Abstract
People and macaque IT cells are more sensitive to nonaccidental than metric differences (e.g., Biederman, et al., 2009; Kayaert, et al., 2003). For example, straight vs. curved contours (a nonaccidental difference) are more readily discriminated (and produce greater IT cell modulation) than two curved contours that differ in their degree of curvature (a metric difference). Similarly, parallel vs. nonparallel contours are more readily distinguished than two nonparallel contours that differ in their angle of convergence. Straight and parallel are singular values, zero curvature or convergence, respectively, as opposed to curvature or nonparallel, which can assume an infinite number of values. Are there spontaneous preferences for one or the other kind of value? And, if so, are these preferences manifested early in life. 5 mo. human infants and adults viewed a pair of geons arranged left and right on the screen. The geons differed in at least one nonaccidental, generalized cylinder property. For example, one geon could be a cylinder with a straight axis and the other a cylinder with a curved axis. Or one could have parallel sides (a cylinder or a brick) and the other nonparallel sides (a cone or a wedge). Both infants and adults showed a strong, significant, preference for initially fixating the geon with a nonsingular value, i.e., curved or nonparallel. Both groups of subjects also fixated longer on that initial value, although this effect was only reliable for the adults. This initial preference for nonsingular values, as well as search asymmetries which show pop out for nonsingular but not for singular values (Treisman & Gormican, 1988), may be a consequence of greater neural activation to such stimuli (and, possibly greater opioid release), as reflected in greater fMRI activation to the nonsingular values of these stimuli in the ventral pathway.
NSF BCS 04-20794, 05-31177, 06-17699.