Low Frequency Sine Wave Research Articles

Fine-to-coarse scale disambiguation in stereopsis

Spatial frequency selectivity has been incorporated into various theories of stereo matching, along with spatial scale interactions operating from coarse-to-fine spatial scales. We concentrate here on the role of fine scale information in the stereo matching process and show that fine scale information is capable of disambiguating matches made at coarser scales. An ambiguous coarse scale stimulus was created by presenting a low frequency (2 c/deg) sine wave in anti-phase to the two eyes, whose endpoints betrayed no information about which way the sine waves should be matched. It could be seen with crossed or uncrossed disparity equally validly and at chance from trial to trial. To this was added a fine scale (8 c/deg) filtered random dot stimulus specifying unambiguously a certain disparity. Observers judged the apparent depth of the two stimuli as the disparity of the fine scale stimulus was varied. The sine wave was usually perceived to have the same sign disparity as the fine scale stimulus. Depth matching with the two superimposed stimuli confirmed that the coarse scale stimulus was actually disambiguated, and seen with disparities equal to half its spatial period. The results suggest the operation of a cross-spatial scale matching disambiguation process, which can operate in a fine-to-coarse fashion.

Degradations due to stimulated Brillouin scattering in multigigabit intensity-modulated fiber-optic systems

The stimulated Brillouin scattering (SBS) process limits the maximum power that can be transmitted in low-loss optical fibers in multigigabit fiber optic systems. It is shown that recently observed large optical fluctuations resulting from SBS degrade the signal-to-noise ratio and consequently the system bit error rate. Since SBS has potentially the lowest power threshold of all fiber nonlinearities: it is critical that it be addressed. It is shown that the SBS threshold can be increased by providing a low frequency sine wave dither to the laser pre-bias current. It is found that a modulation index as low as 2% can quadruple the SBS threshold. Measurements with a 1.5- mu m externally modulated laser at 2.5 Gb/s indicate that this dither in no way degrades the performance in the presence of chromatic dispersion. >

Multi-Gbit/s optical time division multiplexing employing LiNbO3 switches with low-frequency sinewave drive

A four-channel optical time division multiplexing scheme is presented which employs cascaded optical switches and operates on standard non-return-to-zero format optical data channels. Only low-frequency electrical drive signals at the clock speed of the input channels are required for the switches, and low-jitter output signals are obtained after a complete Mux-Demux operation.

Motion capture anisotropy

Two uncorrelated random dot patterns were superimposed and alternated to produce dynamic incoherent noise. When a low spatial frequency sine wave grating was optically superimposed on this noise and moved in step with the alternation of the two frames, the incoherent motion was masked and all the dots were seen to adhere to the grating and to move with it as a single rigid sheet (“Motion Capture”). Over a wide range of displacements subjects could not discriminate uncorrelated noise which was “captured” from correlated noise patterns which moved physically in the same direction as the grating. In fact the motion signal from the low frequency grating was even strong enough to overcome signals from two correlated random dot patterns which moved in the opposite direction. Capture was not as strong if the direction of dot motion was orthogonal to the direction of grating motion. We conclude that in any dynamic visual scene the motion of certain salient features in the image tends to dominate our perceptual experience. The signal from low frequencies masks or inhibits the signal from the high frequencies. Since the latter now have no motion signal of their own they are assumed to move with the low frequencies. Thus, motion capture suggests an important biological role for long-range apparent motion: the process serves to preserve continuity of object identity while at the same time eliminating spurious motion signals that arise from finer image features. In this manner the visual system solves the “correspondence problem” without benefit from either computation or cognition.

Transmission of complex pressure waves through the perilymphatic fluid in cats.

