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Audibility of short-duration tone-glides as a function of rate of frequency change
Hearing Research, 7 ( 1982) Elsevier Biomedical Press
11S- 125
115
Audibility of short-duration tone-glides as a function of rate of frequency change John K. Cullen, Jr. I and M. Jane Collins 1*2 ’ Kresge Hearing Research Laboratory of the South, Depariments of OtorhinolatyngologV and Physiology, Louisiana State University Medical Cenier, New Orleans, LA 70119, and ’ Department of Speech Pathology and Audiologv, Universiiy of Iowa, Iowa City, IA 52242, U.S.A. (Received
28 August 1981; accepted
17 February 1982)
Thresholds for rising and falling tone-glides were determined against a background of 50-6000 Hz noise at a level of 60 dB re 20 pPa. Glides were centered around 2000 Hz and changed frequencies linearly at rates of 24, 48. 96 and 192 Hz/ms; tone-glide durations were 5, IO, 20 and 40 ms. Results demonstrate a rate-dependent asymmetry in the detectability of rising and falling tone-glides. with rising tone-glides detected at lower signal intensities for the higher rates of frequency change (i.e., 96 and I92
Hz/ms). Key words:
signal detection;
frequency
modulation.
Introduction
The detectability of short duration tones has been studied by many investigators (e.g. [7,12,14,17,20]). These studies have shown that thresholds for such signals decrease as signal duration increases. Lower thresholds in conjunction with increased signal duration have been observed also when broadband, steady-state signals are used as stimuli [3,6,11]. There are few reports in the literature of thresholds for short duration signals that vary in frequency such as tone-glides. Van Bergeijk [ 181 and, more recently, Nabelek [9,10] and Collins and Cullen [l] studied the detection of tone-glides and showed that thresholds are affected by duration and bandwidth (extent of frequency change) in a manner that parallels steady-state signals. However, Collins and Cullen [l] and Nabelek [lo] found that thresholds for tone-glides that increased in frequency were lower than those for tone-glides that decreased in frequency when signal durations were less than 50 ms. Fig. 1 is an example of these findings from the Collins and Cullen [l] study for tone-glides which rose and fell, linearly, from fixed end-point frequencies of 1200 and 1700 Hz. These data are representative of threshold differences observed between rising and falling tone-glides across a broad range of frequencies [lo]. The fact that signal phase differences appear to be important in detectability is interest0378-5955/82/0000-0000/$02.75
Q 1982 Elsevier Biomedical
Press
116
60-
45 ;1 I
5
I
io
I j5
,
I ib Signal Duration (ms)
Fig. 1. Detection thresholds Collins and Cullen [I]).
for 1200- 1700 Hz tone-glides
in 60 dB, broadband
noise (adapted
from
ing in the context of models of peripheral auditory function. Moreover, this phenomenon is of importance in understanding speech processing since speech signals are characterized by acoustic segments which rapidly change frequency over brief time intervals. Collins and Cullen [l] and Nabelek [lo] suggested independently that differences in rising and falling tone-glide thresholds depended on the rate at which frequency changed. However, the stimuli for both studies were structured such that duration, endpoint frequencies, and rate of frequency change of the tone-glide stimuli used were confounded. That is, the effects of rate of frequency change could not be evaluated independently since fixed endpoint frequencies were used across durations. Therefore, the experiment reported here was conducted to test the effects of signal duration, rate of frequency change and direction of frequency change in tone-glide detection using a design that reduced this confounding.
Method
Based on the results of Collins and Cullen [l] and Nabelek [lo], four signal durations were chosen: 5, lo,20 and 40 ms. Signal durations fell within the range of
117
time values which yielded significant threshold differences between rising and falling tone-glides (see Fig. 1). Tone-glides were centered at 2000 Hz and changed frequency linearly. Table I shows the rates of frequency change used and the resultant total change in frequency produced for each signal duration. The incomplete block design produced orthogonality of rate (24,48,96 and 192 Hz/ms) and of duration for 5, 10 and 20 ms signals. Signal durations of 10, 20, and 40 ms were also orthogonal with rates of frequency change of 24, 48 and 96 Hz/ms. A rate of 12 Hz/ms was included in the 40 ms duration signal set in order to evaluate possible effects resulting from the extent of frequency change. The particular rate and duration values chosen were based on log, increments subject to the limit imposed by the lowest frequency obtainable (80 Hz). Thresholds were also obtained for 2000 Hz steady-state, pure-tone signals (i.e., the center frequency of all tone-glides) for durations of 5, 10, 20 and 40 ms for comparative purposes. Signals were digitally generated using a Perkin-Elmer 8/32 computer. Each signal was weighted @th a 1 ms Gaussian rise/fall envelope to reduce the degree of spectral spread produced by signal onset and offset. Tone-glides were generated as frequency-rising signals; frequency-falling signals were obtained by simple reversal of the temporal sequence of digital data representing a rising tone-glide. Thus, rising and falling tone-glide pairs had identical amplitude spectra, differing only in phase spectra.
