Evaluation of a sound-generator chip: The AY 3-8910

Despite the continuing decrease in computer prices, psychoacoustic research is still expensive because of the high cost of sound-generation equipment and software. A single-chip sound generator was evaluated as an inexpensive tone/noise generator, amplitude attenuator, envelope modulator, and sound mixer. Although the chip has some limitations, it offers important advantages for pilot research and laboratory demonstrations.     

Low-noise microvolt level calibrator for measurement of performance of biosignal recording systems

A calibrator, the noise level of which is below the noise level generated in the preamplifier system, was needed for testing and development of a multichannel recording system. A multichannel preamplifier head assembly was used for recording cortical, subcortical, and cerebellar slow potentials and multiunit activity in freely moving cats and restrained rabbits. An inexpensive, battery-powered, lownoise voltage signal generator for calibration of the preamplifiers is described. The circuit provides a square-wave output at a frequency of 10 or 1000 Hz, and the peak-to-peak (p-p) amplitude can be selected at 10, 100, or 1000µV. The measured output noise of the calibrator is below 2µV (p-p, 0.1–6000 Hz). The frequency and amplitude values can be easily adapted for different purposes by changing a few component values. An amplified (gain 1,000×) test output for direct oscilloscope monitoring is included in the calibrator circuit.     

A small pulse generator for calibrating EEG recording systems

A battery-powered pulse generator of uncomplicated circuit arrangement has the advantage of being easily constructed and, also, can be positioned in a confined testing area in order to simulate the low-amplitude signals of a S. It may be especially useful for EEG recording systems for small animals. In this way, the complete recording system, including connecting cables, can be calibrated, and its performance readily assessed with respect to frequency response and to susceptibility to noise pickup.     

Coherence masking protection for speech in children and adults

In three experiments, we tested the hypothesis that children are more obliged than adults to fuse components of speech signals and asked whether the principle of harmonicity could explain the effect or whether it is, instead, due to children's implementing speech-based mechanisms. Coherence masking protection (CMP) was used, which involves labeling a phonetically relevant formant (the target) presented in noise, either alone or in combination with a stable spectral band (the cosignal) that provides no additional information about phonetic identity and is well outside the critical band of the target. Adults and children (8 and 5 years old) heard stimuli that were either synthetic speech or hybrids consisting of sine wave targets and synthetic cosignals. The target and cosignal either shared a common harmonic structure or did not. An adaptive procedure located listeners' thresholds for accurate labeling. Lower thresholds when the cosignal is present indicate CMP. Younger children demonstrated CMP effects that were both larger in magnitude and less susceptible to disruptions in harmonicity than those observed for adults. The conclusion was that children are obliged to integrate spectral components of speech signals, a perceptual strategy based on their recognition of when all components come from the same generator.     

A self-contained,regulated, burst-firing constant-current ac shock generator

A line- and load-regulated constant-current ac shock generator has been designed for animal behavior experiments. The self-contained unit has four operating modes, amplitude adjustment, and a leakage current detection circuit. A unique feature of this generator is that the good load regulation achieved by using a high-voltage source is preserved without such problems as arcing and high current density effects. Circuit schematics, along with a discussion of selected circuits, are included. Experimental data are presented to demonstrate the utility of the device.     

Sensorimotor synchronization during gait is altered by the addition of variability to an external cue

Sensorimotor synchronization has been used in the rehabilitation of gait, yet much remains unknown regarding the optimal use of this technique. The purpose of this study was to test the hypothesis that adding small amounts of variability to the motion of a vertically oscillating treadmill would affect the behavior of healthy walkers. Sixteen young adults walked on a treadmill and pneumatically actuated platform for one control trial (no oscillation) and eight trials in which the walking surface oscillated in the vertical direction under different conditions of variability. During the oscillation trials, the mean frequency of oscillation was equal to the preferred step frequency of the participant, but each individual cycle period was allowed to vary within a pre-determined range from 0% (no variability) to ±25% (high variability) of the mean cycle period. The amount of variance of each cycle period within each condition was drawn randomly from a white noise generator. Synchronization was improved when a small amount of noise was added to the platform motion but synchronization significantly decreased at higher levels of noise. Coefficient of variation of stride duration was relatively unchanged at lower levels of variability, but increased significantly at higher levels of variability. Statistical persistence of stride duration was significantly reduced during all trials with vertical oscillation relative to normal walking, but was not significantly altered by variability in the treadmill oscillation. These results suggest that the addition of a small amount of random variability to the cycle period of an oscillator may enhance sensorimotor synchronization of gait to an external signal. These data may have implications for the use of synchronization in a therapeutic setting.     

