In this study we used functional near-infrared spectroscopy (fNIRS) to investigate neural responses in normal-hearing adults as a function of speech recognition accuracy, intelligibility of the speech stimulus, and the manner in which speech is distorted. Participants listened to sentences and reported aloud what they heard. Speech quality was distorted artificially by vocoding (simulated cochlear implant speech) or naturally by adding background noise. Each type of distortion included high and low-intelligibility conditions. Sentences in quiet were used as baseline comparison. fNIRS data were analyzed using a newly developed image reconstruction approach. First, elevated cortical responses in the middle temporal gyrus (MTG) and middle frontal gyrus (MFG) were associated with speech recognition during the low-intelligibility conditions. Second, activation in the MTG was associated with recognition of vocoded speech with low intelligibility, whereas MFG activity was largely driven by recognition of speech in background noise, suggesting that the cortical response varies as a function of distortion type. Lastly, an accuracy effect in the MFG demonstrated significantly higher activation during correct perception relative to incorrect perception of speech. These results suggest that normal-hearing adults (i.e., untrained listeners of vocoded stimuli) do not exploit the same attentional mechanisms of the frontal cortex used to resolve naturally degraded speech and may instead rely on segmental and phonetic analyses in the temporal lobe to discriminate vocoded speech.

Purpose: To determine if listeners with normal hearing and listeners with sensorineural hearing loss give different perceptual weightings to cues for stop consonant place of articulation in noise versus reverberation listening conditions. Method: Nine listeners with normal hearing (23–28 years of age) and 10 listeners with sensorineural hearing loss (31–79 years of age, median 66 years) participated. The listeners were asked to label the consonantal portion of synthetic CV stimuli as either /p/ or /t/. Two cues were varied: (a) the amplitude of the spectral peak in the F4/F5 frequency region of the burst was varied across a 30-dB range relative to the adjacent vowel peak amplitude in the same frequency region, (b) F2/F3 formant transition onset frequencies were either appropriate for /p/, /t/ or neutral for the labial/alveolar contrast. Results: Weightings of relative amplitude and transition cues for voiceless stop consonants depended on the listening condition (quiet, noise, or reverberation), hearing loss, and age of listener. The effects of age with hearing loss reduced the perceptual integration of cues, particularly in reverberation. The effects of hearing loss reduced the effectiveness of both cues, notably relative amplitude in reverberation. Conclusions: Reverberation and noise conditions have different perceptual effects. Hearing loss and age may have different, separable effects.

Purpose: The purpose of the current study was to determine the effects of vowel identity and temporal onset asynchrony on identification of vowels overlapped in time. Method: Fourteen listeners with normal hearing, with a mean age of 24 years, participated. The listeners were asked to identify both of a pair of 200-ms vowels (referred to as double vowels ) presented either simultaneously or with a temporal asynchrony ranging from 25 ms to 150 ms in 25-ms steps. The stimuli were synthetic steady-state vowels /i æ ɑ u ɝ/ arranged in seven combinations: /u i/, /æ ɑ/, /ɝ ɑ/, /ɝ æ/, /æ i/, /ɝ i/, and /ɝ u/. Results: Listeners' responses revealed that one vowel of a pair was identified correctly more often than the other vowel (known as vowel dominance ). Vowel dominance effects were seen for 6 of the 7 vowel pairs, and there was improvement of vowel identification with increasing temporal separation between vowels for 5 of the 7 pairs. Vowel pairs with the vowel /ɝ/ consistently yielded improved identification with increases in temporal asynchrony. Discussion: Peripheral masking cannot explain the patterns of results of this study. A more parsimonious explanation may be perceptual anchoring.

Hearing loss represents a multifaceted and pervasive challenge that deeply impacts various aspects of an individual’s life, spanning psychological, emotional, social, and economic realms. Understanding the molecular underpinnings that orchestrate hearing loss remains paramount in the quest for effective therapeutic strategies. This review aims to expound upon the physiological, biochemical, and molecular aspects of hearing loss, with a specific focus on its correlation with diabetes. Within this context, phytochemicals have surfaced as prospective contenders in the pursuit of potential adjuvant therapies. These compounds exhibit noteworthy antioxidant and anti-inflammatory properties, which hold the potential to counteract the detrimental effects induced by oxidative stress and inflammation—prominent contributors to hearing impairment. Furthermore, this review offers an up-to-date exploration of the diverse molecular pathways modulated by these compounds. However, the dynamic landscape of their efficacy warrants recognition as an ongoing investigative topic, inherently contingent upon specific experimental models. Ultimately, to ascertain the genuine potential of phytochemicals as agents in hearing loss treatment, a comprehensive grasp of the molecular mechanisms at play, coupled with rigorous clinical investigations, stands as an imperative quest.

The two aims of this study were (a) to determine the perceptual weight given formant transition and relative amplitude information for labeling fricative place of articulation perception and (b) to determine the extent of integration of relative amplitude and formant transition cues. Seven listeners with normal hearing and 7 listeners with sensorineural hearing loss participated. The listeners were asked to label the fricatives of synthetic consonant-vowel stimuli as either /s/ or /∫/. Across the stimuli, 3 cues were varied: (a) The amplitude of the spectral peak in the 2500- Hz range of the frication relative to the adjacent vowel peak amplitude in the same frequency region, (b)the frication duration, which was either 50 or 140 ms, and (c) the second formant transition onset frequency, which was varied from 1200 to 1800 Hz. An analysis of variance model was used to determine weightings for the relative amplitude and transition cues for the different frication duration conditions. A 30-ms gap of silence was inserted between the frication and vocalic portions of the stimuli, with the intent that a temporal separation of frication and transition information might affect how the cues were integrated. The weighting given transition or relative amplitude differed between the listening groups and depended on frication duration. Use of the transition cue was most affected by insertion of the silent gap. Listeners with hearing loss had smaller interaction terms for the cues than listeners with normal hearing, suggesting less integration of cues.

The current study explored the changes in weighting of relative amplitude and formant transition cues that may be caused by a K-amp circuit. Twelve listeners with normal hearing and 3 listeners with sensorineural hearing loss labeled the stop consonant place of articulation of synthetic consonant-vowel stimuli. Within the stimuli, two acoustic cues were varied: the frequency of the onset of the second and third formant (F2/F3) transitions and the relative amplitude between the consonant burst and the following vowel in the fourth and fifth formant (F4/ F5) frequency region. The variation in the two cues ranged from values appropriate for a voiceless labial stop consonant to a voiceless alveolar stop consonant. The listeners labeled both the unaided stimuli and the stimuli recorded through a hearing aid with a K-amp circuit. An analysis of variance (ANOVA) model was used to calculate the perceptual weight given each cue. Data from listeners with normal hearing show a change in relative weighting of cues between aided and unaided stimuli. Pilot data from the listeners with hearing loss show a more varied pattern, with more weight placed on relative amplitude. These results suggest that calculation of perceptual weights using an ANOVA model may be worthwhile in future studies examining the relationship between acoustic information presented by a hearing aid and the subsequent perception by the listener with hearing loss.