TABLE RATE USED
I AND EXTENT OF FREQUENCY IN THIS EXPERIMENT
Signal duration (ms)
Rate of frequency
CHANGE
change
W/ms)
FOR
(~1
24 48 96 192
120 240 480 960
IO
24 48 96 192
240 480 960 I 920
20
24 48 96 192
480 960 1920 3 840
40
12 24 48 96
480 960
from tone-glide
1920 3840 initiation
to tone-glide
5, 10, 20 AND
Extent of frequency change
5
’ As measured
THE
termination.
a
40 ms SIGNALS
Monaural thresholds for tone-glides and steady-state signals were obtained in a background of 60 dB SPL band-limited noise (bandwidth 50-6000 Hz) using a computer interactive method of adjustment [1,4]. Subjects controlled the presentation of stimuli via a cathode ray tube computer terminal (i.e., a single stimulus was presented for each press of a designated ‘stimulus’ key on the terminal) and adjusted signal level in a descending sequence from a fixed reference point using a step attenuator with 1 dB resolution (Hewlett-Packard Type 350D). Bracketing was allowed, and subjects were instructed to adjust signal level to achieve a criterion of ‘just masked’. The attenuator contained a signal breaker switch to facilitate anchoring of subjects’ criteria. Signals were produced by direct digital-to-analog conversion at a rate of 50000 conversions/s followed by low-pass filtering at 6000 Hz (48 dB/octave). Stimuli were presented via a Telephonics TDH-49 earphone equipped with MX-41/AR cushions and a standard headband. A second unconnected TDH-49 was mounted on the headband to cover the non-test ear. All testing was performed in an Industrial Acoustics Sound Chamber (Model 1204). Signal and noise intensities were calibrated before and after each experimental session with a Brtiel and Kjaer analog-ear coupler (4153) and Briiel and Kjaer precision sound level meter (2209). A test session lasted approximately 20 min and consisted of determining thresholds for 18 randomized test signals and for two fixed-frequency practice signals that allowed subjects to adjust to test conditions at the beginning of each session. Each subject participated in 10 sessions; odd sessions used randomizations of one-half of the total test-signal set and even sessions used randomizations of the complementary half of the test-signal set. This structuring yielded five judgments per signal per subject. Subjects for this experiment were three adults with hearing better than 5 dB HL [ 161 from 125 to 8000 Hz for the test ear. All were experienced listeners who had previously participated in similar experiments.
Thresholds for tone-glides are shown in Fig. 2, averaged across the three subjects. Thresholds for the fixed-frequency (2000 Hz) signals are also shown on the ordinate with solid squares for comparison purposes. Standard errors of the means are not displayed in this figure because of their small magnitude. Standard deviations for attenuator settings averaged across subjects, sessions and all signal conditions were 1.51 dB and ranged from a maximum of 2.14 dB for the 5 ms, 96 Hz/ms falling tone-glide to a minimum of 0.7 dB for the 40 ms, 24 Hz/ms rising tone-glide. The data for tone-glide rates of 24, 48, 96 and 192 Hz/ms and durations of 5, 10 and 20 ms were statistically analyzed using analysis-of-variance procedures for a within-subject, factorial design (i.e., direction of frequency change, signal duration, rate of frequency change, and replications). This analysis showed significant main effects of signal duration (F(2,4) = 448.13) and rate of frequency change (F(3,6) = 69.75), (P < 0.01). In addition, the interactions between direction of frequency
\I9
change and rate of frequency change (F(3,6) = 22.18) and between signal duration and rate of frequency change (F(6,12) = 24.81) were significant (P < 0.01). A second analysis was performed for tone-glide rates of 24, 48 and 96 Hz/ms and signal durations of 5, lo,20 and 40 ms. The main effects of signal duration (F(3,6) = 944.69) and rate of frequency change (F(2,4) = 53.75) were significant (P C 0.01). The only interaction that reached statistical significance in this second analysis was that between signal duration and rate of frequency change (F(6,12) = 9.86, P c 0.01).
63
61 F5
l& d’ /
IA
/’
F1o
F20
//
/’
20 msec/ /' NA 0' / 0' 0' 40 mse 4 A---4 0
1 I
24
48
Failing Tone Glides l RisingTone Glides
I
I
I
I
96
192
RATE ( HzIms) Fig. 2. Detection thresholds for 5-, IO-, 20- and 40.ms tone-glides function of rate of frequency change.
in 60 dB, broadband
noise plotted
as a
120
The results obtained by statistical analyses can be seen clearly in Fig. 2. First, for glides that change frequency in the same direction, higher threshold values are observed for shorter duration signals. Second, there is a general tendency for threshold values to increase as rate of frequency change increases, with the 5 ms rising tone-glide subset being the exception. Third, differences in thresholds between rising and falling tone-glides are observed consistently only for the shorter durations and the most rapid rates of frequency change (i.e., 96 and 192 Hz/ms). The above analyses were performed with the data collapsed across the parameter
63
61
------a240 Hz L480 Hz ..".."...."09&) k L-1920 Hz I+;+3840 Hz
I_ _
I-
-
I--
F-
I-
-
2
r
5
;o
;o
40
DURATION (ms) Fig. 3. Detection thresholds for falling tone-glides with the extent of frequency change as the parameter.
