How does Daniel Tammet use imagery in Born on a Blue Day: Inside the Extraordinary Mind of an Autistic Savant?

Examples of Imagery:

"I know it was a Wednesday, because the date is blue in my mind and Wednesdays are always blue, like the number 9 or the sound of loud voices arguing." Chapter 1, p. 1

"The cacophony of different noises - magazine pages being flicked and Walkmans playing loud, thudding music and people coughing and sneezing and talking noisily - made me feel unwell and I pressed my fingers into my ears when it felt as though my head was about to shatter into a thousand pieces." Chapter 7, p. 117