Spectral restoration of speech: Intelligibility is increased by inserting noise in spectral gaps

In order to function effectively as a means of communication, speech must be intelligible under the noisy conditions encountered in everyday life. Two types of perceptual synthesis have been reported that can reduce or cancel the effects of masking by extraneous sounds: Phonemic restoration can enhance intelligibility when segments are replaced or masked by noise, and contralateral induction can prevent mislateralization by effectively restoring speech masked at one ear when it is heard in the other. The present study reports a third type of perceptual synthesis induced by noise: enhancement of intelligibility produced by adding noise to spectral gaps. In most of the experiments, the speech stimuli consisted of two widely separated narrow bands of speech (center frequencies of 370 and 6000 Hz, each band having high-pass and low-pass slopes of 115 dB/octave meeting at the center frequency). These very narrow bands effectively reduced the available information to frequency-limited patterns of amplitude fluctuation lacking information concerning formant structure and frequency transitions. When stochastic noise was introduced into the gap separating the two speech bands, intelligibility increased for “everyday” sentences, for sentences that varied in the transitional probability of keywords, and for monosyllabic word lists. Effects produced by systematically varying noise amplitude and noise bandwidth are reported, and the implications of some of the novel effects observed are discussed.     

Noise,Economy, and the Emergence of Information Structure in a Laboratory Language

The acceptability of sentences in natural language is constrained not only grammaticality, but also by the relationship between what is being conveyed and such factors as context and the beliefs of interlocutors. In many languages the critical element in a sentence (its focus) must be given grammatical prominence. There are different accounts of the nature of focus marking. Some researchers treat it as the grammatical realization of a potentially arbitrary feature of universal grammar and do not provide an explicit account of its origins; others have argued, however, that focus marking is a (grammaticalized) functional solution to the problem of efficiently transmitting information via a noisy channel. By adding redundancy to highlight critical elements in particular, focus protects key parts of the message from noise. If this information‐theoretic account is true, then we should expect focus‐like behavior to emerge even in non‐linguistic communication systems given sufficient noise and pressures for efficiency. We tested this in an experiment in which participants played a simple communication game in which they had to click cells on a grid to communicate one of two line figures drawn across the grid. We manipulated the noise, available time, and required effort, and measured patterns of redundancy. Because the lines in many cases overlapped, meaning that only some parts of each line could be used to distinguish it from the other, we were able to compare the extent to which effort was expended on adding redundancy to critical (non‐overlapping) and non‐critical (overlapping) parts of the message. The results supported the information‐theoretic account of focus and shed light on the emergence of information structure in language.     

Two experiments with artificial languages

Two experiments are reported where subjects learnt simple artificial languages which contained synonyms: i.e. there were two equally correct verbal responses paired with each “referent” in the language: “referents” were simple visual patterns. In the first experiment (a memory task) subjects performed better with material of low auditory discriminability than with material of high auditory discriminability when they were asked to use one synonym of each pair more often than the other; the reverse was the case when they were asked to use each synonym equally often. In the second experiment (a two-person communication task with a noisy channel) the degree to which pairs of subjects tended to use the same synonym for the same meaning was found to be non-monotonic with the noise level in the communication channel: subjects tended to use the same synonyms for moderately high noise and very low noise more often than they did for very high noise and moderately low noise.

The concept of decision cost (Smith, 1968) is used to explain these results. Decision cost is a complex function both of discriminability and of response bias, and it is proposed that changes in decision cost in response to changes in response bias are responsible for the results observed in these experiments.     