121
of total extent of frequency change and address the question of the effect of this factor only indirectly. Figs. 3 (falling tone-glides) and 4 (rising tone-glides) display threshold data plotted as a function of signal duration with extent of frequency change as a parameter. These figures show an ordered increase in thresholds as a function of the extent of frequency change for signal durations of 10 ms or greater. The ordered increase in threshold values with extent of frequency change is also seen for the 5 ms falling tone-glides, but not for the 5 ms rising tone-glides.
Discussion
The pattern of threshold change as a function of duration observed in this study is similar to that reported for other studies of short duration, broadband signals (see [3,11]). Differences between threshold values for short duration rising and falling tone-glides for the faster rates of frequency change are consistent with earlier reports of Collins and Cullen [l] and Nabelek [lo]. As mentioned previously, the earlier studies used fixed endpoint-frequencies and varied signal duration; therefore, they did not address directly the question of rate of frequency change in relationship to the threshold differences seen between rising and falling tone-glides. The effects of rate of frequency change on threshold differences between rising and falling toneglides are seen in Fig. 2. As rate of frequency change increases, the differences between threshold values for rising and falling tone-glides become larger. An increase in the rate of frequency change also implies that signal bandwidth broadens when duration is held constant. Figs. 3 and 4 show a tendency for thresholds for both rising and falling tone-glides to increase as bandwidth increases. However, the magnitude of change in threshold values for rising tone-glides per increment in signal bandwidth is less than that for corresponding falling tone-glides. This point is seen in the extreme by comparing threshold values shown in Fig. 3 for the tone-glides of 5 ms duration to those in Fig. 4. Specifically, there is virtually no change in the average threshold values for rising 5-ms tone-glides with frequency changes of 120, 240,480 and 960 Hz (i.e., rates of frequency change of 24,48, 96 and 192 Hz/ms) while a progressive increase in average threshold values is seen for the corresponding falling tone-glide items. * If signal bandwidth was the determining factor of the threshold differences seen between rising and falling tone-glides, one would anticipate that the points for rising and falling tone-glides of similar bandwidths would form parallel lines in Figs. 3 and 4. Functions in Fig. 3 do approximate a family of parallel lines with spacing based on bandwidth; however, the functions plotted in Fig. 4 are divergent as duration increases rather than being parallel. These observations suggest differences in rising and falling tone-glide thresholds result from rate of frequency change rather than stimulus bandwidth, per se. It is interesting to note that Van Bergeijk [18] also observed differences in l
The amount of effective frequency change may be less than specified since I ms rise/fall weightings were used; however, the amount of frequency change was the same for comparable rising and falling tone-glides.
63 61
----a
240 Hz
f480 ..w..---~
59
:--
X-i--
Hz
960 Hz 1920 Hz 3840 Hz
57 55 53 51 49 47 ;
lb DURATION
2’0
4b
(ms)
Fig. 4. Detection thresholds for rising tone-glides with the extent of frequency change as the parameter.
detection thresholds between rising &nd falling tone-glides. However, he found that thresholds for falling tone-glides were lower than those for rising tone-glides, independent of duration. He used both linear and exponential tone-glides of
123
0.75-50ms duration, spanning a frequency range of 3000-6000
Hz. His methodological description indicated that some of the threshold determinations were made in background noise. However, no details of noise level or bandwidth were given and he chose to discuss his results in the context of unmasked thresholds, suggesting that relative differences in auditory sensitivity between the 3000 and 6000 Hz regions of hearing were probably the major factor contributing to the threshold differences he obtained. Collins and Cullen [2] studied tone-glide detection as a function of masking level (albeit with frequency endpoints other than 3000 and 6000 Hz) and found that differences between rising and falling tone-glide thresholds varied as a function of masker level. Differences between rising and falling tone-glide thresholds were maximized for moderate levels of noise and were small or non-existent for conditions which were run either with no masking or with high levels of masking. Thus, differences in the level of masking may account for the disparity between Van Bergeijk’s [ 181 findings and the results of this and other studies. A number of studies have demonstrated that certain units in the ascending auditory system yield differential patterns of response for the frequency-increasing and frequency-decreasing segments of frequency modulated signals (see [5,8,15,19]). Thus, neural mechanisms sensitive to the rate and direction of frequency change appear to be present in mammals. On the other hand, this type of neuronal response specificity may, in part, reflect differences in cochlear partition response patterns produced by frequency-changing signals interacting with the mechanical characteristics of the cochlear partition. That is, when the temporal progression of tone-glide frequency change is opposite that of the high-to-low frequency representation along the co&ear partition (i.e. a frequency-rising tone-glide), displacement of successive points along the basilar membrane may move more nearly in coincidence. Such a phasic displacement of a region of the basilar membrane would, in turn, generate greater synchrony of activity in the array of afferent fibers innervating the region, thereby leading to lower threshold values. If such a process was contributing to differences in thresholds for rising and falling tone-glides, one would anticipate a rate-dependent effect since ‘optimal’ phasing would be obtained with a rising tone-glide having a rate of frequency change that exactly matched the velocity versus distance function of the cochlear partition in a given region. The data displayed in Fig. 2, showing greater differences between rising and falling tone-glides at the faster rates of frequency change, are consistent with this suggestion. Schwartz [13] recently used tone-glide inputs to a computer model of the human cochlea that were identical to the stimuli employed in this experiment. Little difference in the pattern of resulting co&ear partition displacement was obtained as a function of tone-glide direction for slow rates of frequency change (i.e. 24 Hz/ms). However, distinct pattern differences were observed for the 192 Hz/ms signals: IO-ms rising tone-glides produced a displacement of the partition in the region of 2000 Hz that was nearly unitary in nature while the comparable falling tone-glide produced a displacement pattern that was sequential from the higher-to-lower frequency areas. In summary, the present investigation, using a design to minimize confounding effects of signal duration and rate of frequency change, supports the hypothesis that rate of frequency change is a primary determinant of differences in detection
124
thresholds for short duration tone-glides. The previously reported finding of better thresholds for rising tone-glides than for falling tone-glides was maximum in the present study for the most rapid rates of frequency change tested, and may partly be explained on the basis of cochlear partition mechanical characteristics.
