Normal development of pattern motion sensitivity in macaque monkeys.

We studied the development of sensitivity to complex motion using plaid patterns. We hypothesized, based on neurophysiological data showing a dearth of pattern direction-selective (PDS) cells in area medial temporal (MT) of infant macaques, that sensitivity to pattern motion would develop later than other forms of global motion sensitivity. We tested 10 macaque monkeys (Macaca nemestrina) ranging in age from 7 weeks to 109-160 weeks (adult). The monkeys discriminated horizontal from vertical pattern motion; sensitivity for one-dimensional (1D) direction discrimination and detection were tested as control tasks. The results show that pattern motion discrimination ability develops relatively late, between 10 and 18 weeks, while performance on the 1D control tasks was excellent at the earliest test ages. Plaid discrimination performance depends on both the speed and spatial scale of the underlying patterns. However, development is not limited by contrast sensitivity. These results support the idea that pattern motion perception depends on a different mechanism than other forms of global motion perception and are consistent with the idea that the representation of PDS neurons in MT may limit the development of complex motion perception.