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Year:  2003  Vol. 69   Ed. 2 - (15º)

Artigo Original

Pages: 242 to 249

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Controversies or complexity in the relationship between temporal auditory processing and aging?

Author(s): Vera T. das Neves[1],
M. Ângela G. Feitosa[2]

Keywords: auditory aging, auditory temporal processing, gap detection, speech recognition.

Abstract:
The present article contains a brief review of the literature concerning auditory aging, describing specifical studies on aging of temporal auditory processing. Experimental procedures for research on temporal auditory processing are described. Studies about the effects of aging on the detection of gaps in noises and pure tones, as well as studies on the relationship between temporal auditory processing and speech recognition, among young and aged subjects, are discussed. Some of the main controversies about the relationship between temporal auditory processing and speech recognition are described. The differences found among the results of the studies in this area are interpreted in terms of the complexity of the procedures of assessment of temporal auditory processing adopted. Finally, suggestions about future directions of research are presented.

INTRODUCTION

A large portion of the information transmitted through sounds, such as music and speech, for example, is expressed by changes in sound characteristics as time elapses. Temporal auditory processing involves the competence to process these sound aspects that vary in time. The interest in the relationship between aging and temporal auditory processing has been increasing in past years because the elderly have been complaining about difficulties to understand speech that are not related to the hearing loss level they present. That is, whereas some elderly patients that have few difficulties to detect low intensity sounds report difficulties to understand speech, especially in noise or reverberation situations, other elderly people who have evident hearing losses not always report the same complaints. Recent studies1, 2 have shown that such difficulties in speech recognition should be related to losing the capacity of sound temporal processing, associated with aging. The study of this evidence is the purpose of the present paper.

The study of temporal auditory processing is subdivided into two main topics: temporal integration (also called temporal summation) and temporal resolution (also called temporal acuity). The temporal auditory integration consists of the capacity of the auditory system to accumulate information during the time to better detect or discriminate sounds3. Historically, this is the oldest area of the study of temporal auditory phenomena and we can see that the increase in signal duration makes detection easier4. Temporal resolution, in turn, refers to the quick aspects of temporal auditory processing, which enables for example the detection of brief gaps between two stimuli, or detection of sound modulations3, 4.

Temporal resolution tests can be conducted in different ways. Eddins and Green4 classified the numerous variants of these procedure in the study of five large categories: studies of the temporal order perception, phase detection, gap detection, detection of amplitude modulation and temporal asynchrony detection. To present, studies with the elderly have concentrated mainly in gap detection tests with various types of sound signals. Thus, the characteristic of gap detection tests in the elderly is the first topic addressed by the present study. Next, we will examine some studies addressing complex temporal processing tasks and some studies that treat the correlation between temporal auditory processing and speech recognition.

Detection of Gaps and Auditory Aging

General characteristics of gap detection procedures
In its most traditional form, the gap detection studies are conducted by adopting a paradigm of forced choice between two stimuli. That is, two wide band frequency noises are represented monaurally. In one of these two pulses, the noise is broken, with the introduction of a very short duration silence (gap). In the other, the sound has the same duration, but it is continuos, without gaps. The subject's task is to point which of two bursts had the gap, from a sequence presented at random. Thus, we determine the threshold for gap detection, that is, what is the minimum duration for its existence to be detected.

In addition to the studies that try to determine the thresholds of gap detection, there are studies describing the psychometric functions of gap detection with the use of yes-no procedures, using pure tones5, wide band frequency sounds6 and narrow band sounds7. Such studies are described with more details in the text produced by Neves and Feitosa (2002, in press).

It has been noticed that in pure tones and narrow band sounds the gap detection threshold is reduced with the increase in frequency of the presented sounds. In addition, it is noticed that hearing people, both young and old, have difficulties to detect the gaps when the duration is shorter, being that the elderly have more difficulty than young people when the gap is too close to the beginning or end of the sound, that is, in the 5% beginning or end of the duration time, or when the beginning of the gap is unpredictable6.

