Judy R. Dubno

A potential role for thalamocingulate circuitry in human maternal behavior

BACKGROUND Little is known about the regional brain basis of human maternal behavior. To understand this better, we have been examining brain activity in mothers listening to infant cries. METHODS We measured functional Magnetic Resonance Imaging brain activity in healthy, breastfeeding first-time mothers with young infants while they listened to infant cries, white noise control sounds, and a rest condition. Based on the thalamocingulate theory of maternal behavior and pilot work, we hypothesized that the cingulate, medial thalamus, medial prefrontal cortex, and right orbitofrontal cortex would display more activity with infant cries than with white noise (comparison 1) and would uniquely activate with the cries, meaning that these regions would display activity with cry minus rest but not with white noise minus rest (comparison 2). RESULTS In hypothesized regions, the group displayed more activity in the medial thalamus, medial prefrontal and right orbitofrontal cortices with both comparisons. The anterior and posterior cingulate cortex displayed more activity only with comparison 1. In non-hypothesized brain regions, several other structures thought important in rodent maternal behavior displayed activity with both comparisons including the midbrain, hypothalamus, dorsal and ventral striatum, and vicinity of the lateral septal region. CONCLUSIONS Our results partially support our hypotheses and are generally consistent with neuroanatomical studies of rodent maternal behavior.

At the heart of the ventral attention system: The right anterior insula

The anterior insula has been hypothesized to provide a link between attention‐related problem solving and salience systems during the coordination and evaluation of task performance. Here, we test the hypothesis that the anterior insula/medial frontal operculum (aI/fO) provides linkage across systems supporting task demands and attention systems by examining the patterns of functional connectivity during word recognition and spatial attention functional imaging tasks. A shared set of frontal regions (right aI/fO, right dorsolateral prefrontal cortex, bilateral anterior cingulate) were engaged, regardless of perceptual domain (auditory or visual) or mode of response (word production or button press). We present novel evidence that: (1) the right aI/fO is functionally connected with other frontal regions implicated in executive function and not just brain regions responsive to stimulus salience; and (2) that the aI/fO, but not the ACC, exhibits significantly correlated activity with other brain regions specifically engaged by tasks with varying perceptual and behavioral demands. These results support the hypothesis that the right aI/fO aids in the coordination and evaluation of task performance across behavioral tasks with varying perceptual and response demands. Hum Brain Mapp 2009.

Longitudinal study of pure-tone thresholds in older persons.

Objective: Pure-tone thresholds for conventional and extended high frequencies were analyzed for 188 older adult human subjects (91 females, 97 males). The objectives were to study longitudinal changes in thresholds as well as the effects of initial threshold levels, age, gender, and noise history on these longitudinal changes. Design: At the time of entry into the study, subjects’ ages ranged from 60 to 81 years, with a mean age of 68 years. Subjects had between 2 and 21 visits (mean = 9.81 visits) over a period of 3 to 11.5 years (mean = 6.40 years). Conventional pure-tone thresholds at 0.25 to 8 kHz were measured during most visits. Extended high-frequency (EHF) thresholds at 9 to 18 kHz were measured every 2 to 3 years. The slope of a linear regression was used to estimate the rate of change in pure-tone thresholds at 0.25 to 18 kHz for each ear. A questionnaire was used to identify those subjects with a positive noise history. Results: The average rate of change in thresholds was 0.7 dB per year at 0.25 kHz, increasing gradually to 1.2 dB per year at 8 kHz and 1.23 dB per year at 12 kHz. The rate of change for thresholds increased significantly with age, at 0.25 to 3, 10, and 11 kHz for females and at 6 kHz for males. After adjusting for age, females had a significantly slower rate of change at 1 kHz but a significantly faster rate of change at 6 to 12 kHz than males. For 0.25 and 1 kHz, subjects with more hearing loss at higher frequencies had a faster rate of change at these frequencies, whereas for 6 and 8 kHz, subjects with more hearing loss at mid and high frequencies had a slower rate of change at these frequencies. The rates of threshold change for subjects with a positive noise history were not statistically different from those with a negative noise history. Conclusions: On average, hearing threshold increased approximately 1 dB per year for subjects age 60 and over. Age, gender, and initial threshold levels can affect the rate of change in thresholds. Older female subjects (≥70 years) had faster rate of change at 0.25 to 3, 10, and 11 kHz than younger female subjects (60 to 69 years). Older male subjects had faster rate of change at 6 kHz than younger male subjects. Females had a slower rate of change at 1 kHz and a faster rate of change at 6 to 12 kHz than males. Subjects with higher initial thresholds at low and mid frequencies tended to have faster rate of threshold change at 0.25 to 2 kHz in the following years. Subjects with higher initial thresholds at mid and higher frequencies tended to have slower rate of change at 6 to 8 kHz in the following years. Noise history did not have a significant effect on the rate of threshold changes.