Estimating the growth of internal evidence guiding perceptual decisions

Perceptual decision-making is thought to involve a gradual accrual of noisy evidence. Temporal integration of the evidence reduces the relative contribution of dynamic internal noise to the decision variable, thereby boosting its signal-to-noise ratio. We aimed to estimate the internal evidence guiding perceptual decisions over time, using a novel combination of external noise and the response signal methods. Observers performed orientation discrimination of patterns presented in external noise. We varied the contrast of the patterns and the delay at which observers were forced to signal their decision. Each test stimulus (patterns and noise sample) was presented twice. Across two experiments we varied the availability of the visual stimulus for processing. Observer model analyses of discrimination accuracy and response consistency to two passes of the same stimulus, suggested that there was very little growth in the internal evidence. The improvement in accuracy over time characterised by the speed-accuracy trade-off function predominantly reflected a decreasing proportion of non-visual decisions, or pure guesses. There was no advantage to having the visual patterns visible for longer than 80 ms, indicating that only the visual information in a short window after display onset was used to drive the decisions. The remarkable constancy of the internal evidence over time suggests that temporal integration of the sensory information was very limited. Alternatively, more extended integration of the evidence from memory could have taken place, provided that the dominant source of internal noise limiting performance occurs between-trials, which cannot be reduced by prolonged evidence integration.     

Array training in a categorization task

Two components of categorization, within-category commonalities and between-category distinctiveness, were investigated in a categorization task. Subjects learned three prototype categories composed of moderately high distortions, by observing arrays containing patterns that belonged either to a common prototype category or to three different categories; a third group learned patterns presented one at a time, mirroring the standard paradigm. Following 6 learning blocks, subjects transferred to old patterns and new patterns at low-, medium-, and high-level distortions of the category prototype. The results showed that array training facilitated learning, especially when patterns in the array belonged to the same category. Transfer results showed a strong gradient effect across pattern distortion level for all conditions, with the highest performance obtained following array training on different category patterns and worst in the control condition. Interestingly, the old training patterns were classified worse than new low and no better than medium distortions. Neither this ordering nor the steepness of the gradient across prototype similarity for each condition could be predicted by the generalized context model. A prototype model better captured the steep gradient and ordinal pattern of results, although the overall fits were only slightly better than the exemplar model. The crucial role played by category commonalities and distinctiveness on categorical representations is addressed.     

Why Are Judgments Less Consistent in Less Predictable Task Situations?

Subjects made a series of six forecasts for each of four 58-point time-series. The stimulus series were noisy sinusoids of various frequencies. Individual subjects′ forecasts were regressed on to the time period for which they were made. The residual variance in these regressions was greater when the stimulus series were noisier. This effect cannot have arisen from memory overload because simultaneous presentation of all points in the stimulus series meant that there were no memory demands. It cannot have been a side effect of a learning process because presenting each series just once excluded opportunities for learning. It cannot have been caused by deterministic rule switching consequent on feedback about a noisy process because no feedback was presented. Instead it appears that subjects tried to simulate the noise as well as the pattern in the series when making their forecasts. In support of this, similar results were obtained in a second experiment in which subjects were asked to simulate rather than to forecast the series. Two possible reasons for subjects′ simulation of series noise are discussed.     

Determinants of the remembered utility of aversive sounds

Retrospective evaluations of aversive episodes were studied in the context of a general model of "judgment by prototype" that has been applied in other situations. Unpleasant sounds of variable loudness and duration were the stimuli. In Experiment 1, continuous reports of annoyance closely tracked variations of noise intensity. Hypotheses about the determinants of retrospective evaluation were examined in Experiment 2. Experiment 3 confirmed a prediction of judgment by prototype: The effects of sound duration and intensity are additive in multitrial experiments. Experiment 4 confirmed a robust preference for aversive episodes that are "improved" by adding a period of reduced aversiveness.     

The sensory nature of knowledge: Sensory priming effects in semantic categorization

The aim of the present study was to show the perceptual nature of conceptual knowledge by using a priming paradigm that excluded an interpretation exclusively in terms of amodal representation. This paradigm was divided into two phases. The first phase consisted in learning a systematic association between a geometrical shape and a white noise. The second phase consisted of a short-term priming paradigm in which a primed shape (either associated or not with a sound in the first phase) preceded a picture of an object, which the participants had to categorize as representing a large or a small object. The objects were chosen in such a way that their principal function either was associated with the production of noise (“noisy” target) or was not typically associated the production of noise (“silent” target). The stimulus onset asynchrony (SOA) between the prime and the target was 100 ms or 500 ms. The results revealed an interference effect with a 100-ms SOA and a facilitatory effect with a 500-ms SOA for the noisy targets only. We interpreted the interference effect obtained at the 100-ms SOA as the result of an overlap between the components reactivated by the sound prime and those activated by the processing of the noisy target. At an SOA of 500 ms, there was no temporal overlap. The observed facilitatory effect was explained by the preactivation of auditory areas by the sound prime, thus facilitating the categorization of the noisy targets only.     

