Researchers Note Tradeoffs In Auditory Perception

New research published in the open-access journal PLoS Biology
finds error in an often-made assumption in the field of sensory
neuroscience. Merav Ahissar (Hebrew University, Jerusalem, Israel) and
colleagues were studying a key issue regarding the determination of the
greatest amount of task-relevant information that is encoded in our
brain. The researchers showed that contrary to common belief, all of
the information is in fact not available for making perceptual
decisions.



Perception is the process of becoming aware and understanding sensory
information (what we see, hear, taste, etc.) While studying hearing,
Ahissar and colleagues demonstrated that when speech is covered up by
noise, the perception processes of discriminating and understanding the
speech only draw information that is represented at higher cortical
areas rather than from the entire brain. This means that if a listener
is determining whether a speaker said "day" or "night," for example,
the listener is likely to be able to tell the difference. If, however,
a listener must choose between words like "day" and "bay," a finer
discrimination skill is required. Only under certain conditions can the
information pertaining to the fine spectral and temporal details be
used for successful discrimination. One condition, often used in
psychoacoustic experiments, is systematic repetition of the word. A
second condition is when a listener decides to focus solely on word
identification, removing the need for comprehension. The authors note
that these conditions are "non-ecological" and not feasible in most
situations.



The researchers write, "Taken together, the auditory system seems to
favor ecologically more likely conditions and yet retains flexibility
for the less likely ones. Discriminations that are prevalent in natural
situations are fast and still use all low-level information, whereas
discriminations that are less likely to occur are either fast or use
all low-level information. The results presented here, however, show
that the auditory system cannot achieve both."



"Similar defaults and tradeoffs characterize the relations between
processing hierarchies and perception at the various sensory
modalities," they conclude.



Low-level information and high-level perception: The case of
speech in noise

Nahum M, Nelken I, Ahissar M

PLoS Biology (2008). 6(5):e126.

doi:10.1371/journal.pbio.0060126

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of scientists and physicians committed to making the world's
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For more information, visit plos



Written by: Peter M Crosta