Mechanisms of neutropenia involving myeloid maturation arrest in burn sepsis.

OBJECTIVE: To determine the mechanisms that lead to the decrease in bone marrow production of neutrophils during burn sepsis. SUMMARY BACKGROUND DATA: Impaired bone marrow granulopoiesis during burn sepsis often results in neutropenia despite elevated circulating levels of granulocyte colony-stimulating factor (G-CSF). To date, neither the specific stages of neutrophil maturation involved in the bone marrow suppression nor the mechanisms for the impairment have been determined. METHODS: Peripheral blood absolute neutrophil count and G-CSF levels were determined in mice 3 days after randomization to control, burn alone, or burn plus a topical inoculation of Pseudomonas aeruginosa (1000 colony-forming units). Bone marrow aspirates were analyzed for their neutrophil differentiation patterns by Gr-1 antigen expression and their G-CSF receptor status. Histologic analysis of liver, lung, spleen, and wound site was performed. RESULTS: In burn sepsis, absolute neutrophil count was reduced whereas plasma G-CSF levels were elevated, and myeloid differentiation was significantly shifted toward the immature mitotic myeloid cells. Bone marrow G-CSF receptor mRNA levels and G-CSF-stimulated proliferation were substantially decreased in burn sepsis. Histologic analysis revealed no significant neutrophil infiltration into the tissues. CONCLUSIONS: In thermal injury with superimposed sepsis, neutropenia and myeloid maturation arrest, despite the elevated levels of G-CSF, correlate with the reduction in bone marrow G-CSF receptor expression. These observations may provide a potential mechanism for neutropenia in sepsis.

The transmission of phoneme-level information by multichannel tactile speech perception aids.

Current research on the effectiveness of tactile aids for speech perception by hearing-impaired persons suggests that substantial training, lasting over months or years, is necessary for users to achieve maximal benefits from a tactile device. A number of studies have demonstrated the usefulness of training programs that include an analytic component, such as phoneme training, together with more synthetic tasks such as sentence identification and speech tracking. However, particularly in programs for children, it is desirable to structure training experiences so that easy distinctions are trained first, and more difficult distinctions are approached only later in training. In the present study, a systematic evaluation of phoneme-level information provided by the Tactaid VII, a multichannel tactile aid, was performed. Adult subjects were tested in minimal pairs and closed set phoneme discrimination and identification tasks under tactile aid alone, speechreading alone, and speechreading plus tactile aid conditions, to provide an inventory of stimulus identifiability and permit ranking of discriminations as easy or more difficult. Because these rankings might differ as a function of coarticulation effects, three different vowel contexts were tested for consonant stimuli. Results indicated that there were indeed considerable differences across vowel contexts, and that the /ae/ vowel context yielded the most identifiable stimuli. These data could be used by teachers and therapists to construct viable stimulus sets for training programs for tactile aid users.

Comparative effectiveness of correction strategies in connected discourse tracking.

The effectiveness of four correction strategies commonly used in connected discourse tracking was investigated in the present study. The strategies were 1) verbatim repetition of a word or phrase; 2) use of antonyms or synonyms as cues; 3) use of phonemic cues, with no whole word repetition; and 4) going back or ahead in the text, with no repetition of the missed segment. Four normal-hearing adults served as listeners. Live-voice presentation of text by two female talkers was employed for all conditions. Listeners were tested in two stimulus presentation modes, speechreading alone and speechreading plus a multichannel tactile aid. Results indicated that strategy 1, repetition of the missed segment, produced the highest tracking rates, significantly higher than any of the other strategies. Strategy 2 produced the lowest tracking rates. Strategies 1 and 3 yielded the lowest percentage of initially missed words, or blockages, and strategy 4 the highest percentage. Significantly higher tracking rates were found under the speechreading plus tactile aid presentation mode, compared with speechreading alone. Further, tracking rates increased significantly from the beginning to the end of training. Data were compared with a more typical CDT task, in which all correction strategies were operative, and results showed little difference in tracking rates between this task and the constrained CDT employing only strategy 1. Overall, results suggest that simple repetition of missed segments is an effective correction strategy for CDT and argue for its inclusion in computer-assisted tracking implementations.

