Electrophysiological signatures of visual lexical processing: open- and closed-class words.

This paper presents evidence of the disputed existence of an electrophysiological marker for the lexical-categorical distinction between open- and closed-class words. Event-related brain potentials were recorded from the scalp while subjects read a story. Separate waveforms were computed for open- and closed-class words. Two aspects of the waveforms could be reliably related to vocabulary class. The first was an early negativity in the 230- to 350-msec epoch, with a bilateral anterior predominance. This negativity was elicited by open- and closed-class words alike, was not affected by word frequency or word length, and had an earlier peak latency for closed-class words. The second was a frontal slow negative shift in the 350- to 500-msec epoch, largest over the left side of the scalp. This late negativity was only elicited by closed-class words. Although the early negativity cannot serve as a qualitative marker of the open- and closed-class distinction, it does reflect the earliest electrophysiological manifestation of the availability of categorical information from the mental lexicon. These results suggest that the brain honors the distinction between open- and closed-class words, in relation to the different roles that they play in on-line sentence processing.

Electrophysiological manifestations of open- and closed-class words in patients with Broca's aphasia with agrammatic comprehension. An event-related brain potential study.

This paper presents electrophysiological data on the on-line processing of open- and closed-class words in patients with Broca's aphasia with agrammatic comprehension. Event-related brain potentials were recorded from the scalp when Broca patients and non-aphasic control subjects were visually presented with a story in which the words appeared one at a time on the screen. Separate waveforms were computed for open- and closed-class words. The non-aphasic control subjects showed clear differences between the processing of open- and closed-class words in an early (210-375 ms) and a late (400-700 ms) time-window. The early electrophysiological differences reflect the first manifestation of the availability of word-category information from the mental lexicon. The late differences presumably relate to post-lexical semantic and syntactic processing. In contrast to the control subjects, the Broca patients showed no early vocabulary class effect and only a limited late effect. The results suggest that an important factor in the agrammatic comprehension deficit of Broca's aphasics is a delayed and/or incomplete availability of word-class information.

Effect of misoprostol on myocardial contractility in rats treated with cyclosporin A.

The nephrotoxic side effects of the immunosuppressant cyclosporin A in animals and humans are well known. Misoprostol, a prostaglandin E analog, is used clinically in organ-transplant recipients taking cyclosporin A to protect against these side effects. We reported previously that long-term treatment of rats with cyclosporin A causes a diminution in myocardial peak contractile stress. There is an associated spontaneous sarcomere activity and rest depression of force in the absence of a change in myofilaments sensitivity to intracellular Ca2+. Here we investigated the potential protective effects of misoprostol on the myocardium of cyclosporin A-treated rats. Rats were treated with either cyclosporin A, misoprostol, or their combination. Force-[Ca2+]o and -[Sr2+]o, and force-interval relations as well as the sarcomere length were studied in trabeculae isolated from the right ventricles. At suboptimal [Ca2+]o, cyclosporin A shifted the force-[Ca2+]o relation to the left but reduced peak contractile stress by approximately 35% at the highest (optimal) [Ca2+]o. Co-treatment with misoprostol prevented the leftward shift, and treatment with misoprostol alone did not cause a leftward shift. The diminution of peak stress, however, did not recover with misoprostol treatment, and stress was further reduced. Treatment with only misoprostol also reduced stress generated by the muscles more than that by cyclosporin A alone. Intriguingly, activation of the myofilaments by Sr2+ failed to recover peak stress to control levels in any group treated with misoprostol. Unlike cyclosporin A, however, rest potentiation of force was more pronounced, and spontaneous sarcomere activity was absent with misoprostol. No histopathologic changes were observed with cyclosporin A or misoprostol treatment. Misoprostol modifies the cyclosporin A-induced changes in the Ca2+ handling, but further decreases the stress generated by the muscles.

In vitro and in vivo comparison of the low-resistance Groningen and the Provox tracheosophageal voice prostheses.

