Cognitive neuroscientists shed light on how the brain responds to scenes and their mirror-image reversals

August 18, 2011 by Emily Finn
New research suggests that some parts of the brain perceive a scene and its mirror image as one and the same, meaning those regions are involved in scene categorization rather than navigation.

Picture a penny. You can probably recall its color (copper), which historical figure graces its front (Abraham Lincoln), and even the orientation of the portrait (profile, as opposed to straight on). But can you remember which way Lincoln is facing?

According to MIT research scientist Daniel D. Dilks, only about half of us get this right, meaning we’re performing no better than if we had simply guessed. This well-known phenomenon suggests that left-right distinctions are irrelevant to object recognition; in other words, our brains perceive an object and its mirror image as one and the same.

On the other hand, when people look at scenes, it has long been thought that the is sensitive to left-right orientation, since this information is crucial for navigation. (A road curving to the right must be negotiated differently than one curving to the left.)

However, in a recent study at MIT’s McGovern Institute for Brain Research, Dilks and his colleagues identified two parts of the brain that appear to be exceptions to this rule — including one that processes scenes without seeming to distinguish left from right. The results highlight the cognitive differences between perception and action.

The findings were published Aug. 3 in the ; the paper’s senior author is Nancy Kanwisher, the Walter A. Rosenblith Professor of Cognitive Neuroscience, and the co-authors are McGovern Institute technical assistant Joshua B. Julian, graduate student Jonas Kubilius of Belgium’s Katholieke Universiteit Leuven and Professor Elizabeth Spelke of Harvard University.

On the flip side

The researchers started with “a simple hypothesis,” Dilks says: Areas of the brain thought to play a major role in object recognition would be indifferent to right and left, while those that respond to scenes would be sensitive to these distinctions.

To test this idea, the researchers used functional magnetic resonance imaging (fMRI), a technique that measures brain activity associated with perceptual and cognitive tasks. For each trial, participants focused on a pair of images, consisting of two objects or two scenes displayed one after the other. These pairs came in three conditions: two identical images, an image followed by its mirror reversal, or two completely different images.

The researchers predicted that for objects, the brain’s response to a pair of mirror images would closely resemble its response to two identical images; that is, brain activity would drop off upon recognition of the second image as the same or virtually the same as the first. On the other hand, for scenes, they expected that mirror-image pairs would be treated as two different images, with the second image provoking a brain response just as intense as the first.

But “we found that it didn’t work out that way,” Dilks says. Of the two object-selective brain areas they investigated, they found that one was insensitive to left-right reversals, but one, in fact, picked up on these reversals.

More surprising still was the data from the scene-selective regions. Two regions were in line with predictions — that is, they were sensitive to left-right reversals — but one, the parahippocampal place area, or PPA, was not.

Perception versus action

When it comes to processing objects, Dilks says cognitive neuroscientists largely agree that the brain has two separate pathways: one for perception and another for action. When you’re looking at a mug, he says, it doesn’t much matter if the handle is facing left or right; you still recognize it as a mug. If you’re planning to do something with the mug — say, grasp it and bring it to your lips — then “you better [know] left and right, because otherwise you’ll be floundering all around trying to pick it up,” he says.

According to Dilks, the new results suggest that for scenes, just as for objects, there are separate processing pathways for perception and action — but in the case of scenes, action means navigation, and perception means categorization. The PPA, then, is part of a perception stream, perhaps helping to categorize environments.

Doris Tsao, an assistant professor of biology at the California Institute of Technology, reaches the same conclusion, saying the new study “challenges the theory that the PPA plays a direct role in navigation, and suggests instead that it may be involved in scene recognition.”

This in turn implies that there must be some evolutionary advantage to being able to simply characterize one’s surroundings without necessarily needing to navigate them, which makes sense for higher-order social creatures such as humans. Identifying the type of environment you’re in, whether it’s an office, a playground or a bar, gives you clues as to how you should act.

“You’re going to behave very differently at a beach than you would in the city, for example,” Dilks says.

This story is republished courtesy of MIT News (, a popular site that covers news about MIT research, innovation and teaching.

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not rated yet Aug 18, 2011
Interesting. I wonder if they tried this with people who have dyslexia.
not rated yet Aug 19, 2011
In hunter-gatherer environments, landmarks can be approached from several directions and they may look different each for each direction of approach eg mirror image. This is true whether you are out in the desert or in the forest, but is especially true in the forest where tracks and trails may pass landmarks and so are approachable from either of two directions where one scene is the mirror image of the other.

Thus we would expect the mirror symmetry to be more primal and important to survival than more discriminating view.
not rated yet Aug 21, 2011
What better place to vent my aggression than here? So...

Dear Danial,Nancy,Joshua, and Elizabeth,

Put a portable fMRI scanner on the head of a pianist.
Make sure that when the pianist plays, the right hand plays the melody, the left hand plays the accompaniment.

Now when the pianist is finished playing, and hopefully you have recorded the scan and playing, tell the pianist to cross over their arms. Tell the pianist, the right hand is still to play the melody, the left hand is still to play the accompaniment. Now scan and record that too.

Now have the pianist play the music again. This time the hands are back in the normal position. The right hand plays the accompaniment, and the left hand plays the melody. Scan and record. Now have the pianist cross over arms. The right hand continues playing the accompaniment, the left hand the melody. Scan and record.

I feel so much better now, having vented my aggression on you all, at your expense.

When is retraction date of your research?
not rated yet Aug 21, 2011
Now if you all are feeling aggression from the portion I uploaded on you, simply correct the minor typo errors in the above comment. The rest is solid science. Nothing debatable.
Just the opposite of your work. Shush now.

not rated yet Aug 21, 2011
The sky the limit. Why stop there?
Blindfold the pianist. Run the whole test series again.
Remove the blindfold. Both hands play melody. Both hands play accompaniment. Single hand playing. Establish baselines.
The keyboard plays random notes each time the note is engaged.
The pianist is to 'play' the whole test series again despite the sounds no longer reflecting the written music or music memorized. The pianist plays the whole test series again without the keyboard generating any sounds at all.
This all leads the way to what mirror symmetry means to the brain and where what is needed to perform.
We live in exciting times.

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