To achieve more valid data from eye-tracking, the question of how to design a test becomes exigent. However, only a few publications focused on this issue. As a result, large variations in test design were observed in the above-mentioned studies. The variations in the eye-tracking tests include: number of images per picture (varying from 1 to 10); content of question (preference, perception of healthiness, willing to try, willing to purchase, or expected intensities of sensory properties of food
products); and type of evaluation (free viewing-task, forced choice, rating, ranking, or projection mapping).