Vibrotactile temporal masking: effects of multiple maskers.

Previous investigations of temporal masking effects in vibrotactile detection tasks have generally produced results suggesting considerable similarities in stimulus processing between the tactile system and the auditory system. Auditory presentation of combinations of maskers (e.g., two forward maskers) has yielded masking effects in excess of the level of masking predicted by a simple intensity sum of each masker's individual effect. This "additional masking" has led to predictions of compressive nonlinearities in auditory stimulus processing. In the present study, two experiments were conducted to investigate further temporal masking phenomena for the tactile system. In the first experiment vibrotactile temporal masking functions for single forward and backward maskers were generated to examine trade-offs among values of masker duration, masking intensity, and interstimulus interval to maintain constant detectability of a target. Results suggested that stimuli in very close temporal proximity to the target might follow somewhat different trading equations from those farther removed. Overall, results were consistent with previous findings of temporal integration in the tactile system, and support the notion of an energy integrating mechanism. In the second experiment, pairs of maskers were presented to determine whether additional masking effects occurred in vibrotactile detection. In contrast to findings for auditory presentation, in which all masker configurations generated additional masking, the tactile results showed substantial amounts of additional masking only for pairs of backward maskers. Several possible explanations for this results are evaluated, and results are discussed in terms of similarities and dissimilarities in auditory and tactile temporal processing.

Evaluation of a principal-components tactile aid for the hearing-impaired.

Principal component analysis, a statistical data reduction technique which can be used to eliminate redundant information, has shown promising results as a speech coding strategy in auditory perceptual studies. The present study describes the development, modification, and evaluation of a principal components-based tactile aid for speech perception by the hearing-impaired. In this device, the first two principal components of an input speech signal were displayed on two-dimensional arrays of vibrators contacting either the fingertip or the forearm. Initial testing of the device with closed-set recorded speech tokens showed fair recognition performance, reaching 57% for three consonants and 56% for four vowels. Modifications to the processor algorithm designed to improve vowel recognizability resulted in higher levels of performance (66% for eight vowels). A real-time prototype was constructed implementing the revised algorithm. Live-voice testing was conducted with six normal-hearing subjects, three of whom had previous training with the Queen's University vocoder, a multichannel tactile vocoder that has shown promising results. Performance of these "trained" subjects for both single-item and connected speech tasks was excellent, equalling levels obtained with the Queen's vocoder. These results suggest that a principal components design may be a promising alternative to a vocoder strategy for a tactile aid. Results for the "naive" subjects did not reach the levels attained by the trained subjects, a finding partially attributed to the short training period available to the naive subjects. The higher level of performance for the trained subjects, together with the similarity of performance for the principal components aid and the Queen's vocoder for these subjects, suggests that they were able to transfer previous learning with the Queen's vocoder to the principal components device.

Relative performance of single-channel and multichannel tactile aids for speech perception.

Although the results from a number of studies of the performance of multichannel tactile aids for speech perception have suggested that such devices might provide more benefit to hearing-impaired persons than single-channel tactile aids (3,4), recent studies involving direct comparisons of multichannel and single-channel vibrotactile aids (5,6) indicated otherwise. In fact, for some types of speech information, such as rhythm and stress perception, single-channel aids were shown to be superior. The present study attempted to address this apparent discrepancy by comparing the performance of two single-channel devices with two multichannel devices in a variety of speech perception tasks including both single-item and connected speech stimuli. Results indicated that the two classes of tactile device performed similarly in rhythm and stress perception, but that the multichannel aids in many cases showed better performance for tasks in which the identification of fine-structure phoneme information was required (both single-item and connected speech). Results are discussed in terms of the possibility that the performance of a specific multichannel tactile aid cannot be considered indicative of all devices of the same class.

