The interest in the systematic study of the circadian typology (CT) is relatively recent and has developed rapidly in the two last decades. All the existing data suggest that this individual difference affects our biological and psychological functioning, not only in health, but also in disease. In the present study, we review the current literature concerning the psychometric properties and validity of CT measures as well as individual, environmental and genetic factors that influence the CT. We present a brief overview of the biological markers that are used to define differences between CT groups (sleep-wake cycle, body temperature, cortisol and melatonin), and we assess the implications for CT and adjustment to shiftwork and jet lag. We also review the differences between CT in terms of cognitive abilities, personality traits and the incidence of psychiatric disorders. When necessary, we have emphasized the methodological limitations that exist today and suggested some future avenues of work in order to overcome these. This is a new field of interest to professionals in many different areas (research, labor, academic and clinical), and this review provides a state of the art discussion to allow professionals to integrate chronobiological aspects of human behavior into their daily practice.

Circadian typology: a comprehensive review.

The empirical short-form literature has been characterized by overly optimistic views of the transfer of validity from parent form to short form and by the weak application of psychometric principles in validating short forms. Reviewers have thus opposed constructing short forms altogether, implying researchers are succumbing to an inappropriate temptation by trying to abbreviate measures. The authors disagree. The authors do not oppose the development of short forms, but they do assert that the validity standards for short forms should be quite high. The authors identify 2 general and 9 specific methodological sins characterizing short-form construction and offer methodological suggestions for the sound development of short forms. They recommend a set of 6 a priori steps researchers should consider and 9 methodological procedures researchers can use to develop valid abbreviated forms of clinical-assessment procedures.

On the sins of short-form development.

Although peaks and troughs in cognitive performance characterize our daily functioning, time-of-day fluctuations remain marginally considered in the domain of cognitive psychology and neuropsychology. Here, we attempt to summarize studies looking at the effects of sleep pressure, circadian variations, and chronotype on cognitive functioning in healthy subjects. The picture that emerges from this assessment is that beyond physiological variables, time-of-day modulations affect performance on a wide range of cognitive tasks measuring attentional capacities, executive functioning, and memory. These performance fluctuations are also contingent upon the chronotype, which reflects interindividual differences in circadian preference, and particularly upon the synchronicity between the individuals' peak periods of circadian arousal and the time of the day at which testing occurs. In themselves, these conclusions should direct both the clinician's and the researcher's attention towards the utmost importance to account for time-of-day parameters when assessing cognitive performance in patients and healthy volunteers.

A time to think: Circadian rhythms in human cognition

This article reviews various procedures used in the analysis of circadian rhythms at the populational, organismal, cellular and molecular levels. The procedures range from visual inspection of time plots and actograms to several mathematical methods of time series analysis. Computational steps are described in some detail, and additional bibliographic resources and computer programs are listed.

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Procedures for numerical analysis of circadian rhythms.

Review of Principles of Behavior.

Horne & Ostberg morningness-eveningness questionnaire : A reduced scale

Adaptation and standardization of a spanish version of the morningness-eveningness questionnaire: individual differences

Temporal properties of some biological systems and their fractal attractors

Standardization of a reduced scale of morningness in Spanish population: Individual differences. This study presents the standardization of the reduced scale of Horne y Ostberg's questionnaire, constructed by Adan and Almirall. Use of the Horne y Ostberg questionnaire has provided important differential results in parameters that present circadian rhythmicity, however some of the 19 questions had little discriminatory power and/or adduce infomation about other different dimensions. The reduce scale is the result of selecting those items that are related to Morningness and, above all, help to define this dimension better. We have selected a sample of students and workers with different work schedules (morning-afternoon, and night), controlling the age variable. At the same time, information was collected for the EPQ questionnaire in order to correlate preferences and the personality dimensions extraversion and neuroticism, and determine the relationship between them. Also it has been studied the priority of the variables con importance or work schedule in morningness scores an extraversion and morningness, while sex and neuroticism show no significant differences.

Estandarización de una escala reducida de matutinidad en población española: diferencias individuales

Better to understand the relation of auditory to visual reaction time (RT) tasks during a long period (320 min.) as well as the evolution of these performances along time, 24 subjects were tested. RT tasks were delivered at 10-min. intervals for 320 min. Correlations between auditory and visual RTs and cross-correlation functions were calculated. Our results confirmed their association, which was maintained throughout the experiment. There were no significant differences in the mean RT by sex or time of day; however, differences were found for the trend slope between type of stimulus and sex.

Helena Almirall

Papers

Horne & Ostberg morningness-eveningness questionnaire : A reduced scale

Adaptation and standardization of a spanish version of the morningness-eveningness questionnaire: individual differences

Temporal properties of some biological systems and their fractal attractors

Estandarización de una escala reducida de matutinidad en población española: diferencias individuales

Auditory and visual reaction time in adults during long performance