Rapid but specific perceptual learning partially explains individual differences in the recognition of challenging speech.

Perceptual learning for speech, defined as long-lasting changes in speech recognition following exposure or practice occurs under many challenging listening conditions. However, this learning is also highly specific to the conditions in which it occurred, such that its function in adult speech recognition is not clear. We used a time-compressed speech task to assess learning following either brief exposure (rapid learning) or additional training (training-induced learning). Both types of learning were robust and long-lasting. Individual differences in rapid learning explained unique variance in recognizing natural-fast speech and speech-in-noise with no additional contribution for training-induced learning (Experiment 1). Rapid learning was stimulus specific (Experiment 2), as in previous studies on training-induced learning. We suggest that rapid learning is key for understanding the role of perceptual learning in online speech recognition whereas longer training could provide additional opportunities to consolidate and stabilize learning.

Identification, Analysis and Characterization of Base Units of Bird Vocal Communication: The White Spectacled Bulbul (Pycnonotus xanthopygos) as a Case Study.

Animal vocal communication is a broad and multi-disciplinary field of research. Studying various aspects of communication can provide key elements for understanding animal behavior, evolution, and cognition. Given the large amount of acoustic data accumulated from automated recorders, for which manual annotation and analysis is impractical, there is a growing need to develop algorithms and automatic methods for analyzing and identifying animal sounds. In this study we developed an automatic detection and analysis system based on audio signal processing algorithms and deep learning that is capable of processing and analyzing large volumes of data without human bias. We selected the White Spectacled Bulbul (Pycnonotus xanthopygos) as our bird model because it has a complex vocal communication system with a large repertoire which is used by both sexes, year-round. It is a common, widespread passerine in Israel, which is relatively easy to locate and record in a broad range of habitats. Like many passerines, the Bulbul's vocal communication consists of two primary hierarchies of utterances, syllables and words. To extract each of these units' characteristics, the fundamental frequency contour was modeled using a low degree Legendre polynomial, enabling it to capture the different patterns of variation from different vocalizations, so that each pattern could be effectively expressed using very few coefficients. In addition, a mel-spectrogram was computed for each unit, and several features were extracted both in the time-domain (e.g., zero-crossing rate and energy) and frequency-domain (e.g., spectral centroid and spectral flatness). We applied both linear and non-linear dimensionality reduction algorithms on feature vectors and validated the findings that were obtained manually, namely by listening and examining the spectrograms visually. Using these algorithms, we show that the Bulbul has a complex vocabulary of more than 30 words, that there are multiple syllables that are combined in different words, and that a particular syllable can appear in several words. Using our system, researchers will be able to analyze hundreds of hours of audio recordings, to obtain objective evaluation of repertoires, and to identify different vocal units and distinguish between them, thus gaining a broad perspective on bird vocal communication.

Effects of stimulus repetition and training schedule on the perceptual learning of time-compressed speech and its transfer.

Perceptual learning can facilitate the recognition of hard-to-perceive (e.g., time-compressed or spectrally-degraded) speech. Although the learning induced by training with time-compressed speech is robust, previous findings suggest that intensive training yields learning that is partially specific to the items encountered during practice. Here, we asked whether three parameters of the training procedure - the overall number of training trials (training intensity), how these trials are distributed across sessions, and the number of semantically different items encountered during training (set size) - influence learning and transfer. Different groups of participants (69 normal-hearing young adults; nine to 11 participants/group) completed different training protocols (or served as an untrained control group) and tested on the recognition of time-compressed sentences taken from the training set (learning), new time-compressed sentences presented by the trained talker (semantic transfer), and time-compressed sentences taken from the training set but presented by a different talker (acoustic transfer). Compared to untrained listeners, all training protocols yielded both learning and transfer. More intense training resulted in greater item-specific learning and greater acoustic transfer than less intense training with the same number of training sessions. Training on a smaller set size (i.e., greater token repetition during training) also resulted in greater acoustic transfer, whereas distributing practice over a number of sessions improved semantic transfer. Together, these data suggest that whereas practice on a small set that results in stimulus repetition during training is not harmful for learning, distributed training can support transfer to new stimuli, perhaps because it provides multiple opportunities to consolidate learning.

The effects of exposure and training on the perception of time-compressed speech in native versus nonnative listeners.

The present study investigated the effects of language experience on the perceptual learning induced by either brief exposure to or more intensive training with time-compressed speech. Native (n = 30) and nonnative (n = 30) listeners were each divided to three groups with different experiences with time-compressed speech: A trained group who trained on the semantic verification of time-compressed sentences for three sessions, an exposure group briefly exposed to 20 time-compressed sentences, and a group of naive listeners. Recognition was assessed with three sets of time-compressed sentences intended to evaluate exposure-induced and training-induced learning as well as across-token and across-talker generalization. Learning profiles differed between native and nonnative listeners. Exposure had a weaker effect in nonnative than in native listeners. Furthermore, native and nonnative trained listeners significantly outperformed their untrained counterparts when tested with sentences taken from the training set. However, only trained native listeners outperformed naive native listeners when tested with new sentences. These findings suggest that the perceptual learning of speech is sensitive to linguistic experience. That rapid learning is weaker in nonnative listeners is consistent with their difficulties in real-life conditions. Furthermore, nonnative listeners may require longer periods of practice to achieve native-like learning outcomes.

