Changes In Sound Frequency Research Articles

Is there pre‐attentive memory‐based comparison of pitch?

The brain's responsiveness to changes in sound frequency has been demonstrated by an overwhelming number of studies. Change detection occurs unintentionally and automatically. It is generally assumed that this brain response, the so-called mismatch negativity (MMN) of the event-related brain potential or evoked magnetic field, is based on the outcome of a memory-comparison mechanism rather than being due to a differential state of refractoriness of tonotopically organized cortical neurons. To the authors' knowledge, however, there is no entirely compelling evidence for this belief. An experimental protocol controlling for refractoriness effects was developed and a true memory-comparison-based brain response to pitch change was demonstrated.

The magnocellular theory of developmental dyslexia.

Low literacy is termed 'developmental dyslexia' when reading is significantly behind that expected from the intelligence quotient (IQ) in the presence of other symptoms--incoordination, left-right confusions, poor sequencing--that characterize it as a neurological syndrome. 5-10% of children, particularly boys, are found to be dyslexic. Reading requires the acquisition of good orthographic skills for recognising the visual form of words which allows one to access their meaning directly. It also requires the development of good phonological skills for sounding out unfamiliar words using knowledge of letter sound conversion rules. In the dyslexic brain, temporoparietal language areas on the two sides are symmetrical without the normal left-sided advantage. Also brain 'warts' (ectopias) are found, particularly clustered round the left temporoparietal language areas. The visual magnocellular system is responsible for timing visual events when reading. It therefore signals any visual motion that occurs if unintended movements lead to images moving off the fovea ('retinal slip'). These signals are then used to bring the eyes back on target. Thus, sensitivity to visual motion seems to help determine how well orthographic skill can develop in both good and bad readers. In dyslexics, the development of the visual magnocellular system is impaired: development of the magnocellular layers of the dyslexic lateral geniculate nucleus (LGN) is abnormal; their motion sensitivity is reduced; many dyslexics show unsteady binocular fixation; hence poor visual localization, particularly on the left side (left neglect). Dyslexics' binocular instability and visual perceptual instability, therefore, can cause the letters they are trying to read to appear to move around and cross over each other. Hence, blanking one eye (monocular occlusion) can improve reading. Thus, good magnocellular function is essential for high motion sensitivity and stable binocular fixation, hence proper development of orthographic skills. Many dyslexics also have auditory/phonological problems. Distinguishing letter sounds depends on picking up the changes in sound frequency and amplitude that characterize them. Thus, high frequency (FM) and amplitude modulation (AM) sensitivity helps the development of good phonological skill, and low sensitivity impedes the acquisition of these skills. Thus dyslexics' sensitivity to FM and AM is significantly lower than that of good readers and this explains their problems with phonology. The cerebellum is the head ganglion of magnocellular systems; it contributes to binocular fixation and to inner speech for sounding out words, and it is clearly defective in dyslexics. Thus, there is evidence that most reading problems have a fundamental sensorimotor cause. But why do magnocellular systems fail to develop properly? There is a clear genetic basis for impaired development of magnocells throughout the brain. The best understood linkage is to the region of the Major Histocompatibility Complex (MHC) Class 1 on the short arm of chromosome 6 which helps to control the production of antibodies. The development of magnocells may be impaired by autoantibodies affecting the developing brain. Magnocells also need high amounts of polyunsaturated fatty acids to preserve the membrane flexibility that permits the rapid conformational changes of channel proteins which underlie their transient sensitivity. But the genes that underlie magnocellular weakness would not be so common unless there were compensating advantages to dyslexia. In developmental dyslexics there may be heightened development of parvocellular systems that underlie their holistic, artistic, 'seeing the whole picture' and entrepreneurial talents.

