>> Humans have more distinctive hearing than animals, study shows
>>
>> Do humans hear better than animals? It is known that various species
>> of land and
>> water-based living creatures are capable of hearing some lower and
>> higher
>> frequencies than humans are capable of detecting. However, scientists
>> from the
>> Hebrew University of Jerusalem and elsewhere have now for the first
>> time
>> demonstrated how the reactions of single neurons give humans the
>> capability of
>> detecting fine differences in frequencies better than animals.
>>
>> They did this by utilizing a technique for recording the activity of
>> single
>> neurons in the auditory cortex while subjects were exposed to sound
>> stimuli. The
>> auditory cortex has a central role in the perception of sounds by the
>> brain.
>>
>> Current knowledge on the auditory cortex was largely based on earlier
>> studies
>> that traced neural activity in animals while they were exposed to
>> sounds. And
>> while such studies have supplied invaluable information regarding
>> sound
>> processing in the auditory system, they could not shed light on the
>> human
>> auditory system's own distinctive attributes.
>>
>> Experimental study of neural activity in the human auditory cortex has
>> been
>> limited until now to non-invasive techniques that gave only a crude
>> picture of
>> how the brain responds to sounds. But recently, investigators from the
>> Hebrew
>> University, the University of California, Los Angeles (UCLA), the Tel
>> Aviv
>> Sourasky Medical Center and the Weizmann Institute of Science were
>> successful in
>> recording activity of single neurons in the auditory cortex while the
>> subjects
>> were presented with auditory stimuli. They did this by utilizing an
>> opportunity
>> provided during an innovative and complicated clinical procedure,
>> which traces
>> abnormal neural activity in order to improve the success of surgical
>> treatment
>> of intractable epilepsy,
>>
>> The researchers included Prof. Israel Nelken of the Department of
>> Neurobiology
>> at the Alexander Silberman Institute of Life Sciences at the Hebrew
>> University
>> of Jerusalem, Prof. Itzhak Fried from UCLA and Tel Aviv Medical
>> Center, and
>> Prof. Rafi Malach of the Weizmann Institute of Science, together with
>> their
>> students Roy Mukamel and Yael Bitterman. Their work was described in
>> an article
>> appearing in the journal Nature.
>>
>> In tests measuring response to artificial sounds, the researchers
>> found that
>> neurons in the human auditory cortex responded to specific frequencies
>> with
>> unexpected precision. Frequency differences as small as a quarter of a
>> tone (in
>> western music, the smallest interval is half a tone) could be reliably
>> detected
>> from individual responses of single neurons.
>>
>> Such resolution exceeds that typically found in the auditory cortex of
>> other
>> mammalian species (besides, perhaps, bats, which make unique use of
>> their
>> auditory system), serving as a possible correlate of the finding that
>> the human
>> auditory system can discriminate between frequencies better than
>> animals. The
>> result suggests that the neural representation of frequency in the
>> human brain
>> has unique features.
>>
>> Interestingly, when the patients in the study were presented with
>> "real-world"
>> sounds - including dialogues, music (from "The Good, the Bad and the
>> Ugly"
>> soundtrack) and background noise - the neurons exhibited complex
>> activity
>> patterns which could not be explained based solely on the frequency
>> selectivity
>> of the same neurons. This phenomenon has been shown in animal studies
>> but never
>> before in humans.
>>
>> Thus, it can be seen that in contrast to the artificial sounds,
>> behaviorally
>> relevant sounds such as speech and music engage additional, context-
>> dependant
>> processing mechanisms in the human auditory cortex.
>>
>> Source: The Hebrew University of
Jerusalemhttp://www.physorg.com/news126265914.html
