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Abstract
In a repeated measures design, the Vividness of Visual Imagery Questionnaire (VVIQ; Marks, 1973) was administrated to 10 participants each half hour in a single day between 8:00 and 20:00. The questionnaire was also administrated on four consecutive days following the original administration at 8:00, 14:00 and 20:00. These results were then fitted to a model with the superposition of two cosinusoidal functions. An analysis of the results suggested the coexistence of ultradian and circadian cycles in the determination of the vividness of visual imagery.