Central Presbycusis: A Review and Evaluation of the Evidence

BACKGROUND The authors reviewed the evidence regarding the existence of age-related declines in central auditory processes and the consequences of any such declines for everyday communication. PURPOSE This report summarizes the review process and presents its findings. DATA COLLECTION AND ANALYSIS The authors reviewed 165 articles germane to central presbycusis. Of the 165 articles, 132 articles with a focus on human behavioral measures for either speech or nonspeech stimuli were selected for further analysis. RESULTS For 76 smaller-scale studies of speech understanding in older adults reviewed, the following findings emerged: (1) the three most commonly studied behavioral measures were speech in competition, temporally distorted speech, and binaural speech perception (especially dichotic listening); (2) for speech in competition and temporally degraded speech, hearing loss proved to have a significant negative effect on performance in most of the laboratory studies; (3) significant negative effects of age, unconfounded by hearing loss, were observed in most of the studies of speech in competing speech, time-compressed speech, and binaural speech perception; and (4) the influence of cognitive processing on speech understanding has been examined much less frequently, but when included, significant positive associations with speech understanding were observed. For 36 smaller-scale studies of the perception of nonspeech stimuli by older adults reviewed, the following findings emerged: (1) the three most frequently studied behavioral measures were gap detection, temporal discrimination, and temporal-order discrimination or identification; (2) hearing loss was seldom a significant factor; and (3) negative effects of age were almost always observed. For 18 studies reviewed that made use of test batteries and medium-to-large sample sizes, the following findings emerged: (1) all studies included speech-based measures of auditory processing; (2) 4 of the 18 studies included nonspeech stimuli; (3) for the speech-based measures, monaural speech in a competing-speech background, dichotic speech, and monaural time-compressed speech were investigated most frequently; (4) the most frequently used tests were the Synthetic Sentence Identification (SSI) test with Ipsilateral Competing Message (ICM), the Dichotic Sentence Identification (DSI) test, and time-compressed speech; (5) many of these studies using speech-based measures reported significant effects of age, but most of these studies were confounded by declines in hearing, cognition, or both; (6) for nonspeech auditory-processing measures, the focus was on measures of temporal processing in all four studies; (7) effects of cognition on nonspeech measures of auditory processing have been studied less frequently, with mixed results, whereas the effects of hearing loss on performance were minimal due to judicious selection of stimuli; and (8) there is a paucity of observational studies using test batteries and longitudinal designs. CONCLUSIONS Based on this review of the scientific literature, there is insufficient evidence to confirm the existence of central presbycusis as an isolated entity. On the other hand, recent evidence has been accumulating in support of the existence of central presbycusis as a multifactorial condition that involves age- and/or disease-related changes in the auditory system and in the brain. Moreover, there is a clear need for additional research in this area.

Recovery from prior stimulation: masking of speech by interrupted noise for younger and older adults with normal hearing.

In a previous study [Dubno et al, J. Acoust. Soc. Am. 111, 2897-2907 (2002)], older subjects benefitted less than younger subjects from momentary improvements in signal-to-noise ratio when listening to speech in interrupted maskers. It has been hypothesized that the benefit derived from interrupted maskers may be related to recovery from forward masking, i.e., the recovery of a response to a suprathreshold signal from prior stimulation by a masker. The effect of interrupted maskers on speech recognition may be well suited to test hypotheses regarding recovery from prior stimulation, given that both involve the perception of signals following a masker. Here, younger and older adults with normal but not identical audiograms listened to nonsense syllables at moderate and high levels in a speech-shaped noise that was modulated by a 2-, 10-, 25-, or 50-Hz square wave. An additional low-level noise was always present that was shaped to produce equivalent masked thresholds for all subjects. To assess recovery from forward masking, forward-masked thresholds were measured at 0.5 and 4.0 kHz as a function of the delay between the speech-shaped masker and the signal. Speech recognition in interrupted noise was poorer for older than younger subjects. Small but consistent age-related differences were observed in the decrease in score with interrupted noise relative to the score without interrupted noise. Forward-masked thresholds of older subjects were higher than those of younger subjects, but there were no age-related differences in the amount of forward masking or in simultaneous masking. Negative correlations were observed between speech-recognition scores in interrupted noise and forward-masked thresholds. That is, the benefit derived from momentary improvements in speech audibility in an interrupted noise decreased as forward-masked thresholds increased. Stronger correlations with forward masking were observed for the higher frequency signal, for higher noise interruption rates, and when the signal-to-noise ratio was poor. Comparisons of speech-recognition scores at moderate and high levels for younger and older subjects were not consistent with the hypothesis of an age-related difference in the contribution of low-spontaneous-rate fibers to speech recognition in interrupted noise.

Frequency and intensity discrimination measured in a maximum-likelihood procedure from young and aged normal-hearing subjects

A maximum-likelihood method was applied in measurements of frequency and intensity discrimination for aged and young normal-hearing subjects with closely matched audiograms. This method was preferred over other psychophysical procedures because it is efficient and controls experimental variance, features that are highly desirable for testing aged subjects. In order to implement the method, psychometric functions for each task were also measured from young subjects using a constant-stimuli procedure. For the young subjects, the differential thresholds obtained from these two procedures were generally comparable. Further, both sets of data were consistent with previous literature, indicating that the maximum-likelihood method was successfully applied for frequency and intensity discrimination. A frequency-dependent difference between young and aged subjects in both frequency and intensity discrimination was observed. Even with closely matched audiograms, aged subjects demonstrated poorer discrimination abilities than young subjects. The age-related difference was always largest at 500 Hz and decreased as frequency increased.

