Effect of image orientation and size on object recognition: Responses of single units in the macaque monkey temporal cortex

This study examined how cells in the temporal cortex code orientation and s ize of a complex object. The study focused on cells selectively responsive to the sight of the head and body but unresponsive to control stimuli. The majority of cells tested (19/26, 73%) were selectively responsive to a part icular orientation in the picture plane of the static whole body stimulus, 7/26 cells showed generalisation responding to all orientations (three cell s with orientation tuning superimposed on a generalised response). Of all c ells sensitive to orientation, the majority (15/22, 68%) were tuned to the upright image. The majority of cells tested (81 %, 13/16) were selective fo r stimulus size. The remaining cells (3/16) showed generalisation across fo ur-fold decrease in size from life-sized. All size-sensitive cells were tun ed to life-sized stimuli with decreasing responses to stimuli reduced from life-size. These results do not support previous suggestions that cells res ponsive to the head and body are selective to view but generalise across or ientation and size. Here, extensive selectivity for size and orientation is reported. It is suggested that object orientation and size-specific respon ses might be pooled to obtain cell responses that generalise across size an d orientation. The results suggest that experience affects neuronal coding of objects in that cells become tuned to views, orientation, and image size s that are commonly experienced. Models of object recognition are discussed .