Dan Mapes-Riordan

Hearing aid having digital damping

A hearing aid is set forth that includes one or more hearing aid components that introduce an undesired undamped peak into the frequency response of the hearing aid. An electronic damping filter is utilized to compensate for the undamped peak. The electronic damping filter has a notch filter response that includes an inverse peak across the frequency range of the undamped peak thereby electronically damping the frequency response so that the hearing aid output is generally unaffected by the undesired characteristics of the inverse peak. The electronic damping filter may be programmable to vary the magnitude and/or shift the frequency of the inverse peak. A method is set forth that exploits this programmability and allows the same circuit topology to be used in two different hearing aids respectively having two different undamped peaks. A further method allows handling two or more peaks.

The relationship between localization and the Franssen effect

The relationship between localization and the Franssen effect was studied for noise and tones in a sound-deadened and in a live room. The noise was wideband and the tones were 250, 500, 1000, 1500, 2500, and 4000 Hz. Listeners were asked to determine the location of the stimuli in a localization task and to discriminate the difference between a pair of stimuli used to generate the Franssen illusion and a steady-state tone in a Franssen-effect discrimination task. Poor performance in the Franssen-effect discrimination task is consistent with the stimulus conditions leading to a strong Franssen illusion. Poor performance in both the Franssen effect and localization tasks was obtained for midfrequency tones (near 1500 Hz) and in the live room. Thus, the Franssen illusion is strongest for a live room and for midfrequency tones consistent with the difficulty listeners have in localizing sounds under these conditions. These results are consistent with those of Hartmann and Rakerd [J. Acoust. Soc. Am. 86, 1366-1373 (1989)] and support their suggestion of a correlation between the Franssen effect and localization in rooms.

Towards a model of loudness recalibration

The Zwicker (1977, 1990) loudness model is a standard for predicting the loudness of a sound. This model, along with Moore and Glasbergs (see Acustica, vol.82, p.335-45, 1996) revision of it, is fairly accurate at predicting the loudness of steady-state sounds, but falls short for many types of temporally varying sounds. One temporal effect not accounted for in the Zwicker model is loudness recalibration. Loudness recalibration is a fatigue-like effect that makes a quiet tone at one frequency even quieter when it is preceded by a louder tone at the same frequency. The evidence suggests that loudness recalibration occurs in the central nervous system. Two means of modeling loudness recalibration are proposed. The first is an algorithmic description of the recalibration effect that could be added to the later stages of the Zwicker model. The other method uses a neural network and is based on a spike-train timing theory of hearing rather than a rate-place theory as assumed by the Zwicker model. This spike-train timing approach is unique in that spike-train averaging is postponed until a final loudness estimate is made. A more complete and accurate model of loudness recalibration will have to wait until more experimental data is collected.

Pitch strength of regular-interval click trains with different length “runs” of regular intervals

Click trains were generated with first- and second-order statistics following Kaernbach and Demany [J. Acoust. Soc. Am. 104, 2298-2306 (1998)]. First-order intervals are between successive clicks, while second-order intervals are those between every other click. Click trains were generated with a repeating alternation of fixed and random intervals which produce a pitch at the reciprocal of the duration of the fixed interval. The intervals were then randomly shuffled and compared to the unshuffled, alternating click trains in pitch-strength comparison experiments. In almost all comparisons for the first-order interval stimuli, the shuffled-interval click trains had a stronger pitch strength than the unshuffled-interval click trains. The shuffled-interval click trains only produced stronger pitches for second-order interval stimuli when the click trains were unfiltered. Several experimental conditions and an analysis of runs of regular and random intervals in these click trains suggest that the auditory system is sensitive to runs of regular intervals in a stimulus that contains a mix of regular and random intervals. These results indicate that fine-structure regularity plays a more important role in pitch perception than randomness, and that the long-term autocorrelation function or spectra of these click trains are not good predictors of pitch strength.

Temporal properties of loudness recalibration

Loudness recalibration occurs when a loud (recalibration) tone at frequency f1 precedes quieter test tones at frequencies f1 and f2. Recalibration is a reduction in the perceived loudness of the test tone at f1 due to the addition of the recalibration tone. Mapes‐Riordan and Yost [J. Acoust. Soc. Am. 101, 3170(A) (1997)] showed that the temporal onset of loudness recalibration is relatively fast. The current set of experiments addressed the temporal decay properties of loudness recalibration. The first set of experiments examined the ‘‘local’’ temporal characteristics by measuring how the average amount of loudness recalibration varies with the duration of silent gap between the recalibration tone and the first comparison tone. A second set of experiments examined the ‘‘global’’ nature of the decay of loudness recalibration by inducing recalibration and then monitoring the decay using an adaptive tracking procedure. The results of these experiments will be discussed in terms of how assimilation processes influence loudness recalibration, what factors make the decay of loudness recalibration relatively slow, and the effect of attention on loudness recalibration. [Work supported by a Program Project Grant from NIDCD.]

