Assimilation and contrast in the phonetic perception of vowels.

The perceptual mechanisms of assimilation and contrast in the phonetic perception of vowels were investigated. In experiment 1, 14 stimulus continua were generated using an /i/-/e/-/a/ vowel continuum. They ranged from a continuum with both ends belonging to the same phonemic category in Japanese, to a continuum with both ends belonging to different phonemic categories. The AXB method was employed and the temporal position of X was changed under three conditions. In each condition ten subjects were required to judge whether X was similar to A or to B. The results demonstrated that assimilation to the temporally closer sound occurs if the phonemic categories of A and B are the same and that contrast to the temporally closer sound occurs if A and B belong to different phonemic categories. It was observed that the transition from assimilation to contrast is continuous except in the /i'/-X-/e/ condition. In experiment 2, the total duration of t 1 (between A and X) and t 2 (between X and B) was changed under five conditions. One stimulus continuum consisted of the same phonemic category in Japanese and the other consisted of different phonemic categories. Six subjects were required to make similarity judgements of X. The results demonstrated that the occurrence of assimilation and contrast to the temporally closer sound seemed to be constant under each of the five conditions. The present findings suggest that assimilation and contrast are determined by three factors: the temporal position of the three stimuli, the acoustic distance between the three stimuli on the stimulus continuum, and the phonemic categories of the three stimuli.     

Reflectance measurements of aluminium surfaces using integrating spheres

In the investigation of the considerable absorption of visible light in industrially rolled aluminium surfaces, a thorough knowledge of the total reflectance measurement method is required. In this paper a general introduction to the integrating sphere method is given, with emphasis on the current understanding of instrumental artefacts and ways of correcting them. Selected aluminium surfaces were measured employing two spheres; a single-beam instrument equipped with a white-light source and a Si-photoelement detector, and a double-beam sphere, which measures reflectance properties with spectral resolution. It was found necessary to take precautions concerning the orientation of rolled samples relative instrument geometry, to avoid artificial losses from the sphere. The use of a specular reference standard is assumed to minimise the effect of several sphere artefacts, since it produces similar angular distribution of reflected light as the rather glossy aluminium samples. Measurements with spectral resolution show that the total reflectance of aluminium is somewhat red shifted after rolling, a tendency that cannot be revealed in ordinary white-light measurements.     

Coherence in children's speech perception.

Studies with adults have demonstrated that acoustic cues cohere in speech perception such that two stimuli cannot be discriminated if separate cues bias responses equally, but oppositely, in each. This study examined whether this kind of coherence exists for children's perception of speech signals, a test that first required that a contrast be found for which adults and children show similar cue weightings. Accordingly, experiment 1 demonstrated that adults, 7-, and 5-year-olds weight F2-onset frequency and gap duration similarly in "spa" versus "sa" decisions. In experiment 2, listeners of these same ages made "same" or "not-the-same" judgments for pairs of stimuli in an AX paradigm when only one cue differed, when the two cues were set within a stimulus to bias the phonetic percept towards the same category (relative to the other stimulus in the pair), and when the two cues were set within a stimulus to bias the phonetic percept towards different categories. Unexpectedly, adults' results contradicted earlier studies: They were able to discriminate stimuli when the two cues conflicted in how they biased phonetic percepts. Results for 7-year-olds replicated those of adults, but were not as strong. Only the results of 5-year-olds revealed the kind of perceptual coherence reported by earlier studies for adults. Thus, it is concluded that perceptual coherence for speech signals is present from an early age, and in fact listeners learn to overcome it under certain conditions.     

