Methods for improving the signal-to-noise ratio of endogenous-evoked potentials

A stimulus leads to a cortical response (i.e., evoked potential [EP]) which may be recorded from electrodes attached to the scalp. However, background cortical activity, considered as noise (n), is typically of equal or greater magnitude than the response, which is considered as signal (s). This situation leads to the masking of the presence of the electrocortical signal. Two methods are described which enable the enhancement of the signal with respect to the noise. The first method outlined is time-domain averaging. Its relation to Fourier averaging is also presented. Time averaging can lead to an enhancement of the signal with respect to the noise, known as the signal-to-noise ratio (SNR), by a factor of root N; N being the number of trials recorded. However, latency variability (i.e., jitter) present in the signal leads to a decrement in this maximal potential enhancement. The second technique is an adaptive filter method of averaged cross-correlations, developed by Woody (1967), which deals with the variable latency problem. The development of a latency corrected average developed by McGillem and Aunon (1977) is also presented. The final section describes methods for data handling once the electrocortical signal has been enhanced. It is then necessary to describe the EP quantitatively. Principal Components Analysis (PCA) allows for the quantitative compact representation of the evoked potential waveform. The method also allows for the testing of the effects of explanatory variables on the EP.     

A brief neuropsychological screening battery to detect brain damage in a psychiatric population

Seventy-five patients admitted to the psychiatric unit of a general hospital were administered a brief neuropsychological screening battery. Discharge diagnoses obtained from the medical records revealed that 20% had brainbased pathology. A discriminant function analysis resulted in a five-variable model (Symbol-Digit Modalities Test, educational level, Psychiatric-Organic subscale of the MMPI, and Shipley Vocabulary and Abstraction scores) which correctly classified 84% of the subjects, with 87% correct identification of the brain-damaged group. A jackknife cross-validation procedure resulted in comparable hit rates.     

Imaginary companions in childhood and adult creativity.

Case material is presented to illustrate the thesis that the ability to create an imaginary companion during childhood is an early expression of the special ego aptitudes found in creative individuals in adult life. Such "companions" allow these children to attempt to master creatively a variety of narcissistic mortifications suffered in reality and to displace unacceptable affects. In creative adults who had imaginary companions in childhood, the early fantasies serve as an organizing schema in memory for the childhood traumata. Stimuli in adult life which evoke the earlier traumata may revive the original imaginary companion fantasies. These then serve as nodal bases for the creation of specific adult works of art.     

Some effects of positive life events on community mental health

Measures of positive and negative events were derived from a life-event inventory to test the predictions of an equilibrium model and a positive mental health model of psychological well-being. These measures were related to indicators of individual and community well-being with data obtained through a household survey of 454 residents. Residents who reported more negative events also reported more psychological distress and less positive adjustment. Positive events were associated with reports of positive adjustment. An analysis of census tract scores on life events revealed that the relative absence of positive events in census tracts was associated with higher service utilization rates to the community mental health center serving those tracts. The number of negative events was unrelated to service rates for census tracts but was related to several demographic indicators of well-being.     

Child performance on discrimination tasks: Effects of amount of stimulus variation

Two independently conducted studies investigated stimulus variation effects on children's discrimination learning. The stimuli in the first study were generated by a conjunctive rule and were presented in pairs. Mean trials to criterion was significantly lower for the single-feature change treatment (17.4) than for the multiple-feature change treatment (29.9). Single-feature change-treatment transfer scores were significantly higher only for stimuli that differed in terms of one of the features. The second study not only replicated the initial finding concerning the single-feature change treatment but also found that students made more errors in reaching criterion when stimuli were generated by an exclusive disjunctive rule and were presented singly. For all tasks, the single-feature change treatment with stimuli presented in pairs was accompanied by fewer errors to criterion than the other treatments.     

Imaginary companions, fantasy twins, mirror dreams and depersonalization.

Illustrative case material is presented to demonstrate genetic linkages between the presence of imaginary companions or fantasy twins and extensive mirror play in childhood and early adolescence, and the appearance of mirror dreams and depersonalization in later adolescence and adulthood. The defensive splitting of the self-representations observable in these phenomena is viewed as a means of warding off castration anxiety and anxiety about object loss, anxieties which arise because of conflicts primarily centering on intense aggressive drive derivative wishes. Formulations about depersonalization are discussed.