Gap detection in the young and the elderly
Most studies of gap detection in the elderly intend to determine whether there is an aging process that can exclusively affect the temporal auditory processing without necessarily affecting sound sensitivity, that is, its absolute detection threshold. Together with this issue is the need to identify the cause of the difficulty, noticed in the elderly, to process quick changes in sound characteristics, especially in noise. This reduced capacity could be due to a deterioration of the peripheral auditory processes (for example, hair cell damage or spiral ganglion fiber damage), or it could be caused by the deterioration of the central auditory processes, resulting from damage in the central areas of the auditory nervous system. As examples of damage in central auditory areas we may include the loss of neuronal volume in the ventral division of the cochlear nucleus, probably associated with the loss of dendritic ramifications8,, loss of fibers of the lateral lemniscus 9 or some other abnormalities of the dendrites and cellular body of the auditory cortex neurons10. Alternatively, such difficulties could be associated with general cognitive losses, common to the generalized slowness of the cognitive processes in the elderly. This issue guided the studies reported below.

In 1992, Moore, Peters and Glasberg presented a research study involving the detection of temporal gaps in sinusoids for young and elderly subjects with and without hearing loss. They tried to check whether the elderly patients had temporal resolution worse than the young subjects and whether the deficit would be restricted to people with hearing loss. To that end, they made two groups, one with people aged 63 to 86 years with hearing loss and another one with people aged 62 to 83 years with normal hearing, which were compared to a group of people with normal hearing and aged 22 to 43 years, examined in another study11. The task was to detect gaps in sinusoids in frequencies of 100 to 2000Hz, intensity of 25 to 85 dB SPL and 500ms duration, in procedures of forced choice between three alternatives. The results indicated that the gap detection thresholds improved as sound intensity increased, but they reached asymptotic values as the levels increased, such as 55dB SPL for frequencies 100 and 2000Hz. It occurred both among the young and elderly subjects, even though some elderly subjects presented reduction in performance at the most intense level (85dB SPL). The gap detection levels in both groups of elderly patients were similar and both had thresholds higher than the young people group, and results variability was greater in the elderly groups than in the young people group. Such results could indicate that the age, more than the audiometric loss, would be the main reason for the differences between the groups. However, the authors observed that this difference would be owed especially to a small number of elderly subjects who had extremely high gap detection thresholds, whereas most elderly normal hearing people had thresholds within the normal range, regardless of the hearing loss. It allowed them to conclude that the loss of temporal resolution would have been an inevitable consequence of aging.

Schneider, Pichora-Fuller, Kowalchuk and Lamb12 compared young subjects (mean age of 23 years) and elderly people (mean age of 69.2 years) with normal hearing (thresholds of 25dB HL between 0.25 and 3kHz) in a task to detect gaps in sinusoid tones of 2kHz frequency and 9dB SPL intensity and 250ms duration, in a paradigm of forced choice between two alternatives. They noticed that whereas young people had gap detection levels of 3.8 and 3.5ms for right and left ears, the thresholds for elderly subjects were 6.2 and 6.5ms, respectively. In addition, the elderly people thresholds were more variable than those of the young people. However, the audiometric thresholds both of young and elderly subjects did not present statistically significant correlations with the gap detection thresholds. That is, the hearing loss did not predict the temporal resolution loss, or vice-versa and the absolute thresholds were independent from the gap detection thresholds for pure tones.

In a subsequent study, Schneider, Speranza and Pichora-Fuller13 examined the effects of intensity and 2kHz pure tones curves among young subjects (mean age of 23 years) and elderly subjects (mean age of 68 years). They measured the signal detection thresholds for both intensity levels (40 and 60dB SL) and Gauss curves with standard deviation of 0.5 and 2 ms (that is, with crescent amplitudes or longer attack times). The stimuli with lower standard deviations in the curves had greater spectral dispersion, which could allow gaps to be detected through the high frequency hearing, which is better in young than in elderly people.

Conversely, the stimuli with greater standard deviation in the curves showed intensity changes that were slower, thus, if the differences in gap interruption thresholds between young and elderly subject were caused by a longer time of temporal integration in the elderly, the different between the two groups tended to disappear as the curve standard deviations increased. The results indicated that the elderly had greater thresholds than the young people in all curve amplitudes, concluding that the differences determined by age could not be attributed to spectral dispersion. nor to different longer integration time, since the differences between the two groups were not significantly modified for the various amplitudes of the curves. Finally, they noticed that the gap detection thresholds were independent of the audiometric thresholds for both groups. However, approximately half of the elderly people had gap detection thresholds in the same range as the young people, and the differences between the groups were determined only by some elderly with exceptionally high thresholds.

