Frequency Discrimination Performance Research Articles

Contributions of auditory processing and cognition to the development of frequency discrimination performance during adolescence

Performance on auditory perceptual tasks develops throughout adolescence, likely due to the development of auditory and cognitive regions of the brain. We investigated the contributions of auditory processing and cognition to frequency discrimination. Frequency discrimination thresholds were measured in three conditions using a series of 3AFC tasks. For two conditions, each stimulus was two 15-ms tone pips separated by 100 ms. These stimuli were used both with a 3-down, 1-up procedure (threshold = 79.4%) with the method of constant stimuli (threshold = 66.7%). The third condition used a 130-ms stimulus and a 3-down, 1-up procedure. The auditory electrophysiological acoustic change complex was measured passively using an 800-ms tone that changed from 1000 Hz to a lower frequency. Cognitive testing was also administered. Preliminary results suggest thresholds correlate between conditions and performance improves with longer stimuli. Adolescents (10-17 years) performed worse than young adults (18-23) on only the adaptive-tracking conditions. Cognition contributed more to these conditions than the condition using the method of constant stimuli, suggesting that age differences on adaptive conditions are caused by cognitive development. Adolescents had larger acoustic change complex responses to the frequency contrasts. Behavioral data did not correlate with the electrophysiological data. [Funded by NIDCD].

Dual task measures in older adults with and without cognitive impairment: response to simultaneous cognitive-exercise training and minimal clinically important difference estimates

BackgroundResponsiveness and minimal clinically important difference (MCID) are critical indices to understand whether observed improvement represents a meaningful improvement after intervention. Although simultaneous cognitive-exercise training (SCET; e.g., performing memory tasks while cycling) has been suggested to enhance the cognitive function of older adults, responsiveness and MCID have not been established. Hence, we aimed to estimate responsiveness and MCIDs of two dual task performance involving cognition and hand function in older adults with and without cognitive impairment and to compare the differences in responsiveness and MCIDs of the two dual task performance between older adults with and without cognitive impairment.MethodsA total of 106 older adults completed the Montreal Cognitive Assessment and two dual tasks before and after SCET. One dual task was a combination of Serial Sevens Test and Box and Block Test (BBT), and the other included frequency discrimination and BBT. We used effect size and standardized response mean to indicate responsiveness and used anchor- and distribution-based approaches to estimating MCID ranges. When conducting data analysis, all participants were classified into two cognitive groups, cognitively healthy (Montreal Cognitive Assessment ≥ 26) and cognitively impaired (Montreal Cognitive Assessment < 26) groups, based on the scores of the Montreal Cognitive Assessment before SCET.ResultsIn the cognitively healthy group, Serial Seven Test performance when tasked with BBT and BBT performance when tasked with Serial Seven Test were responsive to SCET (effect size = 0.18–0.29; standardized response mean = 0.25–0.37). MCIDs of Serial Seven Test performance when tasked with BBT ranged 2.09–2.36, and MCIDs of BBT performance when tasked with Serial Seven Test ranged 3.77–5.85. In the cognitively impaired group, only frequency discrimination performance when tasked with BBT was responsive to SCET (effect size = 0.37; standardized response mean = 0.47). MCIDs of frequency discrimination performance when tasked with BBT ranged 1.47–2.18, and MCIDs of BBT performance when tasked with frequency discrimination ranged 1.13–7.62.ConclusionsCurrent findings suggest that a change in Serial Seven Test performance when tasked with BBT between 2.09 and 2.36 corrected number (correct responses – incorrect responses) should be considered a meaningful change for older adults who are cognitively healthy, and a change in frequency discrimination performance when tasked with BBT between 1.47 and 2.18 corrected number (correct responses – incorrect responses) should be considered a meaningful change for older adults who are cognitively impaired. Clinical practitioners may use these established MCIDs of dual tasks involving cognition and hand function to interpret changes following SCET for older adults with and without cognitive impairment.Trial registrationNCT04689776, 30/12/2020.

An Active Sensing Paradigm for Studying Human Auditory Perception.

