In Kieran Healy's introductory chapter of his book Data Visualization for Social Science, he informs the reader on how to critically think about data visualization. He opens a discussion regarding how people perceive graphs, what makes some graphs more apparent and accurate than others, and how to develop good judgment about data visualization. He states that human perception often affects the representation of data. People tend to unconsciously alter graphs even before they start plotting the data; trying to decide which graphing system to utilize, or customize labels and colors affect the correctness of the information. A notably interesting point that he makes is that optical illusions can significantly affect the interpretation of a graph. Simple things such as color or form can considerably affect the perception of data in totally unnoticed ways. Color hue, color luminance, and shapes (for example circles) may trick our mind and make it seem as if the gap difference between 2 variables are smaller than they are, or the opposite, broader than what it is. The real task for accurately representing data is to come up with methods that encode the information properly without harming the study. Taking close attention to our unconscious and being honest with the data is harder than what people might think. Human perception may alter data both when trying to represent information and when reading a graph. It is essential that the focus of a graph is solely to convey the information accurately; embellishments such as color or typography may alter data in negative and unexpected ways.