Subsequently, Schneider and Hamstra14 investigated the effect of the duration of gap detection thresholds in young people (mean age of 21.9 years) with normal hearing (threshold of 30dB HL between 200 and 8000Hz) and the elderly (mean age of 72.4 years) in the initial stages of presbycusis, varying systematically the duration of pure tones with 2kHz of frequency and 90dB SPL of intensity involved by masking white noise. The tested duration, in a forced choice procedure with two alternatives, ranged from 5 to 1,000ms. The results showed that the gap detection thresholds were especially greater in shorter duration (2.4 ms). However, the difference tended to reduce as the duration increased, disappearing with a duration of 1,000ms. It was noticed that the gap detection threshold was independent from the absolute hearing threshold, at least among people with relatively normal hearing in 2kHz. The authors concluded, thus, that the changes in temporal acuity related to age could occur regardless of the changes related to age in audiometric acuity.

Snell 15 used gap detection procedures with forced choice between two alternatives using low-pass noise bands with cut-off frequency greater than 1 or 6kHz, constant duration of 150ms and intensity levels of 70 to 80dB SPL, to check the effects of the upper cut-off frequency, intensity and sinusoid modulation of amplitude among the young people (17 to 40 years) and elderly (64 to 77 years) in conditions of absence of noise, white noise masking and high frequency noise masking (frequencies between 6 and 12kHz) added to white noise. These conditions were subsequently tested with an amplitude modulation of 12.6%. With such manipulations, it was intended to check whether the elderly would be more affected by the complexity of the signals presented than the young subjects. The normal hearing people in the two groups were matched in order to have similar hearing thresholds between 0.25 and 6 kHz. The results indicated that the signal detection was strongly influenced by age and frequency of signals, being that thresholds for 6kHz were lower (2.8ms) than for 1kHz (8.3ms), whereas the thresholds in young people were lower than in the elderly in all situations. The thresholds tended to increase in conditions of signal modulation and high frequency masking. In general terms, the performance of the elderly deteriorated more than that of the young people when the complexity of the presented stimuli was increased. According to the author, despite the existence of some overlapping between the two groups, the means did not reflect only the deterioration of the performance of few subjects, but rather the generalized change in distribution of thresholds with aging.

As we have seen so far, there are disagreements in the literature about gap detection and the proportion of affected elderly by reduction of temporal acuity relative to the total number of people in the age range. On the one hand, some authors, such as Moore, Peters and Glasberg11, believe that this proportion is small, whereas on the other hand others, such as Snell16, believe that there is large enough a proportion to affect the distribution of the age range. However, all agree that these changes do not reach evenly all the elderly and that they can be followed or not by audiometric losses. That is, there is considerable evidence that the mechanisms that determine these changes would not be only the peripheral sensorineural losses.

However, studies with gap detection and simple stimuli (pure tone or noise band) are not the only way to assess temporal processing. In fact, as we shall see next, these are not even the measures that better correlate to speech recognition difficulties. These phenomena are better described by studies with temporal processing tasks using complex stimuli, and we describe next some of them.

Temporal processing of complex stimuli, speech recognition and auditory aging
The studies about the correlation between speech recognition and temporal auditory processing have not always clearly defined about the correlation between these two aspects of hearing. Such correlation was denied by Lutman 17 in a study whose objective was to determine if the reductions in resolution of frequencies and temporal resolution in the elderly were associated with reduction of speech perception in noise. The authors conducted measures of frequency resolutions and gap interruption measures in low-pass noise with the central frequency of 2kHz, bandwidth of 300Hz and intensity of 85dB SPL in 229 subjects. The same hearing subjects underwent the sentence identification test in noise, with a uniform level of 70dB SPL. It was noticed that the frequency resolution measures were related to audiometric thresholds for 2kHz and that young people had better frequency resolution than the elderly in most audiometric threshold ranges.

A variance analysis pointed to an incredibly high effect of audiometric thresholds in increase of gap detection thresholds, and it did not find significant age effect, or interaction between the two factors. In addition, a series of multiple regression analysis indicated that the audiometric thresholds were the main predictors of speech comprehension, explaining 36% of its variance, followed by age (explaining 3%). In fact, temporal resolution was no longer predictive when data of the nine greatest gap detection threshold hearing people were excluded. Owing to that, the author concluded that temporal resolution would affect speech recognition in the most extreme cases of deterioration, which would be only 10% of the people with mild and moderate hearing losses.

