title: Retina is structured to process an excess of darkness in natural scenes.
abstract: Retinal ganglion cells that respond selectively to a dark spot on a brighter background (OFF cells) have smaller dendritic fields than their ON counterparts and are more numerous. OFF cells also branch more densely, and thus collect more synapses per visual angle. That the retina devotes more resources to processing dark contrasts predicts that natural images contain more dark information. We confirm this across a range of spatial scales and trace the origin of this phenomenon to the statistical structure of natural scenes. We show that the optimal mosaics for encoding natural images are also asymmetric, with OFF elements smaller and more numerous, matching retinal structure. Finally, the concentration of synapses within a dendritic field matches the information content, suggesting a simple principle to connect a concrete fact of neuroanatomy with the abstract concept of information: equal synapses for equal bits.
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Charles P
authors.initials: CP
authors.lastname: Ratliff
authors.forename: Bart G
authors.initials: BG
authors.lastname: Borghuis
authors.forename: Yen-Hong
authors.initials: YH
authors.lastname: Kao
authors.forename: Peter
authors.initials: P
authors.lastname: Sterling
authors.forename: Vijay
authors.initials: V
authors.lastname: Balasubramanian
mesh_terms: D000818:Animals; D015350:Contrast Sensitivity / Q000502:physiology*; D003624:Darkness; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D006168:Guinea Pigs; D006801:Humans; D012160:Retina / Q000033:anatomy & histology / Q000166:cytology; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000502:physiology; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure; D013997:Time Factors; D014795:Visual Pathways / Q000502:physiology