Increasing stimulus duration improves attention and memory performance in elderly with cognitive impairment.

OBJECTIVES: In this study, we investigated whether increasing stimulus duration could improve performance on a test of attention and short-term memory in cognitively impaired individuals. METHODS: A computer-generated forward digit span test was administered to 65 patients with mild cognitive impairment or dementia (28 intervention and 37 controls). After point of failure, testing in the intervention group was continued at the same rate, but with an average 150% digit lengthening to 800 ms. Testing of controls was continued using the standard digit span test. RESULTS: In the intervention group, 13/28 (46.4%) improved their digit span test performance, compared to 2/37 (5.4%) in the control group (p = 0.00005). CONCLUSION: Cognitively impaired elderly participants improved performance on a test of attention and short-term memory, when stimulus duration was increased in proportion to elongation of the finger tap touch-phase previously found in a similar cohort. A possible mechanism for the effect of increased stimulus duration on attention and short-term memory is discussed.

The effects of training length on the perceptual learning of time-compressed speech and its generalization.

Brief exposure to time-compressed speech yields both learning and generalization. Whether such learning continues over the course of multi-session training and if so whether it is more or less specific than exposure-induced learning is not clear, because the outcomes of intensive practice with time-compressed speech have rarely been reported. The goal here was to determine whether prolonged training on time-compressed speech yields additional learning and generalization beyond that induced by brief exposure. Listeners practiced the semantic verification of time-compressed sentences for one or three training sessions. Identification of trained and untrained tokens was subsequently compared between listeners who trained for one or three sessions, listeners who were briefly exposed to 20 time-compressed sentences and naive listeners. Trained listeners outperformed the other groups of listeners on the trained condition, but only the group that was trained for three sessions outperformed the other groups when tested with untrained tokens. These findings suggest that although learning of distorted speech can occur rapidly, more stable learning and generalization might be achieved with longer, multi-session practice. It is suggested that the findings are consistent with the framework proposed by the Reverse Hierarchy Theory of perceptual learning.

Association between finger tapping, attention, memory, and cognitive diagnosis in elderly patients.

This study examined the association between spontaneous finger tapping and cognitive function, with a detailed analysis of the two main phases of finger tapping, the touch-phase and the off-phase. 170 elderly patients (83 men, 87 women; M age = 82.1 yr., SD = 6.2) underwent cognitive assessment including the Mini-Mental State Examination, a forward digit span test, and 15 sec. of finger tapping. Results indicated a significant increase in the length and variability of the finger-touch phase among participants with mild cognitive impairment or dementia compared to participants with no cognitive impairment, suggesting a relationship between finger tapping and attention, short-term memory, and cognitive diagnosis. Pattern classification analyses on the finger tapping parameters indicated a specificity of 0.91 and sensitivity of 0.52 for ruling out cognitive impairment.

Perceptual learning of time-compressed speech: more than rapid adaptation.

BACKGROUND: Time-compressed speech, a form of rapidly presented speech, is harder to comprehend than natural speech, especially for non-native speakers. Although it is possible to adapt to time-compressed speech after a brief exposure, it is not known whether additional perceptual learning occurs with further practice. Here, we ask whether multiday training on time-compressed speech yields more learning than that observed during the initial adaptation phase and whether the pattern of generalization following successful learning is different than that observed with initial adaptation only. METHODOLOGY/PRINCIPAL FINDINGS: Two groups of non-native Hebrew speakers were tested on five different conditions of time-compressed speech identification in two assessments conducted 10-14 days apart. Between those assessments, one group of listeners received five practice sessions on one of the time-compressed conditions. Between the two assessments, trained listeners improved significantly more than untrained listeners on the trained condition. Furthermore, the trained group generalized its learning to two untrained conditions in which different talkers presented the trained speech materials. In addition, when the performance of the non-native speakers was compared to that of a group of naïve native Hebrew speakers, performance of the trained group was equivalent to that of the native speakers on all conditions on which learning occurred, whereas performance of the untrained non-native listeners was substantially poorer. CONCLUSIONS/SIGNIFICANCE: Multiday training on time-compressed speech results in significantly more perceptual learning than brief adaptation. Compared to previous studies of adaptation, the training induced learning is more stimulus specific. Taken together, the perceptual learning of time-compressed speech appears to progress from an initial, rapid adaptation phase to a subsequent prolonged and more stimulus specific phase. These findings are consistent with the predictions of the Reverse Hierarchy Theory of perceptual learning and suggest constraints on the use of perceptual-learning regimens during second language acquisition.

