Amplitude Modulation Detection Task Research Articles

Neural Responses and Perceptual Sensitivity to Sound Depend on Sound-Level Statistics

Sensitivity to sound-level statistics is crucial for optimal perception, but research has focused mostly on neurophysiological recordings, whereas behavioral evidence is sparse. We use electroencephalography (EEG) and behavioral methods to investigate how sound-level statistics affect neural activity and the detection of near-threshold changes in sound amplitude. We presented noise bursts with sound levels drawn from distributions with either a low or a high modal sound level. One participant group listened to the stimulation while EEG was recorded (Experiment I). A second group performed a behavioral amplitude-modulation detection task (Experiment II). Neural activity depended on sound-level statistical context in two different ways. Consistent with an account positing that the sensitivity of neurons to sound intensity adapts to ambient sound level, responses for higher-intensity bursts were larger in low-mode than high-mode contexts, whereas responses for lower-intensity bursts did not differ between contexts. In contrast, a concurrent slow neural response indicated prediction-error processing: The response was larger for bursts at intensities that deviated from the predicted statistical context compared to those not deviating. Behavioral responses were consistent with prediction-error processing, but not with neural adaptation. Hence, neural activity adapts to sound-level statistics, but fine-tuning of perceptual sensitivity appears to involve neural prediction-error responses.

Preserving Inhibition during Developmental Hearing Loss Rescues Auditory Learning and Perception.

Transient periods of childhood hearing loss can induce deficits in aural communication that persist long after auditory thresholds have returned to normal, reflecting long-lasting impairments to the auditory CNS. Here, we asked whether these behavioral deficits could be reversed by treating one of the central impairments: reduction of inhibitory strength. Male and female gerbils received bilateral earplugs to induce a mild, reversible hearing loss during the critical period of auditory cortex development. After earplug removal and the return of normal auditory thresholds, we trained and tested animals on an amplitude modulation detection task. Transient developmental hearing loss induced both learning and perceptual deficits, which were entirely corrected by treatment with a selective GABA reuptake inhibitor (SGRI). To explore the mechanistic basis for these behavioral findings, we recorded the amplitudes of GABAA and GABAB receptor-mediated IPSPs in auditory cortical and thalamic brain slices. In hearing loss-reared animals, cortical IPSP amplitudes were significantly reduced within a few days of hearing loss onset, and this reduction persisted into adulthood. SGRI treatment during the critical period prevented the hearing loss-induced reduction of IPSP amplitudes; but when administered after the critical period, it only restored GABAB receptor-mediated IPSP amplitudes. These effects were driven, in part, by the ability of SGRI to upregulate α1 subunit-dependent GABAA responses. Similarly, SGRI prevented the hearing loss-induced reduction of GABAA and GABAB IPSPs in the ventral nucleus of the medial geniculate body. Thus, by maintaining, or subsequently rescuing, GABAergic transmission in the central auditory thalamocortical pathway, some perceptual and cognitive deficits induced by developmental hearing loss can be prevented.SIGNIFICANCE STATEMENT Even a temporary period of childhood hearing loss can induce communication deficits that persist long after auditory thresholds return to normal. These deficits may arise from long-lasting central impairments, including the loss of synaptic inhibition. Here, we asked whether hearing loss-induced behavioral deficits could be reversed by reinstating normal inhibitory strength. Gerbils reared with transient hearing loss displayed both learning and perceptual deficits. However, when animals were treated with a selective GABA reuptake inhibitor during or after hearing loss, behavioral deficits were entirely corrected. This behavioral recovery was correlated with the return of normal thalamic and cortical inhibitory function. Thus, some perceptual and cognitive deficits induced by developmental hearing loss were prevented with a treatment that rescues a central synaptic property.

A Decline in Response Variability Improves Neural Signal Detection during Auditory Task Performance.

The detection of a sensory stimulus arises from a significant change in neural activity. However, trial-to-trial variability of the neural response may limit perceptual performance. If the neural response to a stimulus is quite variable, then the response on a given trial could be confused with the pattern of neural activity generated when the stimulus is absent. Therefore, a neural mechanism that served to reduce response variability would allow for better stimulus detection. By recording from the cortex of freely moving animals engaged in an auditory detection task, we found that variability of the neural response becomes smaller during task performance, thereby improving neural detection thresholds.

Task engagement selectively modulates neural correlations in primary auditory cortex.

Noise correlations (r(noise)) between neurons can affect a neural population's discrimination capacity, even without changes in mean firing rates of neurons. r(noise), the degree to which the response variability of a pair of neurons is correlated, has been shown to change with attention with most reports showing a reduction in r(noise). However, the effect of reducing r(noise) on sensory discrimination depends on many factors, including the tuning similarity, or tuning correlation (r(tuning)), between the pair. Theoretically, reducing r(noise) should enhance sensory discrimination when the pair exhibits similar tuning, but should impair discrimination when tuning is dissimilar. We recorded from pairs of neurons in primary auditory cortex (A1) under two conditions: while rhesus macaque monkeys (Macaca mulatta) actively performed a threshold amplitude modulation (AM) detection task and while they sat passively awake. We report that, for pairs with similar AM tuning, average r(noise) in A1 decreases when the animal performs the AM detection task compared with when sitting passively. For pairs with dissimilar tuning, the average r(noise) did not significantly change between conditions. This suggests that attention-related modulation can target selective subcircuits to decorrelate noise. These results demonstrate that engagement in an auditory task enhances population coding in primary auditory cortex by selectively reducing deleterious r(noise) and leaving beneficial r(noise) intact.

