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Fig. 8.4. Internally generated and environmental input patterns. The three top images depict prenatal input patterns on the retina and the PGO pathway in gray scale from black to white (low to high). (a) A sample retinal wave pattern from the ferret (see also Figure 1.2) is used to motivate the actual patterns in HLISSOM experiments. (b) The "noisy disk" representation of retinal waves is used to organize the orientation map prenatally. A light disk models activity in the ON channel and a dark disk that in the OFF channel. (c) A PGO activity configuration of three dark noisy disks, corresponding to the two eyes and the nose/mouth area, is proposed to underlie prenatal development of face preferences. The three bottom images are samples of visual inputs, including those of (d) nature, (e) landscapes, and (f) faces. Randomly located retina-size segments (such as those shown by white squares) are used to train and test V1, and full face images to train and test the FSA, measuring how the variation in postnatal training affects the orientation map and how the face preferences develop postnatally. Sources: (a) Feller et al. (1996), (d) Shouval et al. (1996, 1997), (e) National Park Service (1995), (f) Achermann (1995), copyright 1995 by University of Bern.