The action of selection on codon bias in the human genome is related to frequency, complexity, and chronology of amino acids.

BACKGROUND: The question of whether synonymous codon choice is affected by cellular tRNA abundance has been positively answered in many organisms. In some recent works, concerning the human genome, this relation has been studied, but no conclusive answers have been found. In the human genome, the variation in base composition and the absence of cellular tRNA count data makes the study of the question more complicated. In this work we study the relation between codon choice and tRNA abundance in the human genome by correcting relative codon usage for background base composition and using a measure based on tRNA-gene copy numbers as a rough estimate of tRNA abundance. RESULTS: We term major codons to be those codons with a relatively large tRNA-gene copy number for their corresponding amino acid. We use two measures of expression: breadth of expression (the number of tissues in which a gene was expressed) and maximum expression level among tissues (the highest value of expression of a gene among tissues). We show that for half the amino acids in the study (8 of 16) the relative major codon usage rises with breadth of expression. We show that these amino acids are significantly more frequent, are smaller and simpler, and are more ancient than the rest of the amino acids. Similar, although weaker, results were obtained for maximum expression level. CONCLUSION: There is evidence that codon bias in the human genome is related to selection, although the selection forces acting on codon bias may not be straightforward and may be different for different amino acids. We suggest that, in the first group of amino acids, selection acts to enhance translation efficiency in highly expressed genes by preferring major codons, and acts to reduce translation rate in lowly expressed genes by preferring non-major ones. In the second group of amino acids other selection forces, such as reducing misincorporation rate of expensive amino acids, in terms of their size/complexity, may be in action. The fact that codon usage is more strongly related to breadth of expression than to maximum expression level supports the notion, presented in a recent study, that codon choice may be related to the tRNA abundance in the tissue in which a gene is expressed.

Codon bias as a factor in regulating expression via translation rate in the human genome.

We study the interrelations between tRNA gene copy numbers, gene expression levels and measures of codon bias in the human genome. First, we show that isoaccepting tRNA gene copy numbers correlate positively with expression-weighted frequencies of amino acids and codons. Using expression data of more than 14,000 human genes, we show a weak positive correlation between gene expression level and frequency of optimal codons (codons with highest tRNA gene copy number). Interestingly, contrary to non-mammalian eukaryotes, codon bias tends to be high in both highly expressed genes and lowly expressed genes. We suggest that selection may act on codon bias, not only to increase elongation rate by favoring optimal codons in highly expressed genes, but also to reduce elongation rate by favoring non-optimal codons in lowly expressed genes. We also show that the frequency of optimal codons is in positive correlation with estimates of protein biosynthetic cost, and suggest another possible action of selection on codon bias: preference of optimal codons as production cost rises, to reduce the rate of amino acid misincorporation. In the analyses of this work, we introduce a new measure of frequency of optimal codons (FOP'), which is unaffected by amino acid composition and is corrected for background nucleotide content; we also introduce a new method for computing expected codon frequencies, based on the dinucleotide composition of the introns and the non-coding regions surrounding a gene.

Gene prediction by spectral rotation measure: a new method for identifying protein-coding regions.

A new measure for gene prediction in eukaryotes is presented. The measure is based on the Discrete Fourier Transform (DFT) phase at a frequency of 1/3, computed for the four binary sequences for A, T, C, and G. Analysis of all the experimental genes of S. cerevisiae revealed distribution of the phase in a bell-like curve around a central value, in all four nucleotides, whereas the distribution of the phase in the noncoding regions was found to be close to uniform. Similar findings were obtained for other organisms. Several measures based on the phase property are proposed. The measures are computed by clockwise rotation of the vectors, obtained by DFT for each analysis frame, by an angle equal to the corresponding central value. In protein coding regions, this rotation is assumed to closely align all vectors in the complex plane, thereby amplifying the magnitude of the vector sum. In noncoding regions, this operation does not significantly change this magnitude. Computing the measures with one chromosome and applying them on sequences of others reveals improved performance compared with other algorithms that use the 1/3 frequency feature, especially in short exons. The phase property is also used to find the reading frame of the sequence.

A simple system for the remote detection and analysis of sniffing in explosives detection dogs.

In this article, we describe a device that we have developed, for both research and operational purposes, to assist handlers of sniffer dogs and improve efficiency of search. The device transmits sounds from the dog's muzzle area to a listener, enabling determination of whether the dog is actually sniffing during a search. Both the aural and the computerized sound analyses enable study of the dog's sniffing behavior under a variety of situations. Correlation of these data with the visually monitored behavior of the working dog contributes additional and important information and leads to a greater understanding of detector dogs' behavior and abilities.