Neural representation of discrete and continuous ratios: An fMRI study

Poster Session F - Tuesday, April 16, 2024, 8:00 – 10:00 am EDT, Sheraton Hall ABC

Rebekka Lagacé-Cusiac¹ (rlagacec@uwo.ca), Jessica Grahn¹, Daniel Ansari¹; ¹Brain and Mind, Western University

We often rely on relative magnitudes (ratios and proportions) to make decisions. For example, we can tell from battery icons how much charge is left by comparing the length of the filled bar to the length of the full battery icon, regardless of the overall size of the icon. This leaves the question of how humans process ratios across different formats. Some authors have proposed that all ratios are processed by a perceptually based “ratio processing system” (RPS; Lewis et al., 2016). Though some neuroimaging studies have shown a spatial overlap in brain areas processing ratios across different formats, the assumption that all non-symbolic ratios (e.g., ratios depicted using length or numerosity) have a common representation via the RPS is currently untested. Therefore, the aim of this study was to investigate the neural representation of discrete and continuous ratios using fMRI. Thirty participants completed a ratio match-to-sample task on discrete (sets of dots) and continuous (line lengths) magnitudes while in the MRI scanner. Using representational similarity analysis, we tested a series of models representing low- and high-level features on a range of areas from primary visual cortex to parietal and frontal cortex. Preliminary results suggest that ratios are not represented similarly across these different formats, thereby contracting the RPS theory. In conclusion, this study tested a fundamental assumption composing the RPS theory. Results have implications for theories of ratio processing and how these can be leveraged to improve teaching of fractions.

Topic Area: PERCEPTION & ACTION: Vision