Stuart Rosen

Evidence for a grammar-specific deficit in children.

BACKGROUND Specific language impairment (SLI) is a disorder in which language acquisition is impaired in an otherwise normally developing child. SLI affects around 7% of children. The existence of a purely grammatical form of SLI has become extremely controversial because it points to the existence and innateness of a putative grammatical subsystem in the brain. Some researchers dispute the existence of a purely grammatical form of SLI. They hypothesise that SLI in children is caused by deficits in auditory and/or general cognitive processing, or social factors. There are also claims that the cognitive abilities of people with SLI have not yet been sufficiently characterised to substantiate the existence of SLI in a pure grammatical form. RESULTS We present a case study of a boy, known as AZ, with SLI. To investigate the claim for a primary grammatical impairment, we distinguish between grammatical abilities, non-grammatical language abilities and non-verbal cognitive abilities. We investigated AZs abilities in each of these areas. AZ performed normally on auditory and cognitive tasks, yet exhibited severe grammatical impairments. This is evidence for a developmental grammatical deficit that cannot be explained as a by-product of retardation or auditory difficulties. CONCLUSIONS The case of AZ provides evidence supporting the existence of a genetically determined, specialised mechanism that is necessary for the normal development of human language.

AUDITORY FILTER NONLINEARITY AT 2 KHZ IN NORMAL HEARING LISTENERS

Auditory filters broaden with increasing level. Using a recently developed method of fitting filter shapes to notched-noise masking data that explicitly models the nonlinear changes in filter shape across level, results at 2 kHz from 9 listeners over a wide range of levels and notch widths are reported. Families of roex(p,w,t) filter shapes lead to models which account well for the observed data. The primary effect of level is a broadening in the tails of the filter as level increases. In all cases, models with filter parameters depending on probe level fit the data much better than masker-dependent models. Thus auditory filter shapes appear to be controlled by their output, not by their input. Notched-noise tests, if performed at a single level, should use a fixed probe level. Filter shapes derived in this way, and normalized to have equal tail gain, are highly reminiscent of measurements made directly on the basilar membrane, including the degree of compression evidenced in the input-output function.

Characterising auditory filter nonlinearity

An important aspect of auditory nonlinearity is that psychoacoustically measured auditory filters broaden as the level at which they are measured increases. However, it is not yet clear whether the change in filter shape is controlled primarily by the level of the probe or that of the masker. We have therefore developed a new method for fitting filter shapes to notched-noise data in which filter parameters depend explicitly on signal level (either probe or masker). By applying this technique to a set of notched-noise data in which both fixed-probe and fixed-masker paradigms have been used at a range of levels, we have been able to show that models in which filter parameters depend on probe level are considerably more successful than models in which filter parameters depend upon masker level. The results from this new procedure have enabled us to describe the nonlinear changes in auditory filter shape at 2 kHz with only five parameters. Also discussed are the implications of these findings for the generation of excitation patterns and for the computational implementation of simple, yet reasonably realistic nonlinear auditory filters whose shape depends on their output.

Individual variability in the perception of cues to place contrasts in initial stops

Synthetic continua of two minimal pairs, BAIT-DATE and DATE-GATE, closely modeled on natural utterances by a female speaker, were presented to a group of 16 listeners for identification infull-cue andreduced-cue conditions. Grouped results showed that categorization curves for full-and reduced-cue conditions differed significantly in both contrasts. However, an averaging of results obscures marked variability in labeling behavior. Some listeners showed large changes in categorization between the full- and reduced-cue conditions, whereas others showed relatively small or no changes. In a follow-up study, perception of the BAIT-DATE contrast was compared with the perception of a highly stylized BA-DA continuum. A smaller degree of intersubject and between-condition variability was found for these less complex synthetic stimuli. The amount of variability found in the labeling of speech contrasts may be dependent on cue salience, which will be determined by the speech pattern complexity of the stimuli and by the vowel environment.

Auditory filter bandwidths as a function of level at low frequencies (125 Hz–1 kHz)

Auditory filter bandwidths were measured using the symmetric notched-noise method in five normally hearing listeners at four masker levels (40-70 dB SPL/Hz in 10-dB steps) and four probe frequencies (125-1000 Hz in octave steps). Accurate stimulus spectrum shape and level were ensured by use of a headphone monitoring technique. Auditory filter bandwidths decreased with decreasing frequency from 1 kHz down to 125 Hz. On the whole, bandwidths increased with increasing level, but the effect of level on bandwidth was greater as frequency increased, with little or no effect of level at 125 Hz. Insofar as the results from the notched-noise method reflect basilar membrane vibration patterns, basilar membrane mechanics appear to become less nonlinear as one approaches the apex of the cochlea.

