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.     

The collective representation of affliction: Some reflections on disability and disease as social facts

A perspective is developed for approaching affliction as a social fact. Disability and disease are considered as two ways in which we suffer a disjunction which arises from the need to take initiative with respect to the inexorable, whether that means the mark of disability or the unconquerability of disease. The story of affliction always raises and masks in certain respects the problem of suffering as the collective representation of our experience of subjectivity where that experience passes through the separateness of being marked to the singularity of being without hope.     

Inferential processing of context: Studies of cognitively impaired subjects

Language comprehension tasks involving pronoun coreference were administered to a group of demented patients, a group of patients with cardiac disease, and groups of normal elderly persons and young adults. Pronoun coreference was constrained by either lexical, syntactic, or contextual cues. No differences were found between old and young subjects for any task. While the demented patients were impaired on all tasks, the cardiac patients were specifically impaired in the inferential processing of context.     

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.     

Psychological management and body image issues in facial transplantation

Facial transplantation, although controversial, is proposed as a major advance in facial reconstructive surgery, with the first partial transplant having taken place in France in November 2005. Although the psychological impact of facial transplantation will not be understood until several procedures have been carried out, this article examines the psychological issues likely to arise with particular reference to body image. A detailed framework for anticipation and management of psychological change is proposed. Pre-operative preparation must include thorough psychological preparation for the patient and their family. The immediate post-operative period is likely to be challenging, and a detailed management plan is proposed emphasising early return to function; subsequent psychological issues including altered body image, anxiety, shame, depression, communication and behavioural avoidance are discussed and a management strategy based on cognitive behavioural principles is proposed for the first post-operative year. Previous discussion frames psychological outcome in terms of complication and risk, tending to downplay the potential advantages of a successful procedure; the focus of this paper is on ensuring psychological adjustment as an inevitable consequence of change.