Sound localization acuity of the common marmoset (Callithrix jacchus)

The common marmoset (Callithrix jacchus) is a small arboreal New World primate which has emerged as a promising model in auditory neuroscience. One potentially useful application of this model system is in the study of the neural mechanism underlying spatial hearing in primate species, as the marmosets need to localize sounds to orient their head to events of interest and identify their vocalizing conspecifics that are not visible. However, interpretation of neurophysiological data on sound localization requires an understanding of perceptual abilities, and the sound localization behavior of marmosets has not been well studied. The present experiment measured sound localization acuity using an operant conditioning procedure in which marmosets were trained to discriminate changes in sound location in the horizontal (azimuth) or vertical (elevation) dimension. Our results showed that the minimum audible angle (MAA) for horizontal and vertical discrimination was 13.17° and 12.53°, respectively, for 2 to 32 kHz Gaussian noise. Removing the monaural spectral cues tended to increase the horizontal localization acuity (11.31°). Marmosets have larger horizontal MAA (15.54°) in the rear than the front. Removing the high-frequency (> 26 kHz) region of the head-related transfer function (HRTF) affected vertical acuity mildly (15.76°), but removing the first notch (12-26 kHz) region of HRTF substantially reduced the vertical acuity (89.01°). In summary, our findings indicate that marmosets' spatial acuity is on par with other species of similar head size and field of best vision, and they do not appear to use monaural spectral cues for horizontal discrimination but rely heavily on first notch region of HRTF for vertical discrimination.

Spectral and Temporal Characteristics of Vowels in Konkani

The present study was undertaken to study the acoustic characteristics of vowels using spectrographic analysis in Mangalorean Catholic Konkani dialect of Konkani spoken in Mangalore, Karnataka, India. Recordings were done using CVC words in 11 males and 19 females between the age range of 18-55 years. The CVC words consisted of combinations of vowels such as (/i, i:, e, ɵ, ə, u, o, ɐ, ӓ, ɔ/) and consonants such as (/m, k, w, s, ʅ, h, l, r, p, ʤ, g, n, Ɵ, ṭ, ḷ, b, dh/). Recordings were done in a sound-treated room using PRAAT software and spectrographic analysis was done and spectral and temporal characteristics such as fundamental frequency (F0), formants (F1, F2, F3) and vowel duration. The results showed that higher fundamental frequency values were observed for short, high and back vowels. Higher F1 values were noted for open vowels and F2 was higher for front vowels. Long vowels had longer duration compared to short vowels and females had longer vowel duration compared to males. The acoustic information in terms of spectral and temporal cues helps in better understanding the production and perception of languages and dialects.

Perception of noise-vocoded tone complexes: A time domain analysis based on an auditory filterbank model

When a wideband harmonic tone complex (wHTC) is passed through a noise vocoder, the resulting sounds can have spectra with large peak-to-valley ratios, but little or no periodicity strength in the autocorrelation functions. We measured judgments of pitch strength for normal-hearing listeners for noise-vocoded wideband harmonic tone complexes (NV-wHTCs) relative to standard and anchor stimuli. The standard was a 1-channel NV-wHTC and the anchor was either the unprocessed wHTC or an infinitely-iterated rippled noise (IIRN). Although there is variability among individuals, the magnitude judgment functions obtained with the IIRN anchor suggest different listening strategies among individuals. In order to gain some insight into possible listening strategies, test stimuli were analyzed at the output of an auditory filterbank model based on gammatone filters. The weak periodicity strengths of NV-wHTCs observed in the stimulus autocorrelation functions are augmented at the output of the gammatone filterbank model. Six analytical models of pitch strength were evaluated based on summary correlograms obtained from the gammatone tone filterbank. The results of the filterbank analysis suggest that, contrary to the weak or absent periodicity strengths in the stimulus domain, temporal cues contribute to pitch strength perception of noise-vocoded harmonic stimuli such that listeners' judgments of pitch strength reflect a nonlinear, weighted average of the temporal information between the fine structure and the envelope.

Sound-localization performance of patients with single-sided deafness is not improved when listening with a bone-conduction device

An increased number of treatment options has become available for patients with single sided deafness (SSD), who are seeking hearing rehabilitation. For example, bone-conduction devices that employ contralateral routing of sound (CROS), by transmitting acoustic bone vibrations from the deaf side to the cochlea of the hearing ear, are widely used. However, in some countries, cochlear implantation is becoming the standard treatment. The present study investigated whether CROS intervention, by means of a CROS bone-conduction device (C-BCD), affected sound-localization performance of patients with SSD. Several studies have reported unexpected moderate to good unilateral sound-localization abilities in unaided SSD listeners. Listening with a C-BCD might deteriorate these localization abilities because sounds are transmitted, through bone conduction to the contralateral normal hearing ear, and could thus interfere with monaural level cues (i.e. ambiguous monaural head-shadow cues), or with the subtle spectral localization cues, on which the listener has learned to rely on. The present study included nineteen SSD patients who were using their C-BCD for more than five months. To assess the use of the different localization cues, we investigated their localization abilities to broadband (BB, 0.5-20 kHz), low-pass (LP, 0.5-1.5 kHz), and high-pass filtered noises (HP, 3-20 kHz) of varying intensities. Experiments were performed in complete darkness, by measuring orienting head-movement responses under open-loop localization conditions. We demonstrate that a minority of listeners with SSD (5 out of 19) could localize BB and HP (but not LP) sounds in the horizontal plane in the unaided condition, and that a C-BCD did not deteriorate their localization abilities.

Agonistic sounds signal male quality in the Lusitanian toadfish

Acoustic communication during agonistic behaviour is widespread in fishes. Yet, compared to other taxa, little is known on the information content of fish agonistic calls and their effect on territorial defence. Lusitanian toadfish males (Halobatrachus didactylus) are highly territorial during the breeding season and use sounds (boatwhistles, BW) to defend nests from intruders. BW present most energy in either the fundamental frequency, set by the contraction rate of the sonic muscles attached to the swimbladder, or in the harmonics, which are multiples of the fundamental frequency. Here we investigated if temporal and spectral features of BW produced during territorial defence reflect aspects of male quality that may be important in resolving disputes. We found that higher mean pulse period (i.e. lower fundamental frequency) reflected higher levels of 11-ketotestosterone (11KT), the main teleost androgen which, in turn, was significantly related with male condition (relative body mass and glycogen content). BW dominant harmonic mean and variability decreased with sonic muscle lipid content. We found no association between BW duration and male quality. Taken together, these results suggest that the spectral content of fish agonistic sounds may signal male features that are key in fight outcome.