Inhibitory neurotransmitter GABA is known to play a critical role in perception, yet has been under-explored in humans. Understanding the mechanisms of visual perception is of particular relevance to conditions such as autism spectrum conditions, where differences in sensory perception are a core feature. Here we exploit the high resolution of 7-Tesla Magnetic Resonance Spectroscopy (MRS) to investigate the links between occipital GABA, autistic traits, and perceptual choice in humans. 45 participants (22 Female: 23 Male), aged 19-39 years, completed the Autism Spectrum Quotient questionnaire (AQ-50), a visual search task with target present/absent conditions, and an ultra-high-resolution 7T brain scan. Metabolite concentrations from the occipital cortex voxel were measured by means of MRS. The role of autistic traits in visual search was assessed by means of linear mixed-effects models. We used hierarchical drift diffusion modelling (DDM) to probe inter-individual differences in trial-by-trial drift rate and response caution. A bootstrapped mediation analysis was conducted to examine the mediating effect of AQ on occipital GABA and perceptual choice. The total effect of the model was significant (Total effect =-0.004, p= 0.018), while the direct effect of AQ was insignificant (Average Direct Effect = -0.003, p = 0.072). The mediating effect of AQ was significant (Average Causal Mediation Effect = -0.009, p = 0.024). We found that autistic traits mediate the relationship between occipital GABA and perceptual choice in a visual search task. This has important implications for understanding perceptual choice in neurodiverse populations. ​