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C R Lansing

Publications and source records attributed to C R Lansing.

12 recordsLinked to original sources
PubMed2001

A two-microphone dual delay-line approach for extraction of a speech sound in the presence of multiple interferers.

This paper describes algorithms for signal extraction for use as a front-end of telecommunication devices, speech recognition systems, as well as hearing aids that operate in noisy environments. The development was based on some independent, hypothesized theories of the computational mechanics of biological systems in which directional hearing is enabled mainly by binaural processing of interaural directional cues. Our system uses two microphones as input devices and a signal processing method based on the two input channels. The signal processing procedure comprises two major stages: (i) source localization, and (ii) cancellation of noise sources based on knowledge of the locations of all sound sources. The source localization, detailed in our previous paper [Liu et al., J. Acoust. Soc. Am. 108, 1888 (2000)], was based on a well-recognized biological architecture comprising a dual delay-line and a coincidence detection mechanism. This paper focuses on description of the noise cancellation stage. We designed a simple subtraction method which, when strategically employed over the dual delay-line structure in the broadband manner, can effectively cancel multiple interfering sound sources and consequently enhance the desired signal. We obtained an 8-10 dB enhancement for the desired speech in the situations of four talkers in the anechoic acoustic test (or 7-10 dB enhancement in the situations of six talkers in the computer simulation) when all the sounds were equally intense and temporally aligned.

Algorithms↗
PubMed2000

Localization of multiple sound sources with two microphones.

This paper presents a two-microphone technique for localization of multiple sound sources. Its fundamental structure is adopted from a binaural signal-processing scheme employed in biological systems for the localization of sources using interaural time differences (ITD). The two input signals are transformed to the frequency domain and analyzed for coincidences along left/right-channel delay-line pairs. The coincidence information is enhanced by a nonlinear operation followed by a temporal integration. The azimuths of the sound sources are estimated by integrating the coincidence locations across the broadband of frequencies in speech signals (the "direct" method). Further improvement is achieved by using a novel "stencil" filter pattern recognition procedure. This includes coincidences due to phase delays of greater than 2pi, which are generally regarded as ambiguous information. It is demonstrated that the stencil method can greatly enhance localization of lateral sources over the direct method. Also discussed and analyzed are two limitations involved in both methods, namely missed and artifactual sound sources. Anechoic chamber tests as well as computer simulation experiments showed that the signal-processing system generally worked well in detecting the spatial azimuths of four or six simultaneously competing sound sources.

Adult↗
PubMed1999

Attention to facial regions in segmental and prosodic visual speech perception tasks.

Two experiments were conducted to test the hypothesis that visual information related to segmental versus prosodic aspects of speech is distributed differently on the face of the talker. In the first experiment, eye gaze was monitored for 12 observers with normal hearing. Participants made decisions about segmental and prosodic categories for utterances presented without sound. The first experiment found that observers spend more time looking at and direct more gazes toward the upper part of the talker's face in making decisions about intonation patterns than about the words being spoken. The second experiment tested the Gaze Direction Assumption underlying Experiment 1--that is, that people direct their gaze to the stimulus region containing information required for their task. In this experiment, 18 observers with normal hearing made decisions about segmental and prosodic categories under conditions in which face motion was restricted to selected areas of the face. The results indicate that information in the upper part of the talker's face is more critical for intonation pattern decisions than for decisions about word segments or primary sentence stress, thus supporting the Gaze Direction Assumption. Visual speech perception proficiency requires learning where to direct visual attention for cues related to different aspects of speech.

Adult↗
PubMed1995

Priming the visual recognition of spoken words.

A preliminary investigation was conducted to understand the effects of word visibility and prime association factors on visual spoken word recognition in lipreading, using a related/ unrelated prime-target paradigm. Prime-target pairings were determined on the basis of paper-and-pencil word associations completed by 85 participants with normal hearing. Spoken targets included 60 single-syllable Modified Rhyme Test words, prerecorded on laser video disc. Participants included 20 individuals with normal hearing and at least average lipreading skill for sentence-length materials. In related prime-target pairings, more targets with a high prime association were identified than with a low prime association. In unrelated prime-target pairings, a larger number of more-visible than less-visible targets was correctly identified. Individual participant differences were not statistically significant. Results from the present study suggest implications for models of visual spoken word recognition.

Adult↗
PubMed1995

Visual word recognition in two facial motion conditions: full-face versus lips-plus-mandible.

The present study used a new method to develop video sequences that limited exposure of facial movement. A repeated-measures design was used to investigate the visual recognition of 60 monosyllabic spoken words, presented in an open set format, for two face exposure conditions (full-face vs. lips-plus-mandible). Twenty-six normal hearing college students and 4 adults with bilateral sensorineural hearing loss speechread a video laserdisc presentation of a male talker under the two face exposure conditions. Percent phoneme correct scores were similar in the part-face and full-face conditions. However, scores significantly improved for the repeated measure independent of the face exposure condition observed. The results suggested that speechreaders (a) can recognize monosyllabic words in video sequences that provide information only about movements of the lips-plus-mandible region and (b) are sensitive to practice effects.

Adult↗
PubMed1994

Deriving passage difficulties for a tracking study via the Cloze technique.

