An analysis of behavioral plasticity in male Caenorhabditis elegans.

Caenorhabditis elegans is a simple soil-dwelling nematode which has two sexes, hermaphrodite and male. The male C. elegans is differentiated from the hermaphrodite by the presence of 14 sensory structures in the tail. In this study, we compared the behavioral responses of males and hermaphrodites to head-touch and to tap. We hypothesized that the anatomical difference in sensory structures might result in behavioral differences in the reversal response to vibratory stimulation (a tap to the side of the holding dish). In the response to increasing intensities of tap, both sexes showed an increase in response magnitude, with the males showing larger responses than hermaphrodites. In addition, the male was shown to be capable of simple nonassociative learning: it demonstrated habituation and recovery from habituation in a similar manner as the hermaphrodite. Tail-touch-induced inhibition of the reversal response appeared to be similar in males and hermaphrodites. The evidence suggests that the touch withdrawal circuit in hermaphrodites is also present in the male C. elegans, and that the subtle differences in response to tap seen in males may result from the additional sensory receptors of the copulatory bursa of the tail. It seems clear from these studies that these structures do not play a key role in the male worm's response to tap.     

Stability and change in a perspective reversal illusion

A phenomenologieal explanation is presented for the stability and instability of the appearance of the form of objects as a consequence of changes in (1) the spatial position of the observer with respect to the object, and (2) the amount of time the object is observed from a specific spatial position. In support of the explanation, an object was constructed so that it would have multiple appearances when observed continuously from the same viewpoint. The initial appearance of this object when observed from different spatial positions and the constancy over time of these appearances were demonstrated to be in agreement with the theoretical expectations.     

Modification of excessive drinking by cue exposure

The value of an individual case study depends to a large extent on the nature of the predictions which are tested. If, for example, behaviour is modified by a method which flies in the face of current theory and practice, then it is worth reporting, and if detailed predictions about day-to-day changes are confirmed, so much the better. This individual case study was designed to test the possibility that excessive drinking behaviour can be modified by prolonged exposure to drinking cues.Our approach is based on the hypothesis that addictive behaviour is analogous to discriminated operants. We are also making the assumption that drinking, in the alcoholic, is frequently reinforced through the avoidance of unpleasant consequences (e.g. an escalation in anxiety, frustration or withdrawal symptoms) and that these avoidance responses are discriminated since they are triggered only by certain cues.Avoidance learning has been investigated in humans and animals for at least 50 years but in recent years strong evidence has accumulated which suggests a particular modification procedure. First, it has now been demonstrated that, in animals, a very effective extinction procedure involves exposure to the discriminative stimulus (i.e. cue) whilst blocking the avoidance response (Baum, 1969). Second, psychologists have considered obsessive-compulsive rituals to be analogous to avoidance responses (Hodgson and Rachman, 1972). Compulsive gas-tap checking, for example, avoids both catastrophic events and also unpleasant emotional states. During the last ten years an effective method of modifying obsessive-compulsive rituals has been developed which involves exposure to significant cues followed by response prevention which is either supervised (Meyer, 1966) or self-imposed (Rachman et al., 1971; Hodgson et al., 1972). The same method has also been successful in the modification of compulsive masturbation (Hodgson and Rachman, 1975).     

Pythagorean distance and the judged similarity of schematic stimuli

Independent groups of Ss rated the similarity of pairs of patterns belonging to the same class, either bef ore or af ter a discrimination task of schematic concept formation (SCF). Mean similarity increased as a function of SCF pretraining. A linear relationship was found between a Pythagorean distance measure on the patterns and subjective similarity of pairs of stimuli (r=.88). No such relationship was obtained from an analysis of judgments from a group that viewed random, nonschematic stimuli. A secondary analysis of the discrimination judgments in the SCF task showed that the Pythagorean distance measure was predictive of judgments on pairs of stimuli from the same schema family, but the relationship did not hold for pairs representing two different schemata. Multidimensional scaling analyses indicated that mildly deviant schematic stimuli were perceived to be instances of a single family. The dimensions describing a schema cluster appeared to be specific to the sample of stimuli. A tendency for the Kruskal procedures to collapse certain types of stimulus clusters was observed and discussed.     

