Study finds people can see the forest without the trees

jennifer steeves getting a brain scan

When you look at someone’s office, what do you see – the desk, some pens, a computer? Do you know it’s an office because of the objects in it, or by taking in the entire scene? What York psychology Professor Jennifer Steeves and PhD candidate Caitlin Mullin (MA ’08) have found is that it’s not necessary to recognize the objects to identify the scene, in this case an office.

“Your ability to recognize objects and your ability to recognize scenes are independent,” says Steeves.

Their study is published in the December issue of the Journal of Cognitive Neuroscience – “TMS to the Psychology Professor Jennifer Steeves applies rTMS stimulation to PhD candidate Caitlin Mullin. Images of Mullin's brain can be seen on the adjacent screen Lateral Occipital Cortex Disrupts Object Processing but Facilitates Scene Processing”.

Left: Psychology Professor Jennifer Steeves applies rTMS stimulation to PhD candidate Caitlin Mullin. Images of Mullin’s brain can be seen on the adjacent screen

The finding discounts an earlier theory that scene perception relies on the recognition of individual objects and instead finds that the gist of a scene can be ascertained by its spatial layout alone.

Steeves and Mullin conducted two experiments. Both showed that when the ability to see objects is impaired, the brain can still determine what it’s looking at by taking in the scene. But what surprised the researchers is that when object recognition was temporarily knocked out, the ability to categorize scenes, such as distinguishing a forest from a cityscape, increased.

“It’s like you can see the forest better when you can’t see the trees,” says Steeves, who heads up the Perceptual Neuroscience Lab in York’s Centre for Vision Research. “We didn’t expect this at all. The stimulation must be releasing some inhibitory process in people’s brains.”

The experiments involved nine individuals with healthy brains. Repetitive transcranial magnetic stimulation (rTMS) was applied to the left lateral occipital cortex (LO), the object processing area of the brain just behind each ear, to disrupt object processing. This was done while showing the subjects pictures of scenes and objects.

 Jennifer SteevesRight: Jennifer Steeves

The idea was to see how the LO contributed to the perception of scenes. The rTMS momentarily scrambled the neurons in the LO, preventing the subject from recognizing the objects, but they were able to categorize the scenes more quickly and accurately than before. The first experiment involved using a longer disruption time for object processing than that used in the second experiment.

“There was a split second interruption to the brain in the second experiment,” says Steeves. Still, the second experiment confirmed the findings of the first. “It’s a really robust effect. The TMS showed us that even though the two functions are independent, they still work together.”

Steeves and Mullin are now doing research find out what other parts of the brain are affected when rTMS is applied to specific areas. “We’re finding so far that stimulating one region can have an effect on other areas,” says Mullin.

The research is part of the nuts and bolts of mapping the brain, which could have implications down the road in helping people with brain injuries or informing computer modelling. “What’s nice is we’re learning about networks in the brain,” says Steeves. And that is where it all starts.

The experiments were funded through grants from the Canada Foundation for Innovation, the Ontario Research Fund and the Natural Sciences & Engineering Research Council of Canada.

By Sandra McLean, YFile writer