To a neuroscientist, the trouble with cocktail parties is not that we do not love cocktails or parties (many neuroscientists do). Instead what we call “the cocktail party problem” is the mystery of how anyone can have a conversation at a cocktail party at all.
Consider a typical scene: You have a dozen or more lubricated and temporarily uninhibited adults telling loud, improbable stories at increasing volumes. Interlocutors guffaw and slap backs. Given the decibel level, it is a minor neural miracle that any one of these revelers can hear and parse one word from any other. The alcohol does not help, but it is not the main source of difficulties. The cocktail party problem is that there is just too much going on at once: How can our brain filter out the noise to focus on the wanted information?
This problem is a central one for perceptual neuroscience—and not just during cocktail parties. The entire world we live in is quite literally too much to take in. Yet the brain does gather all of this information somehow and sorts it in real time, usually seamlessly and correctly. Whereas the physical reality consists of comparable amounts of signal and noise for many of the sounds and sights around you, your perception is that the conversation or object that interests you remains in clear focus.
So how does the brain accomplish this feat? One critical component is that our neural circuits simplify the problem by actively ignoring—suppressing—anything that is not task-relevant. Our brain picks its battles. It stomps out irrelevant information so that the good stuff has a better chance of rising to awareness. This process, colloquially called attention, is how the brain sorts the wheat from the chaff.
In collaboration with the laboratories of neuroscientists Jose-Manuel Alonso of the SUNY College of Optometry and Harvey Swadlow of the University of Connecticut, we discovered the initial circuits that mediate attention in the primary visual cortex of the brain. To do this, we observed neurons in this area, some of which encourage activity in their fellow brain cells, so-called excitatory neurons, and others that tamp down activity, known as inhibitory neurons. We compared the activity in brain cells that process specific areas of visual space with that of other visual cells that are unaffected by changes in our gaze and attention. This comparison revealed that when someone attends to a specific spatial location, the inhibitory neurons take action, suppressing the activity in the brain cells that process other visual regions. In short, the brain depends on these inhibitory neurons to enable focus.
Even more interesting, the harder you concentrate, the greater the suppression. One fundamental role of cognition is to select what your brain goes on to process. It does that, at least in part, by blocking irrelevant information.
But that is not attention's only role. As the neural activity associated with attention travels down throughout our visual system's circuits, it can also affect how we perceive and interpret the shapes of objects. The illusions in this article illustrate some of the numerous perceptual consequences of our brain's attentional circuits.
This article was originally published with the title "Pay Attention" in SA Mind 26, 1, 21-23 (January 2015)
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Perceptual Elements in Penn & Teller's “Cups and Balls” Magic Trick. Hector Rieiro, Susana Martinez-Conde and Stephen L. Macknik in PeerJ, Vol. 1, Article No. e19; February 12, 2013.
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ABOUT THE AUTHOR(S)
Stephen L. Macknik is a professor of opthalmology, neurology, and physiology and pharmacology at SUNY Downstate Medical Center in Brooklyn, N.Y. Along with Susana Martinez-Conde and Sandra Blakeslee, he is author of the Prisma Prize-winning Sleights of Mind. Their forthcoming book, Champions of Illusion, will be published by Scientific American/Farrar, Straus and Giroux.
Susana Martinez-Conde is a professor of opthalmology, neurology, and physiology and pharmacology at SUNY Downstate Medical Center in Brooklyn, N.Y. She is author of the Prisma Prize-winning Sleights of Mind, along with Stephen L. Macknik and Sandra Blakeslee. Their forthcoming book, Champions of Illusion, will be published by Scientific American/Farrar, Straus and Giroux.