Selectivity as well as Sensitivity Loss Characterizes the Cortical Spatial Frequency Deficit in Amblyopia

The processing deficit in amblyopia is not restricted to just high spatial frequencies but also involves low-medium spatial frequency processing, for suprathreshold stimuli with a broad orientational bandwidth. This is the case in all three forms of amblyopia; strabismic, anisometropic, and deprivation. Here we use both a random block design and a phase-encoded design to ascertain (1) the extent to which fMRI activation is reduced at low-mid spatial frequencies in different visual areas, (2) how accurately spatial frequency is mapped across the amblyopic cortex. We report a loss of function to suprathreshold low-medium spatial frequency stimuli that involves more than just area VI, suggesting a diffuse loss in spatial frequency processing in a number of different cortical areas. An analysis of the fidelity of the spatial frequency cortical map reveals that many voxels lose their spatial frequency preference when driven by the amblyopic eye, suggesting a broader tuning for spatial frequency for neurons driven by the amblyopic eye within this low-mid spatial frequency range. Hum Brain Mapp 30:4054-4069, 2009. (C) 2009 Wiley-Liss, Inc.