A programmable,multifunction dual-channel waveform generator for visual psychophysics

This paper describes a relatively low-cost, flexible means of presenting patterns on a CRT. The design allows for a number of options, such as presentation of gratings as well as nonstandard stimuli (white noise), the summation and differentiation of outputs to create complex luminance waveforms, and the switching of information from one channel to the other. In addition, the visual pattern generator permits a number of temporal options, such as phase reversals and the ramping on and/or off of a stimulus. This device incorporates a hardware means of scaling grating contrast. Finally, our procedure for producing synchronization signals, which uses internally generated interrupt signals, allows a number of software options, such as keyboard scanning and reaction timing, without significant time losses.     

A personal computer programmable sine-wave generator

A programmable sine-wave generator has been developed that permits microcomputer control of both discrete and continuous variations in the frequency and amplitude of auditory, visual, or vibrotactile stimuli. The function and design of the sine-wave generator as a peripheral to the Apple II/FIRST system are detailed. Moreover, adaptations of the basic sine-wave circuit are briefly described for interfacing it with other microcomputers (e.g., the IBM PC and compatibles), and for altering the waveform, range, and resolution of the output. Sample programs in Apple II/FIRST and Applesoft BASIC for controlling signal frequency and amplitude are used to illustrate the simplicity of programmable control. The sine-wave generator has many of the capabilities of commercially available ones, at a fraction of the cost.     

Spectral frequency and the modulation of the acoustic startle reflex by background noise

The rat's (Long-Evans) acoustic startle reflex to a high-frequency tone burst (10.5 kHz) was depressed by intense high-frequency band-pass noise (8-16 kHz) but enhanced by low frequency noise (1-2 kHz). However, contrary to the hypothesis that the depression of startle in intense background noise is produced by sensory masking, the reflex to a low-frequency tone burst (at 1 kHz) was depressed by both high- and low-frequency band-pass noise. Two additional hypotheses are offered to supplement sensory masking in order to explain the asymmetry in these data. The first is that the intratympanic reflex, which acts as a high pass filter on acoustic input, is elicited in intense backgrounds. The second is that acoustic startle reflexes elicited by intense low-frequency tones are in part elicited by their high-frequency distortion products and that these distortion products are then masked by high-frequency background noise.     

A review of the effects of noise on human performance

The present review is concerned with the effects of noise, especially moderate intensity noise on performance. The review covers recent empirical results and theoretical approaches, and examines the importance of the nature of the noise, individual differences in response to noise, and other factors which modify the effects of noise. A central theme of the review is that it is essential to consider the nature of the task being performed in noise, and a profile of strategies of performance in noise is presented. Finally, recommendations are made about the direction and methodology of future research.     

A context noise model of episodic word recognition

Item noise models of recognition assert that interference at retrieval is generated by the words from the study list. Context noise models of recognition assert that interference at retrieval is generated by the contexts in which the test word has appeared. The authors introduce the bind cue decide model of episodic memory, a Bayesian context noise model, and demonstrate how it can account for data from the item noise and dual-processing approaches to recognition memory. From the item noise perspective, list strength and list length effects, the mirror effect for word frequency and concreteness, and the effects of the similarity of other words in a list are considered. From the dual-processing perspective, process dissociation data on the effects of length, temporal separation of lists, strength, and diagnosticity of context are examined. The authors conclude that the context noise approach to recognition is a viable alternative to existing approaches.     

An inexpensive pure-tone pattern generator

A low-cost sound pattern generator that is remotely programmable has been developed to produce pure-tone auditory patterns. The device, which is compatible with relay programming equipment, can generate either of two auditory patterns in the sequence ABA or BAB. The generator features an independently settable range of ON and OFF durations (0.1 to 1.0 sec) for pure-tone bursts and a selectable range (0.2 to 2.0 sec) of intercycle intervals. The inexpensive construction cost coupled with the flexibility of the timing characteristics of the generator should make it of interest to a wide variety of auditory researchers.     

A method of restraining goldfish during conditioning of electric-shock-induced suppression of breathing movements

An efficient method of holding individual fish in position for delivery of visual conditioned stimuli and electrical unconditioned stimuli, and for registration of breathing movements with a thermistor, is described. The holder restrains the fish gently and is readily opened and closed. In addition, a “mechanical fish” signal generator, for assessing thermistor performance in detecting breathing movements, and a safe constant-current electrical shock stimulus generator are described.     