Our perception is based on active sensing, i.e., the relationship between self-motion and resulting changes to sensory inputs. Yet, traditional experimental paradigms are characterized by delayed reactions to a predetermined stimulus sequence. To increase the engagement of subjects and potentially provide richer behavioral responses, we developed Sensory Island Task for humans (SITh), a freely-moving search paradigm to study auditory perception. In SITh, subjects navigate an arena in search of an auditory target, relying solely on changes in the presented stimulus frequency, which is controlled by closed-loop position tracking. A “target frequency” was played when subjects entered a circular sub-area of the arena, the “island”, while different frequencies were presented outside the island. Island locations were randomized across trials, making stimulus frequency the only informative cue for task completion. Two versions of SITh were studied: binary discrimination, and gradual change of the stimulus frequency. The latter version allowed determining frequency discrimination thresholds based on the subjects’ report of the perceived island location (i.e., target frequency). Surprisingly, subjects exhibited similar thresholds as reported in traditional “stationary” forced-choice experiments after performing only 30 trials, highlighting the intuitive nature of SITh. Notably, subjects spontaneously employed a small variety of stereotypical search patterns, and their usage proportions varied between task versions. Moreover, frequency discrimination performance depended on the search pattern used. Overall, we demonstrate that the use of an ecologically driven paradigm is able to reproduce established findings while simultaneously providing rich behavioral data for the description of sensory ethology.

Logarithmic Versus Linear Change in Step Size When Using an Adaptive Threshold-Seeking Procedure in a Frequency Discrimination Task: Does It Matter?

Different rules for changing step sizes (e.g., logarithmic, linear) are alternately used in adaptive threshold-seeking procedures, with no clear justification. We hypothesized that the linear rule may yield more accurate thresholds for poor performers because the step sizes are predetermined and fixed across listeners and thus can be small, in contrast to the logarithmic rule, in which step sizes are changed with respect to the listener's performance. Purpose The aim of this study was to test the effect of logarithmic and linear rules on frequency discrimination (FD) thresholds. Method Three experiments involving human subjects and Monte Carlo computer simulations were designed and conducted. In the 1st experiment, FD thresholds were estimated in 40 young adults with either 3-interval 2-alternative forced choice (3I2AFC; n = 19) or 2-interval 2AFC (n = 21) in a within-subject design. In the 2nd experiment, thresholds were estimated in 16 children (7-8 years old) in a within-subject design, using 3I2AFC. In the 3rd experiment, thresholds were estimated in 30 young adults in a between-subjects design using 3I2AFC. Results No significant differences were shown between the 2 rules, regardless of age group, method, or level of FD performance. Computer simulations supported the empirical findings, predicting similar FD thresholds for both rules in the majority of runs. However, they also yielded more accurate thresholds with the linear rule, but with a larger number of outliers, which increased as the listener's attention level decreased. Conclusion Overall, the use of a particular rule has little influence on FD thresholds. Possible outliers may be minimized by monitoring the participant's attention at the beginning of the run.

Perception of Small Frequency Differences in Children with Auditory Processing Disorder or Specific Language Impairment.

Frequency discrimination is often impaired in children developing language atypically. However, findings in the detection of small frequency changes in these children are conflicting. Previous studies on children's auditory perceptual abilities usually involved establishing differential sensitivity thresholds in sample populations who were not tested for auditory deficits. To date, there are no data comparing suprathreshold frequency discrimination ability in children tested for both auditory processing and language skills. : This study examined the perception of small frequency differences (∆ƒ) in children with auditory processing disorder (APD) and/or specific language impairment (SLI). The aim was to determine whether children with APD and children with SLI showed differences in their behavioral responses to frequency changes. Results were expected to identify different degrees of impairment and shed some light on the auditory perceptual overlap between pediatric APD and SLI. An experimental group design using a two-alternative forced-choice procedure was used to determine frequency discrimination ability for three magnitudes of ∆ƒ from the 1000-Hz base frequency. Thirty children between 10 years of age and 12 years, 11 months of age: 17 children with APD and/or SLI, and 13 typically developing (TD) peers participated. The clinical groups included four children with APD only, four children with SLI only, and nine children with both APD and SLI. Behavioral data collected using headphone delivery were analyzed using the sensitivity index d', calculated for three ∆ƒ was 2%, 5%, and 15% of the base frequency or 20, 50, and 150 Hz. Correlations between the dependent variable d' and the independent variables measuring auditory processing and language skills were also obtained. A stepwise regression analysis was then performed. TD children and children with APD and/or SLI differed in the detection of small-tone ∆ƒ. In addition, APD or SLI status affected behavioral results differently. Comparisons between auditory processing test scores or language test scores and the sensitivity index d' showed different strengths of correlation based on the magnitudes of the ∆ƒ. Auditory processing scores showed stronger correlation to the sensitivity index d' for the small ∆ƒ, while language scores showed stronger correlation to the sensitivity index d' for the large ∆ƒ. Although children with APD and/or SLI have difficulty with behavioral frequency discrimination, this difficulty may stem from two different levels: a basic auditory level for children with APD and a higher language processing level for children with SLI; the frequency discrimination performance seemed to be affected by the labeling demands of the same versus different frequency discrimination task for the children with SLI.

