Understanding Aided Speech Perception in Noise

Digit Identification

The investigators will measure the behavioral accuracy of listeners identifying digits in a continuous stream of monosyllabic words. In a roughly two-minute run, about 30 digits are presented and listeners are tasked with immediately identifying each one as they are presented. The target stream can be stationary or moving in space, and the masker speech stream can be stationary at the front loudspeaker or diffused around the front speaker (i.e., played from multiple speakers). For static or fixed spatial separations between target and masker (between 0° and 90°), the digit identification accuracy is in percent correct. For multiple spatial separations, the investigators can derive a psychometric curve from which the investigators can extract the spatial separation needed to get a desired percent correct, like 75%, and the investigators call this the Spatial Segregation Boundary (in degrees).

Neural Segregation

Using two neural entrainment models (forward and backward), the investigators will measure the probability that the brain is able to encode attended speech during a speech-on-speech task. Listeners are tasked with identifying digits during the task carried by either the male or female speaker. The neural entrainment models will be conducted for each spatial separation (between 0° and 90°), from which the investigators will derive a single probability metric for fixed spatial separations or for multiple locations, revealing a neurometric curve. From the neurometric curve, the investigators can extract the spatial separation needed to get a desired percent correct, like 75%, and the investigators call this the Neural Spatial Segregation Boundary (in degrees).

Minimum Audible Angle (MAA)

psychophysical test of minimum audible angle at the front (0°) and at the right side (+90°) using a vector-based amplitude panning method for titrating on presentation angle. Listeners perform an adaptive tracking test in which they indicate whether broadband white noises (0.1-8 kHz) were to the left or right of the 0° reference or front or behind the 90° reference. The noise stimuli are a train of three 100-ms bursts of Gaussian noise, with a 500-ms silence between bursts. A 3-down/1-up adaptive procedure is used to determine the reproduction angle for the next trial, which could be smaller or larger than the previous separation, to find the 79.4% correct point on a psychometric function. The angular step sizes in the 0° MAA measurement are determined by Parameter Estimation by Sequential Testing (PEST).

Speech Localization Error

Listeners are presented with 130 monosyllable words, each presented from 1 of 13 loudspeakers spanning (-90 to +90° in 15° steps). After each presentation, listeners indicate point in the direction from where they heard the stimulus come. Localization error is calculated as the average error (in degrees) that listeners achieve per source angle.

Fixed Spatial Release from Masking

To quantify a fixed spatial release-from-masking (SRM) point, listeners will perform an adaptive tracking task. The SNR between target and masker speech streams will be fixed to -3 dB re the co-located SRT50 (separately tested as a method for setting individual levels in the digit identification test), and the spatial separation between the target and masker will be adaptively changed to converge on a 3dB-SRM until threshold is reached. This will identify the amount of spatial separation between target and masker required to achieve a 3-dB improvement in SNR over a co-located condition.

Pure-tone Air Threshold (PTac)

Audibility thresholds in dB HL for pure tone stimuli at octave frequencies from 250 to 8000 Hz measured by air conduction via audiometer and audiometric headphones.

Bone Conduction Threshold (PTbc)

Audibility thresholds in dB HL for pure tone stimuli at octave frequencies from 250 to 8000 Hz measured by bone conduction via audiometer and audiometric headphones.

Wideband Tympanometry (Equivalent Ear Canal Volume)

Wideband tympanometry measures will be obtained using the Interacoustics Titan clinical immittance system to ensure consistent middle ear function prior to each test session and to obtain Equivalent Ear Canal Volume (ECV).

Wideband Tympanometry (Static Peak Pressure)

Wideband tympanometry measures will be obtained using the Interacoustics Titan clinical immittance system to ensure consistent middle ear function prior to each test session and to obtain static peak pressure.