Abstract
Recent neurophysiological observations on the development of orientation and spatial-frequency tuning in the primary visual cortex are equivocal—some studies report that tuning is virtually complete as soon as it can be measured while others report significant sharpening of both aspects of tuning. The issue is important because it bears on the mechanisms that produce the tuning: is tuning acquired simply from careful combination of the weakly tuned lower mechanisms in the midbrain (LGN) or is intra-cortical or even cortico-thalamic interaction required to produce the much tighter tuning seen in cortical cells? Here we provide unequivocal behavioural evidence derived from psychophysical, 2-AFC critical band-masking experiments with human observers, showing that spatial-frequency tuning develops over the first tens of milliseconds. We discuss the implications for the implementation of the characteristics we measure.