Acknowledgements This work was supported in part by USPHS NS-11647. Laboratory facilities were provided through a grant from the Kresge Foundation. The authors thank Judy Knight for her assistance in preparing this manuscript and the many colleagues at the Kresge Hearing Research Laboratory of the South who provided useful comments concerning this work.
References 1 Collins, M.J. and Cullen, J.K., Jr. (1978): Temporal integration of tone glides. J. Acoust. Sot. Am. 63. 469-473. 2 Collins. M.J. and Cullen, J.K.. Jr. (1978): Temporal integration of tone glides as a function of intensity. J. Acoust. Sot. Am. 63. S32 (A). 3 Creelman. C.D. (1961): Detection of complex signals as a function of signal bandwidth and duration. J. Acoust. Sot. Am. 33. 89-94. 4 Cullen, J.K., Jr. and Collins. M.J. (1978): Temporal integration of two-component tone glides, J. Acoust. Sot. Am. 64, 1526- 1527. 5 Erulkar. SD.. Butler. R.A. and Gemstein. G.L. (1968): Excitation and inhibition in the cochlear nucleus II. Frequency modulated tones. J. Neurophysiol. 3 I, 637-648. 6 Gamer, W.R. (I 947): The effect of frequency spectrum on temporal integration of energy in the ear. J. Acoust. Sot. Am. 9. 808-815. 7 Hughes, J.W. (1946): The threshold of audition for short periods of stimulation. Proc. R. Sot. Lond. Ser. B 133,486-490. 8 mler. A.R. (1974): Coding of sounds with rapidly varying spectra in the cochlear nucleus. J. Acoust. Sot. Am. 55,63 I-640. 9 Nabelek, I.V. (1976): Masking of tone glides. In: Hearing and Davis: Essays Honoring Hallowell Davis, pp. 213-224. Editors: SK. Hirsh. D.H. Eldredge, I.J. Hirsh and S.R. Silverman. Washington University Press, St. Louis. MO. IO Nabelek. I.V. (1978): Temporal summation of constant and gliding tones at masked auditor? threshold. J. Acoust. Sot. Am. 64. 75 l-763. I I Northern. J. (1967): Temporal summation for critical bandwidth signals. J. Acoust. Sot. Am. 42. 456-46 I. I2 Plomp, R. and Bouman, M. (I 959): Relation between hearing thresholds and duration for tone pulses, J. Acoust. Sot. Am. 31. 749-758. 13 Schwartz, J.L. (1981): Apport de la psychoacoustique a la modelisation du systeme audtif chez l’homme. Unpublished doctoral dissertation, I’Institut National Polytechnique de Grenoble, Grenoble. 14 Sheely, E.C. and Bilger, R.C. (1964): Temporal integration as a function of frequency. J. Acoust. Sot. Am. 36, 1850-1857. 15 Suga, N. (1968): Analysis of frequency-modulated and complex sounds by single auditory neurons of bats. J. Physiol. (London) 198. 51-80. 16 Specifications for Audiometers (1969) (R1973): ANSI. American National Standards Institute. Nen York.