Object-related brain potentials associated with the perceptual segregation of a dichotically embedded pitch

The cortical mechanisms of perceptual segregation of concurrent sound sources were examined, based on binaural detection of interaural timing differences. Auditory event-related potentials were measured from 11 healthy subjects. Binaural stimuli were created by introducing a dichotic delay of 500-ms duration to a narrow frequency region within a broadband noise, and resulted in a perception of a centrally located noise and a right-lateralized pitch (dichotic pitch). In separate listening conditions, subjects actively discriminated and responded to randomly interleaved binaural and control stimuli, or ignored random stimuli while watching silent cartoons. In a third listening condition subjects ignored stimuli presented in homogenous blocks. For all listening conditions, the dichotic pitch stimulus elicited an object-related negativity (ORN) at a latency of about 150-250 ms after stimulus onset. When subjects were required to actively respond to stimuli, the ORN was followed by a P400 wave with a latency of about 320-420 ms. These results support and extend a two-stage model of auditory scene analysis in which acoustic streams are automatically parsed into component sound sources based on source-relevant cues, followed by a controlled process involving identification and generation of a behavioral response.     

Perceptual equivalence of acoustic cues that differentiate /r/ and /l/

The perceptual effects of orthogonal variations in two acoustic parameters which differentiate American English prevocalic /r/ and /l/ were examined. A spectral cue (frequency onset and transition of F2 and F3) and a temporal cue (relative duration of initial steady state and transition of F1) were varied in synthetic versions of "rock" and "lock." Four temporal variations in each of ten stimuli of a spectral-cue continuum were generated. Phonetic identification and oddity discrimination tasks with the four series showed systematic displacement of perceptual boundaries and discrimination peaks, thus reflecting a trading relation between the two cues. The perceptual equivalence of spectral and temporal cues was investigated by comparing the accuracy of discrimination of three types of stimulus comparisons: phonetically facilitating two-cue pairs, one-cue pairs, and phonetically conflicting two-cue pairs. As predicted, discrimination accuracy was ordered: Facilitating cues greater than one-cue greater than conflicting cues, indicating that perceivers discriminated on the basis of an integrated phonetic percept.     

The Effect of Exposure Duration on Stereopsis and Its Dependency on Spatial Frequency

To investigate the effect of exposure duration on stereopsis and its spatial frequency dependency, we measured disparity threshold for the depth discrimination varying stimulus exposure duration between 0.05 and 2 s for three spatial frequencies (0.23, 0.94 and 3.75 c/deg). The results showed that disparity threshold decreased with increase in exposure duration up to a certain duration, beyond which it was approximately constant (the duration is called critical duration). The critical duration was about 150 ms for gratings with low and middle spatial frequencies (0.23 and 0.94 c/deg) while the duration was about 750 ms for gratings with high spatial frequency (3.75 c/deg). This suggests that temporal integration property varies dependently on stimulus spatial frequency. We also attempted to relate the spatial frequency dependency of the temporal integration property to the differences in temporal frequency tuning to different spatial frequency stimuli.     

Perceptual differences between vowels located in a limited phonetic space

The perception of subphonemic differences between vowels was investigated using multidimensional scaling techniques. Three experiments were conducted with natural-sounding synthetic stimuli generated by linear predictive coding (LPC) formant synthesizers. In the first experiment, vowel sets near the pairs (i-I), (epsilon-ae), or (u-U) were synthesized containing 11 vowels each. Listeners judged the dissimilarities between all pairs of vowels within a set several times. These perceptual differences were mapped into distances between the vowels in an n-dimensional space using two-way multidimensional scaling. Results for each vowel set showed that the physical stimulus space, which was specified by the two parameters F1 and F2, was always mapped into a two-dimensional perceptual space. The best metric for modeling the perceptual distances was the Euclidean distance between F1 and F2 in barks. The second experiment investigated the perception of the same vowels from the first experiment, but embedded in a consonantal context. Following the same procedures as experiment 1, listeners' perception of the (bv) dissimilarities was not different from their perception of the isolated vowel dissimilarities. The third experiment investigated dissimilarity judgments for the three vowels (ae-alpha-lambda) located symmetrically in the F1 X F2 vowel space. While the perceptual space was again two dimensional, the influence of phonetic identity on vowel difference judgments was observed. Implications for determining metrics for subphonemic vowel differences using multidimensional scaling are discussed.     