A Comprehensive Literature Review of the Rank Reversal Phenomenon in the Analytic Hierarchy Process

During the last few decades, several multi‐criteria decision analysis methods have been proposed to help in selecting the best compromise alternatives. Among them, analytic hierarchy process (AHP) and its applications have attracted much attention from academics and practitioners. However, since the early 1980s, critics have raised questions regarding its proper use. One of them concerns the unacceptable changes in the ranks of the alternatives, called rank reversal, upon changing the structure of the decision. Several modifications were suggested to preserve ranks. In this paper, a classification scheme and a comprehensive literature review are presented in order to uncover, classify and interpret the current research on AHP methodologies and rank reversals. On the basis of the scheme, 61 scholarly papers from 18 journals are categorized into specific areas. The specific areas include the papers on the topics of adding/deleting alternatives and the papers published in adding/deleting criteria. The scholarly papers are also classified by (1) year of publication, (2) journal of publication, (3) authors' geographic location and (4) using the AHP in association with other methods. It is hoped that the paper can meet the needs of researchers and practitioners for convenient references of AHP methodologies and rank reversals and hence promote the future of rank reversal research. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous analysis of coupled data matrices subject to different amounts of noise

In many areas of science, research questions imply the analysis of a set of coupled data blocks, with, for instance, each block being an experimental unit by variable matrix, and the variables being the same in all matrices. To obtain an overall picture of the mechanisms that play a role in the different data matrices, the information in these matrices needs to be integrated. This may be achieved by applying a data‐analytic strategy in which a global model is fitted to all data matrices simultaneously, as in some forms of simultaneous component analysis (SCA). Since such a strategy implies that all data entries, regardless the matrix they belong to, contribute equally to the analysis, it may obfuscate the overall picture of the mechanisms underlying the data when the different data matrices are subject to different amounts of noise. One way out is to downweight entries from noisy data matrices in favour of entries from less noisy matrices. Information regarding the amount of noise that is present in each matrix, however, is, in most cases, not available. To deal with these problems, in this paper a novel maximum‐likelihood‐based simultaneous component analysis method, referred to as MxLSCA, is proposed. Being a stochastic extension of SCA, in MxLSCA the amount of noise in each data matrix is estimated and entries from noisy data matrices are downweighted. Both in an extensive simulation study and in an application to data stemming from cross‐cultural emotion psychology, it is shown that the novel MxLSCA strategy outperforms the SCA strategy with respect to disclosing the mechanisms underlying the coupled data.     

False prototype enhancement effects in dot pattern categorization

Results from the classic dot pattern distortion paradigm have sometimes yielded prototype enhancement effects that could not be accounted for by exemplar models of categorization. However, in these experiments the status of the prototype was confounded with certain stimulus-specific properties as well as with the frequency of presentation of the prototype during testing. In two mock-subliminal experiments, participants made categorization judgments to patterns that were generated as prototypes, low-level distortions, or high-level distortions. The participants rated the prototypes as being more likely to be members of a category, although no patterns were presented during training, and there was no objective category structure. In two other experiments, greater prototype enhancement effects were observed when the prototype and low-level distortions were presented with greater frequency during transfer. These results suggest that classic prototype enhancement effects may not be due to the abstraction of a prototype at time of original learning, but rather to other factors not formalized in extant models.     

Weber-Fechner behavior in symmetry perception?