125
17 Stephens, S.D.G. (1973): Some experiments on the detection of short duration stimuli. 81-94. 18 Van Bergeijk, W.A. (1964): Sonic pulse compression in bats and people: A comment. Am. 36, 594-597. 19 Vartanian, LA. (1974): On mechanisms of specialized reactions frequency-modulated sounds. Acoustica 3 1, 305-3 10. 20 Watson, C.S. and Gengel, R.W. (1969): Signal duration and signal sensitivity. J. Acoust. Sot. Am. 46, 989-997.
of central frequency
Br. J. Audiol. J. Acoust.
auditory in relation
7, Sot.
neurons to auditory
to
11S- 125
115
Audibility of short-duration tone-glides as a function of rate of frequency change John K. Cullen, Jr. I and M. Jane Collins 1*2 ’ Kresge Hearing Research Laboratory of the South, Depariments of OtorhinolatyngologV and Physiology, Louisiana State University Medical Cenier, New Orleans, LA 70119, and ’ Department of Speech Pathology and Audiologv, Universiiy of Iowa, Iowa City, IA 52242, U.S.A. (Received
28 August 1981; accepted
17 February 1982)
Thresholds for rising and falling tone-glides were determined against a background of 50-6000 Hz noise at a level of 60 dB re 20 pPa. Glides were centered around 2000 Hz and changed frequencies linearly at rates of 24, 48. 96 and 192 Hz/ms; tone-glide durations were 5, IO, 20 and 40 ms. Results demonstrate a rate-dependent asymmetry in the detectability of rising and falling tone-glides. with rising tone-glides detected at lower signal intensities for the higher rates of frequency change (i.e., 96 and I92
Hz/ms). Key words:
signal detection;
frequency
modulation.
Introduction
The detectability of short duration tones has been studied by many investigators (e.g. [7,12,14,17,20]). These studies have shown that thresholds for such signals decrease as signal duration increases. Lower thresholds in conjunction with increased signal duration have been observed also when broadband, steady-state signals are used as stimuli [3,6,11]. There are few reports in the literature of thresholds for short duration signals that vary in frequency such as tone-glides. Van Bergeijk [ 181 and, more recently, Nabelek [9,10] and Collins and Cullen [l] studied the detection of tone-glides and showed that thresholds are affected by duration and bandwidth (extent of frequency change) in a manner that parallels steady-state signals. However, Collins and Cullen [l] and Nabelek [lo] found that thresholds for tone-glides that increased in frequency were lower than those for tone-glides that decreased in frequency when signal durations were less than 50 ms. Fig. 1 is an example of these findings from the Collins and Cullen [l] study for tone-glides which rose and fell, linearly, from fixed end-point frequencies of 1200 and 1700 Hz. These data are representative of threshold differences observed between rising and falling tone-glides across a broad range of frequencies [lo]. The fact that signal phase differences appear to be important in detectability is interest0378-5955/82/0000-0000/$02.75
Q 1982 Elsevier Biomedical
Press
116
60-
45 ;1 I
5
I
io
I j5
,
I ib Signal Duration (ms)
Fig. 1. Detection thresholds Collins and Cullen [I]).
for 1200- 1700 Hz tone-glides
in 60 dB, broadband
noise (adapted
from
ing in the context of models of peripheral auditory function. Moreover, this phenomenon is of importance in understanding speech processing since speech signals are characterized by acoustic segments which rapidly change frequency over brief time intervals. Collins and Cullen [l] and Nabelek [lo] suggested independently that differences in rising and falling tone-glide thresholds depended on the rate at which frequency changed. However, the stimuli for both studies were structured such that duration, endpoint frequencies, and rate of frequency change of the tone-glide stimuli used were confounded. That is, the effects of rate of frequency change could not be evaluated independently since fixed endpoint frequencies were used across durations. Therefore, the experiment reported here was conducted to test the effects of signal duration, rate of frequency change and direction of frequency change in tone-glide detection using a design that reduced this confounding.
Method
Based on the results of Collins and Cullen [l] and Nabelek [lo], four signal durations were chosen: 5, lo,20 and 40 ms. Signal durations fell within the range of
117
time values which yielded significant threshold differences between rising and falling tone-glides (see Fig. 1). Tone-glides were centered at 2000 Hz and changed frequency linearly. Table I shows the rates of frequency change used and the resultant total change in frequency produced for each signal duration. The incomplete block design produced orthogonality of rate (24,48,96 and 192 Hz/ms) and of duration for 5, 10 and 20 ms signals. Signal durations of 10, 20, and 40 ms were also orthogonal with rates of frequency change of 24, 48 and 96 Hz/ms. A rate of 12 Hz/ms was included in the 40 ms duration signal set in order to evaluate possible effects resulting from the extent of frequency change. The particular rate and duration values chosen were based on log, increments subject to the limit imposed by the lowest frequency obtainable (80 Hz). Thresholds were also obtained for 2000 Hz steady-state, pure-tone signals (i.e., the center frequency of all tone-glides) for durations of 5, 10, 20 and 40 ms for comparative purposes. Signals were digitally generated using a Perkin-Elmer 8/32 computer. Each signal was weighted @th a 1 ms Gaussian rise/fall envelope to reduce the degree of spectral spread produced by signal onset and offset. Tone-glides were generated as frequency-rising signals; frequency-falling signals were obtained by simple reversal of the temporal sequence of digital data representing a rising tone-glide. Thus, rising and falling tone-glide pairs had identical amplitude spectra, differing only in phase spectra.
