Speech Perception In Noise: Factors Affecting Sound Perception In Post-lingual Cochlear Hearing Loss Individuals

Speech Perception in Noise

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Speech perception is the phenomenon through which the sounds of different languages are heard, understood, as well as, interpreted. Speech perception is very important and vital to understand the language that is used in our daily lives. When some individual speaks, there is fluctuation in the air pressure and the waves strike the individual’s ears and in some aspect, the person is capable of turning these sound waves to the meaningful consideration of what the other person who is the speaker is saying about. Hence, the speech perception is the most important aspect that is used for the human communication. The core concept regarding the speech perception is used to explain the various mechanisms that are involved in the perception of the words correctly in spite of  the inconsistent information that is provided by the various speech signals (Távora-Vieira, Marino, Acharya, & Rajan, 2015). The concept can be understood clearly by the fact that the human is able to perceive around fifty phonemes in one second in the language he/she is fluent, which indicates that the speech can be perceived with the marked rapidity. On the other hand, in case the person is not fluent in any kind of language (for instance, foreign language), the individual is capable of perceiving around two third of the single phonemic per second. However, there are various other factors affecting speech perception like frequency selectivity, loudness perception, intensity resolution, temporal resolution, temporal integration, pitch perception and frequency discrimination, binaural hearing, dead regions, as well as, aging. In this essay, we are going to discuss various factors that can affect the speech perception in noise for the person who are suffering from moderate to severe degree of post-lingual cochlear hearing loss (Pisoni, 2000). 

The developmental characteristics of the capability to understand the speech in the background noise can be attributed to the broad range of stimuli. There are various factors that can indicate the difficulties experienced by the individuals when listening and understanding the speech in the presence of noise in the background. Cognitive factors, involving attention, memory, as well as, fatigue can also affect the perception of the speech during difficult listening backgrounds such as in noise (van de Vijver, 2009). However, hearing loss is also one of the factors that contribute to the difficulty in perceiving sound in the noise, thus affecting the sound perception by the individual. Hearing loss  is very common, and when it is severe, it can seriously affect and compromise the ability of an individual to understand the speech, the perception, and hence, the communication. Profound hearing loss can impact the spoken language’s acquisition, as well as, its development, compromise the attainment of the education, and can affect the perception of the speech in the difficult listening backgrounds like in noise (Kitterick & Lucas, 2016).

Hearing loss is the unilateral or bilateral impairment of the hearing capacity. The post-lingual hearing loss is the hearing impairment that has developed or manifested after the speech has been developed in the individual, i.e., usually after the age of six years of age. Understanding the speech needs both the anatomical, as well as, functional integrity of central, as well as, the peripheral auditory system. Moreover, it also requires the acoustically appropriate context regarding the communication. However, noise may decrease the individual’s probability of acoustic information that is available, and moreover, the noise is the parameter that is present in almost most of the communication situations. Noise impacts the understanding of the speech and hence, the speech perception in every person. This issue related to the speech perception in noise is compounded in the individuals with moderate to the minor hearing loss where speech, as well as, noise used to compete with each other at the same time. Thus, affecting the perception of the speech in an individual (Bishop, Littman, Balko, Watson, & Backous, 2003). There are various factors that can influence the sound perception in the post-lingual cochlear hearing impaired individual, which are going to be discussed further.

Factors Affecting Sound Perception in Post-lingual Cochlear Hearing Loss Individuals

Frequency selectivity: It is the ability by which the individual is capable of separating or resolving the multiple spectral peaks of the different sounds in the complex sound system. Frequency selectivity is directly associated with the bandwidth, as well as, the tuning of the auditory filters. There is a lot of variation observed in the frequency selectivity of individuals having the same thresholds of the pure tone. Hence, the ability of the ear to separate or resolve the sound components having different frequencies is the most important part of the speech perception, as well as, hearing in general. However, in the individuals having moderate to severe post-lingual hearing loss, the frequency resolving ability of the ear is compromised, hence, making them difficult to identify, as well as, impairing their ability to interpret and understand the speech. Therefore, the background noise is capable of worsening their ability to perceive the sound appropriately as the ear is less able to resolve or separate the different masking noise attributed to the noise environment from the target speech (Most & Adi-Bensaid, 2001).

Loudness Perception: Hearing loss is the decrease in the perception of the loudness or can be associated with the decreased speech intelligibility or can result in both the parameters. The quantitative unit used to measure loudness is known as decibel. The normal threshold of hearing is from 0 to 10 decibels. However, hearing loss can impact the sound perception ( i.e., partial or full loss of the pure tone) or can impact the understanding of the speech, also known as, the discrimination loss. The summation of the loudness is diminished in the post-lingual cochlear hearing loss individual. The post-lingual cochlear hearing impairment reduces the loudness, as well as, distorts the quality of sound. Hence, the environmental noise will interfere more in these cases as compared to the normal hearing individual with speech perception (Loebach, Pisoni, & Svirsky, 2009).   

