Research groups use the single motion stimulus design of Dr. D.Tadin ​(Tadin, Lappin, Gilroy & Blake, 2003) that allows to putatively assess spatio-contrast excitatory and inhibitory effects from duration threshold data of motion perception. The present work presents the correct neurocomputational model for this experimental design and analyses issues related to data and model comparisons, among which: (1) once the full computational model that predicts the psychophysical results is properly defined, it is shown that two low-level models of how inhibition acts on neuronal activity, i.e. “divisive inhibition” and “subtractive inhibition”, predict exactly the same thresholds and cannot arguably be claimed that one is better than another one, (2) it is excitatory and inhibitory processes that are the mechanisms shaping threshold changes, i.e. perceptual “facilitation” and “suppression” in the behavioural domain, (3) that this experimental design allows a quantitative comparison and usage of such “contrast–size tuning” data, (4) that such studies must be carefully designed once the model is correctly understood and applied, because of the rather large parameter space (~10-12 variables) necessary to explain the behavioural measures even in such simple experiments.