
 difficulty in speech discrimination , particularly in challenging auditory situations such as noisy places and/or when attempting to trace fast speech , is the most common complaint among the elderly .
this difficulty is often attributed to reduced peripheral hearing sensitivity in the elderly ( 1,2 ) .
there is evidence that speech perception in noisy situations is difficult even for normal peripheral hearing sensitivity in the elderly ( 3 ) .
speech discrimination in noise depends on auditory and extra - auditory factors ( 4 ) .
spatial hearing , auditory input representation in different regions of the central auditory system , and spectrotemporal cues for speech processing such as f0 ( the number of human vocal cord vibrations that are affected by age and gender ) are known as auditory elements for speech perception in noise ( 5 ) .
cognitive system functions ( as an internal element ) and physical environmental characteristics ( as external elements ) are known as extra - auditory participating factors for speech perception in noise . attention and memory are the most important cognitive elements that result from bottom - up and top - down mechanisms ( 6 ) .
therefore , auditory  cognitive system interactions are the basis of target signal and background noise segregation in the auditory system ( 712 ) .
the physical characteristics of a communicative environment are the other extra - auditory elements that influence target stimulus detection in the presence of competing background noise ( 13 ) .
the signal - to - noise ratio ( snr ) is the most effective physical characteristic factor for speech perception in noise , and it is defined as the target stimulus power compared with the background noise power , measured in decibels ( db ) ( 3 ) .
several studies have supported the effect of aging on perceptual abilities . a comparison of these potencies in older and younger people revealed that older people required a 34 db higher snr than younger people to have the same proper perception under similar noise conditions .
it appears that age - related changes in auditory  cognitive system functions are responsible for the requirement of an enhanced snr in the elderly ( 1416 ) . 
 

most of the studies on the speech discrimination abilities of the elderly focused on their hearing impaired abilities , clarifying the causes of decreasing perceptual ability .
17 ) ascribed elderly speech difficulties in noise to a deficit in central auditory processing .
clark et al . ( 1 ) and fostick et al . ( 2 ) attributed elderly speech difficulty in noise to peripheral hearing sensitivity loss , known as presbycusis .
wong et al . ( 7 ) found that the speech discrimination ability of the elderly declined more than younger people at a similar snr .
anderson et al . ( 11,15 ) and sung hee et al . ( 18 ) noted that in the elderly , a decreased speech perception in noise ability was the result of chemical changes in the central nervous system neurotransmitters .
parthasarathy et al . ( 19 ) , souza et al . ( 1 ) , kamal et al . (
( 11 ) , bidelman et al . ( 21 ) , and getzmann ( 22 ) attributed the elderly decreased speech in noise discrimination ability to temporal synchronization changes in sub - cortical auditory structures .
walton ( 23 ) also reported prefrontal and hippocampus atrophy in the brains of the elderly .
gordon - salant ( 24 ) found that a decreased discriminative ability in spectro  temporal processing slows the central nervous system of the elderly . according to zekveld et al .
( 26 ) , denise and schwartz ( 27 ) , and sohoglu et al .
( 28 ) , attention and working memory declines are the causes of decreased discriminative skills in the elderly .
wong et al . ( 29 ) studied the role of auditory - cognitive system interactions in speech discrimination and noted inadequate results for higher snr requirements in the elderly compared with younger people under similar noise conditions .
as noted above , the majority of related studies evaluated the effects of auditory  cognitive elements on speech perception in noise of the elderly .
because of the important role of the magnitude of snr on perceptual abilities , it appears that more studies should evaluate auditory and extra - auditory element interactions . 
 
 although it is well known that decreased hearing sensitivity and/or cognitive system dysfunction has a negative effect on the perceptual abilities of the elderly , the importance of physical environmental characteristics such as snr has received less consideration . in this newly designed study , we investigated the role of the snr magnitude as an extra - auditory effect element for the speech in noise perception ability of the elderly .

 this study was performed on 25 elderly people ( 16 women and 9 men ) aged 6574 years with a mean age of 67.9 ( 2.45 sd ) years .
all individuals had normal hearing thresholds at 2502000 hz and were selected from three cultural centers in tehran from october to december 2014 .
safety and morality aspects of the research were approved by iran university of medical sciences . 
 

our study was conducted on right - handed elders with a high school diploma , monolingual with good competency in persian as their native language , with no history of ear diseases , head trauma or accident , head surgery , depression , epilepsy , or neurological drug intake . to ensure normal hearing thresholds at low - mid frequencies ,
pure - tone audiometry was accomplished in a double - walled , sound treated audiometric booth , using a two channel calibrated clinical audiometer ( interacoustic ac40 ) and a supra - aural headphone ( telephonics tdh-49p ) .
pure tone thresholds were obtained at six octave band frequencies from 2508000 hz , using a 10 db up and 5 db down regimen according to the hughson 
westlake method ( 3 ) . in this phase , the participants had hearing thresholds of25 db hl in both ears at 2502000hz .
the mean pt average was 13.64 db and 14.88 db in the right and left ear , respectively .
the mean high frequencies ( 38kh ) hearing thresholds were 48 db and 52 db in the right and left ear , respectively . 
 