Evaluating tactile aids for speech perception and production by hearing-impaired adults and children.

The type and degree of benefit provided by tactile aids for the hearing-impaired varies from device to device, as a function of such variables as the number of tactile transducers, type of stimulation, location of stimulation, and the nature of processing of the input acoustic waveform. In this paper the results from evaluations of tactile devices in our laboratory are discussed, to provide some insights into the amount of assistance that might be expected from the use of different tactile aids in different listening tasks. A number of perceptual tasks have been evaluated, ranging from simple detection of a stimulus to the tracking of connected speech. The results of these evaluations suggest that tactile aids, particularly multichannel devices that employ a number of tactile transducers and convey information about the spectral content of the speech signal, can be of significant benefit in speech perception. Further studies with profoundly hearing-impaired children indicate that aspects of speech production can also be improved through the use of a multichannel tactile aid, as evidenced from judgments of videotaped productions shown to teachers of the hearing-impaired. These findings suggest that even a relatively brief period of training with a tactile aid can lead to improvements in speech production by hearing-impaired children.

Masker fringe and binaural detection.

Yost [J. Acoust. Soc. Am. 78,901-907 (1985)] found that the detectability of a 30-ms dichotic signal (S pi) in a 30-ms diotic noise (No) was not affected by the presence of a 500-ms dichotic forward fringe (N pi). Kollmeier and Gilkey [J. Acoust. Soc. Am. 87, 1709-1719, (1990)] performed a somewhat different experiment and varied the onset time of a 25-ms S pi signal in a 750-ms noise that switched, after 375-ms, from N pi to No. In contrast to Yost, they found that the N pi segment of the noise reduced the detectability of the signal even when the signal was temporally delayed well into the No segment of the noise and suggested that the N pi segment of noise acted as a forward masker. To resolve this apparent conflict, the present study investigated the detectability of a brief S pi signal in the presence of an No masker of the same duration as the signal. The masker was preceded by quiet or an N pi forward fringe and followed by quiet, an No, or N pi backward fringe. The present study differs from most previous studies of the effects of the masker fringe in that the onset time of the signal was systematically varied to examine how masking changes during the time course of the complex fringe-masker-fringe stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of two multichannel tactile aids for the hearing impaired.

Two multichannel tactile devices for the hearing impaired were compared in speech perception tasks of varying levels of complexity. Both devices implemented the "vocoder" principle in their stimulus processing: One device had a 16-element linear vibratory array worn on the forearm and displayed activity in 16 overlapping frequency channels; the other device delivered tactile stimulation to a linear array of 16 electrodes worn on the abdomen. Subjects were tested in several phoneme discrimination tasks, ranging from discrimination of pairs of words differing in only one phoneme under tactile aid alone conditions to identification of stimuli in a larger set under tactile aid alone, lipreading alone, and lipreading plus tactile aid conditions. Results showed both devices to be better transmitters of manner and voicing features of articulation than of place features, when tested in single-item tasks. No systematic differences in performance with the two devices were observed. However, in a connected discourse tracking task, the vibrotactile vocoder in conjunction with lipreading yielded much greater improvements over lipreading alone than did the electrotactile vocoder. One possible explanation for this difference in performance, the inclusion of a noise suppression circuit in the electrotactile aid, was evaluated, but did not appear to account for the differences observed. Results are discussed in terms of additional differences between the two devices that may influence performance.

Evaluation of the Siemens Minifonator vibrotactile aid.

