What do we know:
We can hear individual sounds from a background of sounds; we know some stuff about noises that help us hear sounds separately from other sounds
What don’t we know: How the brain does this; if animals hear the same way
What this study shows: Animals (monkeys) hear sounds the same way as people
What we can do in the future because of this study: Record from neurons (a neuron is a brain cell) in different parts of the brain to see how the brain is figuring out how we hear things in our world
Why you should care: We don’t know how we *normally* perceive sounds, so we don’t really know how we can fix things when stuff goes wrong with our hearing on the brain-side (instead of the ear-side) of things. This helps us figure out how the brain normally hears things, so we can start to address what to do when it’s not working normally.
We hear individual sounds because our brains can either group or separate noises in our environment--a process we call ’auditory streaming’. For many years, scientists have used a particular stimulus--one in which two tones alternate--to figure out what cues in sounds help us group them together or separate them apart. However, because we cannot record from neurons (cells in the brain) in people, and because it is hard to train animals to do this task, we do not know what the brain is doing while we hear this set of sounds. Before we can record from neurons in animals, we have to make sure that they hear and decide about the sounds in this task the same way people do. We found that monkeys make the same kind of decisions in this task as people. We can now record from neurons while monkeys are doing this task, and determine how neurons in different parts of the brain respond.
Our ability to hear sounds as distinct units arises from our ability to segregate and group acoustic features--a process called streaming. Although an ’auditory streaming’ task has been used extensively to study these perceptual processes in humans, we do not know the neural correlates of this ability, in part because all neurophysiological animal studies using this stimulus have been done while animals are passively listening or sedated. Before using this task to examine the neural correlates of auditory streaming, we had to establish whether animals performed the task similarly to humans. We found that monkeys’ behavioral reports were qualitatively consistent with those of human listeners, thus this task may be used in future neurophysiological studies.