Strouse, Ashmead, Ohde and Grantham18 measured monaural and binaural temporal processing and speech perception in young people (aged between 20 and 30 years) and the elderly (between 66 and 75 years of age) with normal thresholds, using gap detection tasks in pure tones with frequencies ranging from 0.25 and 6kHz, in addition to interaural interval detection tasks. For the assessment of speech perception, they used a phoneme discrimination task (/ba/ and /pa/) owing to the differences in time of onset of vocalization, noticing that the elderly subjects were less capable to clearly distinguish these phoneme categories. However, the performance in gap interruption detection was not a good predictor of the performance in syllable discrimination task. The confirmation of non-existence of correlation between measures of the three tasks and absolute thresholds in the elderly suggested that other factors associated with aging, in addition to peripheral hearing loss, would contribute to the deficits of temporal auditory processing in the elderly. Thus, the authors concluded that there was no evidence that the speech perception could be explained by the temporal resolution capabilities.

Conversely, Snell and Frisina16 examined the correlations between gap detection in wide band noise and recognition of spondaic words in noise and in conversation, in subjects with normal hearing or moderate hearing loss, young people (17 to 40 years) and elderly people (61 to 82 years). Before noise with cut-off frequencies higher than 1 or 6kHz and general level of 80dB SPL, the elderly presented greater thresholds than the young people. However, such thresholds were not significantly correlated with the audiometric thresholds for any of the groups. The reduction in the capacity of detecting gaps was associated with the increased age of the young group, but not in the elderly group, which started relatively early in the adult age. Differently, word recognition did not decrease as a result of age increase in the young group, but got much worse with aging of the elderly group, leading to moderate correlations between the two performances. Based on these findings, the authors pointed to the occurrence of changes in the auditory processing that took place during adult life, meaning that changes in temporal acuity started decades before the onset of word recognition deficits.

Such conclusions, however, were contradicted by a series of experiments made by Fitzgibbons and Gordon-Salant in the past nine years, in which more complex stimuli and tasks were used. Such investigations ended by gathering evidence that the complexity of stimuli and demands of perceptual processing are important factors in the determination of age-associated deficits.

In 199519, the authors examined the performance in isolated stimuli duration discrimination and stimuli inserted in tone sequence patterns, examining the independent and interactive effects of age and hearing loss. To that end, 40 subjects were distributed in four groups: 1) elderly (65 to 75 years) with normal hearing (thresholds of 15dB HL, 250-4000Hz), 2) young people (20 to 40 years) normal hearing (same criteria), 3) elderly people (65 to 76 years) with mild to moderate hearing loss, with predominance of high frequencies, 4) young people (20 to 40 years) with audiometric profiles matched by those of hearing people in group 3. These groups conducted differential threshold determination of tone duration discrimination (with 250 ms duration tones as pattern) and differential threshold discrimination of gap duration tasks (with 250ms gaps inserted between pairs of 4kHz and 250 ms duration as pattern). Additionally, they calculated differential thresholds of complex stimuli duration discrimination. These stimuli were formed by sequences of 5 tones with 250ms duration each, and variable frequencies among which one component always of 4000Hz, had its signal duration varied. In the gap duration discrimination, this component of 4000Hz was replaced by a period of silence. These tasks had three levels of complexity. In the low complexity level, one single tone sequence was presented in all attempts with tone (4kHz) or target interruption always on the third position, in the middle of the sequence. On the second level, medium complexity, target location, tone or gap were always on the third position, but the location of the other tones were randomly altered each try. On the third level, the location of all components, including the target, was switched every attempt. The results indicated that the differences in performance between hearing people were determined primarily based on age and there was no systemic effect on hearing loss. The gap duration discrimination of the elderly was less efficient and it varied more than in young people. In general, the performance in the elderly was more affected by complexity of the stimuli that in the young people. Based on the results, the authors concluded that many elderly people would have a reduction of temporal processing capacity, which would be evident by using more complex stimuli and was not detectable with simple tests.

In 199826, temporal processing in young and older people was compared with the use of greater complexity tasks. To that end, Fitzgibbons and Gordon-Salant presented to 4 groups of 10 subjects, formed with the same criteria of the studied groups in 1995, discrimination and identification tasks of temporal order of tone sequences. The sequences consisted of combination of 3 tones of frequencies of 3548, 4000 and 4467Hz. In the discrimination procedures, the duration was varied according to three increasing complexity conditions: 1 - organized sequences in unidirectional order of frequencies (with increasing or decreasing frequency tones), 2 - bi-directional (the frequency order was medium-high-low or high-low-medium), or 3 - random (in each, the order of the tones was randomly switched every try). The subjects were expected to compare the first sequence (pattern) in a forced choice process of three alternatives, pointing at the sequence (second or third) that sounded different from the first one.