The Siemens Hearing Instruments Minifonator, a single-channel, wrist-worn vibrotactile aid, was evaluated in a laboratory setting with hearing-impaired adults. Eight subjects, with hearing loss greater than 70 dB in the better ear, were administered a test battery including sound-field detection, speech awareness threshold, environmental sound identification, syllable rhythm and stress categorization, and sentence identification subtests. Performance on each subtest was compared for hearing-aided and tactile-aided conditions. Mean performance levels for the two conditions were comparable for all but one subtest. However, closer inspection revealed that the data for the hearing-aided condition were bimodal: some subjects proved to be good hearing aid users and other performed at chance levels with their hearing aids. Performance in the tactile-aided conditions did not show such variability and mean levels fell between the hearing-aided levels for "good" and "poor" hearing aid users. The effects of training with the device were assessed for two normal-hearing subjects, who were trained in 1-hour daily sessions over a several week period on the environmental sounds and syllable rhythm and stress subtests. Results indicated substantial improvements in performance over the course of training. The implications of these results for long-term use of the device are discussed.

Comparison of two single-channel vibrotactile aids for the hearing-impaired.

Two commercially available single-channel vibrotactile aids, designed to transmit information about acoustic stimuli to persons who cannot perceive such stimuli through conventional amplification, were compared in a number of tasks with the same subjects. Both devices employed a vibratory transducer worn on the wrist. One device represented characteristics of the envelope of the waveform by using it to modulate the amplitude of a 250-Hz carrier vibration (an amplitude-modulated, or AM, signal). The other device presented and amplitude-modulated a broad-band signal whose spectral characteristics preserved information about the signal. Subjects performed several tasks. On some tasks (sound detection, environmental sound identification, syllable rhythm and stress categorization) information about the envelope of the stimulus was expected to be sufficient for good performance. On others (speech sound recognition) additional information about the spectral fine structure of the signal spectrum was anticipated to be required for good performance. Results indicated that the subjects performed comparably with both devices on all tasks, suggesting that they did not make use of the spectral information available in the more complex signal.

The role of tactile aids in providing information about acoustic stimuli.

Devices that convert sound patterns into patterns of vibrotactile stimulation have been shown in laboratory and clinical studies to enable persons to appreciate many aspects of the acoustic environment, and thus are of potential benefit to deaf persons. In the present article, a framework is outlined for describing normal listening situations as a hierarchy of tasks requiring increasingly complex analysis of the acoustic waveform, including sound detection, environmental sound identification, syllable rhythm and stress categorization, phoneme and word identification, and comprehension of connected speech. The types of benefits provided by tactile aids in each of these tasks are exemplified using data from studies of single-channel commercially available devices and multichannel tactile vocoders in our own and other laboratories. The discussion of these data addresses such issues as the features of the acoustic environment that can or should be transmitted through a tactile aid, the differences in the information transmitted by commercially available versus experimental laboratory devices, the comparison of tactile aids and cochlear implants, and the technical problems that remain to be overcome in the design and evaluation of improved vibrotactile aids.

Development and preliminary evaluation of an earmold sound-to-tactile aid for the hearing-impaired.

A binaural earmold sound-to-tactile aid was constructed by inserting a vibrating element into a Lucite earmold. The earmold could be vibrated at either 80 Hz (when incoming acoustic signals were below 2000 Hz), at 300 Hz (when incoming acoustic signals were above 2000 Hz), or both (when incoming acoustic signals were broadband). Subjects were fitted with one of these bimodal vibrating earmolds in each ear. Normal-hearing and hearing-impaired subjects were tested in three tasks: sound localization, environmental sound identification, and syllable rhythm and stress. The device provided some benefit to performance, although the amounts of improvement varied across tasks and subjects. Possible modifications in device design, and potential combinations of auditory and tactile input via earmold systems, are discussed.

Sensitivity to amplitude-modulated vibrotactile signals.

Temporal modulation transfer functions were measured for sinusoidally amplitude-modulated vibratory stimuli delivered to the thenar eminence of the hand. Results for sinusoidal carriers at 25, 50, 100, and 250 Hz reflected greater sensitivity to modulation than those for either broadband or narrow-band noise carriers. The correspondence of these results to other measures of temporal sensitivity in the tactile system was examined. In addition, findings are discussed in view of their relevance to comparisons across sensory modalities, and to the design of vibrotactile aids for hearing-impaired persons.