TABLE RATE USED
I AND EXTENT OF FREQUENCY IN THIS EXPERIMENT
Signal duration (ms)
Rate of frequency
CHANGE
change
W/ms)
FOR
(~1
24 48 96 192
120 240 480 960
IO
24 48 96 192
240 480 960 I 920
20
24 48 96 192
480 960 1920 3 840
40
12 24 48 96
480 960
from tone-glide
1920 3840 initiation
to tone-glide
5, 10, 20 AND
Extent of frequency change
5
’ As measured
THE
termination.
a
40 ms SIGNALS
Monaural thresholds for tone-glides and steady-state signals were obtained in a background of 60 dB SPL band-limited noise (bandwidth 50-6000 Hz) using a computer interactive method of adjustment [1,4]. Subjects controlled the presentation of stimuli via a cathode ray tube computer terminal (i.e., a single stimulus was presented for each press of a designated ‘stimulus’ key on the terminal) and adjusted signal level in a descending sequence from a fixed reference point using a step attenuator with 1 dB resolution (Hewlett-Packard Type 350D). Bracketing was allowed, and subjects were instructed to adjust signal level to achieve a criterion of ‘just masked’. The attenuator contained a signal breaker switch to facilitate anchoring of subjects’ criteria. Signals were produced by direct digital-to-analog conversion at a rate of 50000 conversions/s followed by low-pass filtering at 6000 Hz (48 dB/octave). Stimuli were presented via a Telephonics TDH-49 earphone equipped with MX-41/AR cushions and a standard headband. A second unconnected TDH-49 was mounted on the headband to cover the non-test ear. All testing was performed in an Industrial Acoustics Sound Chamber (Model 1204). Signal and noise intensities were calibrated before and after each experimental session with a Brtiel and Kjaer analog-ear coupler (4153) and Briiel and Kjaer precision sound level meter (2209). A test session lasted approximately 20 min and consisted of determining thresholds for 18 randomized test signals and for two fixed-frequency practice signals that allowed subjects to adjust to test conditions at the beginning of each session. Each subject participated in 10 sessions; odd sessions used randomizations of one-half of the total test-signal set and even sessions used randomizations of the complementary half of the test-signal set. This structuring yielded five judgments per signal per subject. Subjects for this experiment were three adults with hearing better than 5 dB HL [ 161 from 125 to 8000 Hz for the test ear. All were experienced listeners who had previously participated in similar experiments.
Thresholds for tone-glides are shown in Fig. 2, averaged across the three subjects. Thresholds for the fixed-frequency (2000 Hz) signals are also shown on the ordinate with solid squares for comparison purposes. Standard errors of the means are not displayed in this figure because of their small magnitude. Standard deviations for attenuator settings averaged across subjects, sessions and all signal conditions were 1.51 dB and ranged from a maximum of 2.14 dB for the 5 ms, 96 Hz/ms falling tone-glide to a minimum of 0.7 dB for the 40 ms, 24 Hz/ms rising tone-glide. The data for tone-glide rates of 24, 48, 96 and 192 Hz/ms and durations of 5, 10 and 20 ms were statistically analyzed using analysis-of-variance procedures for a within-subject, factorial design (i.e., direction of frequency change, signal duration, rate of frequency change, and replications). This analysis showed significant main effects of signal duration (F(2,4) = 448.13) and rate of frequency change (F(3,6) = 69.75), (P < 0.01). In addition, the interactions between direction of frequency
\I9
change and rate of frequency change (F(3,6) = 22.18) and between signal duration and rate of frequency change (F(6,12) = 24.81) were significant (P < 0.01). A second analysis was performed for tone-glide rates of 24, 48 and 96 Hz/ms and signal durations of 5, lo,20 and 40 ms. The main effects of signal duration (F(3,6) = 944.69) and rate of frequency change (F(2,4) = 53.75) were significant (P C 0.01). The only interaction that reached statistical significance in this second analysis was that between signal duration and rate of frequency change (F(6,12) = 9.86, P c 0.01).
63
61 F5
l& d’ /
IA
/’
F1o
F20
//
/’
20 msec/ /' NA 0' / 0' 0' 40 mse 4 A---4 0
1 I
24
48
Failing Tone Glides l RisingTone Glides
I
I
I
I
96
192
RATE ( HzIms) Fig. 2. Detection thresholds for 5-, IO-, 20- and 40.ms tone-glides function of rate of frequency change.
in 60 dB, broadband
noise plotted
as a
120
The results obtained by statistical analyses can be seen clearly in Fig. 2. First, for glides that change frequency in the same direction, higher threshold values are observed for shorter duration signals. Second, there is a general tendency for threshold values to increase as rate of frequency change increases, with the 5 ms rising tone-glide subset being the exception. Third, differences in thresholds between rising and falling tone-glides are observed consistently only for the shorter durations and the most rapid rates of frequency change (i.e., 96 and 192 Hz/ms). The above analyses were performed with the data collapsed across the parameter
63
61
------a240 Hz L480 Hz ..".."...."09&) k L-1920 Hz I+;+3840 Hz
I_ _
I-
-
I--
F-
I-
-
2
r
5
;o
;o
40
DURATION (ms) Fig. 3. Detection thresholds for falling tone-glides with the extent of frequency change as the parameter.
