A j2[absinbu cosbujdu 5274

Evaluation of this rather sinister looking integral is made easier when note is made that an even function is being integrated. After some algebra,

The equivalent intensity contrast, CIeSA , is found:

^ eSAmax eSA

Let a = r = b = 1°. These reasonable values give CIeSA = 0.437. If the contrast for one receptor alone directly under the spot is examined, CIe1 = 0.333. Thus, it appears that the SA architecture can improve equivalent intensity contrast.

A more realistic model of the synthetic aperture/MSP architecture that will improve neural signal contrast in a CE is shown in Figure 5.2-11. Here three adjacent retinula cells lying in three adjacent ommatidia with intensity DSFs s1(x), s2(x), and s3(x) have depolarizations due to effective absorbed intensities, Ie1, Ie2, and Ie3, respectively. The depolarizations Vr1, Vr2, and Vr3 are assumed to be summed at a lamina monopolar cell (LMC). The LMC hyperpolarizes by voltage Vm. Vm propagates electrotonically down the LMC axon, where it synapses with a medullary interneuron (MI), causing a hyperpolarization, Vi. It is the contrast in Vi caused by a moving object that is assumed critical in limiting spatial resolution.

FIGURE 5.2-11 Schematic of a three-ommatidia, one-dimensional, synthetic aperture system. The black spot is 2r° in diameter; The axes of the three ommatidia are separated by b°, and the DSF half-intensity angles are 0m/2 = a°.

Let the object be a black spot of radius, r. The DSF relations are s1(x) = 1/(1 + x2/a2) 5.2-77 A

The object is p(x) = Io {1 - [U(x + r) - U(x - r)]} 5.2-78 I F{*}

P(u)_ lo ^2n5(u)-5.2-79 The effective intensity at the kth retinula cell is

Thus, the voltages can be calculated

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