Ciclo di Seminari del Dipartimento di Psicologia, a.a. 2017/2018

The external world experienced through hearing is full of auditory events (that is, perceived sounds) that often overlap in time, because several physical sound sources are active at the same time. Sometimes, one or more of these sounds are higher in level than , and therefore can "cover up" ("mask"),  other co-occurring sounds. In spite of the presence of maskers in noisy environments, listeners can often recognize softer sounds that they attend to (for example, a conversation or the sound of a musical instrument).

Imagine, for example, that you are in a room with a partially open window.  You can hear through the window the sound of two people having a conversation in a nearby garden. The sound of the conversation is somewhat soft, but you can easily recognize the words spoken by the people in the garden. Suddenly, a gust of wind causes the door of the room to shut violently. The noise of the slamming door masked (that is, "covered up") the sound of the conversation for a fraction of a second (enough time to mask a portion of a word). While the noise of the slamming door was present, the information about the word was effectively missing. And yet you did not hear the conversation as being interrupted by the slamming door. Instead, the conversation was heard as continuing "underneath" the sound of the slamming door. This situation is analogous to the perception of visual objects as complete (whole) even though they are partially covered by another object (a situation known as the "picket fence effect" in visual perception).

The seminar will first introduce how an intact auditory system, and particularly the peripheral auditory system, encodes individual sounds, and how it deals with the presence of multiple sounds in noisy environments. Then, the  seminar will focus on sound recognition by people who have greatly reduced or missing auditory input. For many individuals with profound hearing losses, the only way to be able to hear sound is currently offered by direct electrical stimulation of the auditory nerve through a cochlear implant.

Although cochlear implants can be very effective for recognizing speech in quiet environments, the information they are able to transmit to the auditory nerve is much more reduced than the information provided by a normal cochlea. Therefore, cochlear implant users commonly find it difficult to follow conversations in noisy environments. After reviewing the basic functioning of cochlear implants, the final part of the seminar will focus on the results of a study on the perception of masking by users of cochlear implants. This study also investigated the perception of the "auditory continuity" effect, an auditory analogue of the visual picket fence (Miller and Licklider, 1950, Thurlow, 1957; Vicario, 1960;  Warren et al., 1972). The evidence from this study shows that listeners with cochlear implants experience larger amounts of masking than an otherwise comparable group of listeners with normal hearing. The seminar will end with a discussion about the role of masking in the poor recognition of speech in noisy environments by listeners with cochlear implants.