On the detection of stepwise changes in a constant signal level

A stepwise change in the frequency of a continuous pure tone is taken as an element signal. The detectability of a single step is compared with the detectability of a pattern composed of two such steps in order to determine the ways in which the steps interact and how these interactions depend upon the time interval between the steps. It is shown that two positive steps separated by D msec interact by summation (d’ for two steps being greater than d’ for a single step) and that this summation is 100% even when D=100 msec. The extent of summation decreases as D is increased beyond 100 msec, leveling off at about 40% when D is near 1,000 msec. A positive step followed by a negative step (an increment) presents a more complex picture. When D=0 msec, the pattern is the null signal, and, of course, the two steps subtract completely. As D is increased, the extent of subtraction decreases, becoming zero when D is about 400 msec. Increasing D beyond 400 msec results in summation, reaching about 40% when D=2,000 msec. For D less than about 1,000 msec, the sign of the second step in a two-step signal is important: two steps of like sign summate, and two steps of unlike sign subtract. However, when the two steps are separated by about 2,000 msec, the sign of the second step is irrelevant: summation occurs, and the extent, about 40%, is the same for two steps of like sign and two steps of unlike sign. A brief theoretical discussion stresses the extant need for an information-processing theory of signal detection.     

Substance use/abuse as a predictor to illegal and violent behavior: A review of the relevant literature

The preponderance of the research evidence supports the conclusion that abuse of certain types of illicit drugs, separately from the abuse of alcohol, predisposes to subsequent violent behavior. The relationship of cocaine/crack to violent crime has been established more clearly for users of crack in inner city areas than it has for those who are users of other forms of cocaine in the general population.In regard to any race/ethnic or socioeconomic factors in the relationships between substance use/abuse and violent behavior, most clearly established is that a higher proportion of young Black males, compared to other race/ethnic groups, are actively involved in dealing cocaine/crack in some inner city poverty areas.As for gender differences, the research evidence indicates that alcohol abuse as a predictor to and a precipitant of violent behavior, is more clearly established for males than for females. Drug abuse, as distinct from alcohol abuse, has been found to predict subsequent violent behavior, for females as well as for males. “Co-morbidity,” the combination of substance use with and psychopathology, appears more likely to predict for females to later violent behavior. Psychopathology and mental health problems are less likely to predict occurrence of either violent or criminal behavior in the future than are either alcohol abuse or drug abuse.     

Stereoscopic acuity for photometrically matched background wavelengths at scotopic and photopic levels

Two Ss made equidistance settings in a two-rod apparatus using white and four chromatic (red, yellow, Feen, and blue) backgrounds, photometrically matched at each of eight or nine teat levels within a total retinal-illuminance range of 4 log units. The binocular depth setting were analyzed in terms of the angular magnitude of both the Yariable error, η_AD, and the constant error, η_ΔR When η_AD is plotted as a function of retinal illuminance, the curves for each of the four chromatic IIIId white backlfound coditions show that at low retinal illuminances, η_AD, is initially large, and with increasing background illumination, η_AD progressively decreases to approach a final low asymptotic value. As predicted by the duplicity theory of vision, each experimental curve shows a dircontinulty at about ?1.0 lot td (corresponding to a background luminance value of about 0.0069 fL with the 2.5-mm artificial pupil used) reflecting the transition from rod to cone functioning. The curves representing the different wavelengths essentially overlap throughout the total illumination range, indicating that, for both rod and cone vision, wavelength has no differential effect on the variability of depth settings. The data for η_ΔR are less regular than those for η_AD and the rod-cone discontinuities appear less pronounced. The data are analyzed in terms of the relative contribution of the rod and cone mechanisms to performance level.     

Low-variance stimulus-response latencies: Deterministic internal delays?

When special procedures are used to minimize S-R latency variance, all responses fall within a distribution which has a standard deviation near 10 msec. This minimum SD is the same whether the mean latency is at the simple RT limit or as much as 400 msec longer than that limit. Over this range, the latency distribution is everywhere the same, symmetrical and highly-peaked and not typical of RT. Above a mean latency of 550 msec, variance increases as the mean increases in the way that would be expected if SD/M were constant for the delay in excess of 550. By way of interpretation, it is proposed that there are internal time delays which can be inserted into the S-R chain. These delays can be adjusted to any value between 0 and about 400 msec, but once set, they can be deterministic. Other considerations are discussed which suggest that the deterministic time delays are in the afferent part of the S-R chain.     

Memory scanning by children: Meaningfulness and mediation

Two experiments were performed for the purpose of isolating factors that influence speed of memory scanning by children. The first experiment revealed an interaction involving age and type of stimulus. Young children required relatively greater time to process ambiguous stimuli. The second experiment, involving a pretraining phase designed to induce mediation, showed that preschool children scan representations more rapidly when given instructions to apply a mediator.