Mathematics – Logic
Scientific paper
Apr 1973
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1973slsci...4..231r&link_type=abstract
Space Life Sciences, Volume 4, Issue 2, pp.231-239
Mathematics
Logic
Scientific paper
In this research we raise two questions: (1) which is the order of magnitude of repeat variability of visual responsiveness during prolonged sessions, (2) does visual responsiveness depend on the time of the day. Because of the complexity of the visual process the reference to biological rhythm is rather vague. To answer the above questions we reviewed the available literature and we produce some findings recorded by us. By assuming as an index of variability the ratio of SD/Mean, the following conclusions may be drawn: Speed of reading suprathreshold material 5 26% Absolute threshold luminance 25 50% Amplitude of the electroretinographic response 7 14% Cortical potential evoked by sinusoidally modulated light 12 29% These figures refer to data recorded during sessions lasting a number of hours (covering the whole morning or the whole afternoon), the successive trials being suitably spaced in order to avoid fatigue. Circadian periodicity and morning vs afternoon differences are assumed to exist, although some authors deny them. Intra-session periodicities of a few ten minutes, of a few minutes, of a few seconds as well as of about 30 ms have been put into evidence by various authors, in psychophysical experiments. Their electrophysiological counterpart is found, partially at least, at the site of resting potential, of the discharge of retinal neurons, of electro-retinographic response as well as in spontaneous bioelectric brain activity. However, a complete picture of the phase relationships betwen peripheral and central periodicities is still lacking. The gamut of frequencies covered by visual periodicities is very wide. We do not know yet which are of basic importance and which are due to the overlap of finer periodicities, in the form of beats. In our opinion, this field of investigation is of interest from both theoretical and practical point of view. Many controversies might be solved by assuming a suitable sampling interval. The three-four hour interval has to be discarded in any case. In our sessions we adopt an intertrial interval no larger than 15 min. This seems the suitable compromise to avoid fatigue and to gain information about intradian periodicities.
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