 in the speech perception in the noise test ( spin ) , each participant was instructed as follows .
this simple test was designed to assess the ability to recognize normal words in the presence of noise .
spin was performed using four persian , monosyllabic , phonetically - balanced , phoneme - balanced lists ( n=25 ) based on 29 persian language phonemes ( 6 vowels and 23 consonants ) ( 31 ) .
participants responded by repeating the heard words and an adequate response time was given to them .
competing white noise was delivered at three snrs ipsilaterally : 0 , + 5 , and + 10db ( 32 ) .
word discrimination scores were calculated based on correct repeated words by each snr and for each ear . 
 

cognitive screening was performed using persian mini - mental state examination ( mmse ) test .
analysis of variance ( anova ) was conducted to compare word recognition scores at silence and three snrs .
pearson correlations was used for the age - relationship study with word recognition scores in silence and at 0 , + 5 , and + 10dbs . 


 statistical analysis was performed using spss.18 software ( chicago , il , usa ) .
analysis of variance ( anova ) was conducted to compare word recognition scores at silence and three snrs .
pearson correlations was used for the age - relationship study with word recognition scores in silence and at 0 , + 5 , and + 10dbs . 


 the kolmogorov  smirnov test indicated that data were normally distributed among all spin test scores ( p>0.086 ) .
there was a significant difference among word discrimination scores in silence and all snrs for both ears ( tables 1 and 2 ) . the 0 ,
+ 5 , and + 10db snrs were 0.030 , 0.024 , and 0.023 in the right ear and 0.034 , 0.019 , and 0.017 in the left ear , respectively ( p<0.034 ) .
the mean of word discrimination scores in silence and at 0 , + 5 , and + 10db snrs were 85.07% ( 2.94 ) , 64.76% ( 2.19 ) , 71.82% ( 1.17 ) , and 78.24% ( 1.78 ) in the right ear and 84.08% ( 2.84 ) , 64.74% ( 2.22 ) , 70.56% ( 1.60 ) , and 78.31% ( 1.57 ) in the left ear , respectively .
moreover , we observed a significant difference between word discrimination scores for each pair of three snrs ( 0 and + 5 , 0 and + 10 , and + 5 and + 10db ) ( p<0.095 ) ( table 3 ) .
there was no significant correlation between age and word discrimination scores for total in silence and three snrs in both ears ( p>0.30 ) ( table 4 ) . 
 

wds : word discrimination scores ( wds ) , snr : signal to noise ratio 
 
 wds : word discrimination scores ( sds ) , snr : signal to noise ratio 
 
 wds : word discrimination score ( wds ) , snr : signal to noise ratio 
 
 * * pearson correlation is significant at the < 0.05 level ( 2-tailed ) 
 
 wds : word discrimination score ( wds ) 
 
 snr : signal to noise ratios 


 the main finding of this study was the significant difference between word discrimination scores in silence and at 0 , + 5 , and + 10db snrs in both ears .
we found that the word discrimination ability in the elderly was significantly reduced in noisy conditions , and this is in agreement with martin and jerger ( 33 ) , pichora - fuller et al ( 17 ) , gordon - salant ( 23 ) , walton ( 24 ) , and doberva et al .
( 34 ) who all believed that speech perception disability by the elderly is related to non - peripheral auditory factors . with regards to the participants ' normal auditory sensitivity at 2502000 hz and remarkable decreased word discrimination at higher noise levels
, it appears that the ability of the elderly to discriminate word in noise is considerably dependent on the snr magnitude as an extra - auditory element .
moreover , comparison of word discrimination scores in silence and at 0 db snr revealed that the perceptual ability of the elderly was considerably reduced at equal signal and noise levels . 
 

the remarkable difference between word discrimination scores for each pair of snrs ( 0 and + 5 , 0 and + 10 , and + 5 and + 10db ) showed that decreasing the signal level and increasing the competing noise amount extremely reduced the perceptual ability of the elderly .
it appears that when increasing the background noise , elderly people need compensatory strategies for adequate speech sound perception . 
 

