Fig 5. Extended examples of complex ISA models’ responses to sine-gratings.

Four complex model responses are shown as combinations of two linear subunits. The two left-hand sine-grating plots show the simple linear responses of individual subunits to sine-gratings varying between–π and π in each view. The right gratings (after the >) show the complex model response (sum of squares of the subunits). The complex models are chosen to illustrate different ‘types’ of complex cell model, A & B show models with high binocular disparity discrimination scores (see DDI section). In both models the sub-units exhibit strong binocular tuning in phase, resulting in a strong response to particular left/right phase combinations and low responses elsewhere. Phase separation of approximately π⁄2 between the two sub-units results in a quadrature pairing and consistently strong response to a particular disparity. C & D show models with low DDI. In model C, both sub-units are monocular (responses modulated only one eye) resulting in a monocular complex cell. Model C is not phase invariant however the DDI index is not sensitive to monocular phase invariance, other monocular phase invariant models may exist. Model D also shows monocular sub-units, however in contrast to model C the sub-unit are differently monocular in each eye. Model D does not show any invariance in phase and appears to be specialised to detect particular phase combinations.