Modeling the approximate number system to quantify the contribution of visual stimulus features.

•A novel, descriptive, non-redundant specification of dot array stimuli is given.•A model of the ANS that accounts for non-numerical stimulus features is proposed.•The Weber fraction (w) from the model is shown to be more valid and reliable.•All participants are biased by non-numerical stimulus features.•Most participants primarily rely on number, as instructed.