Relation between temporal envelope coding, pitch discrimination, and compression estimates in listeners with sensorineural hearing loss

Recent physiological studies in animals showed that noise-induced sensorineural hearing loss (SNHL) increased the amplitude of envelope coding in single auditory-nerve fibers. The present study investigated whether SNHL in human listeners was associated with enhanced temporal envelope coding, whether this enhancement affected pitch discrimination performance, and whether loss of compression following SNHL was a potential factor in envelope coding enhancement. Envelope processing was assessed in normal-hearing (NH) and hearing-impaired (HI) listeners in a behavioral amplitude-modulation detection task. Fundamental frequency difference limens (F0DLs) were obtained in the same listeners for complex tones with varying harmonic resolvability. Basilar-membrane input/output functions were measured to assess individual compression ratios. For NH listeners, F0DLs decreased with increasing harmonic resolvability. For the unresolved conditions, all five HI listeners performed as good as or better than NH listeners with matching musical experience. Two HI listeners showed lower amplitude-modulation detection thresholds than NH listeners for low modulation rates, and one of these listeners also showed a loss of cochlear compression. Overall, these findings suggest that some HI listeners may benefit from an enhancement of temporal envelope coding in pitch discrimination of unresolved complex tones, and that this enhancement may be also ascribed to a reduction of cochlear compression following SNHL.

Few juvenile auditory perceptual skills correlate with adult performance.

Measures of human mental development suggest that behavioral skills displayed during early life can predict an individual's subsequent cognitive performance. Support for this draws from longitudinal studies that reveal compelling within-subject correlations during childhood. If this idea applies across the life span, then correlations in performance should persist into adulthood. Here, we address this prediction in juvenile and adult gerbils by evaluating within-subject measures of auditory learning and perception. Animals were trained and tested as juveniles on either an amplitude modulation (AM) or a frequency modulation (FM) detection task. Measures of learning and perception obtained from juveniles were then compared to similar measures obtained when each subject was tested in adulthood on either the same task or the untrained task. For animals trained and tested on the AM detection task as juveniles and adults, there was no correlation between juvenile and adult learning metrics, or perceptual sensitivity. For animals trained and tested on FM detection as juveniles, we observed a significant relationship to their adult performance. Juveniles that performed the best on FM detection were the poorest at AM detection, and the best at FM detection, when tested as adults. Thus, across-age correlations for sensory and cognitive measures, obtained during development and in adulthood, depend heavily on the specific type of developmental experience and the outcome measure.

Estimating critical bandwidths of temporal sensitivity to low-frequency amplitude modulation

Auditory filter bandwidths are measured for a temporal process using an amplitude-modulation detection task. The signal is a 200 Hz wide, sinusoidally amplitude-modulated band of noise centered within an unmodulated notched-noise masker. A modulation rate of 10 Hz is used to avoid possible information loss at more central processing levels for high modulation rates. Threshold functions are obtained for 10-14 notch widths for each of four different center frequencies (0.6, 1, 2, and 4 kHz) to determine the maximum notch width at which the masker has an effect. The ratio of center frequency to maximum notch width is ~2 at all center frequencies. It is proposed that the bandwidths observed in temporal tasks, which are consistently greater than expected from the viewpoint of critical band theory, be characterized as "temporal critical bands." This proposal does not oppose, but provides a complement to the traditional critical band obtained in tasks involving spectral discrimination.

Perceptual learning and generalization resulting from training on an auditory amplitude-modulation detection task.

Fluctuations in sound amplitude provide important cues to the identity of many sounds including speech. Of interest here was whether the ability to detect these fluctuations can be improved with practice, and if so whether this learning generalizes to untrained cases. To address these issues, normal-hearing adults (n = 9) were trained to detect sinusoidal amplitude modulation (SAM; 80-Hz rate, 3-4 kHz bandpass carrier) 720 trials/day for 6-7 days and were tested before and after training on related SAM-detection and SAM-rate-discrimination conditions. Controls (n = 9) only participated in the pre- and post-tests. The trained listeners improved more than the controls on the trained condition between the pre- and post-tests, but different subgroups of trained listeners required different amounts of practice to reach asymptotic performance, ranging from 1 (n = 6) to 4-6 (n = 3) sessions. This training-induced learning did not generalize to detection with two untrained carrier spectra (5 kHz low-pass and 0.5-1.5 kHz bandpass) or to rate discrimination with the trained rate and carrier spectrum, but there was some indication that it generalized to detection with two untrained rates (30 and 150 Hz). Thus, practice improved the ability to detect amplitude modulation, but the generalization of this learning to untrained cases was somewhat limited.

Prolonged maturation of auditory perception and learning in gerbils.