121
of total extent of frequency change and address the question of the effect of this factor only indirectly. Figs. 3 (falling tone-glides) and 4 (rising tone-glides) display threshold data plotted as a function of signal duration with extent of frequency change as a parameter. These figures show an ordered increase in thresholds as a function of the extent of frequency change for signal durations of 10 ms or greater. The ordered increase in threshold values with extent of frequency change is also seen for the 5 ms falling tone-glides, but not for the 5 ms rising tone-glides.
Discussion
The pattern of threshold change as a function of duration observed in this study is similar to that reported for other studies of short duration, broadband signals (see [3,11]). Differences between threshold values for short duration rising and falling tone-glides for the faster rates of frequency change are consistent with earlier reports of Collins and Cullen [l] and Nabelek [lo]. As mentioned previously, the earlier studies used fixed endpoint-frequencies and varied signal duration; therefore, they did not address directly the question of rate of frequency change in relationship to the threshold differences seen between rising and falling tone-glides. The effects of rate of frequency change on threshold differences between rising and falling toneglides are seen in Fig. 2. As rate of frequency change increases, the differences between threshold values for rising and falling tone-glides become larger. An increase in the rate of frequency change also implies that signal bandwidth broadens when duration is held constant. Figs. 3 and 4 show a tendency for thresholds for both rising and falling tone-glides to increase as bandwidth increases. However, the magnitude of change in threshold values for rising tone-glides per increment in signal bandwidth is less than that for corresponding falling tone-glides. This point is seen in the extreme by comparing threshold values shown in Fig. 3 for the tone-glides of 5 ms duration to those in Fig. 4. Specifically, there is virtually no change in the average threshold values for rising 5-ms tone-glides with frequency changes of 120, 240,480 and 960 Hz (i.e., rates of frequency change of 24,48, 96 and 192 Hz/ms) while a progressive increase in average threshold values is seen for the corresponding falling tone-glide items. * If signal bandwidth was the determining factor of the threshold differences seen between rising and falling tone-glides, one would anticipate that the points for rising and falling tone-glides of similar bandwidths would form parallel lines in Figs. 3 and 4. Functions in Fig. 3 do approximate a family of parallel lines with spacing based on bandwidth; however, the functions plotted in Fig. 4 are divergent as duration increases rather than being parallel. These observations suggest differences in rising and falling tone-glide thresholds result from rate of frequency change rather than stimulus bandwidth, per se. It is interesting to note that Van Bergeijk [18] also observed differences in l
The amount of effective frequency change may be less than specified since I ms rise/fall weightings were used; however, the amount of frequency change was the same for comparable rising and falling tone-glides.
63 61
----a
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f480 ..w..---~
59
:--
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960 Hz 1920 Hz 3840 Hz
57 55 53 51 49 47 ;
lb DURATION
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4b
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Fig. 4. Detection thresholds for rising tone-glides with the extent of frequency change as the parameter.
detection thresholds between rising &nd falling tone-glides. However, he found that thresholds for falling tone-glides were lower than those for rising tone-glides, independent of duration. He used both linear and exponential tone-glides of
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0.75-50ms duration, spanning a frequency range of 3000-6000
Hz. His methodological description indicated that some of the threshold determinations were made in background noise. However, no details of noise level or bandwidth were given and he chose to discuss his results in the context of unmasked thresholds, suggesting that relative differences in auditory sensitivity between the 3000 and 6000 Hz regions of hearing were probably the major factor contributing to the threshold differences he obtained. Collins and Cullen [2] studied tone-glide detection as a function of masking level (albeit with frequency endpoints other than 3000 and 6000 Hz) and found that differences between rising and falling tone-glide thresholds varied as a function of masker level. Differences between rising and falling tone-glide thresholds were maximized for moderate levels of noise and were small or non-existent for conditions which were run either with no masking or with high levels of masking. Thus, differences in the level of masking may account for the disparity between Van Bergeijk’s [ 181 findings and the results of this and other studies. A number of studies have demonstrated that certain units in the ascending auditory system yield differential patterns of response for the frequency-increasing and frequency-decreasing segments of frequency modulated signals (see [5,8,15,19]). Thus, neural mechanisms sensitive to the rate and direction of frequency change appear to be present in mammals. On the other hand, this type of neuronal response specificity may, in part, reflect differences in cochlear partition response patterns produced by frequency-changing signals interacting with the mechanical characteristics of the cochlear partition. That is, when the temporal progression of tone-glide frequency change is opposite that of the high-to-low frequency representation along the co&ear partition (i.e. a frequency-rising tone-glide), displacement of successive points along the basilar membrane may move more nearly in coincidence. Such a phasic displacement of a region of the basilar membrane would, in turn, generate greater synchrony of activity in the array of afferent fibers innervating the region, thereby leading to lower threshold values. If such a process was contributing to differences in thresholds for rising and falling tone-glides, one would anticipate a rate-dependent effect since ‘optimal’ phasing would be obtained with a rising tone-glide having a rate of frequency change that exactly matched the velocity versus distance function of the cochlear partition in a given region. The data displayed in Fig. 2, showing greater differences between rising and falling tone-glides at the faster rates of frequency change, are consistent with this suggestion. Schwartz [13] recently used tone-glide inputs to a computer model of the human cochlea that were identical to the stimuli employed in this experiment. Little difference in the pattern of resulting co&ear partition displacement was obtained as a function of tone-glide direction for slow rates of frequency change (i.e. 24 Hz/ms). However, distinct pattern differences were observed for the 192 Hz/ms signals: IO-ms rising tone-glides produced a displacement of the partition in the region of 2000 Hz that was nearly unitary in nature while the comparable falling tone-glide produced a displacement pattern that was sequential from the higher-to-lower frequency areas. In summary, the present investigation, using a design to minimize confounding effects of signal duration and rate of frequency change, supports the hypothesis that rate of frequency change is a primary determinant of differences in detection
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thresholds for short duration tone-glides. The previously reported finding of better thresholds for rising tone-glides than for falling tone-glides was maximum in the present study for the most rapid rates of frequency change tested, and may partly be explained on the basis of cochlear partition mechanical characteristics.
