Ifat Yasin

Heritable risk factors associated with language impairments.

There is a strong genetic contribution to children’s language and literacy impairments. The aim of this study was to determine which aspects of the phenotype are familial by comparing 34 parents of probands with language/literacy impairments and 33 parents of typically developing probands. The parents responded to questionnaires regarding previous history for language/reading impairment and participated in psychometric testing. The psychometric test battery consisted of tests assessing non‐verbal IQ, short‐term memory, articulation, receptive grammar, reading abilities and spelling. Self‐report measures demonstrated a higher prevalence of language and literacy impairments in parents of affected probands (32%) compared with parents of unaffected probands (6%). The two groups of parents differed significantly in their performance on the non‐word repetition, oromotor and digit span tasks. Non‐word repetition gave the best discrimination between the parent groups even when the data from the parents who actually were impaired as ascertained by direct testing or self‐report were removed from the analyses. This suggests that non‐word repetition serves as a marker of a family risk for language impairment. The paper concludes with a discussion of issues associated with ascertainment of specific language impairment (SLI).

The effects of a high-frequency suppressor on tuning curves and derived basilar-membrane response functions

Forward-masked psychophysical tuning curves were obtained using a fixed, low-level signal at a frequency of 4 kHz, and masker frequencies of 2.0, 2.5, 3.0, 3.5, 3.75, 4.0, 4.25, 4.5, 4.75, 5.0, and 5.5 kHz, at masker-signal gaps of 20, 30, 40, 60, 80, and 100 ms. An adaptive two-interval, two alternative forced-choice (21-2AFC) procedure was used to obtain the masker level at threshold. This procedure was repeated with the addition of a 4.75-kHz suppressor at 50 or 60 dB SPL, gated with the masker. Tuning curves were broader, and estimates of compression and gain from derived input/output functions were decreased in the presence of a suppressor as compared to the no-suppressor condition. The results are consistent with physiological results, which show that suppression leads to a broadening of tuning curves and a partial linearization of the midlevel portion of the basilar-membrane input/output function.

Speech versus tone processing in compensated dyslexia: discrimination and lateralization with a dichotic mismatch negativity (MMN) paradigm.

This study investigated the possibility of a pervasive auditory-processing deficit in 10 adult dyslexics who had compensated for their reading disability, compared to 10 matched controls. Unlike previous studies [Baldeweg, T., Richardson, A., Watkins, S., Foale, C. & Gruzelier, J. (1999). Impaired auditory frequency discrimination in dyslexia detected with mismatch evoked potentials. Annals of Neurology, 45(4): 495-503], the current EEG study used a dichotic presentation of stimuli in order to probe the relationship between ear advantage and left- and right-hemisphere dominance for processing speech and non-speech stimuli respectively. A dichotic presentation is thought to maximise lateralization effects, as well being a more ecologically valid paradigm. The Mismatch Negativity (MMN) was measured for both speech [consonant-vowel pairs: /ta/ vs. /ka/ and ba/ vs. /da/] and non-speech stimuli (pure tones: 1 kHz vs. 1.2 kHz). Smaller MMNs to tone stimuli were obtained for dyslexics versus controls, but no differences were found for speech stimuli. Controls differentiated between speech and tones, with larger MMNs to tone stimuli. Dyslexics showed significantly greater MMNs to one stop consonant discrimination (/ta/ vs /ka/) than the other (/ba/ vs /da/), but did not differentiate speech from tones, and no or minimal lateralization was found for either group or stimulus type, in line with recent studies [Kershner and Micallef, 1992; Bellis, T.J., Nicol, T., & Kraus, N. (2000). Aging affects hemispheric asymmetry in the neural representation of speech sounds. Journal of Neuroscience, 20, 791-797]. However, analysis of left and right dipole source activity suggested right hemispheric preference for tones in controls, and the lack of such a preference in dyslexics. Lateralization of the auditory system in general may be less specialized in compensated dyslexia, although no specific differences in speech lateralization were seen. The present study also extends previous findings to show that the frequency range over which dyslexics are shown to display impaired frequency discrimination can be extended to 20% (1 kHz vs. 1.2 kHz) if using a dichotic presentation.