Statistically robust evidence of stochastic resonance in human auditory perceptual system

In human perception, exogenous noise is known to yield a masking effect, i.e. an increase of the perceptual threshold relative to a stimulus acting on the same modality. However, somehow counter-intuitively, the opposite mechanism can occasionally occur: a decrease of the perceptual threshold for a non-vanishing, virtuous amount of noise. This mechanism, called stochastic resonance, is deemed to provide important information about the role of noise in the human brain. In this paper, we investigate stochastic resonance in a detection task in the auditory modality. Normal-hearing participants were asked to judge the presence of acoustic stimuli of different intensity and superimposed to different levels of white noise. The matrix-like outcomes of a behavioural experiment were fitted by a two-dimensional, noise-dependent psychometric function. The fit revealed a statistically significant stochastic resonance in 43% of the experimental runs. We conclude that, in the auditory modality, stochastic resonance is a tiny effect that, under conventional circumstances, is largely overrun by standard masking.     

Percept-related activity in the human somatosensory system: functional magnetic resonance imaging studies

In this paper, we review blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies addressing the neural correlates of touch, thermosensation, pain and the mechanisms of their cognitive modulation in healthy human subjects. There is evidence that fMRI signal changes can be elicited in the parietal cortex by stimulation of single mechanoceptive afferent fibers at suprathreshold intensities for conscious perception. Positive linear relationships between the amplitude or the spatial extents of BOLD fMRI signal changes, stimulus intensity and the perceived touch or pain intensity have been described in different brain areas. Some recent fMRI studies addressed the role of cortical areas in somatosensory perception by comparing the time course of cortical activity evoked by different kinds of stimuli with the temporal features of touch, heat or pain perception. Moreover, parametric single-trial functional MRI designs have been adopted in order to disentangle subprocesses within the nociceptive system.

Available evidence suggest that studies that combine fMRI with psychophysical methods may provide a valuable approach for understanding complex perceptual mechanisms and top-down modulation of the somatosensory system by cognitive factors specifically related to selective attention and to anticipation. The brain networks underlying somatosensory perception are complex and highly distributed. A deeper understanding of perceptual-related brain mechanisms therefore requires new approaches suited to investigate the spatial and temporal dynamics of activation in different brain regions and their functional interaction.     

A spectral invariant representation of spectral reflectance

Spectral image acquisition as well as color image is affected by several illumination factors such as shading, gloss, and specular highlight. Spectral invariant representations for these factors were proposed for the standard dichromatic reflection model of inhomogeneous dielectric materials. However, these representations are inadequate for other characteristic materials like metal. This paper proposes a more general spectral invariant representation for obtaining reliable spectral reflectance images. Our invariant representation is derived from the standard dichromatic reflection model for dielectric materials and the extended dichromatic reflection model for metals. We proof that the invariant formulas for spectral images of natural objects preserve spectral information and are invariant to highlights, shading, surface geometry, and illumination intensity. It is proved that the conventional spectral invariant technique can be applied to metals in addition to dielectric objects. Experimental results show that the proposed spectral invariant representation is effective for image segmentation.     

Sensor for the detection of local contrast gloss of products

We introduce a sensor for providing information on the local contrast gloss (or luster) of products. The sensor also provides information of the local specular gloss of the object. The signals of this sensor are produced by diffractive optical elements from fields that are scattered in the diffuse and specular directions from the object. We present specular gloss, diffuse-reflectance factor related to the contrast gloss, and visibility maps measured from black prints on paper. High variation can be observed in the relevant gloss parameters obtained from the printed area. In addition, borders of the print can be clearly detected from the diffuse-reflectance-factor maps. The sensor also allows detection of raster points of a print. This sensor opens up entirely new means to study prints and other substances.     

