It is well-known that physically salient stimuli often inadvertently capture attention. Three factors affecting capture by such distractors have previously been identified as physical saliency, search goals, and selection history. In the present study, we set out to show that, in addition to these factors, uncertainty about the context in which distractors appear is a critical determinant of attentional capture by highly physically salient distractors. For this purpose, we manipulated singleton location and context uncertainty separately from set size in a series of capture-probe experiments. Specifically, in three experiments, we examined the effects of location and context uncertainty on attentional capture. We found that recall of letters at singleton locations remained higher than at non-singleton distractor locations when uncertainty about the location of the target and singleton was reduced, but when contextual uncertainty was reduced, either by fixing part of the search display or by exposing participants to a restricted set of displays, this difference disappeared. Our findings support the notion that contextual uncertainty is another critical factor determining whether salient distractors capture attention.

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Introduction: Functional magnetic resonance spectroscopy (fMRS) is a non-invasive technique for measuring dynamic changes in neurometabolites. While previous studies have observed concentration changes in metabolites during neural activation, the relationship between neurometabolite response and stimulus intensity and timing requires further investigation. To address this, we conducted an interleaved fMRS and functional magnetic resonance imaging (fMRI) experiment using a visual stimulus with varying contrast levels. Methods: A total of 20 datasets were acquired on a 7T MRI scanner. The visual task consisted of two STIM blocks (30s/20s ON/OFF, four minutes), with 10% or 100% contrast, interleaved with a four minutes REST block. A dynamic fitting approach was used for fMRS data analysis. For metabolite level changes, the STIM conditions were modeled in two different ways: either considering the full STIM block as active condition (full-block model) or only modeling the ON blocks as active condition (sub-block model). For linewidth changes due to the BOLD effect, STIM conditions were modeled using the sub-block model. Results: For both models, we observed significant increases in glutamate levels for both the 10% and 100% visual contrasts, but no significant difference between the contrasts. Decreases in aspartate, and glucose, and increases in total N-acetylaspartate and total creatine were also detected, although less consistently across both 10% and 100% visual contrasts. BOLD-driven linewidth decreases and fMRI-derived BOLD increases within the MRS voxel were observed at both 10% and 100% contrasts, with larger changes at 100% compared to 10% in the fMRI-derived BOLD only. We observed a non-linear relation between visual contrast, the BOLD response, and the glutamate response. Conclusion: Our study highlights the potential of fMRS as a complementary technique to BOLD fMRI for investigating the complex interplay between visual contrast, neural activity, and neurometabolism. Future studies should further explore the temporal response profiles of different neurometabolites and refine the statistical models used for fMRS analysis.