Characterising contrast response functions using salience-matched achromatic and chromatic Gabor patches Joel T. Martin1, Zoé Darrasse1,2 and Jasna Martinovic1 1 School of Philosophy, Psychology and Language Sciences, University of Edinburgh 2 Neuropsychology and Clinical Neurosciences, University Paul Sabatier Toulouse III Background • The human visual system processes achromatic and chromatic information in distinct parallel pathways (L+M; L-M; S- [L+M]). • Visual evoked potentials to chromatic and luminance stimuli differ in morphology and with respect to stimulus contrast (Porciatti et al., 1999). • Here we present the beginnings of a normative dataset characterising contrast response functions to salience-matched chromatic and achromatic Gabors. Experiment • 31 participants; chromatic (L-M; S-[L+M]) and achromatic (luminance: L+M) Gabors (±2σ = ~3.65 dva; SF = 0.8 cpd) with 4 logarithmically spaced contrast levels (Ach: 3.9—26%; RG: 2.5—14.3%; BY: 13.5—57.7%); task: respond to horizontal stimuli. • Heterochromatic flicker photometry was used to ensure isoluminance of chromatic stimuli. • Normal colour vision was established with the Cambridge Colour Test (CCT). • Asymmetric matching (L+M or S-[L+M] matched to L-M contrasts) to verify if salience was indeed equated across mechanisms. • Stimuli and their LMS coordinates are shown below. Results • All participants provided CCT scores within the normal limits for colour vision. • The stimulus matching procedure demonstrated close agreement between our participants. Their data generally fell close to the standards selected for the EEG experiment. Conclusion • Chromatic and achromatic VEP morphology is consistent with previous findings (Porciatti et al., 1999; Ellemberg et al., 2001). • These data are the beginnings of a normative data set that will eventually be used for control comparisons in a large-scale study on visual function in individuals with bipolar disorder (Roguski et al., 2024). HELIOS-BD Scan QR code to learn more about the HELIOS-BD project (226787/Z/22/Z). • Overall scalp topographies and EEG responses to chromatic and achromatic stimuli are shown below for all electrodes. • VEP amplitudes for each condition were fit using the Naka-Rushton equation (Naka & Rushton, 1966) to estimate the overall shape of the contrast response functions. Contact joel.martin@ed.ac.uk zoe.darrasse@gmail.com j.martinovic@ed.ac.uk References • Ellemberg, D., Hammarrenger, B., Lepore, F., Roy, M. S., & Guillemot, J. P. (2001). Contrast dependency of VEPs as a function of spatial frequency: the parvocellular and magnocellular contributions to human VEPs. Spatial vision, 15(1), 99-111. • Naka, K. I., & Rushton, W. A. (1966). S‐potentials from luminosity units in the retina of fish (Cyprinidae). The Journal of physiology, 185(3), 587-599. • Porciatti, V., & Sartucci, F. (1999). Normative data for onset VEPs to red-green and blue-yellow chromatic contrast. Clinical Neurophysiology, 110(4), 772-781. • Roguski, A., Needham, N., MacGillivray, T., Martinovic, J., Dhillon, B., Riha, R. L., ... & Smith, D. J. (2024). Investigating light sensitivity in bipolar disorder (HELIOS-BD). Wellcome Open Research, 9. L-M S-(L+M) Scan for link to online poster. • Grand average VEP are shown above for electrodes Pz, Oz, O1, O2, Iz. Achromatic-driven contrast VEPs are characterised by a robust P1 component that saturates at higher levels of contrast, followed by a non-contrast dependent N1 component. Chromatic Gabors elicited a single, strong negative deflection whose amplitude and latency depend on stimulus contrast more linearly. Grey regions were selected for calculation of N1 and P1 mean amplitude responses. P1 N1 N1 N1 Amplitude L+M Amplitude Amplitude Global field power Amplitude Amplitude Amplitude Amplitude Amplitude Lum/4 Lum/3 Lum/2 Lum/1 LM/4 LM/3 LM/2 LM/1 S/4 S/3 S/2 S/1