This study has been performed to evaluate and compare two frequently used indwelling tracheoesophageal voice prostheses, the low-resistance (LR) Groningen and the Provox voice prosthesis. The airflow resistance in vitro of the Provox prosthesis has been measured and compared to our reported results of the LR Groningen prosthesis. The in vivo study involved fifteen non-myotomized laryngectomees who randomly received one of the two prostheses. Measurements were performed of the intratracheal phonatory pressure and of voice parameters. The intelligibility of speech in noise was evaluated in eight patients. Patients preferences regarding the two prostheses were assessed. Aerodynamic measurements show the Provox voice prosthesis to have a lower airflow resistance. The median intratracheal phonatory pressure for phonation of 75 dB was significantly lower (2.1 kPa) in patients using the Provox voice prosthesis. Speech rate, maximal phonation time and maximal vocal intensity showed no significant difference. The intelligibility of speech in noise produced with the Provox was significantly better than the speech produced with the LR Groningen prosthesis. Subjectively, most patients preferred the Provox prosthesis because speech required less effort. Patients with a hypotonic pharyngoesophageal segment tended to prefer the LR Groningen prosthesis.

Excitation-contraction coupling in rat heart: influence of cyclosporin A.

OBJECTIVE: The aim was to investigate the steps in the excitation-contraction coupling process by which chronic exposure to cyclosporin A (cyclosporin) affects twitch force development by rat cardiac trabeculae. METHODS: The interval dependence and [Ca2+]o dependence of twitch force development by intact trabeculae isolated from myocardium of untreated rats and rats treated with cyclosporin (15 mg.kg-1.d-1 for 21 d) were studied in Krebs-Henseleit solution (K-H; pH 7.4 and 25 degrees C) and the force-pCa relation was examined in all trabeculae. RESULTS: The force-[Ca2+]o relation of cyclosporin treated trabeculae was shifted leftward compared to that of controls, but these trabeculae generated 35% less stress (force/cross sectional area) at optimal [Ca2+]o. Unlike control trabeculae, cyclosporin treated trabeculae showed spontaneous activity at all diastolic intervals, even at low [Ca2+]o. Treated and control trabeculae generated the same maximum stress [control: 78.1 (SEM 7.7) mN.mm-2, cyclosporin treated: 70.2(7.4) mN.mm-2] in the presence of extracellular Sr2+ ions in the Krebs-Henseleit medium. Maximum stress observed in the presence of Sr2+ was similar to the stress generated by maximum activation of chemically skinned trabeculae in both groups [control: 70(4.6) mN.mm-2; cyclosporin treated: 73(6.2) mN.mm-2). The force-pCa relation of cyclosporin treated muscles and control muscles after skinning were also indistinguishable [control pCa50 = 5.56(0.04); cyclosporin treated pCa50 = 5.58(0.03)]. The twitch force-interval relation at 0.7 mM [Ca2+]o in intact control trabeculae revealed postrest potentiation with a maximum [equivalent to 70% of twitch force at optimal [Ca2+]o -61.0(2.1) mN.mm-2] at 100 s and subsequent rest depression. Under the same conditions, twitch force development by cyclosporin treated trabeculae was closer to optimal force [41.4(7.1) mN.mm-2] at all intervals, and rest potentiation was reduced. Pronounced rest potentiation (as well as postextrasystolic potentiation) was still observed in cyclosporin treated trabeculae at [Ca2+]o < 0.7 mM. Postextrasystolic potentiation was reduced at 0.7 mM [Ca2+]o in these trabeculae, but the rate of decay of postextrasystolic potentiation and the rate of relaxation of the twitch force were unaffected. CONCLUSIONS: These results suggest that the changes in the sensitivity of intact rat myocardium to [Ca2+]o and in maximum force development induced by cyclosporin are not due to changes in myofilament properties. The increased twitch force development as well as the spontaneous activity at low [Ca2+]o may be due to facilitated Ca2+ release from the sarcoplasmic reticulum due to altered properties of the sarcoplasmic reticular Ca2+ release channel, as both are observed when twitch force is submaximal, suggesting that the sarcoplasmic reticulum was not overloaded with Ca2+. The decline in peak stress with cyclosporin at [Ca2+]o > approximately 1.0 mM can be explained on the basis of spontaneous release of Ca2+ during the interval between twitches which leaves less Ca2+ for release from the sarcoplasmic reticulum with each action potential.

Limited resolution of spectral contrast and hearing loss for speech in noise.

