using the model of lamb & simon ( j . physiol. , lond . 263 , 257 ( 1976 ] , which treats the photoreceptor layer as a square array of cells , each coupled through a resistive gap junction to the four cells around it , we show that the signal : noise ratio for small-area stimuli is much greater than would be expected from a model in which receptors are assumed to be perfectly coupled .
C0206117
gap junction
C0007634
cells