Ultrafast VLS growth of epitaxial beta- Ga(2)O(3) nanowires.

Well-defined monoclinic nanostructures of beta- Ga(2)O(3) were grown in a chemical vapor deposition apparatus using metallic gallium and oxygen as sources. Stable growth conditions were deduced for nanorods, nanoribbons, nanowires and cones. The types of nanostructures are determined by the growth temperature. We suppose that the vapor-solid growth mechanism rules the growth of nanoribbons and rods. For the nanowires we observed catalytic gold droplets atop, characteristic for the VLS growth mechanism with an extremely high growth rate of up to 10 microm min(-1). Nanowires grown on Al(2)O(3) substrates showed an excellent tendency to grow epitaxially, mapping the hexagonal symmetry of Al(2)O(3)(0001).

Enhanced speechreading in deaf adults: can short-term training/practice close the gap for hearing adults?

This study investigated effects of short-term training/practice on group and individual differences in deaf and hearing speechreaders. In two experiments, participants speechread sentences with feedback during training and without feedback during testing, alternating 10 times over six sessions spanning up to 5 weeks. Testing used sentence sets balanced for expected mean performance. In each experiment, participants were adults who reported good speechreading and either normal hearing (n = 8) or severe to profound hearing impairments (n = 8). The experiments were replicates, except that in one participants received vibrotactile speech stimuli in addition to visible speech during training, testing whether vibrotactile speech enhances speechreading learning. Results showed that (a) training/practice did not alter the relative performance among individuals or groups; (b) significant learning occurred when training and testing were conducted with speechreading only (although the magnitude of the effect was small); and (c) there was evidence that the vibrotactile training depressed rather than raised speechreading scores over the training period.

Is subjective word familiarity a meter of ambient language? A natural experiment on effects of perceptual experience.

The present study examined the sensitivity of a subjective familiarity measure to differences in word exposure within and between populations that differ dramatically in their perceptual experience. Descriptive measures of language ability and subjective familiarity ratings for 450 words were collected from a group of college-educated adults with normal hearing and a group of college-educated deaf adults. The results demonstrate the sensitivity of subjective familiarity ratings to both between- and within-group differences in word experience. Specifically, the deaf participants consistently rated words as less familiar than did hearing participants. Furthermore, item-level correlations within a participant group were higher than ones between groups. Within groups, mean familiarity ratings were correlated with descriptive measures of language ability. The results are discussed in relation to a simple sampling model of word experience and the language experience of the participant groups.

Phonetic priming, neighborhood activation, and PARSYN.

Perceptual identification of spoken words in noise is less accurate when the target words are preceded by spoken phonetically related primes (Goldinger, Luce, & Pisoni, 1989). The present investigation replicated and extended this finding. Subjects shadowed target words presented in the clear that were preceded by phonetically related or unrelated primes. In addition, primes were either higher or lower in frequency than the target words. Shadowing latencies were significantly longer for target words preceded by phonetically related primes, but only when the prime-target interstimulus interval was short (50 vs. 500 msec). These results demonstrate that phonetic priming does not depend on target degradation and that it affects processing time. We further demonstrated that PARSYN--a connectionist instantiation of the neighborhood activation model--accurately simulates the observed pattern of priming.

Phonotactics, neighborhood activation, and lexical access for spoken words.

Probabilistic phonotactics refers to the relative frequencies of segments and sequences of segments in spoken words. Neighborhood density refers to the number of words that are phonologically similar to a given word. Despite a positive correlation between phonotactic probability and neighborhood density, nonsense words with high probability segments and sequences are responded to more quickly than nonsense words with low probability segments and sequences, whereas real words occurring in dense similarity neighborhoods are responded to more slowly than real words occurring in sparse similarity neighborhoods. This contradiction may be resolved by hypothesizing that effects of probabilistic phonotactics have a sublexical focus and that effects of similarity neighborhood density have a lexical focus. The implications of this hypothesis for models of spoken word recognition are discussed.

Potential perceptual bases for successful use of a vibrotactile speech perception aid.

This paper examines the possibility that perception of vibrotactile speech stimuli is enhanced in adults with early and life-long use of hearing aids. We present evidence that vibrotactile aid benefit in adults is directly related to the age at which the hearing aid was fitted and the duration of its use. The stimulus mechanism responsible for this effect is hypothesized to be long-term vibrotactile stimulation by high powered hearing aids. We speculate on possible mechanisms for enhanced vibrotactile speech perception as the result of hearing aid use: (1) long-term experience receiving degraded or improverished speech stimuli results in a speech processing system that is more effective for novel stimuli, independent of perceptual modality; and/or (2) long-term sensory/perceptual experience causes neural changes that result in more effective delivery of speech information via somatosensory pathways.

Temporal and spatio-temporal vibrotactile displays for voice fundamental frequency: an initial evaluation of a new vibrotactile speech perception aid with normal-hearing and hearing-impaired individuals.

Four experiments were performed to evaluate a new wearable vibrotactile speech perception aid that extracts fundamental frequency (F0) and displays the extracted F0 as a single-channel temporal or an eight-channel spatio-temporal stimulus. Specifically, we investigated the perception of intonation (i.e., question versus statement) and emphatic stress (i.e., stress on the first, second, or third word) under Visual-Alone (VA), Visual-Tactile (VT), and Tactile-Alone (TA) conditions and compared performance using the temporal and spatio-temporal vibrotactile display. Subjects were adults with normal hearing in experiments I-III and adults with severe to profound hearing impairments in experiment IV. Both versions of the vibrotactile speech perception aid successfully conveyed intonation. Vibrotactile stress information was successfully conveyed, but vibrotactile stress information did not enhance performance in VT conditions beyond performance in VA conditions. In experiment III, which involved only intonation identification, a reliable advantage for the spatio-temporal display was obtained. Differences between subject groups were obtained for intonation identification, with more accurate VT performance by those with normal hearing. Possible effects of long-term hearing status are discussed.

Speechreading and the structure of the lexicon: computationally modeling the effects of reduced phonetic distinctiveness on lexical uniqueness.

A lexical modeling methodology was employed to examine how the distribution of phonemic patterns in the lexicon constrains lexical equivalence under conditions of reduced phonetic distinctiveness experienced by speech-readers. The technique involved (1) selection of a phonemically transcribed machine-readable lexical database, (2) definition of transcription rules based on measures of phonetic similarity, (3) application of the transcription rules to a lexical database and formation of lexical equivalence classes, and (4) computation of three metrics to examine the transcribed lexicon. The metric percent words unique demonstrated that the distribution of words in the language substantially preserves lexical uniqueness across a wide range in the number of potentially available phonemic distinctions. Expected class size demonstrated that if at least 12 phonemic equivalence classes were available, any given word would be highly similar to only a few other words. Percent information extracted (PIE) [D. Carter, Comput. Speech Lang. 2, 1-11 (1987)] provided evidence that high-frequency words tend not to reside in the same lexical equivalence classes as other high-frequency words. The steepness of the functions obtained for each metric shows that small increments in the number of visually perceptible phonemic distinctions can result in substantial changes in lexical uniqueness.