Detection of gaps in sinusoids and pulse trains by patients with cochlear implants

Gap detection thresholds were measured in patients with the Nucleus and Symbion cochlear implants as a function of several current waveform parameters. Detection of gaps in an electrical sinusoidal stimulus or in a train of biphasic pulses by implanted patients was similar to detection of gaps in comparable acoustic stimuli by normal listeners. Threshold gaps were 20-50 ms for low-level stimuli and improved with stimulus level to 2-5 ms for high-level stimuli. Gap detection performance was not affected by the electrode position in the cochlea or by the distance between stimulating electrodes. The data from most patients were well fitted by a trading relation between the duration of the gap and the square of stimulus intensity, indicating energy detection. The similarity of gap thresholds for normal subjects and implant patients suggests that many details of the peripheral neural activity are probably not important for this task, and that there is no retrocochlear loss of auditory temporal resolution with sensorineural hearing loss.     

Call recognition in the bullfrog, Rana catesbeiana: generalization along the duration continuum

Male bullfrogs emit multicroak, quasiharmonic advertisement calls that function in mate attraction and neighbor recognition. The degree of variability of acoustic features in these calls can influence perceptual decisions by conspecific receivers. Analysis of duration of individual croaks in spontaneous advertisement calls of a sample of males shows considerable intraindividual variability in this feature, even within short chorusing bouts. The influence of this intraindividual variability on behavior was examined in a series of evoked calling experiments. When presented with synthetic calls whose croak durations varied over the range of the natural variability in this feature, males responded similarly to intermediate and long duration croaks, but significantly less to short duration croaks. When presented with playbacks of calls with croak durations outside the natural range of variability, males again responded significantly less to shorter durations. The response gradient for duration is thus asymmetrical, with stimuli at the shorter end of the continuum evoking fewer responses than stimuli at the longer end. This asymmetry may be related to the biological demands of rejecting perception of heterospecific advertisement calls, and of mediating appropriate responses to conspecific aggressive calls. The shape of the response gradient for duration may reflect a process of stimulus generalization.     

The effect of rate of stimulation on perception of spectral shape by cochlear implantees

The effect of rate of stimulation on spectral shape perception was measured in six users of the Nucleus CI24 cochlear implant. Three spectral shapes were created by using three profiles of current across seven electrode positions. Each current profile was replicated in three stimuli that interleaved stimulus pulses across the seven electrodes with cycle rates (rate per electrode) of 450, 900, and 1800 Hz. The stimulus space resulting from a multidimensional scaling experiment showed a clear dimension related to the rate of stimulation that was orthogonal to the dimension related to the spectral shapes. A second experiment was performed with the same subjects to investigate whether the perceptual dimension related to rate in Experiment 1 could be attributed to different perceptual flatness of the profiles at different rates. In Experiment 2, the rate of stimulation was fixed at 900 Hz and three profiles were created for each spectral shape that differed in flatness. This experiment did not, however, result in an independent perceptual dimension related to the flatness of the profile. In conclusion, rate of stimulation provided an independent perceptual dimension in the multiple-electrode stimuli, in spite of the rates being not discriminable or barely discriminable in single-electrode stimulation.     

基于函数拟合的玉米叶片反射光谱时间变化规律分析

为了探索玉米(Zea mays L.)叶片反射光谱时间变化规律,对21个叶位的玉米叶片进行了每天一次的反射光谱测量,获得了玉米活体叶片整个生命周期反射光谱数据1 261条。在此基础上采用光谱相关图方法,对400～960 nm的可见光、近红外波段的玉米叶片反射光谱进行分段拟合,获得了7个表征玉米叶片反射光谱时间变化规律的拟合参数,并对这7个参数的时间变化趋势采用二元二次多项式进行拟合。结果表明该方法对单片叶片反射光谱的拟合效果非常理想,其中98.7%的叶片反射光谱拟合复相关系数r大于0.99,80.9%的叶片反射光谱拟合均方根误差RMSE小于0.001 5。将所有数据的拟合结果与原始数据进行比较,复相关系数r为0.9978,均方根误差RMSE为0.010 5,拟合结果表明该方法较好地保持了反射光谱时间变化的趋势,能够充分利用叶片反射光谱的相关性,有效地表征玉米叶片反射光谱随时间变化的规律。     