Speech pattern hearing aids for the profoundly hearing impaired: Speech perception and auditory abilities

A family of prototype speech pattern hearing aids for the profoundly hearing impaired has been compared to amplification. These aids are designed to extract acoustic speech patterns that convey essential phonetic contrasts, and to match this information to residual receptive abilities. In the first study, the presentation of voice fundamental frequency information from a wearable SiVo (sinusoidal voice) aid was compared to amplification in 11 profoundly deafened adults. Intonation reception was often better, and never worse, with fundamental frequency information. Four subjects scored more highly in audio-visual consonant identification with fundamental frequency information, five performed better with amplified speech, and two performed similarly under these two conditions. Five of the 11 subjects continued use of the SiVo aid after the tests were complete. A second study examined a laboratory prototype compound speech pattern aid, which encoded voice fundamental frequency, amplitude envelope, and the presence of voiceless excitation. In five profoundly deafened adults, performance was better in consonant identification when additional speech patterns were present than with fundamental frequency alone; the main advantage was derived from amplitude information. In both consonant identification and connected discourse tracking, performance with appropriately matched compound speech pattern signals was better than with amplified speech in three subjects, and similar to performance with amplified speech in the other two. In nine subjects, frequency discrimination, gap detection, and frequency selectivity were measured, and were compared to speech receptive abilities with both amplification and fundamental frequency presentation. The subjects who showed the greatest advantage from fundamental frequency presentation showed the greatest average hearing losses, and the least degree of frequency selectivity. Compound speech pattern aids appear to be more effective for some profoundly hearing-impaired listeners than conventional amplifying aids, and may be a valuable alternative to cochlear implants.

Lip-reading the BKB sentence lists: Corrections for list and practice effects

Two groups of 21 adult subjects with normal hearing viewed the video recordings of the Bamford-Kowal-Bench standard sentence lists issued by the EPI Group in 1986. Each subject viewed all of the 21 lists and attempted to write down the words contained in each sentence. One group lip-read the lists with no sound (the LR:alone condition). The other group also heard a sequence of acoustic pulses which were synchronized to the moments when the talkers vocal folds closed (the LR&Lx condition). Performance was assessed both by loose (KW(L)) and by tight (KW(T)) keyword scoring methods. Both scoring methods produced the same pattern of results: performance was better in the LR&Lx condition; performance in both conditions improved linearly with the logarithm of the list presentation order number; subjects who produced higher overall scores also improved more with experience of the lists. The data were described well by a logistic regression model which provided a formula which can be used to compensate for practice effects and for differences in difficulty between lists. Two simpler, but less accurate, methods for compensating for variation in inter-list difficulty are also described. A figure is provided which can be used to assess the significance of the difference between a pair of scores obtained from a single subject in any pair of presentation conditions.

Apparatus for use in conjunction with lipreading by the profoundly deaf

The profoundly deaf benefit in lipreading if the larynx frequencies of speech are presented to them by means of acoustic sine waves. In the present invention the sine waves required are generated using a microcomputer and analogue output circuits, with the microcomputer providing digital level samples for the required sine waves from a stored look-up table. The wide frequency range of sine waves required is achieved by omitting some samples in each cycle at high frequencies, and the wide range of output levels required is provided by employing two digital to analogue converters, one acting as an attenuator.

Acoustic reflexes in the measurement of auditory filters at high levels in normal listeners

The possible influence of the acoustic reflex in auditory filter shape measurements was investigated in 4 normal listeners by measuring contralateral acoustic reflexes to stimuli used in the notched-noise method. For probe/masker combinations centred at 125 and 250 Hz, the reflex was, at most, barely detectable even at masker levels of 80 dB SPL/Hz. On the other hand, all listeners had a measurable reflex at a masker level of 70 dB SPL/Hz for a probe/masker combination centred at 1 kHz. Some listeners also evidenced reflexes at a masker level of 60 kB SPL/Hz at this frequency and at 70 dB SPL/Hz at 500 Hz. As it is known that the acoustic reflex significantly attenuates frequency components of sounds below about 2 kHz as they pass through the middle ear, it appears that estimates of auditory filter bandwidths at high levels at 0.5 and 1 kHz can be influenced to some degree by the reflex.

Electrode placements for cochlear implants: A review

Of the variety of different sites that have been proposed and used for cochlear implants, only two are now seeing widespread use. For single-channel electrodes, it appears that a placement at the round window, or just inside it, leads to no disadvantages (and perhaps some advantages) over deeper insertions. For multichannel implants, it appears that intra-cochlear electrodes are, generally speaking, preferable to extra-cochlear ones in a variety of ways, especially as the early fears about the dangers of intra-cochlear placement now seem exaggerated. One way in which extra-cochlear approaches may play an important accessory role in multichannel intra-cochlear implants is in allowing access to the apical end of the cochlea where residual nerve survival is likely to be best. Special considerations may apply for groups of patients who until recently have been implanted relatively infrequently--adults with significant residual hearing and children.