Effect of Vehicle Speed on Sound Frequency Spectra

During analysis conducted on data collected by the University of Central Florida for the Florida Department of Transportation (FDOT), which was doing research to develop reference energy mean emission levels for high-speed traffic, other interesting data trends became apparent. One such trend was the relationship of vehicle speed and sound emission spectra. The data base contained real-time one-third octave band data and vehicle characteristics (e.g., speed) and permitted a detailed review of sound emission spectra with respect to vehicle speed. The purpose of this research was to attempt to develop a mathematical relationship between increasing vehicle speed and sound emission spectra. Based on the results of this research several important conclusions were drawn: (a) a trend in the change in sound frequency spectra with respect to vehicle speed may exist for all vehicle types defined in STAMINA 2.0; (b) the change in dominant frequency followed no apparent trend with respect to vehicle speed; (c) the data base used for this research was too small for accurate mathematical modeling of the change in sound frequency versus vehicle speed; and (d) the sound attenuation provided by noise barriers may be underestimated using the current method of estimating barrier attenuation based on an effective frequency of 500 Hz regardless of vehicle speed.

Effect of Vehicle Speed on Sound Frequency Spectra

During analysis conducted on data collected by the University of Central Florida for the Florida Department of Transportation (FDOT), which was doing research to develop reference energy mean emission levels for high-speed traffic, other interesting data trends became apparent. One such trend was the relationship of vehicle speed and sound emission spectra. The data base contained real-time one-third octave band data and vehicle characteristics (e.g., speed) and permitted a detailed review of sound emission spectra with respect to vehicle speed. The purpose of this research was to attempt to develop a mathematical relationship between increasing vehicle speed and sound emission spectra. Based on the results of this research several important conclusions were drawn: (a) a trend in the change in sound frequency spectra with respect to vehicle speed may exist for all vehicle types defined in STAMINA 2.0; (b) the change in dominant frequency followed no apparent trend with respect to vehicle speed; (c) the data base used for this research was too small for accurate mathematical modeling of the change in sound frequency versus vehicle speed; and (d) the sound attenuation provided by noise barriers may be underestimated using the current method of estimating barrier attenuation based on an effective frequency of 500 Hz regardless of vehicle speed.

Physics of directional hearing in the cricket Gryllus bimaculatus

In the cricket ear, sound acts on the external surface of the tympanum and also reaches the inner surface after travelling in at least three pathways in the tracheal system. We have determined the transmission gain of the three internal sound pathways; that is, the change of amplitude and phase angle from the entrances of the tracheal system to the inner surface of the tympanum. In addition, we have measured the diffraction and time of arrival of sound at the ear and at the three entrances at various directions of sound incidence. By combining these data we have calculated how the total driving force at the tympanum depends on the direction of sound. The results are in reasonable agreement with the directionality of the tympanal vibrations as determined with laser vibrometry. At the frequency of the calling song (4.7 kHz), the direction of the sound has little effect on the amplitudes of the sounds acting on the tympanum, but large effects on their phase angles, especially of the sound waves entering the tracheal system at the contralateral side of the body. The master parameter for causing the directionality of the ear in the forward direction is the sound wave entering the contralateral thoracic spiracle. The phase of this sound component may change by 130–140° with sound direction. The transmission of sound from the contralateral inputs is dominated by a very selective high-pass filter, and large changes in amplitude and phase are seen in the transmitted sounds when the sound frequency changes from 4 to 5 kHz. The directionality is therefore very dependent on sound frequency. The transmission gains vary considerably in different individuals, and much variation was also found in the directional patterns of the ears, especially in the effects of sounds from contralateral directions. However, the directional pattern in the frontal direction is quite robust (at least 5 dB difference between the 330° and 30° directions), so these variations have only little effect on how well the individual animals can approach singing conspecifics.

Comparison of rapid and short-term adaptation in the auditory nerve

Events during the first few milliseconds of auditory-nerve adaptation appear to differ qualitatively from those occurring later on. This has previously been revealed using PST analysis with various bin-width sizes, and also by dissecting the perstimulatory response into two components: rapid and short-term adaptation. In order to further evaluate the extent of these differences, a series of perstimulatory and post-stimulatory comparisons were made involving the recovery from prior stimulation and the effects of sound frequency and intensity. Post-stimulatory effects on both rapid and short-term firing rates appear to be proportional to the magnitude of the conditioning or adapting response, and otherwise to be independent of sound frequency. Following stimulation, the rapid component recovers more quickly than does the short-term component. Changes in sound frequency do not alter the amount of perstimulatory short-term adaptation, but effect the rapidly adapting component in a complex manner. This may be due in part to frequency splatter produced by non-CF tones, and also to phase locking to individual cycles of low-frequency tones. Implications for models of adaptation will be discussed. [Work supported by NSF and NIH.]