Nondestructive testing of objects of complex shape using infrared thermography: Determination of the spatiotemporal distribution of the irradiation heat flux

The existing inverse methods used to determine the heat flux density require that the forward problem and the problem domain (geometry) be known. In this paper, in order to determine the spatiotemporal heat flux density without knowing the real problem domain, we propose an approach based on temporal tracking of the thermal front. The proposed approach is particularly relevant when a three-dimensional formulation is adopted for nondestructive testing using infrared thermography. For such a formulation, heat flux density resulting from the external thermal stimulus is needed and must be determined to accurately characterize the defects and reconstruct the internal geometry of the inspected objects. The proposed approach uses only two inputs: the time-dependent temperature of the frontal surface recorded by an infrared camera and the 3D point cloud of the frontal surface collected by a 3D scanner. The method is evaluated numerically on an object of complex shape. We consider the case of pulsed thermal stimulus as well as the cases of unit step and modulated thermal stimuli. An experimental validation is performed on a cylindrical object submitted to a pulsed thermal stimulus and a modulated thermal stimulus. The results show the accuracy of the method which can easily be implemented as the initial step of the three-dimensional quantitative nondestructive testing of objects using infrared thermography.     

漫反射光谱技术对文物保护及相关问题的研究

应用自行研制的光导纤维反射分光光度计,研究了漫反射光谱技术在文物保护研究中的应用。主要工作包括： (1)通过比较待测颜料和标准颜料反射光谱曲线的形状和特征反射峰或一阶导数峰的位置,实现对彩绘文物颜料的分析鉴定。(2)用漫反射光谱技术监测金属表面状态的变化。文中通过对铜及其锈蚀产物漫反射光谱的研究得到了铜表面的一些信息,可见漫反射光谱技术对金属表面状态的研究具有特殊的功能。(3)通过研究文物保护修复材料的反射光谱特性,指导人们选择适宜的材料。作者的研究证实了漫反射光谱法是一种新的文物保护研究技术,具有简便、快捷和不损坏文物的特点,该工作使漫反射光谱技术成为文物保护研究的一种新的检测手段,同时也为漫反射光谱分析开辟了新的研究应用领域。     

Model of bidirectional reflectance distribution function for metallic materials

Based on the three-component assumption that the reflection is divided into specular reflection,directional diffuse reflection,and ideal diffuse reflection,a bidirectional reflectance distribution function(BRDF) model of metallic materials is presented.Compared with the two-component assumption that the reflection is composed of specular reflection and diffuse reflection,the three-component assumption divides the diffuse reflection into directional diffuse and ideal diffuse reflection.This model effectively resolves the problem that constant diffuse reflection leads to considerable error for metallic materials.Simulation and measurement results validate that this three-component BRDF model can improve the modeling accuracy significantly and describe the reflection properties in the hemisphere space precisely for the metallic materials.     

On the influence of interaural differences on temporal perception of noise bursts of different durations

The perception of a composite sound's temporal cues, like synchronous onsets, is considered essential to correct perceptual grouping of its constituent components. The processing of a single sound's spatial cues, already present at its onset, may interact with temporal perception of the onset. The current study investigated the influence of interaural differences on temporal perception of a sound's onset. As a measure of temporal perception, the ability to position the onset of a temporally displaced target sound to the regular meter of diotic reference marker sound onsets was measured for various target sound lateralizations, sensation levels, and target and marker sound durations. For target sounds presented in quiet, no influence of interaural differences on temporal positioning of the onset was found. However, increasing a sound's duration systematically shifted the perceived onset position into its "interior." For target sounds presented at low sensation levels in a noise masker, the precision of temporally positioning the onset generally degraded, though faster for dichotic conditions and for longer durations. The level below which temporal perception precision starts to degrade was found to depend on signal-to-noise ratio rather than on sensation level or duration, and is influenced by the presence of interaural differences.