The response of the perilymphatic fluid to complex pressure waves, composed of low-frequency sine waves superimposed on square-wave pressure pulses of varying amplitude was studied. In cats with a patent cochlear aqueduct a pronounced positive pressure change could be induced in the perilymphatic fluid when complex pressure waves were used. The time constants associated with the stabilization of the perilymphatic pressure after the application of pressure complexes were longer than those associated with square-wave pulses alone. The results indicate that the functional patency of the cochlear aqueduct could be influenced by the transmission of complex pressure waves. The results also indicate that when trying to influence the inner ear hydrodynamic balance in patients with Meniere's disease, the effect of complex pressure waves is far superior to the effect of square-wave pressure pulses in patients with an open cochlear aqueduct.

Displacement thresholds for coherent apparent motion in random dot-patterns

Two correlated random-dot patterns (A and B) were generated on a CRT screen and presented in rapid alternation; (B) was shifted horizontally by varying amounts in relation to (A) so that coherent apparent motion was seen. We found that larger shifts were tolerated if (i) the stimulus onset asynchrony (SOA) was longer; (ii) if the patterns were optically blurred; and (iii) if there were fewer dots on the screen. Hence apparent motion in random-dot patterns may involve a global pattern matching operation as in stereopsis. Two uncorrelated random-dot patterns were alternated to produce incoherent dynamic “noise”. A low spatial frequency sine wave grating was then projected on this “noise” and moved in step with the alternating random-dot patterns. This resulted in “motion-capture”—i.e. all the dots now seemed to move synchronously with the moving grating. The effect could not be obtained with high spatial frequency gratings or with stationary dots. As a tentative solution to the “correspondence problem” it is suggested that low spatial frequencies are matched first and these matches impose constraints on subsequent high frequency matches—thus allowing the system to home in on a unique solution.

A new electroreceptive teleost:Xenomystus nigri (Osteoglossiformes: Notopteridae)

The African knife fish,Xenomystus nigri, is found to be sensitive to weak electric fields by the method of averaged evoked potentials from the brain. Slow waves and spikes were recorded in or near the lateral line area of the medulla and the torus semicircularis of the mesencephalon in response to long pulses (best > 50 ms) and low frequency sine waves (best ca. 10 Hz) of voltage gradients down to < 10 μV/cm. Evoked waves in the lateral line area are a sequence of negative and positive deflections beginning with a first peak at ca. 24 ms; in the torus semicircularis the first peak is at ca. 37 ms. Spikes are most likely in the torus between 50 and 80 ms after ON. At each recording locus there is a best axis of the homogeneous electric field and a better polarity. Effects of stimulus intensity, duration and repetition are described. The physiological properties are similar to those of ampullary receptor systems in mormyriforms, gymnotiforms and siluriforms. Confirming Braford (1982),Xenomystus has a large medullary nucleus resembling the nucleus otherwise peculiar to mormyriforms, gymnotiforms and siluriforms and now called the electrosensory lateral line lobe (ELLL; formerly the posterior lateral line lobe). We describe the projections of anterior and posterior lateral line nerves by HRP applied to the proximal stump of a cut nerve. A descending central ramus of the anterior lateral line nerve and a lateral component of the ascending ramus of the posterior lateral line nerve end in part in the ELLL. Electroreception, including the system of discrete central structures mediating it, is for the first time found to be less than an ordinal or even a family character, but apparently a characteristic of the subfamily Xenomystinae. Species of the other subfamily, Notopterinae as well as of the other families of osteoglossiforms (Osteoglossidae, Hiodontidae and Pantodontidae), lack the ELLL.Notopterus andPantodon are found to lack the evoked potential. The positive finding of evoked activity to feeble electric field is found to be the most practical method for searching widely among fishes for the presence of the electrosense modality and its central pathways. The anatomical criterion of an ELLL can now be taken to be a good criterion for the presence of this sensory system. The absence of evoked response correlates well with the absence of an ELLL.

Fractional order sinusoidal oscillators: Optimization and their use in highly linear FM modulation

After recalling the major disadvantages of integer order sinusoidal oscillators, we use noninteger order filters to make oscillators of fractional order greater than 2. These oscillators are unusual not only in their order but also in their properties, due to an uncommon form of the oscillator frequency as regards the direct production of low frequency sine waves. An algebraic performance criterion for the quality of systems just above the threshold of oscillation gives the optimum fractional order ensuring the sharpest tuning and the greatest frequency stability. The fact that the special form of the oscillation frequency in such systems satisfies the requirements of linearization of frequency modulation characteristics, is used in low frequency FM at large deviation and high linearity.