Loudness recalibration as a function of recalibration and comparison tone level

Presenting loud tones at one frequency and quiet tones at a different frequency makes the quiet tones appear relatively louder. This phenomenon, dubbed loudness recalibration [Marks, J. Exp. Psychol. 20, 382–396 (1994)], was studied using an adaptive, two‐track loudness comparison procedure. In this study, a baseline loudness comparison was initially established between two tones. Immediately following this baseline sequence, a sequence of trials were given in which the two comparison tones were preceded by a recalibration tone. The amount of steady‐state loudness recalibration was measured as a function of the recalibration tone level and the baseline comparison tone level. The results showed that loudness recalibration is present when the recalibration tone level is much larger than the comparison tone level and that no loudness recalibration is generated when the recalibration tone level is less than or equal to the comparison tone level. In addition, it was found that a recalibration tone did not affe...

Discrimination of first- and second-order regular intervals from random intervals as a function of high-pass filter cutoff frequency

This study extends the work of Kaernbach and Demany [J. Acoust. Soc. Am. 104, 2998–2306 (1998)] in which regular interval stimuli (RIS) click trains with first-order intervals could be discriminated from random-interval click trains, but RIS with second-order intervals could not. Kaernbach and Demany concluded that their results cast doubt on autocorrelation as a method of analysis for such stimuli. The present study investigated the same stimuli, but for a variety of filter conditions. The results suggest that while RIS click trains with first-order intervals are more easily discriminated from random-interval stimuli than second-order interval RIS click trains, discrimination based on second-order intervals is possible except when the stimuli are high-pass filtered above 8 kHz, i.e., above the spectral region of phase locking.

Head movements in localization

Head movements in all three planes were measured while listeners localized a pulse of transient sounds (train of 100 μs broadband impulses) located in the frontal azimuth plane. The eight loudspeakers were at the same height as the head of the seated listener. They were located every 25.7° from +90° to −90°, where 0° is straight ahead. Some listeners were able to see the eight sound sources, while for other listeners the sound sources were hidden from view. In addition, listeners were instructed differently in terms of the necessity for high accuracy or fast reaction. In all cases, the primary means of the listener locating the sound source was head movements. Listeners were instructed to face the source of the sound so that their nose was facing directly at the perceived sound source. The results will be discussed in terms of processing sounds in dynamic listening situations. [Research supported by the Air Force Office of Scientific Research and a Program Project Grant from the NIDCD, DC00293.]

The effect of interval order and highpass filtering on the pitch strength of shuffled click‐train regular interval stimuli

Regular interval stimuli (RIS) contain temporal regularities that are known to produce a pitch percept. Previous experiments [Mapes‐Riordan and Yost, ARO MidWinter meeting proceedings (2000)] showed that shuffled, wide‐band first‐order ‘‘kxkx’’ click‐train RIS have a stronger pitch strength than the original, unshuffled stimuli, where ‘‘k’’ is a fixed duration interval and ‘‘x’’ is a random interval. The primary difference between ordered and shuffled click‐train sequences is that shuffled sequences contain multiple instances of regular ‘‘k’’ intervals. This result provides evidence for the importance of the short‐term periodicity within RIS in determining its pitch strength. The current experiments investigated whether this phenomenon also occurred when the RIS were created from higher‐order intervals and/or whose spectrum was limited to unresolved frequency channels. A set of trials was run in which listeners compared the pitch strength of an ordered click‐train RIS and a shuffled version of the same se...

Loudness recalibration and complex tones

Loudness recalibration occurs when a loud (recalibration) tone at frequency f1 precedes quieter test tones at frequencies f1 and f2. Previous experiments [Mapes‐Riordan and Yost, J. Acoust. Soc. Am. 101, 3170(A) (1997)] have shown that the recalibration tone can decrease the loudness of the test tone at f1 by more than 6 dB. The current experiments addressed loudness recalibration when the test signal and/or recalibration signal was harmonic complex tones. In the first experiment an adaptive tracking procedure measured the equal loudness point between a harmonic complex and a pure tone. In the recalibration conditions, the loudness comparisons were preceded by a recalibration signal consisting of various combinations of frequencies contained in the harmonic complex, or by a pure tone corresponding to the pitch of the missing fundamental. In the second experiment, listeners were asked to adjust the level of a single harmonic (f3) in a harmonic complex (f1−f5) until it was heard as a separate tone in conditions with and without a recalibration tone at f3. The results of these experiments will be discussed in terms of the loci of loudness recalibration relative to perceptual stream formation. [Work supported by a NIDCD Program Project Grant.]