Binaural Low Latency

[Yazmín Bohon]

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Binaural interaction occurs in the auditory evoked potentials when the sum of the monaural auditory evoked potentials are not equivalent to the binaural evoked auditory potentials. Binaural interaction of the early- (0-10 ms), middle- (10-50 ms) and long-latency (50-200 ms) auditory evoked potentials was studied in 17 normal young adults. For the early components, binaural interaction was maximal at 7.35 ms accounting for a reduction of 21% of the amplitude of the binaural evoked potentials. For the middle latency auditory evoked potentials, binaural interaction was maximal at 39.6 ms accounting for a reduction of 48% of the binaural evoked potential. For the long-latency auditory evoked potentials, binaural interaction was maximal at 145 ms accounting for a reduction of 38% of the binaural evoked potential. In all of the auditory evoked potentials binaural interaction was long lasting around the maxima. The binaural interaction component extends for several milliseconds in the brainstem to tens of milliseconds in the middle- and long-latency components. Binaural interaction takes the form of a reduction of amplitude of the binaural evoked potential relative to the sum of the monaural responses, suggests that inhibitory processes are represented in binaural interaction using evoked potentials. Binaural processing in the auditory pathway is maximal in the time domain of the middle-latency components reflecting activity in the thalamo-cortical portions of the auditory pathways.

My experience for the past 2 years is that my Widex Moment 330 HAs work very well with the Moment app installed on my iPhone SE (2020) as regards a solid, no-problems Bluetooth connection.

Widex control apps for their HAs have only recently (past 18 months?) been available on the Android platform; until then, the apps only ran on the Apple iOS platform. So Widex have lots of experience in developing apps on iOS but are relatively inexperienced wrt apps running on the Android platform. That may explain your issues with the Widex Moment app on Android.

Brent Butterworth posted some measurements using a credible rig that show PureSound and Universal coming in at 0.48 ms and 1.60 ms, respectively, using a logarithmic chirp tone:

Fresh From the Bench: Widex Moment mRIC RD Hearing Aid audioXpress

As for Signia AX: their claim is 60% reduced binaural latency which, I gather, applies to the communication between the left and right HAs. That said, you can likely get a quick demo at the audiologist, if they carry those.

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Binaural interaction (BI) in brainstem auditory evoked response (BAER) were examined in normal term neonates. The BI components coincided consistently with the latency range of BAER wave IV through wave VII. Most BI components seen in the adults could be identified in the neonates, but the later components, i.e. those with longer latency, were underdeveloped in wave form. Wave DV was the most consistent and reproducible BI component. A marked difference between the neonatal and adult BI wave forms was that wave DVII was particularly small in the neonates. It appears that neuronal responses contributing to later BI components such as wave DVII are particularly immature at birth. Wave latencies and interpeak intervals were longer and amplitudes were smaller in the neonates than in the adults, which was associated with the differences between the neonates and adults in the BAER components. Changes in the BI components with stimulus intensity and rate in the neonates were fundamentally similar to but more significant compared with those in the adults. These findings suggest that neural connections in human auditory brainstem subserving the BI are established at birth but, particularly at higher levels of the brainstem, are immature.

The BI depends on functional integrity of binaurally innervated neurons along the central auditory pathway. Development of BI in the BAER relies on the maturation of binaurally innervated neurons in the brainstem. Alterations in the BI during early childhood may impair speech development and comprehension. Animal experiments have suggested that early auditory experience affects the development of binaural processing in the brain(18). Binaural hearing is more susceptible to alterations in sound experience than other types of hearing. The period of normal development and susceptibility to altered sound experience is more protracted for binaural processing than for other aspects of auditory perception. An animal experiment has shown that conductive hearing loss caused marked alteration in the maturation of BI components in the BAER(19). In a human study of the long-term effects of early conductive hearing loss on auditory electrophysiology, Gunnarson and Funitzo(20) found a significant difference between the affected children and controls in the presence of the BI. These observations suggest that the BI is likely to be a sensitive index for exploring altered development or neural abnormalities in central auditory pathways.