Apparatus for the measurement of thermal diffusivity featuring a low-frequency sine-wave generator and a digital phase meter

The apparatus enables the thermal diffusivity of a wide range of solids to be measured to an accuracy of +or-2% using the Angstrom method. It features a low-frequency sine-wave generator which produces stable sinusoidal temperature conditions at the heater, and a digital phase meter which measures phase directly in degrees with a resolution of 0.1 degrees . A low-noise amplifier and an active bandpass filter are used to improve the signal-to-noise ratio whenever conditions are such that the signals from thermocouples or probes are weak. Results are reported of the thermal conductivity of samples of single-crystal silicon and germanium in the temperature range 300-700K.

A New Class of Scaled-Frequency SinusoidalRCOscillators

A novel scheme of a class of RC oscillators with operational amplifiers for low frequency sine wave output is described. Distribution of the RC parameters, grouped in four driving point functions which in turn are oriented in a fixed pattern with respect to the active devices, gives rise to a number of cases in the specified class. A few cases are listed here and appropriate stability study has been made for them. One of the schemes has also been experimentally tested and results tabulated.

A Three Phase Sine Wave Reference Generator For Thyrisitorised Motor Controllers

A variable frequency, variable amplitude three-phase low frequency sine wave reference generator is discussed in this paper. The frequency and amplitude are independently capable of being varied by means of two independent dc control voltages. This reference generator is well suited for closed loop control applications such as constant frequency power supplies, constant amplitude power supplies, induction motor control requiring a finite ratio between amplitude and frequency, etc. The reversal of polarity of the dc voltage controlling the frequency reverses the phase sequence. The reference generator has been very satisfactorily used in the control of a three-phase ``subharmonic'' pulse width modulated inverter. The reference generator is also suitable for cycloconverter control.

Contrast additivity: An alternative approach

Several investigators have demonstrated luminance additivity when subjects are required to detect the presence of abrupt luminance discontinuities (“edges”) in chromatically mixed fields. Experiment I shows that this result occurs for stimuli other than edges. Low and high frequency and contrast sine wave gratings approximate additivity more than homogeneous fields. Experiment II shows that additivity of contrast detection is destroyed when the B-W system is fatigued by a black and white grating. This non-additive result is explained within an opponent process model assuming that contrast detectors pool information from chromatic and B-W systems. The model can also explain additive results during conditions in which the B-W system is not fatigued.

On second order effects in a galvanic cell: Part I. Polarization by a sine wave modulated high frequency current

A theoretical study is presented concerning the application of a high-frequency alternating current, amplitude modulated by a low-frequency sine wave, to a galvanic cell. Based on the correlation with the faradaic rectification technique, expressions are given for the low-frequency demodulation voltages of the faradaic process and for the double-layer capacity. Both responses, which are in-phase with the modulation signal, are combined by considering them as voltage sources, having respectively the faradaic impedance and the double-layer impedance as internal impedances. The resulting demodulation voltage appears to possess an in-phase and a quadrature component, from which information can be obtained of the high-frequency as well as the low-frequency behaviour of the cell.

Linear and non-linear performance of transducer and pupil in Calliphora retinula cells.