no significant correlation was found between age and word discrimination scores in silence and at 0 , + 5 , and + 10db snrs .
( 29 ) who found that the ability of speech discrimination in noise was not only related to the auditory system function , but also to the compensatory interaction of the auditory  cognitive systems .
therefore , one can say there is an assistive factor in the central nervous system of the elderly that prevents further speech in noise discrimination deterioration at higher ages .
it appears that increased activity in general cortical cognitive regions such as the prefrontal area acts as an assistive factor to compensate for the sensory representation deficit in other cortical areas .
this enhanced prefrontal activity following attention has been supported by behavioral - neurophysiologic studies ( 15 - 21 ) .
the ability of speech perception in the elderly affects peripheral / central auditory , cognitive , and environmental elements .
peripheral age - related hearing loss effects on elderly perceptual abilities is caused by a reduced auditory input transition from the cochlea to the higher auditory centers .
central auditory system dysfunction resulted from processing declines at the brainstem and in higher auditory regions ( 15,21 ) .
conversely , cognitive system dysfunction reduces the working memory and attention capacity of the elderly .
physical environmental characteristic deterioration reduces the speech sound transportation from the speaker to the listener ( 37 ) .
mid frequencies , the participants ' speech perception dropped considerably even at equal signal and noise levels .
it appears that reparative strategies such as prosodic rhythm tracing at the phoneme level can help reduce speech sounds transition and processing compensation . increasing the background noise and decreasing
moreover , the effect of auditory training to improve perceptual ability through neural plasticity in the central nervous system of the elderly is supported in various studies .
it appears that acetylcholine levels increase following auditory training and is responsible for exhibitory - inhibitory mechanism interactions resulting in speech representation improvements at sub - cortical and cortical levels ( 40 ) .
therefore , simple stimuli based auditory training and/or memory auditory based cognitive training ( impact : improvement in memory with plasticity - based adaptive cognitive training ) ( 45 ) is the best strategy to improve brain plasticity in the elderly and improve their speech in noise perception ( 4144 ) . 
 

recent findings are only reliable in the frame of this research because of our small sample size .
we could not eliminate the effect of peripheral high frequency loss of speech in noise perception in the elderly .
a study of the snr effect on hearing impaired elders perceptual abilities and the effect of negative snrs on speech perception in noise is recommended to evaluate auditory / extra - auditory element interactions . 


 this study revealed considerably reduced speech perception ability in the presence of background noise in normal , low 
moreover , decreasing the signal level and increasing the competing noise significantly reduced the perceptual abilities of the elderly .
it appears that the snr has an important critical role for proper speech perception in noise for the elderly , even those who have normal peripheral auditory  cognitive function systems .
according to recent findings , elderly people may need adaptive strategies such as auditory training to facilitate speech perception in the presence of background noise . 


 we would like to sincerely thank the eshragh , andishe , bahman cultural centers for their extensive cooperation .
this study was supported by a grant ( contract number 4723/260/90/d/ on 2009/1/12 ) from the rehabilitation research center of iran university of medical sciences , whose financial support is much appreciated .
kobra esfandiyari for sample selection and we also thank all the participants in this research . 

 
 background : speech perception ability depends on auditory and extra - auditory elements . 
 the signal- 
 to - noise ratio ( snr ) is an extra - auditory element that has an effect on the ability to normally 
 follow speech and maintain a conversation . 
 speech in noise perception difficulty is a common complaint 
 of the elderly . in this study , 
 the importance of snr magnitude as an extra - auditory effect on 
 speech perception in noise was examined in the elderly . 

 
 methods : the speech perception in noise test ( spin ) was conducted on 25 elderly participants who 
 had bilateral low  mid frequency normal hearing thresholds at three snrs in the presence of ipsilateral 
 white noise . 
 these participants were selected by available sampling method . 
 cognitive screening was 
 done using the persian mini mental state examination ( mmse ) test . 

 
 results : independent t- test , annova and pearson correlation index were used for statistical 
 analysis . 
 there was a significant difference in word discrimination scores at silence and at three 
 snrs in both ears ( p0.047 ) . 
 moreover , there was a significant difference in word discrimination 
 scores for paired snrs ( 0 and + 5 , 0 and + 10 , and + 5 and + 10 ( p0.04 ) ) . 
 no significant correlation 
 was found between age and word recognition scores at silence and at three snrs in both ears 
 ( p0.386 ) . 

 
 conclusion : our results revealed that decreasing the signal level and increasing the competing 
 noise considerably reduced the speech perception ability in normal hearing at low  
 mid thresholds in 
 the elderly . 
 these results support the critical role of snrs for speech perception ability in the elderly . 
 
 furthermore , our results revealed that normal hearing elderly participants required compensatory 
 strategies to maintain normal speech perception in challenging acoustic situations . 
 
Introduction
Methods

Statistical Analysis

Results
Discussion
Conclusion
Acknowledgement
Conflict of Interest