Use of context by young and aged adults with normal hearing

Word recognition in sentences with and without context was measured in young and aged subjects with normal but not identical audiograms. Benefit derived from context by older adults has been obscured, in part, by the confounding effect of even mildly elevated thresholds, especially as listening conditions vary in difficulty. This problem was addressed here by precisely controlling signal-to-noise ratio across conditions and by accounting for individual differences in signal-to-noise ratio. Pure-tone thresholds and word recognition were measured in quiet and threshold-shaped maskers that shifted quiet thresholds by 20 and 40 dB. Word recognition was measured at several speech levels in each condition. Threshold was defined as the speech level (or signal-to-noise ratio) corresponding to the 50 rau point on the psychometric function. As expected, thresholds and slopes of psychometric functions were different for sentences with context compared to those for sentences without context. These differences were equivalent for young and aged subjects. Individual differences in word recognition among all subjects, young and aged, were accounted for by individual differences in signal-to-noise ratio. With signal-to-noise ratio held constant, word recognition for all subjects remained constant or decreased only slightly as speech and noise levels increased. These results suggest that, given equivalent speech audibility, older and younger listeners derive equivalent benefit from context.

Factors Affecting Speech Understanding in Older Adults

This chapter reviews various factors that affect the speech-understanding abilities of older adults. Before proceeding to the identification of several such factors, however, it is important to clearly define what is meant by “speech understanding.” This term is used to refer to either the open-set recognition or the closed-set identification of nonsense syllables, words, or sentences by human listeners. Many years ago, Miller et al. (1951) demonstrated that the distinction between open-set recognition and closed-set identification blurs as the set size for closed-set identification increases. When words were used as the speech material, Miller et al. (1951) demonstrated that the closed-set speech-identification performance of young normal-hearing listeners progressively approached that of open-set speech recognition as the set size doubled in successive steps from 2 to 256 words. Clopper et al. (2006) have also demonstrated that lexical factors (e.g., word frequency and acoustic-phonetic similarity) impacting word identification and word recognition are very similar when the set size is reasonably large for the closed-set identification task and the alternatives in the response are reasonably confusable with the stimulus item. Thus the processes of closed-set speech identification and open-set speech recognition are considered to be very similar and both are referred to here as measures of “speech understanding.”

Predicting consonant confusions from acoustic analysis

Acoustic measurements of nonsense syllables in quiet and in noise were used to predict the pattern of consonant confusions made under those conditions. Eleven sets of nonsense syllables were presented to normal-hearing subjects in quiet and at a +5 dB speech-to-noise ratio, at five speech levels. A set of acoustic characteristics of the speech stimuli were chosen for analysis and measured using digital processing techniques. Results of the recognition task revealed significant effects of consonant voicing, position and vowel context on syllable recognition. The performance-intensity function of the quiet condition rises more steeply than the function obtained in noise. The effect of noise on consonant recognition is dependent upon the manner in which the consonant is produced, and the location of maximum constriction. Differences in the absolute values of the acoustic parameters of syllable pairs were used to predict their percentage of confusion. A set of acoustic variables was isolated which was found to be the best predictor of confusion percentages. Although the sets of acoustic variables were different for various syllable types and test conditions, three variables (consonant energy, consonant spectral peaks, consonant-to-noise ratio) were used in a majority of the predictions.

Speech Recognition in Younger and Older Adults: A Dependency on Low-Level Auditory Cortex

A common complaint of older adults is difficulty understanding speech, especially in challenging listening environments. In addition to well known declines in the peripheral auditory system that reduce audibility, age-related changes in central auditory and attention-related systems are hypothesized to have additive negative effects on speech recognition. We examined the extent to which functional and structural differences in speech- and attention-related cortex predicted differences in word recognition between 18 younger adults (19–39 years) and 18 older adults (61–79 years). Subjects performed a word recognition task in an MRI scanner where the intelligibility of words was parametrically varied. Older adults exhibited significantly poorer word recognition in a challenging listening condition compared with younger adults. An anteromedial Heschls gyrus/superior temporal gyrus (HG/STG) region, engaged by the word recognition task, exhibited age group differences in gray matter volume and predicted word recognition in younger and older adults. Age group differences in anterior cingulate (ACC) activation were also observed. The association between HG gray matter volume, word recognition, and ACC activation was present after controlling for hearing loss. In younger and older adults, causal path modeling analyses demonstrated that individual variation in left HG/STG morphology affected word recognition performance, which was reflected by error monitoring activity in the dorsal ACC. These results have clinical implications for rehabilitation and suggest that some of the perceptual difficulties experienced by older adults are due to structural changes in HG/STG. More broadly, the results suggest the possibility that aging may exaggerate developmental limitations on the ability to recognize speech.