1. Intracellular recordings have been made from the blowfly (Calliphora erythrocephala) retinula cell; apart from the transducer mechanism, these cells also feature a pupil mechanism. 2. At several mean intensity levels, within the apparently linear range of response, frequency characteristics of amplitude and phase and responses to 'delta'-flashes and 'delta'-flash pairs have been obtained. 3. Fourier methods have shown these responses to be mutually compatible, confirming linearity in these circumstances. 4. Non-linear behaviour can be made to appear at the lower frequencies when the modulation depth is increased. 5. Non-linearities can also appear through application of the superposition test: a low frequency sine wave, modulated so as to elicit an apparently linear response, and a high frequence sine wave which does not give rise to non-linearity even at the highest modulation depths can, when superimposed, yield a greater response to the latter when situated at the minima of the former than at its maxima. 6. At frequencies above approximately 1 Hz these superposition non-linearities are attributed to the transducer mechanism gain control. Below this frequency the pupil mechanism takes part considerably in the retinula cell's total observed gain control: its characteristics remain yet to be cleared up. 7. The transducer's linear and non-linear properties fit in closely with those of the Fuortes-Hodgkin model which couples increases in gain and time constants. 8. The Fuortes-Hodgkin model will probably require some quantitative modifications in the originally treated case of Limulus, on account of its pupil. 9. Finally, the merits of Veringa's diffusion model, and the possibility of eventually joining this model with the Fuortes-Hodgkin one are pointed out briefly.

A low frequency sine wave oscillator†

A now variable frequency oscillatory system is described. For certain system conditions the circuit produces a sine wave oscillation whose Frequency is varied over n wide range from ft very low to a high value simply by varying the gain of an amplifier rather than by changing the circuit time constant and accordingly no ganged condensers are used. Another important feature of the circuit is that the generation of a very low frequency oscillation is possible without incorporating a large value of the KC product. The oscillator utilizes an amplitude stabilizer operating on the controlled linear resistance of the initial region of the characteristic of a junction KET. The frequency relation is derived and the results are compared with experiment and found in agreement.

The instrumental assessment of visual range

The theory of a transmissometer is described in which low-frequency sine wave modulation is applied to two light sources separated by the atmosphere whose transmittance is to be measured. The phase difference between the signals detected by two photocells, one at each end of the system, is related to the transmittance by an almost linear relationship.

Binaural fusion: its limits as defined by signal duration and signal onset.

The results of two experiments on the interaural frequency limits for binaural fusion indicate that (1) the limits for binaural fusion decrease as a direct function of signal duration for both low- and high-frequency sine waves, and (2) signal onset is a significant factor in the determination of the spectral limits for binaural fusion only for high-frequency sine waves and low-frequency sine waves of short duration. In general, these results are consistent with a model of binaural interaction in which fusion is determined by a tonotopically organized mechanism, fusion being the product of binaural activity in a channel of limited bandwidth.

Digital Generation of Low-Frequency Sine Waves

Generation of approximately sinusoidal waveforms by a digital method is described. Very low frequencies (below 1 Hz) are easily obtained without the use of large inductors or capacitors, and the method is fully compatible with integrated circuit techniques. A process equivalent to nonrecursive digital filtering is used to remove the majority of harmonics from a binary waveform generated by a feedback shift register, leaving the fundamental together with only a few high-order harmonics of small amplitude.

A Low Frequency Sine Wave Generator for Observing the Frequency Response of the EEG Console

(1968). A Low Frequency Sine Wave Generator for Observing the Frequency Response of the EEG Console. American Journal of EEG Technology: Vol. 8, No. 1, pp. 1-6.

Tracking performance with advanced and delayed visual displays.

Human operator performance in continuous pursuit tracking when the stimulus either disappeared prior to the appropriate response time or appeared subsequently to that time was investigated. Tracking was one-dimensional, the stimulus appeared to vary randomly, and feedback of results wasn't provided. The stimulus, consisting of the sum of three low-frequency sine waves, appeared on recording paper tape, moving at 1.0 cm/sec. Masks hid the display in steps up to 1.0 secs, before or 0.5 secs. after the position of a manually-controlled pointer. Timing performance was measured by the peaks of cross-correlations of stimulus/response data pairs which had been successively shifted in time. Tracking performance was measured by RMS error. Timing was increasingly too early for advanced displays but followed closely the actual appearance time of delayed displays. RMS tracking error increased with increasingly advanced and delayed displays. Practice effects were negligible.