Intensity resolution: It is the ability of the individual to detect the various changes in the intensity of different sounds or to compare the differences in the intensity of the different or separate sounds. In post-lingual cochlear hearing loss individuals, the intensity resolution capability is decreased as compared to the normal hearing individuals. Hence, when noise is present in the background, the speech perception will be difficult in the cochlear hearing loss individuals due to decreased intensity resolution and discrimination of sounds of different intensities and frequencies (Kilman, Zekveld, Hallgren, & Ronnberg, 2015).

Temporal Resolution: Temporal resolution is the precision of the measurement of the ability of sound perception with respect to time. It is the ability of the individual to detect various changes or gaps in the different signals across time, as well as, across and within the different channel cues. The temporal resolution is measured with the help of three parameters that are gap detection task,  the rate of recovery of the forward masking, and the TMTF. It has been observed that the individuals having post-lingual cochlear hearing loss have decreased performance the gap detection when noise is present, indicating more difficulty in following the temporal structures related to the sounds. Thus, having more difficulty in speech perception in noise. Moreover, the poor TMTF results into the poor perception of the speech in post-lingual cochlear hearing loss individuals (Jin & Nelson, 2006).

Frequency Selectivity

Temporal integration: It is the fundamental process, which the brain carries out for constructing coherent percepts from the serial of different sensory events. Deficits occurring in the temporal processing may impact the ability of the individual to understand the speech, more prominently in the noisy surroundings. The improvement in the various auditory thresholds by increasing the duration of signals is less in the individuals suffering from cochlear hearing loss in comparison to those with normal-hearing. Thus, the capability of the one’s auditory system to integrate the required acoustic energy in sounds with noisy environment tends to appear reduced when there is presence of the hearing loss, hence decreasing the sound perception of those individuals in the noisy environment (Heming & Brown, 2005).

Pitch perception and frequency discrimination: Pitch is the qualitative dimension of the process of hearing that varies mainly as the function of frequency, or in other terms, it can be said that pitch can be defined as the perceptual correlate of the frequency. While, the frequency discrimination can be defined as the ability of the individual to reliably understand or perceive that the two sounds that differs only their frequency are different. However, in individual having cochlear hearing loss, the ability to discriminate between the frequency is reduced. Hence, separation of noise from speech is extremely difficult in the individuals having post-lingual hearing loss due to the various errors in the analysis of the pitch perception and frequency discrimination, which prevents accurate selection and hence, the speech perception from the noisy environment (Oxenham, 2008).

Binaural hearing: It refers to the ability of the individual to integrate the information received by the brain from the two ears. Moreover, binaural hearing helps the ability of an individual to listen in the complex and noisy auditory environments, as well as, to localize the different sources of the sound. The advantage of the binaural hearing that occurs because of the spatial separation of speech, as well as, noise sources (for e.g speech occurring in the front while noise in the back) is reduced in the post-lingual cochlear hearing loss. Hence, the individuals with hearing imipairment have poor speech perception as compared to the individuals with normal hearing, as noise occurring on the contralateral side of the individual will be attenuated in the normal individual in comparison to the speech that is occurring on the ipsilateral side of the individual, and thus improving the speech perception (Moore, 2003).

Dead regions: Hearing impairment or hearing loss is mostly associated with the damage or destruction of the hair cells present in the cochlea. However, in some cases, there may occur complete loss of inner hair cells’ function over the specific region of the cochlea, which is known as the dead region. Hence, due to the presence of the dead regions in the individuals having post-lingual cochlear hearing loss, there can occur off-frequency listening in the noisy environment, which means that the different frequency components can be perceived by the surrounding places. Hence, this frequency-place, as well as, temporal-place mismatch results in the decreased speech perception in the noisy environment (Jepsen & Dau, 2011).

Loudness Perception

Aging: Aging is found to be exacerbating factor in speech perception by the individuals having post-lingual cochlear hearing loss in the noisy environment. There is reduced recognition of the speech in the noisy environment by the individuals with hearing impairment, which is increased with the increasing age and hence causing reduction in the processing time, as well as, reduction of the necessary acoustic information present in the signal. With increase in age, there is poorer performance by the individual in detection of the modulation in the background noise, as well as, there is poor frequency selectivity, which is already experienced by the individuals with hearing impairment. Hence, aging increases the chances of reduction of speech perception by the individuals having post-lingual cochlear hearing loss (Innes-Brown & Marozeau, 2015). 

Conclusion

People having sensorineural hearing impairment have more difficulty in understanding and interpreting the speech, especially in the presence of background sounds. It has been observed that the speech perception by the individuals having hearing impairment is affected to the large extent by the presence of the noise in the environment as compared to the speech perception by the individuals having normal hearing ability (Tsuruoka, Masuda, Usui, Hattori, & Takeuchi, 2009). The reduction in the individual’s ability to resolve or separate the components of different frequencies of the complex sounds is found to be  one of the major factor attributing to the difficulty of speech perception in those individuals. However, other factors like reduced ability of the individual to process the different temporal structure of the different sounds also plays the important role in the speech perception.  The cochlea is the important and dynamic system, which operates on the various auditory signals in the nonlinear, as well as, the time-varying manner. Hence, the temporal envelope, which codes the significant information from the speech, gets distorted when there is any kind of impairment in the auditory system, hence causing the distorted speech perception by the individual (Barac-Cikoja, 2004). 

References

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