Acoustic Reflex Growth Functions Research Articles

Crossed and uncrossed acoustic reflex growth functions in normal-hearing adults, typically developing children, and children with suspected auditory processing disorder

Objective: Previous data suggested that children with suspected auditory processing disorders (APD) often show elevated or absent acoustic reflex thresholds, especially in crossed conditions (e.g. Allen & Allan, 2014). This study further explored these effects by measuring acoustic reflex growth functions (ARGF). Design: Crossed and uncrossed ARGF slopes were obtained by linear fits between reflex amplitudes and increases in activator level from threshold to 15 dB above it. Study sample: Normal-hearing adults, typically developing children and children with reported listening difficulties and suspected of having an APD, participated. Results: The ARGF slopes were shallower in crossed than in uncrossed conditions for all groups but the magnitude of the effect was significantly greater in the children with suspected APD. There were no differences between the typically developing children and the adults. Conclusions: The results suggest shallower ARGFs in children with suspected APD. Given the role of the acoustic reflex in facilitating hearing speech in noise these findings may begin to shed light on physiologic explanations for some of the difficulties that are reported by children with suspected APD.

The effects of probe-tone frequency on the acoustic-reflex growth function.

Acoustic-reflex growth functions (ARGFs) were obtained from 20 normal-hearing listeners. Contralateral acoustic reflexes (ARs) were elicited with pure tones of 2000 Hz. The magnitude of changes in static compliant susceptance (BA) and conductance (GA) were monitored with probe-tone frequencies of 226 Hz, 678 Hz and 1000 Hz. ARGFs were obtained with six combinations of probe-tone frequency/admittance component: 226 Hz BA, 226 Hz GA, 678 Hz BA, 678 Hz GA, 1000 Hz BA, and 1000 Hz GA. Peak conductance (GA) and susceptance (BA) ARs were largest within the 678 Hz GA and 1000 Hz BAARGFs, respectively. Among high-frequency probe tones, the patterns of AR growth were larger and less variable for the 678 Hz GA ARGF and the 1000 Hz BA ARGF as determined by the magnitude of their linear (b1) and quadratic (b2) polynomial coefficients and the value of their squared correlation coefficients (R2).

Improved intensity coding at faster click-rates within the acoustic reflex pathway.

This investigation was designed to study the effect of click repetition rates on the slopes of the ipsilateral acoustic reflex growth functions. Sixteen normal female subjects within the age range 20 to 26 years participated in the study. Following the determination of ipsilateral acoustic reflex thresholds at the click repetition rates of 50, 100, 150, 200, 250 and 300 clicks/sec, reflex amplitudes were measured at 5 and 10 dB above the threshold values. The amplitudes of the acoustic reflex grew more rapidly at higher click rates, resulting in steeper slopes of the acoustic reflex growth functions. These results suggest better coding of intensity at higher click repetition rates within the ipsilateral acoustic reflex pathway.

Aural acoustic-immittance measurements: inter-aural differences.

Bilateral measurements of the aural acoustic-immittance characteristics of the middle-ear transmission system of 48 subjects were made with an acoustic-admittance meter. The measurements, including static acoustic-immittance, acoustic-reflex thresholds, and acoustic-reflex growth functions, were made using a 220-Hz probe. The contralateral reflex data for three pure tones (500, 1000, and 2000 Hz) and for broadband noise were acquired in 2-dB steps at sound-pressure levels from 84-116 dB (tones) and 66-116 dB (noise) during ascending- and descending-intensity level runs. For all acoustic-immittance measurements, right ear and left ear comparisons were made and found not to be significantly different. The individual subject data then were expressed as the absolute differences between ears. In this manner normative inter-aural immittance differences were defined. The peak static immittance data were analyzed in terms of median inter-aural differences and upper 80% cut-off values. The 80% ranges for normal immittance values were smaller for a within subject versus an across subject comparison. For acoustic-reflex thresholds, a disparity between ears of greater than 10 dB was suggested as indicative of an abnormality in the auditory mechanism. Finally, the reflex-growth data indicated mean inter-aural absolute differences that ranged to .040-.043 acoustic mmhos (300-400 acoustic ohms) at the higher reflex activator sound-pressure levels.

Temporal summation in acoustic reflex growth functions.

Acoustic reflex growth functions for pure tone activators of 500, 1000 and 2000 Hz and a broad-band noise (BBN) were obtained with activator durations of 20, 200 and 1000 msec (10 msec rise/decay) in four young, normal subjects. The lowest reflex thresholds were obtained for the 1000 msec activators, followed by 200 msec and then 20 msec. The reflex growth functions revealed lower reflex magnitudes for the shorter duration activators. When normalized to account for temporal summation at reflex threshold, reflex magnitude growth was similar among the three durations at 500 Hz, slower for 20 msec than for 200 and 1000 msec at 1000 Hz, and became progressively slower with decreasing duration from 1000 to 200 to 20 msec at 2000 Hz. When expressed in SPL, the BBN growth functions reasonably resembled those at 2000 Hz. No particular pattern was revealed for the normalized BBN growth functions.