Reduced GABAergic inhibition and abnormal sensory symptoms in children with Tourette syndrome.

Tourette Syndrome (TS) is characterized by the presence of chronic tics. Individuals with TS often report difficulty with ignoring (habituating to) tactile sensations, and some patients perceive that this contributes to a "premonitory urge" to tic. While common, the physiological basis of impaired tactile processing in TS, and indeed tics themselves, remain poorly understood. It has been well established that GABAergic processing plays an important role in shaping the neurophysiological response to tactile stimulation. Furthermore, there are multiple lines of evidence suggesting that a deficit in GABAergic transmission may contribute to symptoms found in TS. In this study, GABA-edited magnetic resonance spectroscopy (MRS) was combined with a battery of vibrotactile tasks to investigate the role of GABA and atypical sensory processing in children with TS. Our results show reduced primary sensorimotor cortex (SM1) GABA concentration in children with TS compared with healthy control subjects (HC), as well as patterns of impaired performance on tactile detection and adaptation tasks, consistent with altered GABAergic function. Moreover, in children with TS SM1 GABA concentration correlated with motor tic severity, linking the core feature of TS directly to in vivo brain neurochemistry. There was an absence of the typical correlation between GABA and frequency discrimination performance in TS as was seen in HC. These data show that reduced GABA concentration in TS may contribute to both motor tics and sensory impairments in children with TS. Understanding the mechanisms of altered sensory processing in TS may provide a foundation for novel interventions to alleviate these symptoms.

Enhanced cortical representation of auditory frequency as a result of early blindness

A fundamental ability found to be enhanced by early blindness is frequency discrimination; however, the neural basis of this enhancement is unclear. Responses to a variety of auditory stimuli have been found throughout occipital cortex, but clear evidence for frequency tuning has not been reported. In auditory cortex, attenuated responses to pure tones have been found in early blind and anophthalmic individuals (Stevens and Weaver, 2009; Watkins et al., 2013). Here, we measured responses to pure tones in 5 early-blind and 5 age-matched sighted subjects to assess group differences in the organization of auditory frequency representations within occipital and auditory cortex. Methods: Stimuli consisted of pure tones ranging from 88 to 8000 Hz, which were presented in partially randomized order while subjects performed a 1-back frequency matching task. Data were analyzed using an adaptation of the population receptive field technique (Dumoulin and Wandell, 2008). We modeled the aggregate receptive field underlying each voxel's response as a one-dimensional Gaussian function of frequency, with a center and standard deviation that reflect preferred frequency and tuning bandwidth, respectively. Results: Within auditory cortex, we could reliably measure individual tonotopic maps in both subject groups, and we saw no evidence for an attenuation of responses. Relative to controls, early-blind subjects showed an enhanced representation of low to middle frequencies (<4 kHz) and narrower tuning bandwidths. In occipital cortex, blind but not sighted subjects showed evidence of auditory frequency tuning. Frequency tuned voxels in occipital cortex favored the mid-frequency range (1-8 kHz) and had narrower bandwidths then those found in auditory cortex. Conclusions: Early blindness results in an increased cortical representation of behaviorally relevant frequencies within both auditory and occipital cortex. Future work will examine how responses in these cortical areas relate to frequency discrimination performance in individual subjects. Meeting abstract presented at VSS 2014

Do normal-reading listeners use “perceptual anchors” in frequency-discrimination tasks?

