By using near-infrared spectroscopy (NIRS), we measured the changes in the oxygenated and deoxygenated hemoglobin (oxy-Hb and deoxy-Hb, respectively) concentrations while performing visual tasks. We conducted experiments using two tasks: a shape recognition task and a position recognition task. It was found that the oxy-Hb concentration was substantially higher in the lateral occipital regions during shape recognition than during position recognition. The changes in the oxy-Hb concentration were considered to reflect the activation difference between the two tasks. No difference was observed in the oxy-Hb concentration during the memorization of shape and memorization of position. The deoxy-Hb concentration was different between the two tasks only when different stimuli were used but not when identical stimuli were used. In addition, it was suggested that the deoxy-Hb concentration is more sensitive to activation difference between the hemispheres and the activation at some regions. Measurements of the oxy-Hb and deoxy-Hb concentrations would reflect different aspects of cortical activations. The present results showed that measuring the oxy-Hb and deoxy-Hb concentrations separately can differentiate the activation of the regional cortical functions.
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