The literature contains several allusions to the idea that detection of (mirror) symmetry in the presence of noise follows the Weber-Fechner law. This law usually applies to first-order structures, such as length, weight, or pitch, and it holds that just-noticeable differences in a signal vary in proportion to the strength of the signal. Symmetry, however, is a higher order structure, and this theoretical note starts from the idea that, in noisy symmetry, the regularity-to-noise ratio defines the strength of the signal to be considered. We argue that the detectability of the symmetry follows a psychophysical law that also holds for Glass patterns. This law deviates from the Weber-Fechner law in that it implies that, in the middle range of noise proportions, the sensitivity to variations in the regularity-to-noise ratio is disproportionally higher than in both outer ranges.     

Behavioral and electrophysiological measures of click audibility compared in the cat

Cats were trained to make an avoidance response to clicks in the presence of different levels of white masking noise. The audibility of the clicks at different masking intensities could be determined from the percentage of CRs made by the animals. Click-evoked responses were also recorded from the left inferior colliculus of each cat in the presence of several intensities of masking noise. The results showed that the noise level that just obscured the click-evoked response was quite close in intensity to the noise level that produced threshold click detection in the behavioral situation. While both behavioral and electrophysiological methods yielded similar measures of auditory sensitivity, the electrophysiological measure was obtained in a fraction of the time required to obtain the behavioral measure.     

Learning on a response continuum: Comparison of a linear change and a functional learning model

Two reinforcement schedules were used to compare the predictive validity of a linear change model with a functional learning model. In one schedule, termed “convergent,” the linear change model predicts convergence to the optimum response, while in the other, termed “divergent,” this model predicts that a subject's response will not converge. The functional learning model predicts convergence in both cases. Another factor that was varied was presence or absence of random error or “noise” in the relationship between response and outcome. In the “noiseless” condition, in which no noise is added, a subject could discover the optimum response by chance, so that some subjects could appear to have converged fortuitously. In the “noisy” conditions such chance apparent convergence could not occur.The results did not unequivocally favor either model. While the linear change model's prediction of nonconvergence in the divergent conditions (particularly the “noisy” divergent condition) was not sustained, there was a clear difference in speed of convergence, counter to the prediction inferred from the functional learning model. Evidence that at least some subjects were utilizing a functional learning strategy was adduced from the fact that subjects were able to “map out” the relation between response and outcome quite accurately in a follow-up task. Almost all subjects in the “noisy” conditions had evidently “learned” a strong linear relation, with slope closely matching the veridical one.The data were consistent with a hybrid model assuming a “hierarchy of cognitive strategies” in which more complex strategies (e.g., functional learning) are utilized only when the simpler ones (e.g., a linear change strategy) fail to solve the problem.     

The Lower Visual Search Efficiency For Conjunctions Is Due To Noise and Not Serial Attentional Processing

Models of human visual processing start with an initial stage with parallel independent processing of different physical attributes or features (e.g. color, orientation, motion). A second stage in these models is a temporally serial mechanism (visual attention) that combines or binds information across feature dimensions. Evidence for this serial mechanism is based on experimental results for visual search. I conducted a study of visual search accuracy that carefully controlled for low-level effects: physical similarity of target and distractor, element eccentricity, and eye movements. The larger set-size effects in visual search accuracy for briefly flashed conjunction displays, compared with feature displays, are quantitatively predicted by a simple model in which each feature dimension is processed independently with inherent neural noise and information is combined linearly across feature dimensions. The data are not predicted by a temporally serial mechanism or by a hybrid model with temporally serial and noisy processing. The results do not support the idea that a temporally serial mechanism, visual attention, binds information across feature dimensions and show that the conjunction-feature dichotomy is due to the noisy independent processing of features in the human visual system.     