Data obtained about temporal discrimination showed significant effects over aging and discrimination conditions and a significant interaction between these factors. The main effect of hearing losses on discrimination was not significant, and there were no significant interactions with this factor. The thresholds of order discrimination in elderly hearing for example, were much greater than in the young people considering bi-directional and random conditions, but not for uni-directional conditions. Moreover, there was progressive decrease of performance as tone duration reduced for all groups. Thus, it was concluded that the deficits of temporal processing associated with age would vary according to the complexity of stimuli considering speed of processing of hearing people.

Finally, in 2001, Fitzgibbons and Gordon-Salant21 reported a study approaching changes related to age in temporal sensitivity and increase in interval between the onset of successive components of tone sequences. In this study, 52 hearing people were distributed in four groups, according to the same criteria as previous studies, and there were monosyllable recognition scores of 80%. The stimuli were sequences of five tones of 4000Hz and 50ms separated by silence intervals of equal duration. The duration of silence intervals between tones was changed each attempt, between 100 and 600ms, changing the total duration of the sequences. In conditions of low complexity all intervals between tones had similar duration that was increased at the same extent. In conditions of medium complexity, only the silence interval preceding the third tone had abnormal duration, keeping the same duration for the remaining sequences. In high complexity conditions, the interval whose duration was increased was changed randomly each try. All tones had adjusted intensity to produce at least sensation levels of 25 to 30 dB SL in people with hearing loss.

We noticed that in all groups, there was a tendency to reduce differential thresholds as the duration of silence intervals increased. The authors observed significant effects for age and duration of intervals, but no data analyses revealed systemic or significant influences of the hearing loss among the elderly nor the young people. In conditions in which the complexity of the task varied. the elderly had increasing difficulties as the task complexity increased. These results, to the authors, did not show significant influences in sensorineural losses, and the differences indicated changes in temporal resolution, characteristic of aging.

As shown up to present, even though Lutman had concluded that the main determining factor of the difficulty in speech recognition in the elderly was the extension of the sensorial losses suffered by the hearing people, being little attributed to aging, the studies by Fitzgibbons and Gordon-Salant revised to the moment, led to different conditions, since they demonstrated that many tasks of temporal processing were affected by auditory processing speed, with no significant influence of hearing loss. Similar conclusions were found in the experiments of the same authors about the relations between spoken speech recognition and characteristics of temporal auditory processing in young and elderly people, as reviewed below.

In 199322, Gordon-Salant and Fitzgibbons published a study in which they investigated the factors that affected the recognition of speech sounds degraded by temporal distortions. To that end, they presented 4 groups of 10 subjects, similarly to previous studies, with single words recognition scores of 80%, sentences with low predictability that provided little semantic and linguistic clues for the recognition of the last word in the sentences, which were expected to be written by the tested person. The recognition of sentences was made without distortion and with three types of distortion, at four levels of intensity: (1) temporal compression (30, 40, 50 and 60%); (2) reverberation (after 200, 300, 400 and 600ms), and (3) interruption (with rates of 12.5, 25, 50 and 100/s). In addition, they also measured tone duration discrimination and gaps, similarly to the previous study, and measured gap detection thresholds, between tones of similar frequencies and tones of different frequencies, from 500 to 4000Hz. The results indicated that the subjects with normal hearing had performed significantly better than the subjects with hearing loss in the tasks of sentence recognition without distortion. However, in sentence recognition with temporal compression they noticed significant effects of the age range, hearing loss and temporal compression ratio, and in speech data with gaps they found the effects of aging and hearing loss, without significant interactions. The measures of tone duration and gap discrimination and gap detection thresholds had predictive relations with speech recognition measures, observing that: 1) the presence of high frequency hearing loss was associated with lower scores in speech recognition tests without distortion and in almost all distorted speech tests; 2) the age and discrimination of gap duration were related to speech recognition in reverberation; and 3) the advanced age and high thresholds of gap discrimination were associated with lower scores of speech recognition.

