Three-dimensional orientation tuning in macaque area V4

articles Three-dimensional orientation

tuning in macaque area V4.comDavid A. Hinkle and Charles E. Connor2002 Nature Publishing Group http://neurosci.natureTuning for 2D orientation in the image plane is prominent in

many areas of visual cortex and in multiple species15. Because

orientation tuning is so prevalent, especially in early visual

areas, most models of object recognition incorporate orientation analysis as the major initial stage in image processing69.

An important issue for such models is whether orientation signals are purely 2D or at least partially 3D. Orientation in the

real world is 3D. Elongated image elements (such as lines and

edges) are usually slanted in depth with respect to the viewer.

3D orientation is perceptible based on binocular disparity and

other depth cues, and could be useful for appreciating shapein-depth. Here we observed explicit tuning for 3D orientation

in area V4. This implies that orientation processing in the ventral pathway is 3D, and that initial stages of shape analysis

involve depth information.RESULTSWe studied 286 V4 neurons in two awake, fixating rhesus monkeys. We deliberately selected neurons tuned for 2D bar orientation (that is, orientation in the image or frontoparallel

plane). For each neuron, optimum 2D bar orientation, color,

width and binocular position disparity were determined in preliminary tests. These optimum values were then held constant

while stereoscopic slant (rotation about an axis in the image

plane positioned at the stimulus center and orthogonal to bar

orientation) was varied at 11.25 intervals.For the example neuron in Fig. 1a, the optimum 2D orientation was 146.25 (counterclockwise from horizontal). Preliminary tests showed that this neuron was not tuned for

position in depth (binocular position disparity) of standard

frontoparallel bars. Stimuli in the slant test were therefore centered in depth at the fixation plane (0 disparity). Thus, each

slanted bar appeared to be half in front of and half behind the

fixation plane. Bar length was set at twice the estimated classical receptive field (CRF) diameter, and bars were drifted backDepartment of Neuroscience, Johns Hopkins University School of Medicine and Zanvyl Krieger Mind/Brain Institute, 338 Krieger Hall,

3400 North Charles Street, Johns Hopkins University, Baltimore, Maryland 21218, USACorrespondence should be addressed to C.E.C. ([email protected])Published online: 17 June 2002, doi:10.1038/nn875Tuning for the orientation of elongated, linear image elements (edges, bars, gratings), first

discovered by...