A controversial hypothesis about the origins of dyslexia states that dyslexic listeners are poor at frequency discrimination when the standard frequency is fixed from trial to trial because they find it difficult to use “perceptual anchors.” This hypothesis tacitly assumes that normal listeners use perceptual anchors during fixed-frequency discrimination, which they cannot do when the standard frequency is random (“roved”). To test this assumption, we measured frequency-discrimination performance in normal listeners for tones separated by silent intervals (ISIs) of up to 10 s. Critically, in either the first or second half of the experiment (counterbalanced across listeners), the frequency of the first tone was the same on each trial (“fixed” conditions); in the other half, the frequency of this tone was random (“roved” conditions). The data were analyzed using a model that estimated the precision of frequency representations. In the roved conditions, frequency representations were less precise at longer ISIs, indicating that they experienced decay. By contrast, frequency representations experienced little decay in the fixed conditions. The results are consistent with the assumption that normal listeners used perceptual anchors in the fixed conditions because, by definition, perceptual anchors should be stored in long-term memory and therefore less susceptible to decay.

Impaired tactile processing in children with autism spectrum disorder

Impaired responses to tactile stimulation are a commonly reported symptom among children with autism spectrum disorder (ASD). Furthermore, impairments in filtering or habituation to tactile input have been described in ASD. This study measured different aspects of tactile processing to investigate atypical touch sensitivity in children with ASD, methodology that has not been previously used in this population. Sixty-seven typically developing children (TDC) and 32 children with ASD (ages 8-12) completed vibrotactile tasks assessing: reaction time (RT); static and dynamic detection threshold (DT); amplitude discrimination with and without single-site adaptation; frequency discrimination; and temporal order judgment (TOJ) with and without concurrent stimulation. Children with ASD showed raised static detection thresholds and an absence of the effect of a dynamically increasing subthreshold stimulus on static detection threshold. Children with ASD also showed poorer amplitude discrimination than TDC, as well as decreased adaptation. There were no significant differences in frequency discrimination or TOJ performance between the groups. Differences in the effect of dynamic stimulation on detection threshold suggest impaired feed-forward inhibition in autism, which may be linked to poor sensory filtering. Increased baseline amplitude discrimination thresholds in ASD suggest that lateral inhibitory connections are weaker in ASD, and an absence of the effect of adaptation suggests impaired modulation of lateral inhibitory connections in ASD, which may relate to aberrant habituation. These results suggest a functional deficit in the somatosensory inhibitory system in autism. Understanding the specific mechanisms underlying sensory symptoms in autism may allow for more specific therapeutic or drug targeting in the near future.

Crossmodal Induction of Thalamocortical Potentiation Leads to Enhanced Information Processing in the Auditory Cortex

Sensory systems do not work in isolation; instead, they show interactions that are specifically uncovered during sensory loss. To identify and characterize these interactions, we investigated whether visual deprivation leads to functional enhancement in primary auditory cortex (A1). We compared sound-evoked responses of A1 neurons in visually deprived animals to those from normally reared animals. Here, we show that visual deprivation leads to improved frequency selectivity as well as increased frequency and intensity discrimination performance of A1 neurons. Furthermore, we demonstrate invitro that in adults visual deprivation strengthens thalamocortical (TC) synapses in A1, but not in primary visual cortex (V1). Because deafening potentiated TC synapses in V1, but not A1, crossmodal TC potentiation seems to be a general property of adult cortex. Our results suggest that adults retain the capability for crossmodal changes whereas such capability is absent within a sensory modality. Thus, multimodal training paradigms might be beneficial in sensory-processing disorders.

