PubMed Health⌕ Search

Biomedical subjects

V S Johnston

Publications and source records attributed to V S Johnston.

At least 19 recordsLinked to original sources
PubMed1999

Gender differences in late positive components evoked by human faces.

Event-related potentials (ERPs) were recorded in male and female participants in response to 32 male and 32 female faces. Participants were instructed to simply look carefully at each face; after ERP collection they were asked to rate each face on a 5-point attractiveness scale. A positive correlation between average rating and average P300 scores to opposite sex faces was observed in male (r = .40) and in preovulatory (r = .41) and postovulatory (r = .44) female subjects. Correlations to same sex faces were only found in postovulatory females (r = .61). Male participants showed a much larger average P300 than did female participants, and the P300 evoked in female participants was unexpectedly larger to female than to male faces. Neither task relevance nor stimulus probability is a plausible explanations for these findings because they were experimentally controlled. These results support the emotional value hypothesis, according to which classical P300 processes reflect an affective evaluation of the stimulus, which in turn produces context updating.

Adolescent↗
PubMed1993

Changes in cognitive and emotional processing with reproductive status.

Behavioral ratings on several affective scales (non-erotic/erotic, unpleasant/pleasant, simple/complex and low arousal/high arousal), and electrophysiological responses (event-related brain potentials) to emotional pictures, were collected from 30 female subjects, at different phases of their menstrual cycle. The pictures belonged to 5 emotional categories, whose content was babies, dermatological cases, ordinary people, male models and female models. The subjects were grouped into hormone defined phases, according to their expected levels of androgens, estrogen or progesterone. The data were analyzed to determine if emotional or cognitive processing was sensitive to the reproductive status, as indicated by menstrual phase. Only one component of event-related potentials, the P3 component, varied with menstrual phase. Baby and male model pictures elicited larger P3 waves when progesterone level was high. High progesterone was also associated with a decrease in complexity and eroticism to all picture categories. An increase in the pleasantness of all categories was evident when estrogen levels were high. The results are interpreted as support for a general proximal design, whereby emotional and cognitive processes are adaptively regulated by reproductive status.

Adult↗
PubMed1991

The relationship between menstrual phase and the P3 component of ERPs.

Event-related potentials (ERPs) and behavioral ratings were collected from 30 female subjects who were exposed to picture slides. The slides belonged to five affective categories whose content was babies, dermatological cases, ordinary people, male models, and female models. Based on the day of testing relative to their menstrual cycle, the subjects were grouped according to their expected levels of androgens, estrogen, or progesterone. The data were examined to determine whether any ERP component or behavioral rating (non-erotic/erotic, unpleasant/pleasant, simple/complex, and low arousal/high arousal) varied as a function of subjects' hormone defined menstrual phase. Only the P3 component was sensitive to menstrual phase. The P3 to babies and male models was largest when progesterone levels were high. High progesterone was also associated with a decrease in the complexity and eroticism of all slide categories. An increase in the pleasantness of all categories was evident when estrogen levels were high. The results are interpreted as support for an "adaptive context updating" theory of the P3 component of ERPs.

Adult↗
PubMed1984

Computer programs as theories in biology.

Complex theories in biology may be developed, refined, and tested by the use of computer programmed simulations. The computer is recognized as a powerful tool for theory development; it is, in fact, the only means of thoroughly testing and examining a large and intricate theory. A program as a text is a statement of a theory and when run on the computer it is model of that theory. As the program's behavior is then the major argument for the credibility of a large and complex theory, the program itself is the only irrefutable statement of the theory. Bur programs written in the currently available programming languages tend to be incomprehensible. We argue that the program should be the definitive statement of the theory. In addition, the program plus a series of abstractions is a vehicle for effective communication of complex theories in biology. Several techniques of computer science are borrowed, for the purpose of developing a methodology for abstraction and a language for representing abstractions. The arguments are fully illustrated with a recently published biological theory.

Communication↗
PubMed1983

A neural theory of cognitive development.

A physiologically based model of the neocortex has been developed in an attempt to elucidate possible structural and functional mechanisms of the mammalian cortex and account for a wide range of low level cognitive behavior. The model has been constrained by diverse empirical data. At the level of structural details, neuroanatomical and neurophysiological data have been considered and at the level of gross behavior, psychological data has been used. From the theory that groups of reverberating neurons provide a short term memory mechanism and that primary drive reduction triggers consolidation of a memory, a mechanism for selective learning has been developed. Fundamental to the model is the postulate of a novelty drive mechanism that functions in a manner analogous to the more widely accepted primary drives (e.g. hunger and fear). This paper examines the novelty drive mechanism and demonstrates its utility in accounting for a wide range of habituation behaviors. The success of the model is evaluated by comparing its behavior to appropriate empirical data. Finally, it is argued that a computer program is both a theory and a model, and that important advantages accrue from such a viewpoint.

Animals↗
PubMed1974

Electrophysiological correlates of meaning.

The use of context-sensitive symbols offers an appropriate methodology for investigating the representation of meaning in the brain. This approach revealed that late components of frontal, but not occipital, evoked potentials reflect the change of meaning of a symbolic stimulus when it appears in different temporal contexts.

Evoked Potentials↗