People Faculty

Bertram Scharf
Professor Emeritus
125 Nightingale
(617) 373-3795 (office)
(617) 373-8714 (fax)
scharf@neu.edu

• See curriculum vitae (pdf)

Research

I continue active research and publishing in the general area of psychoacoustics, i.e., the study of the relation between sound input and the auditory experience. My two primary specialties are currently auditory attention and loudness.

Auditory Attention

Dr. Reeves and I have measured the time it takes to shift attention from listening to any kind of sound to listening to a particular tone or note. People and, no doubt, animals are very quick in shifting from one sound to another. We need less than a tenth of a second to be able to detect a very weak tone in a background of noise. However, that ability to shift attention or to focus on a particular tone is greatly disrupted when another sound comes on close in time to the targeted sound. Turning on a noise just before a tone is presented may make the tone times harder to hear, harder in the sense that the tone must be made ten times more intense than if the tone were turned on a fifth of a second after the noise onset. In a series of recent experiments we have shown that the onset of the noise disrupts auditory focusing. This effect needs to be taken into account when designing communication systems so as to avoid severe disturbances from one sound on another.

Loudness

Although many people treat loudness as a property of sound, it is, in fact, a property of the listener. With no listener, there is no loudness. The loudness of a sound does depend mainly on the intensity of the sound, but for a human listener, a very intense sound at a very high frequency, above 20,000 Hz, would have no loudness at all and would be inaudible. However, loudness depends not only on intensity and frequency but also on many other factors including what sounds came on in the recent past. Together with colleagues from the Department of Speech-Language Pathology and Audiology at NU, I have been measuring the effect of presenting first a stronger tone followed after a second or so by a weaker tone. Presenting the two tones repeatedly over and over results in a large decrease in the loudness of the weaker tone. After a minute or two, the weaker tone sounds half as loud as when it was first presented. We do not know why this so-called induced loudness reduction comes about. It is not at all like what happens when a very loud sound is followed by a very weak sound. In our experiments the stronger tone is not very much more intense than the weaker one. It must be the case that this kind of influence of one sound on a succeeding sound plays a role in how we hear natural sounds like speech and music.