Contrast-dependent dissociation of visual recognition and detection fields.

Seeing an object 'as something' is different from simply seeing it (see Watanabe, S., 1985, Pattern Recognition: Human and Mechanical, John Wiley). This distinction between recognition and detection often goes unnoticed in physiology and clinical practice, where visual performance is characterized in terms of acuity, visual field and contrast sensitivity. The corresponding functions of stimulus detection are consistent with the neural projection properties from the retina to the striate cortex, i.e. the 'cortical magnification theory'. Yet recognition performance for characters (Strasburger, H. et al., 1994, Eur. J. Neurosci., 6, 1583-1588) and grey-level patterns (Jüttner, M. and Reutschler, I., 1996, Vision Res., 36, 1007-1022) does not fit into this scheme. Here we show that this discrepancy results in the dissociation of visual recognition and detection fields, which is dramatic at low pattern contrast. Form proper can be appreciated exclusively within the much narrower field of recognition, the window of visual intelligence. Its function is, at low contrast, probably mediated by the magnocellular pathway and at all contrasts is determined by the processing characteristics of higher stages of the ventral visual pathway.