The latency range of BI components in man has been reported to occur between the latencies of BAER wave V to wave VI(3, 5, 7, 9). In term infants, Hosford-Dunn et al.(6) described only one BI component that appeared shortly before BAER wave V, whereas McPhersonet al.(12) reported that BI wave form occurred during BAER waves IV, V, and VI. In the adults we have observed that the BI wave form occurs beyond these latency range and is composed of seven components that coincide consistently with the latency range of BAER waves IV through VII. Wave DVII, which has never been described before, is the most prominent BI component at high stimulus intensity levels. In this study we sought to ascertain whether the BI components found in the adults exist in term neonates and to examine the effects of stimulus intensity on the BI to gain insights into the maturational properties of binaural processing in human infants at birth.

Subjects. Fifteen full-term neonates were recruited into this study. Their BAER thresholds met the following two criteria: 1) monaural response threshold in the infants better than 20 dB HL and2) BAER threshold interaural difference less than 5 dB. All neonates had a birth weight above the 10th percentiles of normal population and ranged in conceptional age (gestational age plus chronologic age) between 37 and 42 wk. The gestational age was determined by maternal history or, if there were no adequate obstetric data, by Dubowitz criteria(21). All infants were judged to be stable and healthy in the nursery with an Apgar score greater than 8 at 5 min. Infants with any perinatal complications such as asphyxia, periventricular hemorrhage and intrauterine infection or growth retardation, hearing loss, or congenital abnormality of CNS were excluded. Seven adults with normal hearing and no known neurologic disorders served as controls.

BAER recording and BI deriving. The test was undertaken between 1 and 11 d after birth in an electrically shielded, darkened, and soundproofed room. Infants lay supine comfortably in their cribs. The BAER was recorded during unsedated sleep after breast or milk feeding. Three silver cup electrodes, filled with commercial electrode paste, were placed along the midline of the scalp with an active electrode (positive) at the vertex, an inactive electrode (negative) at the nape of the neck, and a common (ground) electrode at the upper forehead.

Acoustic stimuli to evoked BAER were alternate clicks that were generated by passing 0.1-ms square pulses through an attenuator to a pair of matched TDH-39 earphones encased in cushions. Brain responses were band passed(100-2000 Hz) and averaged by a signal processor. For each recording, the responses to 2048 stimulus repetitions were averaged. BAER to monaural and binaural stimulation were recorded separately. The first session of recording was made in the sequence of left monaural, right monaural, and binaural stimulation. The second session was simply a replication of the recording but in reverse sequence. Two or more runs were made for each recording condition. The sequence for BAER recording was the responses to left, right, and binaural stimulation. Replicate BAER recordings were made in reverse order. The clicks were started at the intensity of 70 dB HL and the repetition rate of 10/s. Previous studies have shown that BI wave form could be contributed by ACT at high stimulus intensity, and this effect can be reduced or avoided by decreasing stimulus intensity to moderate and low levels(3, 5). The maximum level to avoid ACT is 46 dB above the threshold of the opposite ear. Because BAER usually cannot be detected until it is at least 5 dB above threshold, a level of around 51 dB may be still safe(5). Thus, to examine and reduce the effect of ACT on BI components, subjects were tested at both 50 and 70 dB HL. To observe the intensity effect in more detail, subjects were also tested at 30 and 10 dB HL clicks and, if the subjects kept sleep, the test was continued at 80, 40, and 20 dB HL clicks. Some subjects were also tested at faster stimulus repetition rates: 20, 40, and 60/s.

The latencies of all BI components in the neonates were significantly longer than those in the adults. This was associated or concomitant with the longer BAER wave latencies in the monaural and binaural responses (Fig. 1). Tables 1 and 2 present, respectively, latencies and interpeak intervals of the BI components and the corresponding BAER waves recorded at 70 dB HL clicks with a repetition rate of 10/s.

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