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.     

A method for calibrating an eye-monitoring system for use with infants

An algorithm for calibrating data from an infrared corneal reflection eye movement monitor is described. The algorithm is designed for use with infants and other noninstructable subjects.     

A recruitment theory of force-time relations in the production of brief force pulses: the parallel force unit model

A theory, the parallel force unit model, is advanced in which the buildup and decline of force in rapid responses of short duration are assumed to reflect variability in timing of several parallel force units. Response force is conceived of as being a summation of a large number of force units, each acting independently of one another. Force is controlled by either the number of recruited force units or the duration each unit contributes its force. Several predictions are derived on the basis of this theory and are shown to be in qualitative agreement with empirical findings about both the mean and variability of brief force impulses. The model also has consequences for the temporal properties of a response. For example, under certain circumstances, it predicts a reciprocal relation between reaction time and response force. Although the theory is proposed as a psychological account, relations between the assumptions and basic principles in neurophysiology are considered. Possible future applications and generalizations of the theory are discussed.     

A method for calibrating the spatial coordinates of a visual display to high accuracy

High-resolution CRT displays are subject togeometric distortion: lines that are straight in the internal coordinates of the graphics software and hardware are curved when projected onto a plane in the observer’s line of sight. As the available resolution of CRT screens increases, it becomes more difficult to measure and correct for this distortion. We present a simple, highly accurate method for determining the mapping between internal coordinates and the viewing plane. It requires that an observer, using a calibration program, adjust triples of displayed points until they are collinear. A metal straightedge placed between the observer and the screen aids in this judgment. We describe the calibration of an IBM Enhanced Graphics Display in high-resolution mode (350 × 640 pixels), and illustrate how to use the estimated mapping to choose internal coordinates to draw undistorted figures that are accurate to within 0.5 pixel. The method can be used to assess or to correct the accuracy of visual displays. The method is relevant to experiments in spatial vision, spatial perception, perception of dot patterns, and any application in which geometrically accurate stimuli are required.     

Magnitude estimates for electrical pulses: evidence for two neural mechanisms

The hypothesis that there are two neural mechanisms for electrocutaneous stimulation--one that is sensitive to low current and is adaptive to repeated stimulation and another that is responsive to high current and is less adaptive--was tested in a control and four main experiments. In the main experiments, magnitude estimates obtained for single electrical pulses (of 2-msec duration) were described by a simple power function for each combination of high- and low-current levels and 10 trial blocks. The results were: (1) The slope of the power function for low current was steeper than was that for high current; (2) for low current, the intercept of the power function decreased with increasing block, whereas for high current, it remained constant over blocks; (3) this decrease of the intercept for low current disappeared when judgmental blocks were separated by a rest period of 8 min; (4) the modulus did not affect the slope; (5) for a large modulus combined with low current, the intercept decreased rapidly over trial blocks, whereas for a small modulus combined with high current, the intercept increased over trial blocks. The first four findings support the two-mechanism hypothesis, but the last one may also be interpretable in terms of the regression to absolute scale values.     

A day unit for families

The Family Day Unit at the Maryborough Hospital, London, carries out an intensive treatment programme for highly dysfunctional families. Up to ten families attend the Unit five days per week from nine a.m. to three p.m. They stay for a period of at least three months and not longer than fifteen months. Normally some twenty to thirty patients, adults and children, attend every day. This paper gives the reasons for setting up this Family Day Unit. The aims and structure of the Unit are described, the treatment method outlined and some preliminary results are discussed.     

Detection of tactile pulses

ROC curves were obtained by the rating-scale method for the detection of brief mechanical pulses presented to the finger and dorsal forearm to study differences in detection processes at the two sites. An adaptive psychophysical procedure was successful in equating detectability at the two sites when data were averaged across sessions. Criteria adopted by the Os appeared to depend on locus of stimulation, since fewer false alarms were given at the arm than at the finger. These findings were discussed with respect to continuous and multistate detection models.     

Simulated alcoholic delirium

Of 200 diagnosed cases of alcoholic delirium 5 (= 2.5%) involved, from the differential diagnostic viewpoint, simulation of alcoholic delirium with all the symptoms involved. The symptoms of the simulation case are compared with the acute symptoms, and points in common to all simulation cases are presented: Definite alcoholic anamnesis, wide experience of treatment for alcohol abuse, dynamics of a pronounced purposeful action when social complications are imminent and course of the symptoms when the interview turns to simulation. In connection with therapy, special attention is drawn to Distraneurin treatment, which is not indicated in such cases.     

Multiple independent identification decisions: a method of calibrating eyewitness identifications

Two experiments (N = 147 and N = 90) explored the use of multiple independent lineups to identify a target seen live. In Experiment 1, simultaneous face, body, and sequential voice lineups were used. In Experiment 2, sequential face, body, voice, and clothing lineups were used. Both studies demonstrated that multiple identifications (by the same witness) from independent lineups of different features are highly diagnostic of suspect guilt (G. L. Wells & R. C. L. Lindsay, 1980). The number of suspect and foil selections from multiple independent lineups provides a powerful method of calibrating the accuracy of eyewitness identification. Implications for use of current methods are discussed.     

An aversive conditioning unit for ants

An apparatus is described for studying aversive conditioning in ants. The aversive stimulus is mechanically produced vibration. Responses are recorded automatically by an infrared photocell system.     

Magnitude estimation of short electrocutaneous pulses

Summary A comparison was made of electrocutaneous magnitude estimation data across two experiments with contextual differences not involving stimulus parameters, such as number and range of stimuli and relative position of the standard in the stimulus range. The data were fitted by 2-parameter linear, log-linear and power functions. When the data are fitted by either linear or log-linear equations, both intercept and slope parameters are significantly affected by the different contextual factors. When the data are fitted by a power function, however, only the intercept is altered; the slope remains invariant despite contextual changes introduced in the second experiment.Although the empirically derived psychophysical power law has been applied to magnitude estimation data for all other sensory modalities, its application to electrocutaneous stimuli has been less successful.     

Partial integration of single electrocutaneous pulses

Psychometric functions generated by single eleetroeutaneous stimuli yielded a median coefficient of variation ( σ/μ ) of 0.23. These data are consistent with other psychometric data recently reported by us which yielded σ/μ ratios of this size. The data are discussed and related to conflicting data reported in the recent literature indicating coefficients of variation for this mode of stimulation which are only 1/3 as large. Evidence is presented for partial temporal summation (time-intensity reciprocity) for electrocutaneous stimuli ranging from 175 to 610 microseconds. The data are best fitted by the equation I x t^a = k, where a is approximately 0.57. This equation and exponent also fit summation data reported by the same authors who report finding steep psychometric functions. Clearly, then, the mechanism responsible for the very limited temporal summation found for eleetrocutaneous stimulation and the mechanism responsible for very steep psychometric functions are not identical. The discussion also includes speculation regarding possible mechanisms and suggestions for research.