Infant perception of audio-visual speech synchrony.

Three experiments investigated perception of audio-visual (A-V) speech synchrony in 4- to 10-month-old infants. Experiments 1 and 2 used a convergent-operations approach by habituating infants to an audiovisually synchronous syllable (Experiment 1) and then testing for detection of increasing degrees of A-V asynchrony (366, 500, and 666 ms) or by habituating infants to a detectably asynchronous syllable (666 ms; Experiment 2) and then testing for detection of decreasing degrees of asynchrony (500, 366, and 0 ms). Following habituation to the synchronous syllable, infants detected only the largest A-V asynchrony (0 ms vs. 666 ms), whereas following habituation to the asynchronous syllable, infants detected the largest asynchrony (666 ms vs. 0 ms) as well as a smaller one (666 ms vs. 366 ms). Experiment 3 investigated the underlying mechanism of A-V asynchrony detection and indicated that responsiveness was based on a sensitivity to stimulus-energy onsets rather than the dynamic correlation between acoustic and visible utterance attributes. These findings demonstrated that infant perception of A-V speech synchrony is subject to the effects of short-term experience and that it is driven by a low-level, domain-general mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensory dominance in infants: I. Six-month-old infants' response to auditory-visual compounds.

To investigate sensory dominance in early development, a series of studies was conducted to examine 6-month-old infants' processing of multisensory stimulus compounds. The infants were first habituated with a compound stimulus consisting of a flashing checkerboard and a pulsing sound. To assess attention to aspects of the compound stimulus, the infants received separate test trials where compounds differed in the rate and/or duration at which the visual, the auditory, or both components were presented. One consistent finding was that the infants discriminated changes in the temporal characteristics of the auditory component but not in the visual component. Their responsiveness to the auditory information depended on the number of discriminative cues available during either the habituation or the test phases and on the temporal distinctiveness of the auditory and visual components during the habituation phase. This consistent failure to respond to changes in the visual component led to the conclusion that auditory dominance was operating. This conclusion was reinforced by the finding that the infants failed to discriminate a change in the rate of the visual component even when the intensity of the visual component was increased relative to that of the auditory component, and by the finding that the infants could discriminate temporal changes in the visual component following habituation with just the visual component. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bisensory response to temporal frequency in 4-month-old infants.

Three studies investigated detection of auditory–visual equivalence of rate among 55 4-mo-olds. In the 1st 2 studies, Ss were shown pairs of check patterns flashing at 2, 4, and 8 Hz either in silence or while listening to a tone corresponding in rate to 1 member of the pair. In Study 1, rate of stimulation varied, whereas duty cycle (i.e., intensity) was kept constant. No evidence of bisensory matching of rate was found. In Study 2, rate and duty cycle covaried. Although no matching was found, the presence of the 2 most intense sounds led to a shift in looking toward lower rates of visual stimulation. In Study 3, rate was kept constant (2 Hz), whereas duty cycle was varied. No matching was found, but as in Study 2, the presence of the most intense sound led to a shift in looking toward the less intense visual stimuli. Although these findings are contrary to previous reports of auditory–visual matching of rate, they do indicate that sound influences visual preferences via an intensity-based response mechanism. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning and discrimination of audiovisual events in human infants: The hierarchical relation between intersensory temporal synchrony and rhythmic pattern cues.

This study examined 4- to 10-month-old infants' perception of audio-visual (A-V) temporal synchrony cues in the presence or absence of rhythmic pattern cues. Experiment 1 established that infants of all ages could successfully discriminate between two different audiovisual rhythmic events. Experiment 2 showed that only 10-month-old infants detected a desynchronization of the auditory and visual components of a rhythmical event. Experiment 3 showed that 4- to 8-month-old infants could detect A-V desynchronization but only when the audiovisual event was nonrhythmic. These results show that initially in development infants attend to the overall temporal structure of rhythmic audiovisual events but that later in development they become capable of perceiving the embedded intersensory temporal synchrony relations as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental changes in infants' visual response to temporal frequency.

Investigated the development of visual responsiveness to variations in temporal frequency in 6 studies that were conducted when infants were at 4 and 6 mo of age. Groups of 12 infants each were tested in each study. In the 1st 2 studies, Ss viewed pairs of identical check patterns flashing at 2, 4, and 8 Hz, and their visual preferences were observed. When rate covaried with duty cycle (overall intensity), both age groups exhibited differential fixation as a function of frequency. To find out whether intensity variations were responsible for these results, intensity variations were eliminated (by equating duty cycle at 50%), and only frequency was varied. This manipulation resulted in the elimination of the previously observed differential response in the 4-mo-olds but had no effect on the 6-mo-olds' differential response. As a final check on the role of intensity, overall intensity was varied while temporal frequency was kept constant. Results show that 4-mo-old Ss continued to respond differentially whereas 6-mo-olds did not. These data show that at 4 mo of age Ss attended to the overall intensity of stimulation and ignored its temporal characteristics, whereas at 6 mo of age they no longer attended to the overall intensity and instead attended to temporal frequency per se. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Convex invertible cones of state space systems

In the paper [CL1] the notion of a convex invertible cone,cic, of matrices was introduced and its geometry was studied. In that paper close connections were drawn between thiscic structure and the algebraic Lyapunov equation. In the present paper the same geometry is extended to triples of matrices andcics of minimal state space models are defined and explored. This structure is then used to study balancing, Hankel singular values, and simultaneous model order reduction for a set of systems. State spacecics are also examined in the context of the so-called matrix sign function algorithm commonly used to solve the algebraic Lyapunov and Riccati equations.     

Investigating the effects of vasodilator drugs on the turbulentsound caused by femoral artery stenosis using short-term Fourier andwavelet transform methods

The effects of vasodilator drugs on the turbulent sound generation mechanisms during femoral artery stenoses were investigated using the wavelet analysis of the turbulent sounds to characterize these sounds before and after the injection of vasodilator drugs. Results showed that the injection of drugs drastically improved the diagnostic performance of the turbulent sounds in detecting stenoses by increasing the signal-to-noise ratio of the sounds. Results also suggested that the sound above 250 Hz was drastically increased in response to the injection of the vasodilator drug for the partially occluded cases. The turbulence sounds caused by partially occluded femoral arteries are directly related to the slope of baseline of blood flow and to the velocity of the flow. For the 0% occlusion case, initially, sounds were produced with the injection of drugs. However, the sounds totally disappeared when the slope of average blood how was zero. These results show that the diagnostic performance of diastolic heart sounds associated with occluded arteries can be improved by using vasodilator drugs, which increase the acoustic energy in the first and second wavelet bandwidths due to the turbulence. The short-term Fourier transform (STFT) method was also applied to the same data base. Results using the STFT showed somewhat similar power distributions in that the acoustical power above 250 Hz was increased after the injection of drugs for the occluded cases. However, the WT method provided better time-frequency resolution than the STFT method, showing details of the change in the frequency characteristics with respect to time after the injection of drug