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The Impossible Staircase in Our Heads: How We Visualize the World Around Us

March 28, 2012 1 comment

Our interpretation of the world around us may have more in common with the impossible staircase illusion than it does the real world, according to research published today in the open access journal PLoS ONE.

A ‘Penrose stairs’ optical illusion, or impossible staircase. Image adapted from public domain image shared by Sakurambo on Wikimedia

The study, which was funded by the Wellcome Trust, suggests that we do not hold a three-dimensional representation of our surroundings in our heads as was previously thought.

Artists, such as Escher, have often exploited the paradoxes that emerge when a 3D scene is depicted by means of a flat, two-dimensional picture. In Escher’s famous picture ‘Waterfall’, for example, it is impossible to tell whether the start of the waterfall is above or below its base.

Paradoxes like this can be generated in a drawing, but it is not possible to create such a 3D structure. The illusion is possible because drawings of 3D scenes are inherently ambiguous, so there is no one-to-one relationship between the picture and 3D locations in space.

Most theories of 3D vision and how we represent space in our visual system assume that we generate a one-to-one 3D model of space in our brains, where each point in real space maps to a unique point in our model. However, there is an ongoing debate about whether this is really the case.

To test this idea, researchers at the University of Reading placed participants wearing a virtual reality headset in a virtual room in which they had to judge which of two objects was the nearest. On some occasions, the size of the room was increased four-fold – previous research by the team showed that participants fail to notice this expansion.

In this new study, the researchers found that people’s judgement of the relative depth of objects depended on the order in which the objects were compared. Although the results are readily explained in relation to the expansion of the room, the participants had no idea that the room changed at any stage during the experiment. It is the properties of this stable perception that the experiment tested.

Dr Andrew Glennerster from the University of Reading, who led the study, explains: “In the impossible staircase illusion, you cannot tell whether the back corner is higher or lower than the front one as it depends which route you take to get there. The same is true, we find, in our task. This means that our own internal representations of space must be rather like Escher’s paradoxes, with no one-to-one relationship to real space.”

“Even when the size of the room increases four-fold, people think they are in a stable room throughout the experiment. Their interpretation of the room does not update itself when the room itself changes.

“Does it make sense for their representation of the room to have 3D coordinates, as a proper staircase would? No – there is no way to write down the coordinates of the objects that could explain the judgements people made. Visual space – the internal representation – is much more like the paradoxical staircase than a physically realisable model.”

Source:

Wellcome Trust press release
Image Source: NeuroscienceNews.com image adapted from public domain image with credit to Sakurambo on Wikipedia.
Original Research: Research article “A demonstration of ‘broken’ visual space” by Svarverud E et al. to appear in PLoS ONE 2012

Researchers Partially Control a Memory


Scripps Research Institute Team Wrests Partial Control of a Memory

The work advances understanding of how memories form and offers new insight into disorders such as schizophrenia and post traumatic stress disorder.

Scripps Research Institute scientists and their colleagues have successfully harnessed neurons in mouse brains, allowing them to at least partially control a specific memory. Though just an initial step, the researchers hope such work will eventually lead to better understanding of how memories form in the brain, and possibly even to ways to weaken harmful thoughts for those with conditions such as schizophrenia and post traumatic stress disorder.

The results are reported in the March 23, 2012 issue of the journal Science.

Researchers have known for decades that stimulating various regions of the brain can trigger behaviors and even memories. But understanding the way these brain functions develop and occur normally—effectively how we become who we are—has been a much more complex goal.

“The question we’re ultimately interested in is: How does the activity of the brain represent the world?” said Scripps Research neuroscientist Mark Mayford, who led the new study. “Understanding all this will help us understand what goes wrong in situations where you have inappropriate perceptions. It can also tell us where the brain changes with learning.”

On-Off Switches and a Hybrid Memory

As a first step toward that end, the team set out to manipulate specific memories by inserting two genes into mice. One gene produces receptors that researchers can chemically trigger to activate a neuron. They tied this gene to a natural gene that turns on only in active neurons, such as those involved in a particular memory as it forms, or as the memory is recalled. In other words, this technique allows the researchers to install on-off switches on only the neurons involved in the formation of specific memories.

For the study’s main experiment, the team triggered the “on” switch in neurons active as mice were learning about a new environment, Box A, with distinct colors, smells and textures.

Next the team placed the mice in a second distinct environment—Box B—after giving them the chemical that would turn on the neurons associated with the memory for Box A. The researchers found the mice behaved as if they were forming a sort of hybrid memory that was part Box A and part Box B. The chemical switch needed to be turned on while the mice were in Box B for them to demonstrate signs of recognition. Alone neither being in Box B nor the chemical switch was effective in producing memory recall.

“We know from studies in both animals and humans that memories are not formed in isolation but are built up over years incorporating previously learned information,” Mayford said. “This study suggests that one way the brain performs this feat is to use the activity pattern of nerve cells from old memories and merge this with the activity produced during a new learning session.”

Future Manipulation of the Past

The team is now making progress toward more precise control that will allow the scientists to turn one memory on and off at will so effectively that a mouse will in fact perceive itself to be in Box A when it’s in Box B.

Once the processes are better understood, Mayford has ideas about how researchers might eventually target the perception process through drug treatment to deal with certain mental diseases such as schizophrenia and post traumatic stress disorder. With such problems, patients’ brains are producing false perceptions or disabling fears. But drug treatments might target the neurons involved when a patient thinks about such fear, to turn off the neurons involved and interfere with the disruptive thought patterns.

Notes about this memory research article

In addition to Mayford, other authors of the paper, “Generation of a Synthetic Memory Trace,” are Aleena Garner, Sang Youl Hwang, and Karsten Baumgaertel from Scripps Research, David Rowland and Cliff Kentros from the University of Oregon, Eugene, and Bryan Roth from the University of North Carolina (UNC), Chapel Hill.

This work is supported by the National Institute of Mental Health, the National Institute on Drug Abuse, the California Institute for Regenerative Medicine, and the Michael Hooker Distinguished Chair in Pharmacology at UNC.

Source:

Source: The Scripps Research Institute press release

Original Research: Abstract for “Generation of a Synthetic Memory Trace” by Aleena R. Garner, David C. Rowland, Sang Youl Hwang, Karsten Baumgaertel, Bryan L. Roth, Cliff Kentros & Mark Mayford in Science