Backward Masking: Different Durations of the Masking Stimulus

Download Backward Masking: Different Durations of the Masking Stimulus

Post on 29-Mar-2017

215 views

Category:

Documents

3 download

Embed Size (px)

TRANSCRIPT

  • Letters to the Editor

    In the Interest of Architectural Acoustics

    PAUL S. VENEKLASEN

    Western Electro-Acoustic Laboratory, Inc. 2222 South Barrington Avenue Los Angeles, California

    T is not unusual that severe problems in a field stimulate its advancement. During such a period, it is also to be expected that diverging approaches and opinions may be espoused in all sincerity by various groups. The field of architectural acoustics is in such a state at the present time. My consulting group is pleased to be active in this field.

    It is important that the Acoustical Society and its members should be presented all views of a problem with complete ob- jectivity so that they may find their way individually and jointly to the truths that should ultimately emerge for the advancement of our science. It is in this spirit that I have decided to terminate my editorial responsibilities so that the Society may have no doubt that further papers on the subject of auditorium acoustics will have the freest review and editorial independence. I am pleased to know that this function will be continued by Dr. Northwood.

    I wish to express my appreciation to the Council, and especially to Editor-in-Chief Lindsay for the opportunity of serving the Society and the field in an editorial capacity during the past four years.

    Editor's Note: Mr. Veneklasen's resignation of his Associate Editorship is noted in the Acoustical News Section in this issue with an expression of appreciation for his contribution to the Journal and the Society.

    and 100 msec with a 10-uec rise time. Testing was conducted at masking intervals of 1, 3, 5, 10, 15, 25, 50, and 100 msec. Eighteen subjects listened to monotic backward masking (probe tone and masking stimulus presented to the same ear), and another eighteen to the dichotic condition (probe tone and masking stimulus led to different ears). Subjects were intelligent, experimentally naive, adult male listeners with normal audiograms. Each subject judged all three masking durations, completing all judgments for a given duration at a single test session. Order of presenting masking durations, as well as order of masking intervals, was counter- balanced.

    Results of both experiments showed no differences in backward masking that could be attributed to the duration of the masking stimulus. Curves for the three durations were essentially identical. Both monotic and dichotic sets of curves were very similar to those reported previously for the 50-msec-duration masking stimulus and tended to change slope at masking intervals of 10 or 15 msec. Since essentially the same degree of backward masking occurred for the three durations of the masking stimulus, it seems reasonable to conclude that the important variable is time of onset of the masking stimulus. This suggests that the neural onset effect triggered by initiation of the masking stimulus is largely responsi- ble for backward-masking phenomena.

    * Present address: Central Institute for the Deaf, St. Louis, Mo. L. L. Elliott, "Backward Masking: Monotic and Dichotic Conditions,"

    J. Acoust. Soc. Am. 34, 1108-1115 (1962). L. L. Elliott, "Backward and Forward Masking of Probe Tones of Differ-

    ent Frequencies," J. Acoust. Soc. Am. 34, 1116-1117 (1962).

    Loudness Function in the Presence of Masking Noise

    Backward Masking: Different Durations of the Masking Stimulus Los L. ELLIOTT*

    U.S. Air Force School of Aerospace Medicine, Brooks Air Force Base, Texas (Received 7 October 1963)

    No differences were obtained in the backward masking produced by masking stimulus durations of 25, 50, and 100 msec for either monotic or dichotic masking.

    WO experiments were conducted to explore the effect of duration of the masking stimulus in the backward-masking situation. Briefly, backward masking refers to the situation in which the stimulus that is masked precedes the stimulus that masks it. The apparatus and stimulus conditions were identical to those reported previousIf' the subject determined his own threshold for the 5-msec, 1000-cps probe tone, which had 1-msec rise time? White noise at 90 dB SPL re 0.0002 dyn/cm - served as the masking stimulus and was presented for durations of 25, 50,

    }XORMAN GLEISS* AND EBERHARD ZWICKER

    Institut far Nachrichtentechnik, Technische Hochschule, Stuttgart, Germany (Received 30 August 1963)

    Partly masked loudness curves given by different authors are compared. It is shown that the curves depend upon the spectrum of the masking sound and so cannot be calculated in general from one simple formula.

    A RECENT paper I contains curves that describe the loudness of tones masked by noise. Figures 12 and 13 in that paper show the level of a 1000-Hz comparison tone in relation to the level of a masked 1000-Hz tone of equal loudness. As masking sound, either narrow-band noise (Af equal to the critical band- width) or uniform stimulating noise with sound-pressure levels of 40 and 60 dB per critical band was used.

    These curves invite a comparison with similar curves published by Lochner and Burger. ' They used octave-band noise (700-14 Hz) to mask a 1000-Hz tone. Their diagram indicates the masked loudness as a function of sensation level. In order to make a direct

    comparison possible, we have transferred the loudness scale into a loudness-level scale (Fig. 1). For the transformation, we used lhe

    393

    Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 132.177.236.161 On: Mon, 24 Nov 2014

    15:34:39