam Gale, Ph.D., a scientist at the Allen Institute.
When the rain of photons impinges on our retinas, the information takes a prescribed path from our eyeballs through different regions of the brain, terminating in higher processing areas of the cortex, the wrinkled outermost shell of the brain.
From previous studies of visual masking, scientists know that neurons in the retina and parts of the brain early in that pathway are activated even when a person is not consciously aware that they’re seeing an image. In other words, your brain is seeing things without your knowledge.
To explore the point where unconscious sensation transitions into conscious perception and action, the scientists first trained 16 mice to turn a tiny LEGO wheel toward the direction of a quickly flashed image in exchange for a treat if they chose the correct direction.
The scientists then added a different masking image on both sides of the screen, directly following the target image. With the addition of the mask, the animals could no longer perform the task correctly, suggesting they were no longer aware of the original image.
Because visual masking had never been tested in mice before, the research team had to create a new task for them, differing from previous human studies in how the images were shown and how they were used.
Moreover, to confirm the relevance of the optical illusion they showed the rodents to humans, the team also tested it in 16 people. Human perception (or lack thereof) and mouse perception of this specific visual masking illusion turned out to be remarkably similar.
These results imply that conscious perception either occurs in the visual cortex or in higher areas of the cortex downstream of it. Aligning with the general consensus in the field, Koch noted that the cortex is the seat of conscious perception in mammals, including humans.
About this visual neuroscience research news
Author: Peter Kim
Source: Allen Institute
Contact: Peter Kim – Allen Institute
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Backward masking in mice requires visual cortex” by Shawn Olsen et al. Nature Neuroscience
Abstract
Backward masking in mice requires visual cortex
Visual masking can reveal the timescale of perception, but the underlying circuit mechanisms are not understood.
Here we describe a backward masking task in mice and humans in which the location of a stimulus is potently masked.
Humans report reduced subjective visibility that tracks behavioral deficits. In mice, both masking and optogenetic silencing of visual cortex (V1) reduce performance over a similar timecourse but have distinct effects on response rates and accuracy.
Activity in V1 is consistent with masked behavior when quantified over the long, but not short, time windows. A dual accumulator model recapitulates both mouse and human behavior.
The model and the subjects’ performance imply that the initial spikes in V1 can trigger a correct response, but subsequent V1 activity degrades performance. Crucially, optogenetically suppressing mask-evoked activity in V1 fully restores accurate behavior.
To conclude, these results highlight that mice, like humans, are susceptible to visual masking and that target and mask information is first confounded downstream of V1.