Influence of manipulated category knowledge on prototype classification and recognition

The recognition and classification of category members was explored, following a variable number of learning trials. In Experiment 1, subjects received 1 or 9 learning trials, followed by a recognition-then-classification test containing old, new, prototype, and foil patterns. In Experiment 2, subjects received 1, 6, or 12 trials, and made either classification or recognition judgments. In each experiment, classification accuracy for all item types was at near-chance -performance after a single trial but steadily increased with increased learning trials. On the transfer test, oldness judgments were highest for the category prototype after a single trial. However, with increased learning trials, oldness judgments increased for old instances and decreased for the category prototype and new instances. We suggest that false recognition of the category prototype, especially after a single learning trial, need not reflect an abstraction process. We discuss the possibility that an abstracted prototype may emerge with additional learning as an unfamiliar, ideal point.     

A window on the normal development of sensitivity to global form in Glass patterns

We studied the development of sensitivity to global form in 6-year-olds, 9-year-olds, and adults (n = 24 in each group) using Glass patterns with varying ratios of paired signal dots to noise dots. The developmental pattern was similar whether the global structure within the Glass patterns was concentric or parallel. Thresholds were equally immature for both types of pattern at 6 years of age (about twice the adult value) but were adult-like at 9 years of age. Together, the results indicate that the cortical structures involved in the processing of global form achieve functional maturity between 6 and 9 years of age. During middle childhood, the mechanisms mediating sensitivity to concentric structure develop at the same rate as those mediating sensitivity to parallel structure.     

The modulating influence of category size on the classification of exception patterns

Generalization gradients to exception patterns and the category prototype were investigated in two experiments. In Experiment 1, participants first learned categories of large size that contained a single exception pattern, followed by a transfer test containing new instances that had a manipulated similarity relationship to the exception or a nonexception training pattern as well as distortions of the prototype. The results demonstrated transfer gradients tracked the prototype category rather than the feedback category of the exception category. In Experiment 2, transfer performance was investigated for categories varying in size (5, 10, 20), partially crossed with the number of exception patterns (1, 2, 4). Here, the generalization gradients tracked the feedback category of the training instance when category size was small but tracked the prototype category when category size was large. The benefits of increased category size still emerged, even with proportionality of exception patterns held constant. These, and other outcomes, were consistent with a mixed model of classification, in which exemplar influences were dominant with small-sized categories and/or high error rates, and prototype influences were dominant with larger sized categories.     

The modulating influence of category size on the classification of exception patterns

Generalization gradients to exception patterns and the category prototype were investigated in two experiments. In Experiment 1, participants first learned categories of large size that contained a single exception pattern, followed by a transfer test containing new instances that had a manipulated similarity relationship to the exception or a nonexception training pattern as well as distortions of the prototype. The results demonstrated transfer gradients tracked the prototype category rather than the feedback category of the exception category. In Experiment 2, transfer performance was investigated for categories varying in size (5, 10, 20), partially crossed with the number of exception patterns (1, 2, 4). Here, the generalization gradients tracked the feedback category of the training instance when category size was small but tracked the prototype category when category size was large. The benefits of increased category size still emerged, even with proportionality of exception patterns held constant. These, and other outcomes, were consistent with a mixed model of classification, in which exemplar influences were dominant with small-sized categories and/or high error rates, and prototype influences were dominant with larger sized categories.     

Short-term retention of visually presented stimuli: some evidence of visual encoding.

Subjects saw two visual stimuli on each trial, separated by an interval ranging from 0 to 8 sec. Each stimulus was composed of a subset of the dots of a 7 × 5 dot matrix. In particular, it was a composite of two patterns, one of which formed a capital English letter and the other of which was an arrangement formed by 8 randomly selected dots. The task was to decide as quickly as possible whether the two stimuli contained the same letter. Under one condition (correlated noise) the same noise pattern was used with both letters; thus the decision as to whether the letters were the same could be based on a test of congruence of the two stimuli, noise and all. Under another condition (uncorrelated noise) the noise patterns differed, assuring that the composite patterns differed, and thus precluding congruence testing as an adequate way to determine whether the two letters were the same. Performance was better (RTs and error rates were smaller) with the correlated noise than with the uncorrelated noise. The result was taken as evidence that visual information was retained in memory, and used to advantage, when the situation clearly warranted the direct comparison of visual patterns.