Weak hand preference in children with down syndrome is associated with language deficits

This study explores associations between language ability and hand preference in children with Down syndrome. Compared to typically developing children of the same age, children with Down syndrome showed weaker hand preference, were less consistent in the hand they used and also less willing to reach to extreme positions in contralateral space. Within the group of children with Down syndrome, those who showed a stronger or more consistent hand preference had better language and memory skills. This association could not be explained by differences in non-verbal cognitive ability or hearing loss. These findings are discussed within the theory of neurolinguistic development proposed by Locke [Locke (1997). Brain & Language, 58, 265-326].

Duration of auditory sensory memory in parents of children with SLI: A mismatch negativity study

In a previous behavioral study, we showed that parents of children with SLI had a subclinical deficit in phonological short-term memory. Here, we tested the hypothesis that they also have a deficit in nonverbal auditory sensory memory. We measured auditory sensory memory using a paradigm involving an electrophysiological component called the mismatch negativity (MMN). The MMN is a measure of the brains ability to detect a difference between a frequent standard stimulus (1000 Hz tone) and a rare deviant one (1200 Hz tone). Memory effects were assessed by varying the inter-stimulus interval (ISI) between the standard and deviant. We predicted that parents of children with SLI would have a smaller MMN than parents of typically developing children at a long ISI (3000 ms), but not at a short one (800 ms). This was broadly confirmed. However, individual differences in MMN amplitude did not correlate with measures of phonological short-term memory. Attenuation of MMN amplitude at the longer ISI thus did not provide unambiguous support for the hypothesis of a reduced auditory sensory memory in parents of affected children. We conclude by reviewing possible explanations for the observed group effects.

Estimating peripheral gain and compression using fixed-duration masking curves

Estimates of human basilar membrane gain and compression obtained using temporal masking curve (TMC) and additivity of forward masking (AFM) methods with long-duration maskers or long masker-signal silent intervals may be affected by olivocochlear efferent activation, which reduces basilar membrane gain. The present study introduces a fixed-duration masking curve (FDMC) method, which involves a comparison of off- and on-frequency forward masker levels at threshold as a function of masker and signal duration, with the total masker-signal duration fixed at 25 ms to minimize efferent effects. Gain and compression estimates from the FDMC technique were compared with those from TMC (104-ms maskers) and AFM (10- and 200-ms maskers) methods. Compression estimates over an input-masker range of 40-60 dB sound pressure level were similar for the four methods. Maximum compression occurred at a lower input level for the FDMC compared to the TMC method. Estimates of gain were similar for TMC and FDMC methods. The FDMC method may provide a more reliable estimate of BM gain and compression in the absence of efferent activation and could be a useful method for estimating effects of efferent activity when used with a precursor sound (to trigger efferent activation), presented prior to the combined masker-signal stimulus.

Effect of human auditory efferent feedback on cochlear gain and compression.

The mammalian auditory system includes a brainstem-mediated efferent pathway from the superior olivary complex by way of the medial olivocochlear system, which reduces the cochlear response to sound (Warr and Guinan, 1979; Liberman et al., 1996). The human medial olivocochlear response has an onset delay of between 25 and 40 ms and rise and decay constants in the region of 280 and 160 ms, respectively (Backus and Guinan, 2006). Physiological studies with nonhuman mammals indicate that onset and decay characteristics of efferent activation are dependent on the temporal and level characteristics of the auditory stimulus (Bacon and Smith, 1991; Guinan and Stankovic, 1996). This study uses a novel psychoacoustical masking technique using a precursor sound to obtain a measure of the efferent effect in humans. This technique avoids confounds currently associated with other psychoacoustical measures. Both temporal and level dependency of the efferent effect was measured, providing a comprehensive measure of the effect of human auditory efferents on cochlear gain and compression. Results indicate that a precursor (>20 dB SPL) induced efferent activation, resulting in a decrease in both maximum gain and maximum compression, with linearization of the compressive function for input sound levels between 50 and 70 dB SPL. Estimated gain decreased as precursor level increased, and increased as the silent interval between the precursor and combined masker-signal stimulus increased, consistent with a decay of the efferent effect. Human auditory efferent activation linearizes the cochlear response for mid-level sounds while reducing maximum gain.

