How knowledge of regional brain dysfunction in depression will enable new somatic treatments in the next millennium

New knowledge about the specific brain regions involved in depression is rapidly evolving due to advances in functional neuroimaging techniques. Several new regionally specific somatic interventions build on this modern neuroanatomic information. These latest methods promise to revolutionize the understanding and treatment of depression. This article reviews the past and current use of these techniques, with an eye toward where they are heading in the next century.     

Second-order reversed phi

In a first-order reversed-phi motion stimulus (Anstis, 1970), the black-white contrast of successive frames is reversed, and the direction of apparent motion may, under some conditions, appear to be reversed. It is demonstrated here that, for many classes of stimuli, this reversal is a mathematical property of the stimuli themselves, and the real problem is in perceiving forward motion, which involves the second- or third-order motion systems or both. Three classes of novel second-order reversed-phi stimuli (contrast, spatial frequency, and flicker modulation) that are invisible to first-order motion analysis were constructed. In these stimuli, the salient stimulus features move in theforward (feature displacement) direction, but the second-order motion energy model predicts motion in thereversed direction. In peripheral vision, for all stimulus types and all temporal frequencies, all the observers saw only the reversed-phi direction of motion. In central vision, the observers also perceived reversed motion at temporal frequencies above about 4 Hz, but they perceived movement in the forward direction at lower temporal frequencies. Since all of these stimuli are invisible to first-order motion, these results indicate that the second-order reversed-phi stimuli activate two subsequent competing motion mech-anisms, both of which involve an initial stage of texture grabbing (spatiotemporal filtering, followed by fullwave rectification). The second-order motion system then applies a Reichardt detector (or equiva-lently, motion energy analysis) directly to this signal and arrives at the reversed-phi direction. The third-order system marks the location of features that differ from the background (the figure) in a salience map and computes motion in the forward direction from the changes in the spatiotemporal location of these marks. The second-order system’s report of reversed movement dominates in peripheral vision and in central vision at higher temporal frequencies, because it has better spatial and temporal resolu-tion than the third-order system, which has a cutoff frequency of 3–4 Hz (Lu & Sperling, 1995b). In cen-tral vision, below 3–4 Hz, the third-order system’s report of resolvable forward movement of something salient (the figure) dominates the second-order system’s report of texture contrast movement.     

In defense of Southern Fundamentalism

The order of authorship is the reverse of the order of a previous paper by the same authors. The paper is a thoroughly collaborative project. We are grateful to a number of people for comments on earlier drafts, most especially Denny Bradshaw, Peter Clark, David Henderson, Harold Kincaid, Georges Rey, John Tienson, and an anonymous referee. The second author also wishes to thank the Centre for Philosophy and Public Affairs, Department of Moral Philosophy, University of St. Andrews, Scotland, and its award of a Tennent Caledonian Research Fellowship, which helped to fund his work on this paper.     

The conjunction fallacy? A reply to Bar-Hillel

In her commentary on our article, Bar-Hillel (1991) argues that our normative interpretation of the Lindaproblem is inaccurate and that the representativeness heuristic can account for all of the relevant data. I argue that the normative interpretation of the Linda problem remains slippery and that representativeness fails to account for much of the data. Furthermore, substantial evidence supports our suggestion that subjects use different underlying models in estimating likelihoods in different con problems.     

Developmental epidemiologically based preventive trials: Baseline modeling of early target behaviors and depressive symptoms

Describes a conceptual framework for identifying and targeting developmental antecedents in early childhood that have been shown in previous work to predict delinquency and violent behavior, heavy drug use, depression, and other psychiatric symptoms and possibly disorders in late adolescence and into adulthood. Criteria are described that guided choices of targets for two epidemiologically based, randomized preventive trials carried out in 19 elementary schools in the eastern half of Baltimore, involving more than 2,400 first-grade children over the course of first and second grades. Baseline models derived from the first of two cohorts show the evolving patterns of concurrence among the target antecedents. The central role of concentration problems emerged. From Fall to Spring in first grade, concentration problems led to shy and aggressive behavior and poor achievement in both genders and to depressive symptoms among girls. There was evidence for reciprocal relationships in girls. For example, depressive symptoms led to poor achievement in both girls and boys, whereas poor achievement led to depressive symptoms in girls but not boys, at least over the first-grade year. These results provide important epidemiological data relevant to the developmental paths leading to the problem outcomes and suggest preventive trials.     

A developmental study of the effects of irrelevant information on speeded classification

The study examined how well subjects were able to ignore the presence of irrelevant stimulus information as a function of age. Children aged 6, 9, and 12, as well as adult subjects sorted cards with one binary dimension relevant, and zero, one, or two dimensions irrelevant. Speed of classification was measured. Significant effects of age, sex, number of irrelevant dimensions, and relevant dimension on speed of classification were obtained, as well as a number of interactions of these variables. The most important finding was that the presence of irrelevant information interfered with the performance of the task by child subjects and that the magnitude of the interference declined with age. The results were interpreted as implying that developmental trends in attention may be most clearly demonstrated in tasks which require speeded processing of stimuli. The ease of administration of the speeded classification task, coupled with the clear developmental trends obtained, recommend this paradigm as a useful one with which to study the development of selective attention.     

Enhancement and summation in the perception of two successive vibrotactile stimuli

Enhancement and summation were found to be fundamentally different perceptual processes affecting the sensation magnitude of two successive vibrotactile stimuli. Enhancement, defined operationally as an increment in the subjective magnitude of one stimulus due to the presentation of a prior stimulus, and summation, defined as an increment in overall subjective magnitude of the two stimuli, were measured for sinusoidal vibration of the thenar eminence of the hand. The effect of summation was maximum when the two stimuli greatly differed in frequency, whereas maximum enhancement effects were found when both stimuli were close in frequency. The summation effect showed little decay as the interstimulus interval was increased to as much as 500 msec, whereas enhancement effects decayed to zero at approximately 500 msec. Results were similar to those obtained in comparable studies of audition and support the hypothesis that there are at least two distinct information-processing channels for the perception of cutaneous vibration.     

Memory trace strength and response biasing in short-term motor memory

Two experiments, which attempted to create differential memory trace strengths in a response biasing paradigm, were performed. After the presentation of the criterion location, an interpolated target was presented which was either ±40 deg from the criterion. The S’s task was to attend to both targets and recall each when instructed. The first experiment involved strengthening the criterion trace via repetition (0, 5, or 14 rep.) while the second involved providing additional feedback via visual, auditory, and heightened kinesthetic cues. In the initial experiment, a Repetition by Response Biasing interaction revealed that repetition systematically reduced error shifts at recall. The second experiment found that, in the combined feedback and visual conditions, response biasing was reduced. It seems feasible to suggest that both studies successfully manipulated memory trace strength which appears to be one determiner of error shifts at recall.     

Maximizing the coefficient of generalizability in multi-facet decision studies

For random-model, fully-crossed, two- and three-facet experimental designs the following two problems were considered. First, equations were developed for determining the optimal number of conditions of a facet for maximizing the coefficient of generalizability under the constraint that the total number of observations per subject is constant. Second, the problem of determining the minimum number of observations per subject for a specified generalizability coefficient is solved for the two-facet crossed design.