Visual masking: Your brain can see and process information without "your" knowledge

In a recent study led by Dr. Shawn Olsen at the Allen Institute, researchers have made significant strides in understanding how our brains perceive – or fail to perceive – visual stimuli. The research, focusing on a mind-blowing phenomenon known as visual masking, reveals intriguing insights into the mechanisms of conscious perception in the brain.

What is visual masking?

Visual masking occurs when an individual fails to consciously perceive an image due to the rapid succession of another image. 

For the effect to occur, the first image must appear and disappear swiftly, followed rapidly (within about 50 milliseconds) by the second image. The current study explores visual masking in mice for the first time.

Scientists discovered this puzzling phenomenon in the 19th century, but the underlying mechanisms remain a mystery. 

From previous studies, the scientists knew that neurons in the retina and parts of the brain in that pathway are activated even when a person is not aware that they are seeing an image. This means that your brain can see things without your knowledge.

Visual masking and awareness

Dr. Olsen and his team, including Dr. Christof Koch and Dr. Sam Gale, trained mice to respond to visual stimuli. The mice were taught to turn a tiny LEGO wheel in the direction of a briefly flashed image to receive a treat. 

When a masking image was introduced immediately after the target image, the mice failed to perform the task correctly, indicating a loss of conscious perception of the original image.

“This is an interesting observation, where what is present in the world is not accurately reflected in your perception,” said Dr. Olsen. “Like other visual illusions, we think that it tells us something about the way the visual system works and ultimately about the neural circuits that underlie visual awareness.”

Conscious perception

Conscious perception refers to the awareness that one has of their surroundings and internal states through sensory experiences. It involves the recognition and interpretation of sensory inputs, such as sights, sounds, and tactile sensations, as well as internal stimuli like thoughts and emotions.

The researchers pinpointed a specific brain region that is necessary for visual masking illusion to work. They propose that the visual cortex or higher areas of the cortex are responsible for conscious perception.

Human and mouse perception 

The experts wanted to confirm that the optical illusion they showed the rodents is relevant to humans. They tested 16 people using a keystroke instead of the wheel. The results showed that human and mouse perception – or lack thereof – is very similar. 

The fact that human and mouse perceptions of this visual masking illusion were similar reinforces the theory that conscious perception resides in the cortex of mammals. That fits with the general sentiment in the field that the cortex is the seat of conscious perception in mammals, including us, said Dr. Koch.

In summary, the Allen Institute’s research offers profound insights into how our brains process visual information and what factors contribute to our conscious perception of the world. It opens new avenues for understanding more about the visual system and the neural circuits that govern visual awareness.

More about visual masking

As discussed above in the Allen Institute study analysis, visual masking is a fascinating phenomenon in the realm of perceptual psychology that offers key insights into how our visual system processes information. It occurs when the perception of one visual stimulus (the mask) impairs the visibility of another stimulus (the target) when they are presented in close temporal succession.

To reiterate and further clarify, the process of visual masking can be broken down into two primary types: backward masking and forward masking. In backward masking, the mask appears after the target, disrupting the processing of the initial stimulus. This type is particularly intriguing because it suggests that our perception is not instantaneous but rather involves a certain degree of processing time.

Forward masking, on the other hand, involves the mask appearing before the target. It demonstrates the preparatory effect of the visual system in anticipating and processing incoming stimuli.

Visual masking has significant implications in understanding the temporal dynamics of visual processing. It reveals that our perception of the present is partially influenced by recent visual experiences. This aspect is crucial in fields like cognitive psychology, neurology, and even in practical applications like the design of user interfaces and visual displays.

In summary, visual masking is not just a curious trick of perception but a window into the complex and dynamic nature of how we interpret and understand visual information. Its study continues to uncover the intricate workings of the human visual system, enhancing our comprehension of the brain and perception.

The study is published in the journal Nature Neuroscience. 

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