In 1999, Gordon-Salant and Fitzgibbons23 reexamined speech recognition in the elderly and young people, trying to identify the set of measures of temporal processing that discriminated appropriately the performance in young and old people, with and without hearing loss. The subjects formed 4 groups, similarly to previous studies. The stimuli to assess speech perception were the low predictability sentences used in the 1993 study, with the same temporal distortion presented in silence and in conversational background noise. The measures of temporal processing were : 1) differential threshold of duration discrimination; 2) differential threshold of gap discrimination, and 3) differential threshold of duration discrimination of complex tone sequences containing a tone as a target; 4) silence interval; 5) discrimination threshold in order sequenced tones, with duration and variations equal to all components of the sequence. They noticed that data variance was associated with performance of differential threshold measures in detecting gap complex stimuli (task 3), differential threshold of temporal ordering discrimination (task 5), performance in four measures of speech recognition (speech without distortion in silence, speech in temporal compression + reverberation in silence; speech with temporal compression + reverberation against background noise, and speech in 50% temporal compression in background noise). Based on the results, they built discrimination functions that enabled the separation of the groups of young people from the elderly and separation of the groups of hearing loss from the normal hearing ones. The classification of hearing people according to the discrimination functions was correct in 90% of the cases referring to the classification of hearing loss, and there were no classification mistakes based on age. They got a combination of temporal processing and speech perception measures capable of distinguishing performance patterns in young and elderly patients, with and without hearing loss.

Finally, in 200024, Phillips, Gordon-Salant, Fitzgibbons and Yeni-Komshian tried to identify the variables that enabled the differentiation between elderly with good speech recognition capacity and elderly who had difficulty to recognize speech. To that end, they formed three groups: (1) hearing people with normal thresholds (20dB HL) between 500 and 4000Hz and excellent word recognition in quiet (90% to 100% score), (2) hearing people with slow and progressive cochlear losses, mild to moderate and good word recognition skills, and (3) hearing people with hearing loss matched in all frequencies of group 2 and poor word recognition skills (below 70%). They accomplished the task of recognizing senseless syllables in quiet and noise conditions and discrimination task of high and low complexity signal frequencies. Finally, they measured the temporal resolution with (1) detection of gaps inserted between two tones with randomly varied frequencies between 1 and 2 kHz; (2) gap detection inserted on the second and third positions, with sequences of 5 tones with randomly varied frequencies, and (3) location of gaps in the same sequences with randomly located variations.

The analysis of multivariate linear regression enabled the construction of two regression equations, one having the criterion of syllable discrimination in quiet, and the other syllable discrimination in noise. In both conditions, the only significant predictive factor was found in the mean of absolute thresholds for pure tones in 1, 2 and 4kHz. When the mean for absolute thresholds was not included in the analysis, the main predictive factor for syllable discrimination in silence was discrimination of frequencies in complex stimuli in a complex task. To recognize the syllables in noise the only significant predictive factors was gap detection of pure tones in varied frequencies (task 1). The results indicated that the elderly with poor word recognition skills had more difficulty to process spectral characteristics of complex stimuli than the elderly with good word recognition skills, being that the differences could not be attributed to peripheral auditory problems, since they had all appropriately conducted the simple stimuli task.

CLOSING REMARKS

The studies reviewed above are common in an area of research in which there is still much contradiction, probably owing to the different methods adopted to describe the temporal processing. The studies that adopt simple procedures, such as gap detection, can only state that there are differences in temporal resolution between young and elderly people, which are not explained by the hearing loss alone and do not affect all people similarly, and there are earlier and more severe affections in some people than in the others. Conversely, the studies that adopt simple procedures to examine the correlation between temporal processing and speech recognition and do not find clear correlations between the two types of auditory processing, suggest that speech recognition difficulties would be associated with loss of sensitivity only. The studies that make use of complex stimuli and tasks indicate that the differences in speech understanding in the elderly, with and without hearing loss, can not be attributed only to sensorineural loss.

Therefore, current research studies indicate the existence of temporal auditory processes of varied complexity which can be affected at different degrees by damage to various areas, both in the peripheral auditory system, the central auditory system, or in the cognition areas that are not exclusively involved with hearing. Future research efforts should try to discriminate which processes are more affected by each type of lesion, discriminating how they are correlated with hearing loss and temporal processing deficits on the one side, and on the other side how temporal processing and speech recognition are related to the physiological changes expected in aging.

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1 Master - University of Brasilia and Federal University of Rio Grande.
2 Ph.D. - University of Brasilia.
Address correspondence to: Universidade de Brasília, Instituto de Psicologia/ Depto de Processos
Psicológicos Básicos/ Laboratório de Psicobiologia 70910-900 Brasília DF.
Tel: 307-2625 Ext. 512 or 520 - E-mail: vtn@terra.com.br or afeitosa@unb.br
Financial support: The author relied on PICD grant provided by CAPES; the co-author had a productivity grant provided by CNPq.
Article submitted on December 12, 2002. Article accepted on January 17, 2003.

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