This paper examines the relations among the spectral contrast needed for speech intelligibility, hearing loss for speech in noise, and auditory filter bandwidth. Fifteen hearing-impaired listeners with relatively flat, mild-to-moderate sensorineural losses and eight normal-hearing listeners participated in the study. The spectral contrast needed for speech intelligibility was determined by reducing spectral contrast in the speech signal and measuring the reduction in contrast beyond which the speech-reception threshold (SRT) for sentences in noise increases. Reduction of spectral contrast was accomplished by smearing the envelope of the squared short-time fast Fourier transform by a convolution with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. Auditory filter bandwidth was determined by estimating auditory filter shapes at center frequencies of 0.8, 1.6, and 3.2 kHz, using a notched-noise masking paradigm. The results show that limited resolution of spectral contrast is only loosely associated with hearing loss for speech in noise. Moreover, the correlations between the SRT for unsmeared speech and the auditory filter bandwidth at various frequencies were weak.

Effect of spectral envelope smearing on speech reception. II.

This paper describes two experiments on the effect of reduced spectral contrast on the speech-reception threshold (SRT) for sentences in a background of interfering sound. Signal processing is performed by smoothing the envelope of the squared short-time fast Fourier transform by a convolution with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. In the first experiment the effect of reduced spectral contrast on the SRT for male speech is investigated and compared with previously obtained results for female speech [ter Keurs et al., J. Acoust. Soc. Am. 91, 2872-2880 (1992)]. Spectral energy is smeared over bandwidths of 1/8, 1/4, 1/3, 1/2, 1, 2, and 4 oct. The results show that, despite the differences in spectral pattern between male and female voices, the SRT in noise increases similarly for both voices for smearing bandwidths over 1/3 oct. In terms of the ripple density of the spectral envelope the results indicate that the range of lower spectral modulations, up to a limit of about 1.5 periods/oct, is sufficient for the intelligibility of speech in interfering sounds. In the second experiment the extent of the threshold difference between a speech masker and a noise masker is investigated for spectral smearing bandwidths of 1/2, 1, and 2 oct. The release from masking found for the speech masker relative to the (steady-state) noise masker decreases with spectral envelope smearing.

Effect of spectral envelope smearing on speech reception. I.

The effect of reduced spectral contrast on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification, was investigated with 16 normal-hearing subjects. Signal processing was performed by smoothing the envelope of the squared short-time fast Fourier transform (FFT) by convolving it with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. Spectral energy in the frequency region from 100 to 8000 Hz was smeared over bandwidths of 1/8, 1/4, 1/3, 1/2, 1, 2, and 4 oct for the SRT experiment. Vowel and consonant identification was studied for smearing bandwidths of 1/8, 1/2, and 2 oct. Results showed the SRT in noise to increase as the spectral energy was smeared over bandwidths exceeding the ear's critical bandwidth. Vowel identification suffered more from this type of processing than consonant identification. Vowels were primarily confused with the back vowels /c,u/, and consonants were confused where place of articulation is concerned.

Inotropic effects of cyclosporine in rat heart muscle.

Previous experiments have shown that long-term cyclosporine treatment in rats causes decreased systolic pressure development at any given preload of the left ventricle. The current experiments were designed to investigate the force-length and force-calcium relationship of papillary muscles from the right ventricles of rats that had received 15 mg/kg/day of cyclosporine subcutaneously for 3 weeks. Cyclosporine caused an increase of passive force at all muscle lengths, independent of the calcium concentration [Ca2+]o. Furthermore, cyclosporine enhanced twitch force at all muscle lengths at low [Ca2+]o relationship showed a decrease in the [Ca2+]o at which 50% of maximal force was generated in cyclosporine-treated muscle preparations compared with controls; at [Ca2+]o above 2.4 mmol/L, active force decreased by approximately 20% in muscles from cyclosporine-treated animals. The maximal force developed by papillary muscles from cyclosporine-treated animals was not different from that of control muscles: 45 mN/mm2 cross-sectional area, compared with 53 mN/mm2 respectively. We conclude that cyclosporine treatment causes increase in sensitivity for extracellular calcium, very likely reflecting an increased intracellular calcium concentration which, in the rat, may lead to calcium overload and decreased force development.