SLOWING DUE TO ACUTE-HYPOXIA ORIGINATES EARLY IN THE VISUAL-SYSTEM

Background: Experiments in the visual modality show that acute hypoxia slows the earliest stage of information processing-preprocessing. It is unknown, however, whether a later stage, feature extraction, is als o slowed. Methods: To answer this question, an additive factors method (AFM) experiment was conducted which employed seven well trained subj ects whose arterial oxyhaemoglobin saturation was controlled at 63% wi th low oxygen mixtures. The subjects responded to oddball names presen ted on a computer screen and both reaction time (RT) and the event-rel ated brain potential P300 were measured. The luminance and quality of the names was varied factorially to influence the preprocessing and fe ature extraction stages, respectively. Results: RT and P300 latency sh owed the same pattern of results: stimulus luminance and signal qualit y were additive, indicating that AFM assumptions were met; hypoxia and stimulus luminance were interactive but hypoxia and signal quality we re additive. Conclusion: In conjunction with other evidence, we interp ret these results to indicate that the locus of slowing produced by hy poxia is largely at the preprocessing stage, at least in the visual mo dality. Slowing at the preprocessing stage can be explained by hypoxia shifting the function relating RT and stimulus luminance to the right by a constant amount.