In humans, auditory perception reaches maturity over a broad age range, extending through adolescence. Despite this slow maturation, children are considered to be outstanding learners, suggesting that immature perceptual skills might actually be advantageous to improvement on an acoustic task as a result of training (perceptual learning). Previous non-human studies have not employed an identical task when comparing perceptual performance of young and mature subjects, making it difficult to assess learning. Here, we used an identical procedure on juvenile and adult gerbils to examine the perception of amplitude modulation (AM), a stimulus feature that is an important component of most natural sounds. On average, Adult animals could detect smaller fluctuations in amplitude (i.e., smaller modulation depths) than Juveniles, indicating immature perceptual skills in Juveniles. However, the population variance was much greater for Juveniles, a few animals displaying adult-like AM detection. To determine whether immature perceptual skills facilitated learning, we compared naïve performance on the AM detection task with the amount of improvement following additional training. The amount of improvement in Adults correlated with naïve performance: those with the poorest naïve performance improved the most. In contrast, the naïve performance of Juveniles did not predict the amount of learning. Those Juveniles with immature AM detection thresholds did not display greater learning than Adults. Furthermore, for several of the Juveniles with adult-like thresholds, AM detection deteriorated with repeated testing. Thus, immature perceptual skills in young animals were not associated with greater learning.

Enhanced discrimination of low-frequency sounds for subjects with high-frequency dead regions

Research using animals suggests that a lesion in the basal portion of the cochlea, causing a high-frequency 'dead region', leads to cortical reorganization, such that frequencies just below the edge frequency of the dead region, fe, become over-represented. We set out to determine if this reorganization has functional benefits. Two groups of subjects were tested, with and without acquired high-frequency dead regions, as assessed using the TEN(HL) test. For the ears with dead regions, the value of fe was close to 1000 or 1500 Hz. The two groups were matched in terms of audiometric thresholds for frequencies below fe and in terms of age. Three subjects with unilateral dead regions (with matched low-frequency audiometric thresholds across ears) were also tested. Three tasks were used: (i) frequency discrimination of sinusoidal tones. The level of every stimulus was roved over a 12-dB range to reduce the salience of loudness cues. The center frequencies used ranged from 250 Hz to just below fe; (ii) detection of sinusoidal amplitude modulation of a sinusoidal carrier. Carrier frequencies of 500 and 800 Hz were used with all subjects, and an additional carrier frequency of 1200 Hz was used for ears with fe close to 1500 Hz and their matched counterparts. Modulation frequencies were 4, 50 and 100 Hz; (iii) identification of consonants in nonsense syllables. The syllables were lowpass filtered at 1000 or 1500 Hz (depending on the value of fe) and complementary highpass-filtered noise was presented to prevent use of information from neurons tuned above fe. For the frequency-discrimination task, the ears with dead regions showed a significant local improvement ('enhanced' thresholds) for frequencies just below fe, as has been reported previously. For the subjects with unilateral dead regions, the enhancement occurred only for the ears with dead regions. For the amplitude-modulation detection task, thresholds were generally lower for the ears with dead regions than for the ears without, and this effect was statistically significant. For the subjects with unilateral dead regions, thresholds were lower for the ears with dead regions than for the ears without. Consonant identification was significantly better for the ears with than without dead regions, and this was true for the subjects with unilateral dead regions. We conclude that a dead region at high frequencies is associated with a better ability to process information at low frequencies. These effects may reflect cortical plasticity induced by the dead regions.

No adaptation in the amplitude modulation domain in trained listeners

The present study shows that on average, exposure to a 15 min, 5 kHz tone modulated sinusoidally in amplitude at 16 Hz with a 100% depth does not affect significantly amplitude modulation (AM) detection thresholds measured between 4 and 64 Hz when listeners are extensively trained to the AM detection task, with and without adaptor before data collection. These results are compatible with previous work given that a clear 6-dB adaptation effect was observed during the first pilot trials. However, the results reveal that adaptation effects are not robust, and suggest that the mechanisms underlying adaptation to AM must be reevaluated.

Amplitude modulation detection for band-limited noise stimuli.

In a recent investigation of temporal gap detection, Eddins, Hall, and Grose observed that gap-detection thresholds were highly dependent on stimulus bandwidth and were relatively independent of stimulus frequency region. The present study investigated the relative importance of these two stimulus variables using an amplitude-modulation detection task. Thresholds for modulation depth were obtained as a function of modulation frequency. The stimulus bandwidth was either 200, 400, 800, or 1600 Hz. The frequency region was varied by adjusting the high-frequency cutoff of the noise which was either 600, 2200, or 4400 Hz. Temporal modulation transfer functions demonstrated the typical low-pass characteristic with modulation thresholds decreasing monotonically with increasing modulation frequency. Neither stimulus bandwidth nor the frequency region of the noise influenced the form of the temporal modulation transfer function, implying that the time constant of the temporal process is essentially the same for all stimulus conditions. Absolute sensitivity to amplitude modulation was better at the larger noise bandwidths. The ability to detect amplitude modulation was essentially the same at 2200 and 4400 Hz and was slightly poorer at 600 Hz.