Acknowledgements This work was supported in part by USPHS NS-11647. Laboratory facilities were provided through a grant from the Kresge Foundation. The authors thank Judy Knight for her assistance in preparing this manuscript and the many colleagues at the Kresge Hearing Research Laboratory of the South who provided useful comments concerning this work.
References 1 Collins, M.J. and Cullen, J.K., Jr. (1978): Temporal integration of tone glides. J. Acoust. Sot. Am. 63. 469-473. 2 Collins. M.J. and Cullen, J.K.. Jr. (1978): Temporal integration of tone glides as a function of intensity. J. Acoust. Sot. Am. 63. S32 (A). 3 Creelman. C.D. (1961): Detection of complex signals as a function of signal bandwidth and duration. J. Acoust. Sot. Am. 33. 89-94. 4 Cullen, J.K., Jr. and Collins. M.J. (1978): Temporal integration of two-component tone glides, J. Acoust. Sot. Am. 64, 1526- 1527. 5 Erulkar. SD.. Butler. R.A. and Gemstein. G.L. (1968): Excitation and inhibition in the cochlear nucleus II. Frequency modulated tones. J. Neurophysiol. 3 I, 637-648. 6 Gamer, W.R. (I 947): The effect of frequency spectrum on temporal integration of energy in the ear. J. Acoust. Sot. Am. 9. 808-815. 7 Hughes, J.W. (1946): The threshold of audition for short periods of stimulation. Proc. R. Sot. Lond. Ser. B 133,486-490. 8 mler. A.R. (1974): Coding of sounds with rapidly varying spectra in the cochlear nucleus. J. Acoust. Sot. Am. 55,63 I-640. 9 Nabelek, I.V. (1976): Masking of tone glides. In: Hearing and Davis: Essays Honoring Hallowell Davis, pp. 213-224. Editors: SK. Hirsh. D.H. Eldredge, I.J. Hirsh and S.R. Silverman. Washington University Press, St. Louis. MO. IO Nabelek. I.V. (1978): Temporal summation of constant and gliding tones at masked auditor? threshold. J. Acoust. Sot. Am. 64. 75 l-763. I I Northern. J. (1967): Temporal summation for critical bandwidth signals. J. Acoust. Sot. Am. 42. 456-46 I. I2 Plomp, R. and Bouman, M. (I 959): Relation between hearing thresholds and duration for tone pulses, J. Acoust. Sot. Am. 31. 749-758. 13 Schwartz, J.L. (1981): Apport de la psychoacoustique a la modelisation du systeme audtif chez l’homme. Unpublished doctoral dissertation, I’Institut National Polytechnique de Grenoble, Grenoble. 14 Sheely, E.C. and Bilger, R.C. (1964): Temporal integration as a function of frequency. J. Acoust. Sot. Am. 36, 1850-1857. 15 Suga, N. (1968): Analysis of frequency-modulated and complex sounds by single auditory neurons of bats. J. Physiol. (London) 198. 51-80. 16 Specifications for Audiometers (1969) (R1973): ANSI. American National Standards Institute. Nen York.
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17 Stephens, S.D.G. (1973): Some experiments on the detection of short duration stimuli. 81-94. 18 Van Bergeijk, W.A. (1964): Sonic pulse compression in bats and people: A comment. Am. 36, 594-597. 19 Vartanian, LA. (1974): On mechanisms of specialized reactions frequency-modulated sounds. Acoustica 3 1, 305-3 10. 20 Watson, C.S. and Gengel, R.W. (1969): Signal duration and signal sensitivity. J. Acoust. Sot. Am. 46, 989-997.
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