fMRI data reveals brain activity in object recognition
In an effort to decrypt some of the most intriguing secrets of the brain, researchers have found that visual recognition of objects is not a one-step process.
Research performed at the University of Pittsburgh suggests that visual recognition is a stepwise process in which different parts of the brain process information before an object is actually recognized.
Mark Wheeler, psychology professor at Pitt, led researchers from the Learning Research and Development Center in investigating the neural behavior that underlies object recognition. A paper on this research was published in the Oct. 31 edition of the Journal of Neuroscience.
Prior to the experiment, researchers knew that if an object is slowly revealed to a person, the person gathers information about the object and retains it in his or her brain. After processing this information in the brain, the person is able to recognize the object through a decision-making process.
Wheeler and his team wanted to find the neural pathways where these decisions are made. Similar experiments have been carried out on monkeys but not on humans.
In Wheeler’s experiment, participants were presented with grayscale pictures that were “masked” from view by a black screen. Initially, the complete picture was hidden from view, but every two seconds, a small portion of the mask was removed. This revelation process took 16 seconds per picture.
Participants were then asked to press a button when they felt comfortable recognizing the picture. They were asked to press the button a second time when the complete picture was revealed and only if their initial decision about the picture had been correct.
Using functional magnetic resonance imaging (fMRI), researchers mapped the regions of the brain in which activity took place during the experiment. Brain activity was monitored until participants made the final decision of recognition.
Elisabeth Ploran, a psychology graduate student at Pitt who worked alongside Wheeler on the paper, explained the fundamental difference between this experiment and similar experiments performed in the past.
“The other studies only look at one time point, and that’s the time point at which they [the participants of the study] make the ‘yes I recognize it’ decision,” she said. “Our innovative technique is to look at the time leading up to that decision.”
The results of this study revealed that three separate brain regions are involved in object recognition.
The first is the set of “sensory areas” that responds to the amount of stimulus. Researchers found that activity in these areas increased as more of the picture was revealed.
Conversely, there was no activity in these regions when the object was completely hidden from view.
The next set of areas is the “evidence gathering areas.” Activity in these areas correlated with the amount of time that it took participants to recognize the object.
More specifically, these areas process bits and pieces of sensory information as more of the picture is revealed to participants. Hence, these areas collect the “evidence” and match it up at the end to get the solution or the complete picture.
Wheeler said, “The activity in these areas increased rapidly when recognition occurred early and increased much more slowly when recognition occurred later.”
The third set of areas is related to decision-making processes. This set of areas includes three brain regions: the bilateral thalamus, part of the supplementary motor area, and the dorsal anterior cingulate cortex.
Wheeler’s study revealed something that had not been previously known about these areas — they are active when the final decision is made, but not before that.
Wheeler said, “What was really surprising was that we could clearly dis0sociate those signals [from the ‘evidence gathering areas’] from other regions which just showed responses when you recognized the object. We could dissociate the ‘decision-end result’ signals from the ‘evidence gathering signals.’ For us, that was really exciting.”
Ploran said, “This means that there’s activity going on in the brain that’s not necessarily accepted by consciousness until you reach some point when you know what the object is.”
According to a Pitt press release, the findings from this study may lead to future work that reveals how people make good and bad decisions.
Wheeler said, “Once we understand what the finer-grain mechanisms [of the decision-making pathway] are, it would be really nice if we could use the information to understand why we make poor decisions. It may apply to situations where people make bad decisions that have lifelong consequences, like why a person starts taking drugs.”