Orientation-selective fMRI adaptation in primary visual cortex revisited

Abstract

The ability to discriminate orientations is at the core of our visual experience. Orientation selectivity in human visual cortex has been inferred from psychophysical experiments and more recently demonstrated with functional magnetic resonance imaging (fMRI). One method to identify orientation-selective responses is fMRI adaptation, in which two stimuli – either with the same or with different orientations – are presented successively. A region processing orientation should demonstrate an adapted response to the ‘same orientation’ condition in contrast to the ‘different orientation’ condition. So far human primary visual cortex (V1) showed orientation-selective fMRI adaptation only in experimental designs employing long adaptation periods (∼ 40 s) and so-called top-up stimuli that are thought to keep up the adapted level. This finding has led to the notion that short-term adaptation in V1 (but not V2 or V3) cannot be detected using fMRI. The present study aimed at re-evaluating this question by testing three differently timed adaptation designs. With the use of a more sensitive analysis technique, we show for the first time orientation-selective fMRI adaptation in V1 evoked by a short-term adaptation design.