A comparison of ranking and rating procedures for value system measurement

Compared the validity and reliability of 2 value measurement techniques. 296 Ss (161 females and 135 males) in introductory psychology filled out the 2 measurement techniques and an attitude survey. The Rokeach Value Survey instructed Ss to separately rank 2 sets of 18 values in order of importance. A rating version of the Value Survey instructed Ss to rate the same 36 values from 1 to 99. 236 Sreturned 6 weeks later and again filled out both measurement techniques. Results of the multimethod factor analysis indicate very good convergent validity among the 4 measures of a given value (2 techniques × 2 sessions) and very good discriminant validity between measures of different values. Probably due to the ipsative nature of the ranking procedure, the test-retest reliabilities were higher for the ranked measurements than for the rated measurements. The construct validity of both measurement techniques, as determined by multiple regression and analysis of variance, were similar. Despite criticisms of ranking procedures, both the ranked and the rated versions were of equal reliability and validity.     

A structural analysis of stability in the perceived form of objects rotating in depth

Summary The stability and form of the two different appearances of a simple rotating object were explained by considering both the geometric transformations interrelating these appearances and their degree of organization. The analysis was then used to guide the construction of two complex rotating objects each expected to have multiple appearances. The results of an experiment confirmed the predicted form of the objects' initial appearances (illusory), the relative stability in time of these appearances and the form of the subsequent appearances (also illusory). The veridical appearances were never seen despite continued observation during two 10 min periods.We wish to thank P. Hamilton, A. Pearsall, A. Vadum, and H. Vadum for their help with this research. Requests for reprints should be sent to the first author at 1 Howatson Way, Worcester, Massachusetts, 01609, USA     

Is writing affected by spelling performance and beliefs about spelling?

This study examined relations between self-efficacy and outcome expectancy beliefs and spelling and writing performance. Perceptions about spelling and writing were assessed in 258 collegeage participants. Spelling performance was measured through a 50-item spelling test and writing performance by a holistically scored writing sample. The most highly correlated variables included spelling outcome expectancy and writing outcome expectancy, spelling selfefficacy and writing self-efficacy, spelling performance and spelling self-efficacy, and spelling and writing performance. A causal model relating perceptions, spelling performance, and writing performance was proposed and its appropriateness estimated. Direct effects on spelling were found for spelling self-efficacy, while spelling self-efficacy had indirect effects on writing performance and spelling had a direct effect on writing performance. The causal model was discussed in terms of changing conceptions of writing instruction and traditional views of the role of spelling as a necessary component of good writing.     

Behavioral and genetic characterization of habituation using Caenorhabditis elegans

This review surveys the literature that investigates the behavioral characterization and cellular and molecular mechanisms of habituation using the model organism Caenorhabditis elegans. In 1990, C. elegans was first observed to show habituation to a non-localized mechanical tap. The parameters that govern this behavioral plasticity in C. elegans were subsequently characterized, which lead to the important hypothesis that habituation is mediated by multiple mechanisms. Many tools are available to C. elegans researchers that allow for relatively easy genetic manipulation. This has lead to a number of recent genetic studies that have begun to identify key genes and molecules that play a role in the mechanisms of habituation. Some of these genes include a vesicular glutamate transporter, a glutamate receptor subunit, a dopamine receptor and downstream intracellular signaling molecules, such as G proteins and kinases. Some of these genes only affect certain parameters of habituation, but not others supporting the hypothesis that multiple mechanisms mediate habituation. The field of research has also led to the dissection of different phases of memory (short-term vs. long-term memory for habituation), which are triggered by different training paradigms. The differences in mechanism between these various forms of memory are also beginning to be revealed.