In this paper, we analyze the activity of single fibers in the optic nerve of a frog. Our method is to find what sort of stimulus causes the largest activity in one nerve fiber and then what is the exciting aspect of that stimulus such that variations in everything else cause little change in the response. It has been known for the past 20 years that each fiber is connected not to a few rods and cones in the retina but to very many over a fair area. Our results show that for the most part within that area, it is not the light intensity itself but rather the pattern of local variation of intensity that is the exciting factor. There are four types of fibers, each type concerned with a different sort of pattern. Each type is uniformly distributed over the whole retina of the frog. Thus, there are four distinct parallel distributed channels whereby the frog’s eye informs his brain about the visual image in terms of local pattern independent of average illumination. We describe the patterns and show the functional and anatomical separation of the channels. This work has been done on the frog, and our interpretation applies only to the frog.

This chapter discusses retinal anatomy and proposes that a deciphering of this anatomy is possible. The relative size of dendritic field to receptive field is such that the anatomical and functional groups can be matched. In attempting to decipher the anatomical differences by means of the functional differences, the discussion comes to the hypothesis that, with respect to the discrimination of silhouettes, the inner levels of the inner plexiform layer are concerned with boundaries, whereas the outer levels are concerned with average, or changes in the average, illumination. This hypothesis can be extended to account for the fact that bipolar cells that end exclusively in the outer levels of the inner plexiform layer are connected only to cones, whereas those that end deepest in the inner layers are connected to both sorts of rods as well as the cones.

Key words: retinal anatomy, dendritic field, receptive field, anatomical differences, functional differences, inner plexiform layer, boundaries, illumination, bipolar cells

The frog’s retina projects into the superficial neuropil of the opposite tectum in four functionally different layers of terminals. Each layer displays a continuous map of the retina in terms of its particular function. The four maps are in register. The fourth-dimensional order is reconstituted after section and regeneration of the optic fibers.

Two neural mechanisms are described which exhibit recognition of forms. Both are independent of small perturbations at synapses of excitation, threshold, and synchrony, and are referred to partiular appropriate regions of the nervous system, thus suggesting experimental verification. The first mechanism averages an apparition over a group, and in the treatment of this mechanism it is suggested that scansion plays a significant part. The second mechanism reduces an apparition to a standard selected from among its many legitimate presentations. The former mechanism is exemplified by the recognition of chords regardless of pitch and shapes regardless of size. The latter is exemplified here only in the reflexive mechanism translating apparitions to the fovea. Both are extensions to contemporaneous functions of the knowing of universals heretofore treated by the authors only with respect to sequence in time.