Interactions between two spatially separated letters presented in succession.

The interactions between two letters presented in succession to neighboring regions of retina were investigated. The interstimulus intervals were: 0, 20, 60, 250 ms, 2.5 s. In control trials single letters were presented in two positions corresponding to the positions of letters in pairs. The recognition of a letter presented as the first element of pairs with either simultaneous presentation or with 250 ms delay of the second element was significantly better than the recognition of single letters. On the contrary, the interstimulus interval 20 and 60 ms yielded an increase of errors made in the recognition of the first letter. The results are interpreted in terms of inhibitory interactions between transient and sustained channels, and in terms of hypothesized excitatory connections between the cortical cells responding to visual elements forming more complex patterns.