Low-cost equipment for schedule generation III: Variable ratio and ancillary equipment

Circuits are described that extend earlier designs for schedule-generating equipment using complementary metal oxide semiconductor (CMOS) logic. Specifically, the circuits consist of a variable-ratio generator and a series of circuits providing ancillary equipment, including a simple elapsed-timer meter, a logic probe, a variety of logic functions, a pulse generator, and circuits for interfacing. All circuits are compatible with those previously described.     

Asymmetry of masking between noise and tone

A pure tone was used to mask narrow and wide bands of noise centered on the frequency of the tone. In a given experimental session, the sound-pressure level (SPL) of the tone was held constant and loudness balances were obtained between a masked and unmasked noise band of equal width. These results are compared to earlier measures of the partial masking of tone by noise. The comparison shows that noise masks a tone more effectively than the tone masks the noise. Although the effect of the tone on a critical band of noise is greater than its effect on either an octave-band noise or wide-band noise, it is considerably smaller than the effect of the noise on the tone. Decreasing the noise bandwidth still further to a subcritical width reduces the asymmetry of masking somewhat, but a difference at high intensities of about 20 dB between the masking effects of an equally intense noise and tone remains. Whether the masker is a tone or noise, masking ceases when the effective energy of the masked and masking stimuli is the same.     

Self-organization of cognitive performance

Background noise is the irregular variation across repeated measurements of human performance. Background noise remains after task and treatment effects are minimized. Background noise refers to intrinsic sources of variability, the intrinsic dynamics of mind and body, and the internal workings of a living being. Two experiments demonstrate 1/f scaling (pink noise) in simple reaction times and speeded word naming times, which round out a catalog of laboratory task demonstrations that background noise is pink noise. Ubiquitous pink noise suggests processes of mind and body that change each other's dynamics. Such interaction-dominant dynamics are found in systems that self-organize their behavior. Self-organization provides an unconventional perspective on cognition, but this perspective closely parallels a contemporary interdisciplinary view of living systems.     

The effects of different intensity levels of background noise on dichotic listening to consonant-vowel syllables

It has previously been shown that the right ear advantage in dichotic listening to consonant-vowel syllables is affected if a background noise is presented at the same time as the dichotic stimuli. What is not known is, however, if there is also an effect of varying the intensity level of the background noise. We therefore presented conversation or traffic noise background noise simultaneously with the dichotic syllable stimuli to healthy adult subjects. The intensity of the background noises varied between 50-65 dB in steps of 5 dB. The results showed that the right ear correct reports decreased, while left ear correct reports increased as a consequence of increasing background noise intensity. The effects were also stronger for the right ear, and for the traffic background noise condition, particularly at the two highest intensity levels. The results are discussed in terms of alertness and attentional mechanisms.     

The effects of road traffic noise and meaningful irrelevant speech on different memory systems

To explore why noise has reliable effects on delayed recall in a certain text-reading task, this episodic memory task was employed with other memory tests in a study of road traffic noise and meaningful but irrelevant speech. Context-dependent memory was tested and self-reports of affect were taken. Participants were 96 high school students. The results showed that both road traffic noise and meaningful irrelevant speech impaired recall of the text. Retrieval in noise from semantic memory was also impaired. Attention was impaired by both noise sources, but attention did not mediate the noise effects on episodic memory. Recognition was not affected by noise. Context-dependent memory was not shown. The lack of mediation by attention, and road traffic noise being as harmful as meaningful irrelevant speech, are discussed in relation to where in the input/storing/output sequence noise has its effect and what the distinctive feature of the disturbing noise is.     

Differential effects of noise and incentives on learning.

Three experiments are reported. In the first, monetary incentives improved the learning of nonsense words in response to colours only when the test order was the same as presentation order. In the second, incentives increased the recall of spatial location which served as an additional retrieval cue for nonsense words. In the third, noise was used to manipulate arousal. Noise during learning produced a significant decline in recall of locations for nonsense words. The results suggest that incentives increase attentional capacity, while noise does not. Previous results showing that noise increases the use of order cues are discussed and it is suggested that noise induces a type of learning which depends on order cues. Existing hypotheses about the nature of this process are noted but it is argued that further work is needed to select between them.