Subcortical Neural Synchrony and Absolute Thresholds Predict Frequency Discrimination Independently

The neural mechanisms of pitch coding have been debated for more than a century. The two main mechanisms are coding based on the profiles of neural firing rates across auditory nerve fibers with different characteristic frequencies (place-rate coding), and coding based on the phase-locked temporal pattern of neural firing (temporal coding). Phase locking precision can be partly assessed by recording the frequency-following response (FFR), a scalp-recorded electrophysiological response that reflects synchronous activity in subcortical neurons. Although features of the FFR have been widely used as indices of pitch coding acuity, only a handful of studies have directly investigated the relation between the FFR and behavioral pitch judgments. Furthermore, the contribution of degraded neural synchrony (as indexed by the FFR) to the pitch perception impairments of older listeners and those with hearing loss is not well known. Here, the relation between the FFR and pure-tone frequency discrimination was investigated in listeners with a wide range of ages and absolute thresholds, to assess the respective contributions of subcortical neural synchrony and other age-related and hearing loss-related mechanisms to frequency discrimination performance. FFR measures of neural synchrony and absolute thresholds independently contributed to frequency discrimination performance. Age alone, i.e., once the effect of subcortical neural synchrony measures or absolute thresholds had been partialed out, did not contribute to frequency discrimination. Overall, the results suggest that frequency discrimination of pure tones may depend both on phase locking precision and on separate mechanisms affected in hearing loss.

G020033 基底板形状が周波数弁別能に及ぼす影響

The basilar membrane (BM) plays an important role for sound reception in the cochlea because the BM has frequency discrimination characteristics. Echolocating bats can perceive objects in the environment by emitting ultrasonic sound. Therefore, the frequency discrimination of the echolocating bats is presumably more highly accurate than that of humans. The shape of the BM of the echolocating bats is different from that of humans, and its thickness changes remarkably at the base. To clarify the effects of the shape of the BM with respect to frequency discrimination performance, two types of finite-element models of the cochlea were created, i, e, the human model (H model) and the modified human model (MH model). The shape of the BM of MH model was modified considering the aspect ratio of the BM (thickness/width) of a horseshoe bat which is a species of echolocating bat. The traveling wave on the BM was found to have only one peak at the input frequencies in the H model. By contrast, two peaks were observed in the MH model around 3 kHz or 9 kHz The maximum amplitude position of the BM shifted greatly in the MH model because the amplitude ratio of the two peaks was reversed. This result suggests that the shape of the BM can affect frequency discrimination performance.

The role of local separation in spatial frequency discrimination

Spatial frequency discrimination could simply reflect the ability to discriminate local differences in width when sinusoidal gratings are used. We introduced random fluctuations in the half-cycle widths of both extended 1 c/° gratings and those restricted to 1.5 cycles (i.e. two bars of identical phase), as we hypothesised that discrimination for large gratings would be more robust to this distortion in the presence of a genuine spatial frequency sensitive mechanism that averaged information across a wide area. To exclude the possibility of a local mechanism that averaged through scanning eye movements, experiments were repeated with a short presentation time. We also repeated the experiment with a fixation point and the central 4° of the grating masked. Discrimination thresholds were more robust to spatial distortion for large gratings vs. two bars, and were not significantly altered by either a short presentation time or masking of the central part of the grating. We therefore find that spatial frequency discrimination performance is undistinguishable from width discrimination performance when regular sinusoidal stimuli are used. When spatial distortion is introduced to make measures of spatial width unreliable, spatial pooling of information is both possible and results in clear performance benefits.

Regionally Specific Human GABA Concentration Correlates with Tactile Discrimination Thresholds

The neural mechanisms underlying variability in human sensory perception remain incompletely understood. In particular, few studies have attempted to investigate the relationship between in vivo measurements of neurochemistry and individuals' behavioral performance. Our previous work found a relationship between GABA concentration in the visual cortex and orientation discrimination thresholds (Edden et al., 2009). In the present study, we used magnetic resonance spectroscopy of GABA and psychophysical testing of vibrotactile frequency thresholds to investigate whether individual differences in tactile frequency discrimination performance are correlated with GABA concentration in sensorimotor cortex. Behaviorally, individuals showed a wide range of discrimination thresholds ranging from 3 to 7.6 Hz around the 25 Hz standard. These frequency discrimination thresholds were significantly correlated with GABA concentration (r = -0.58; p < 0.05) in individuals' sensorimotor cortex, but not with GABA concentration in an occipital control region (r = -0.04). These results demonstrate a link between GABA concentration and frequency discrimination in vivo, and support the hypothesis that GABAergic mechanisms have an important role to play in sensory discrimination.