Psychophysical tuning curves at very high frequencies

For most normal-hearing listeners, absolute thresholds increase rapidly above about 16 kHz. One hypothesis is that the high-frequency limit of the hearing-threshold curve is imposed by the transmission characteristics of the middle ear, which attenuates the sound input [Masterton et al., J. Acoust. Soc. Am. 45, 966-985 (1969)]. An alternative hypothesis is that the high-frequency limit of hearing is imposed by the tonotopicity of the cochlea [Ruggero and Temchin, Proc. Nat. Acad. Sci. U.S.A. 99, 13206-13210 (2002)]. The aim of this study was to test these hypotheses. Forward-masked psychophysical tuning curves (PTCs) were derived for signal frequencies of 12-17.5 kHz. For the highest signal frequencies, the high-frequency slopes of some PTCs were steeper than the slope of the hearing-threshold curve. The results also show that the human auditory system displays frequency selectivity for characteristic frequencies (CFs) as high as 17 kHz, above the frequency at which absolute thresholds begin to increase rapidly. The findings suggest that, for CFs up to 17 kHz, the high-frequency limitation in humans is imposed in part by the middle-ear attenuation, and not by the tonotopicity of the cochlea.

Hemispheric differences in processing dichotic meaningful and non-meaningful words

Classic dichotic-listening paradigms reveal a right-ear advantage (REA) for speech sounds as compared to non-speech sounds. This REA is assumed to be associated with a left-hemisphere dominance for meaningful speech processing. This study objectively probed the relationship between ear advantage and hemispheric dominance in a dichotic-listening situation, using event-related potentials (ERPs). The mismatch negativity (MMN) and a late negativity (LN) were measured for bisyllabic meaningful words and non-meaningful pseudowords, which differed in their second syllable. Eighteen normal-hearing listeners were presented with a repeating diotic standard ([beI-gi:] or [leI-gi:]) and an occasional dichotic deviant (a standard presented to one ear and a deviant [beI-bi:], [beI-di:], [leI-bi:] or [leI-di:] presented to the opposite ear). As predicted there was a REA for meaningful words compared to non-meaningful words. Also, dipole source analysis suggested that dipole strength was stronger in the left than the right cortical region for meaningful words. However, there were differences in response within meaningful words as well as between meaningful and non-meaningful words which may be explained by the characteristics of embedded words and the position-specific probability of phoneme occurrence in words.

The effects of low- and high-frequency suppressors on psychophysical estimates of basilar-membrane compression and gain.

Physiological studies suggest that the increase in suppression as a function of suppressor level is greater for a suppressor below than above the signal frequency. This study investigated the pattern of gain reduction underlying this increase in suppression. Temporal masking curves (TMCs) were obtained by measuring the level of a 2.2-kHz sinusoidal off-frequency masker or 4-kHz on-frequency sinusoidal masker required to mask a brief 4-kHz sinusoidal signal at 10 dB SL, for masker-signal intervals of 20-100 ms. TMCs were also obtained in the presence of a 3- or 4.75-kHz sinusoidal suppressor gated with the 4-kHz masker, for suppressor levels of 40-70 dB SPL. The decrease in gain (increase in suppression) as a function of suppressor level was greater with a 3-kHz suppressor than with a 4.75-kHz suppressor, in line with previous findings. Basilar membrane input-output (I/O) functions derived from the TMCs showed a shift to higher input (4-kHz masker) levels of the low-level (linear) portion of the I/O function with the addition of a suppressor, with partial linearization of the function, but no reduction in maximum compression.