Point process analysis of noise in early invertebrate vision
Fig 7
The dominant noise transition from extrinsic to mean delay, with intensity β, is consistent for light models with differing relative flicker speed, γ.
Parameter γ indicates the number of bumps which can be received per Markov switch time of the light model. Higher γ therefore means a relatively slower flicker. At lower γ less information is available and hence the MSE higher. The ‘Snyder, delay’ curves are MMSE values obtained with the Snyder filter optimised for a deterministic delay set to the mean QB latency. These lower bound the noise introduced by the cascade. The ‘Integrate-fire, all noise’ ones are upper bounds as they involve processing the QBs from the fully stochastic Nikolic model. The closeness of both of these curve sets reflects the dominance of mean delay among cascade noise components. This hypothesis is further confirmed by the closeness of ‘Integrate-fire, all noise’ with the MSE generated by applying the integrate-fire-Snyder on the deterministic Nikolic model, which only featured the mean delay (‘Integrate-fire, delay’) and fixed QB shapes. The ‘Snyder, photon noise’ gives the noise floor since it is the MMSE achievable at the front of the cascade. Convergence with this at low β shows cascade noise is unimportant in that regime. All curves are averages over 10 independent 8000 photon-QB streams with error bars indicating the maximum and minimum MSE swings around this value.