Auditory temporal processing and dyslexia in an orthographically consistent language

We examined two hypotheses relating auditory processing to dyslexia in Greek, an orthographically consistent language. Study I examined the “P-center” or “beat detection” hypothesis (Goswami et al., 2002) in a sample of Grade 6 dyslexics, Grade 6 chronological age (CA) controls, and Grade 4 reading age (RA) controls. Study II examined the “temporal processing,” or “rapid auditory processing” hypothesis (Tallal, 1980) in a sample of Grade 7 dyslexics, CA controls, and in two groups of CA matched children with low frequency discrimination or low tone sequencing performance. Both studies indicate that (a) as a group, dyslexic children did not perform significantly worse on auditory processing measures than the control groups; (b) measures of auditory processing mostly did not account for unique amount of variance in phonological processing, reading, or spelling; and (c) at an individual level of analysis, some of the dyslexic children experienced auditory temporal processing deficits. Implications on the importance of auditory processing in reading in orthographically consistent languages are discussed.

Widespread Auditory Deficits in Tune Deafness

The goal of this study was to investigate auditory function in individuals with deficits in musical pitch perception. We hypothesized that such individuals have deficits in nonspeech areas of auditory processing. We screened 865 randomly selected individuals to identify those who scored poorly on the Distorted Tunes test (DTT), a measure of musical pitch recognition ability. Those who scored poorly were given a comprehensive audiologic examination, and those with hearing loss or other confounding audiologic factors were excluded from further testing. Thirty-five individuals with tune deafness constituted the experimental group. Thirty-four individuals with normal hearing and normal DTT scores, matched for age, gender, handedness, and education, and without overt or reported psychiatric disorders made up the normal control group. Individual and group performance for pure-tone frequency discrimination at 1000 Hz was determined by measuring the difference limen for frequency (DLF). Auditory processing abilities were assessed using tests of pitch pattern recognition, duration pattern recognition, and auditory gap detection. In addition, we evaluated both attention and short- and long-term memory as variables that might influence performance on our experimental measures. Differences between groups were evaluated statistically using Wilcoxon nonparametric tests and t-tests as appropriate. The DLF at 1000 Hz in the group with tune deafness was significantly larger than that of the normal control group. However, approximately one-third of participants with tune deafness had DLFs within the range of performance observed in the control group. Many individuals with tune deafness also displayed a high degree of variability in their intertrial frequency discrimination performance that could not be explained by deficits in memory or attention. Pitch and duration pattern discrimination and auditory gap-detection ability were significantly poorer in the group with tune deafness than the normal control group. Approximately one-third of our participants with tune deafness displayed evidence of attention deficit with hyperactivity disorder on the Test of Variables of Attention. Test of Variables of Attention scores were significantly correlated with gap-detection scores, but not significantly correlated with any of the other experimental measures, including the DTT, DLF, and auditory pattern discrimination tests. Short- and long-term memory was not significantly related to any of the experimental measures. Individuals with tune deafness identified by the DTT have poor performance on many tests of auditory function. These include pure-tone frequency discrimination, pitch and duration pattern discrimination, and temporal resolution. Overall, reduction in performance does not seem to derive from deficits in memory or attention. However, because of the prevalence of attention deficit with hyperactivity disorder in those with tune deafness, this variable should be considered as a potentially confounding factor in future studies of tune deafness and its characteristics. Pure-tone frequency discrimination varied widely in individuals with tune deafness, and the high degree of intertrial variability suggests that frequency discrimination may be unstable in tune-deaf individuals.

