The effect of stimulus size on binocular luster and its implications for the interocular conflict model

Using a series of dichoptic center-ring-surround stimuli in a psychophysical experiment, we examined how the phenomenon of binocular luster is affected by the size of the central target area. Generally, we found that the lustrous sensation continuously decreases with increasing patch size. However, this effect also depends on further stimulus features such as the interocular contrast polarity pairings and the width of the ring element. To account for these complex influences on the magnitude of the lustrous response, significant extensions had to be made to our interocular conflict model. We present two improved versions of our model, a summation and an averaging model, which differ in the way the local conflict values are spatially integrated. Both versions have a very high predictive power. At least for the summation model, we show that the modifications are in good agreement with physiological processes. In particular, we provide evidence that the influence of stimulus size on the lustrous effect can be explained by the combination of two mechanisms: An increasing receptive field size of contrast detector cells and at the same time a decrease of the local density of these cells with increasing retinal eccentricity.