The current report demonstrates the importance of formally accounting for passage difficulty when using the tracking procedure. Cloze responses to 82 encyclopedia excerpts (343-349 words each) were obtained from a large pool of normal-hearing adults and scored verbatim. Passage difficulty, derived via ANOVA, was then defined as the deviation of a passage's mean Cloze score from the score for all passages, corrected for differences among respondents. The passage difficulties were applied in an alternating conditions tracking experiment with one adult cochlear implant user. Conditions included conventional auditory-visual and auditory-only tracking and experimental mode-switching techniques in which the talker changed modalities during the correction phase. An ANCOVA of the word-per-minute scores was conducted, with passage difficulty as a covariate and passage adjustment values as the output. Tracking rates and percentage of words correct from the beginning and end of training were examined. Use of adjusted data reversed the interpretation of performance change, demonstrating the need for determining passage difficulties a priori.

Audiometry↗
PubMed1994

Communication strategies of adult cochlear implant candidates.

Adult cochlear implant candidates' abilities to cope with communication breakdown were assessed using the Communication Strategies Task (CST). Forty adult cochlear implant candidates with acquired hearing losses and 10 adults with normal hearing served as subjects. Appropriateness of responses to the CST were rated by 10 certified speech-language pathologists and audiologists. Seventy-six percent of the subjects demonstrated difficulty identifying onset or resolution of communication breakdown, communicators' feelings, factors contributing to communication breakdown, and appropriate repair strategies. The responses of individuals with sudden hearing losses did not differ significantly from the responses of individuals with progressive hearing losses. Response patterns did not correlate with the age of onset of the hearing loss, duration of deafness, age at the time of evaluation, or educational background. The results of this study suggest that ability to cope with communication breakdown must be evaluated on an individual basis.

Adaptation, Psychological↗
PubMed1992

Natural vowel perception by patients with the ineraid cochlear implant.

Vowel recognition was tested in 10 patients using the Ineraid cochlear implant. The vowels were produced by a male speaker in the context 'heed, hid, head, had, hawed, hood, who'd, hud' and 'heard'. Performance varied from 34 to 93% correct. A descriptive feature system for the vowels was determined from an acoustic analysis. An information transfer analysis of these features suggested that information about the first formant frequency, vowel duration and fundamental frequency was transmitted. Information about the second and third formant frequency was transmitted less well. A sequential information transmission analysis suggested that the features of the first formant and duration accounted for nearly 80% of the information transmitted. The fundamental frequency and second formant frequency information accounted for an additional 8%. Information provided by the third formant frequency was largely redundant.

Adult↗
PubMed1991

Melodic, rhythmic, and timbral perception of adult cochlear implant users.

The purpose of this pilot study was to investigate adult Ineraid and Nucleus cochlear implant (CI) users' perceptual accuracy for melodic and rhythmic patterns, and quality ratings for different musical instruments. Subjects were 18 postlingually deafened adults with CI experience. Evaluative measures included the Primary Measures of Music Audiation (PMMA) and a Musical Instrument Quality Rating. Performance scores on the PMMA were correlated with speech perception measures, music background, and subject characteristics. Results demonstrated a broad range of perceptual accuracy and quality ratings across subjects. On these measures, performance for temporal contrasts was better than for melodic contrasts independent of CI device. Trends in the patterns of correlations between speech and music perception suggest that particular structural elements of music are differentially accessible to cochlear implant users. Additionally, notable qualitative differences for ratings of musical instruments were observed between Nucleus and Ineraid users.

Adult↗
PubMed1990

The relationship between communication problems and psychological difficulties in persons with profound acquired hearing loss.

Communication strategies, accommodations to deafness, and perceptions of the communication environment by profoundly deaf subjects were correlated with indices of psychosocial adjustment to determine whether accommodations to deafness could play a role in the presence of psychological difficulties among deaf persons. Persons with postlingually acquired profound deafness were administered the Communication Profile for the Hearing Impaired (CPHI) and several standardized tests of psychological functioning and adjustment. Inadequate communication strategies and poor accommodations to deafness reported on the CPHI were associated with depression, social introversion, loneliness, and social anxiety. Limited communication performance at home and with friends was related to both social introversion and the experience of loneliness; perceived attitudes and behaviors of others correlated with depression as well as loneliness. In general, the pattern of correlations obtained suggests that specific communication strategies and accommodations to deafness, rather than deafness per se, may contribute to the presence of some psychological difficulties in individuals.

Adult↗
PubMed1986

Previous experience as a confounding factor in comparing cochlear-implant processing schemes.

It is of great importance to compare the relative merits of different cochlear-implant speech-processing strategies. Some groups have compared different strategies within single subjects, but usually the subject has prior experience with one strategy, and no allowance is made for this prior experience. We show in the present study that this is inappropriate. We tested one subject using the Melbourne (Cochlear Corp.) multichannel implant with the device set to process sounds in two different ways. In the first processing scheme, the device functioned normally, extracting information about voicing frequency, amplitude and second-formant frequency. This information activated the 21-channel device, determining pulse rate, pulse amplitude and electrode position (respectively). In the second processing scheme, a single electrode (with the largest dynamic range) was activated. This electrode coded overall amplitude and voicing frequency. The subject was tested on an audiovisual test of a 14-choice consonant recognition in the form /iCi/ over a period of over 4 months. During this time the subject used the 21-channel processor outside of the laboratory. Upon initial connection, there was little difference between the results obtained with the two schemes when tested in sound alone or in sound plus vision. However, after about 4 months, scores obtained with the 21-channel processor in sound plus vision were superior to the scores obtained with the one channel. This advantage came from a superiority in the features of voicing and nasality, but not place. Scores for sound-alone conditions between the two processing schemes remained similar for the 4-month period.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Threshold↗