An eye-tracking study in Switzerland found that adults make 2.5 times more fixations (focusing their eyes on a single point) when reading short numbers compared to short words. For long numbers and long words, the number of fixations was seven times higher when reading numbers. The findings were published in Acta Psychologica.
Reading is a skill that everyone needs and frequently uses in daily life. This includes reading words and sentences, as well as numbers. Reading numbers is also commonly assessed in tests designed to measure mathematical abilities.
However, reading numbers is fundamentally different from reading words. These two activities engage different cognitive processes due to the distinct nature of language and numerical symbols. Reading words primarily relies on language-based regions of the brain, mostly in the left hemisphere, where familiar words are recognized and decoded using phonetic and semantic cues. In contrast, reading numbers involves additional or distinct brain regions, including those associated with numerical cognition and quantity processing.
Numbers are typically interpreted based on symbolic value rather than phonetics. This requires readers to recognize numerical relationships and quantities. Studies suggest that reading numbers can be more taxing for the brain, especially when dealing with larger or more complex sequences, as it demands greater working memory and attention to detail.
Study author Anne-Françoise de Chambrier and her colleagues investigated the eye movements of normal-reading adults while reading short and long Arabic numerals (i.e., numbers). They compared this to reading words and pseudowords of equal length. Pseudowords are strings of letters that follow a given language’s structure and phonetic rules but lack any actual meaning.
The study included 36 psychology students from the University of Lausanne in Switzerland, 27 of whom were women. Their average age was 21 years. All participants were native French speakers with normal or corrected-to-normal vision. They received course credit and 15 CHF (approximately $17) for their participation.
Participants were asked to read a total of 96 items in a single session lasting approximately 10 minutes. These items included 12 short numbers without separators (four digits), 12 long numbers with separators (8–11 digits), and 12 long numbers without separators. They also read words and pseudowords: 12 short words, 12 long words, 12 short pseudowords, and 12 long pseudowords. The words used were frequent French nouns, verbs, adjectives, and adverbs. The researchers tracked participants’ eye movements using specialized equipment.
The results showed that participants were 99% accurate in reading both words and numbers, with only 35 instances of misreading (out of 3,456 reads). These errors occurred most often with long numbers without separators.
Overall, participants made 2.5 times more fixations when reading short numbers compared to words of equal length. They made seven times more fixations when reading long numbers compared to long words. Additionally, participants made three times more saccades when reading short numbers compared to short words and nine times more saccades when reading long numbers compared to long words.
Fixation duration and saccade amplitude were similar when reading short words and short numbers. However, reading long numbers resulted in longer fixation durations than reading long words (300 ms vs. 250 ms), and saccade amplitude was lower when reading long numbers.
Saccades are rapid eye movements that shift focus from one point to another. Saccade amplitude refers to the angular distance or extent of each saccadic movement, indicating how far the eyes travel between fixations. Fixation duration is the length of time the eyes remain relatively still and focused on a single point, allowing for detailed visual processing and information encoding.
“The pattern of findings for long numerals—more and shorter saccades as well as more and longer fixations—shows the extent to which reading long Arabic numerals is a cognitively costly task. Within the phonographic writing system, this pattern of eye movements stands for the use of the sublexical print-to-sound correspondence rules. The data highlight that reading large numerals is an unautomatized activity and that Arabic numerals must be converted into their oral form by a step-by-step process even by expert readers,” study authors concluded.
The study sheds light on the cognitive processes underpinning reading numbers. However, it should be noted that the study was conducted on a small number of participants who were all psychology students. Studies on different age and demographic groups might not yield identical results.
The paper, “Reading numbers is harder than reading words: An eye-tracking study,” was authored by Anne-Françoise de Chambrier, Marco Pedrotti, Paolo Ruggeri, Jasinta Dewi, Myrto Atzemian, Catherine Thevenot, Catherine Martinet, and Philippe Terrier.