Effect of Attentional State on Frequency Discrimination: A Comparison of Children With ADHD On and Off Medication

Debate continues over the hypothesis that children with language or literacy difficulties have a genuine auditory processing deficit. Several recent studies have reported deficits in frequency discrimination (FD), but it is unclear whether these are genuine perceptual impairments or reflective of the comorbid attentional problems that exist in many children with language and literacy difficulties. The present study investigated FD in children with attention deficit hyperactivity disorder (ADHD) when their attentional state was altered with stimulant medication. Auditory thresholds were obtained using FD and frequency modulation detection (FM) tasks. In the FD task, participants judged which of 2 pairs contained a high-low frequency sound, and in the FM task, children judged which of two tones "wobbled" (i.e., modulated). Children with ADHD had significantly poorer and more variable FD performance when off compared to on stimulant medication, and did significantly worse than controls on all FD runs when off but not on stimulant medication. However, children with ADHD did not differ from controls on the FM task. These findings demonstrate that certain auditory discrimination tasks are influenced by the child's attentional status. In addition, significant relationships between FD and measures of language and reading were abolished when comorbid attentional difficulties were taken into account. The study has implications for design and interpretation of studies investigating links between auditory discrimination and difficulties in language and literacy.

Comorbid Attentional Factors and Frequency Discrimination Performance in a Child with Reading Difficulties

This research investigated the frequency discrimination performance of a 6‐year‐old boy (MH) with language and attentional difficulties. MH had been reported to have literacy problems not paralleling an advanced verbal ability, and he showed difficulties in discriminating non‐verbal tones of different frequencies in comparison with children of his own age. A series of auditory training sessions were conducted to examine whether his frequency discrimination performance could be improved. Thresholds were shown to be inconsistent over six sessions. MH showed no improvement on a test of phonological short‐term memory and his sustained attention level was comparable with a child with Attention Deficit Hyperactivity Disorder (ADHD). Clinical assessments confirmed a diagnosis of ADHD, and methylphenidate (Ritalin) was prescribed. Five weeks later, following the establishment of a medication regime, repeated assessment showed a significant improvement in frequency discrimination performance. Performance also improved on the test of sustained attention. A follow‐up study 4 months later, while still medicated, confirmed MH had maintained his frequency discrimination performance.

Rehabilitation plasticity: Influence of hearing aid fitting on frequency discrimination performance near the hearing-loss cut-off

Several studies have already demonstrated that patients with steeply sloping hearing loss of cochlear origin exhibit an improvement in frequency discrimination performance at or around the cut-off frequency. This enhancement cannot be explained in terms of peripheral mechanisms and should rather be interpreted in terms of central reorganization: i.e., injury-induced cortical plasticity. However, the reversibility and time course of such reorganization has not yet been described. The main goal of the present study was therefore to investigate the occurrence of rehabilitation plasticity associated with hearing-aid fitting in human subjects. Nine subjects with steeply sloping hearing loss and who were candidates for auditory rehabilitation were tested. Discrimination-limen-for-frequency (DLF) enhancement was investigated at the frequency with the best DLF (bDLF) for each individual subject before and during auditory rehabilitation (at 1 month, 3 months and 6 months). From 1 month on, frequency discrimination performance decreased significantly at the bDLF frequency, while remaining stable at other frequencies. This normalization may reflect a new central reorganization reversing the initial injury-induced changes in the cortical map. A correlation between subject’s age and alteration in DLF at 1 month was also found, suggesting that plasticity operates faster in younger patients.

Simple reaction times in subjects with steeply sloping hearing loss: Is there an alteration at the edge of the loss?

The aim of the present study was to investigate the simple reaction time (RT) performance of patients with steeply sloping sensorineural hearing loss. This kind of hearing loss has the particularity of inducing a reorganization of the primary auditory cortex (Dietrich et al, ), the edge frequency of the loss being over-represented. It is assumed that a consequence of this plasticity could be reflected in an improvement in frequency discrimination performances around the edge of the loss (McDermott et al, ). In the present study we used pure tones equalized in loudness to investigate whether RT might be altered at the cut-off frequency (Fc) of the loss, or at the frequency that presented the best discrimination-limen-for-frequency (bDLF). The effect of auditory rehabilitation on RT was also studied. A great variability in RT was noted in all our subjects. Our results demonstrated that RT was unmodified at Fc or bDLF, be it before or after hearing aid fitting. However, an improvement in the correlation between RT and frequency discrimination performance was observed at three months post-rehabilitation.