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UBC Theses and Dissertations

The relationship between speed of visual perception and flicker-induced harmonic cortical activity Wright, Robert Leslie Douglas


The hypothesis was presented that speed of visual perception is related to degree of harmonic cortical response which can be elicited by intermittent photic stimulation, through some mechanism of CNS sensitivity to afferent stimulation. This hypothesis was based on Hebb's theory of the neuron assembly, and on Mundy-Castle's observations of the cortical effects of photic stimulation. Experimental examination of this hypothesis was made on a sample of fifty young adult volunteer subjects of both sexes. Recognition threshold was measured by tachistoscopic presentation of ten simple geometric patterns at exposures ranging upwards from ten milliseconds, until correct identifications of all patterns were made. The MRT score (recognition threshold) consisted of the average for the ten scores over an ascending and descending series. The EEG measurements were made in the conventional manner, and scored for variations in frequency pattern by measurement of electronic frequency analysis records. Photic stimulation at frequencies of 6 to 16 c/sec. was provided by an electronic stroboscope during the EEG recording. The results obtained from these procedures did not support the original hypothesis. The obtained correlation of 0.27 was not significant at the .05 level of confidence. An after-the-fact inspection of the data showed that the original hypothesis was applicable to roughly half of the subjects tested, and that these subjects could be selected by means of a third independent variable. The group showing this relationship was characterized by relatively high dominant EEG frequencies, and relatively loose organization of frequency pattern with little or no alpha activity In the normal or low frequency ranges. Due to limitations of method and sample size, this relationship could not be conclusively determined. While a generalization of universal validity was not established, one of restricted application was suggested. The possibility was discussed that speed of visual perception may be related to certain EEG criteria of cortical sensitivity to extrinsic stimulation. Further experiments in this field were proposed.

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