Attention can be focused on specific locations in our visual field (space-based attention), but also spreads along objects (object-based attention). However, object-based effects are prone to large individual differences and seem not as prevalent as previously assumed. Here we investigated whether the low prevalence of object-based effects is related to individual differences in temporal dynamics of attentional selection. We measured space- and object-based effects on reaction times for individual participants in a two-rectangle discrimination task. Cue-to-target intervals were varied between 50 and 600 ms. We used bootstrapping to investigate in which cue-to-target intervals object-based effects were maximal, and fast Fourier transform (FFT) to investigate rhythmic samplings of visual space within and between objects. Whereas overall, space-based effects were robust and stable across all cue-to-target intervals for most participants, object-based effects were small and were only found for a small subset of participants. In the frequency domain, our results confirm rhythmic patterns of visual-target detection within (8 Hz) and between objects (4 and 8 Hz). However, we found large inter-individual variability for the phase of the sampling rhythms and no consistent phase relationship. Our results show that the low-prevalence of object-based effects cannot be explained by inter-individual variability in the temporal dynamics of attentional selection, and provide further evidence for considering individual variations in developing theories of visual attention.

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Visual attention can be allocated to locations or objects, leading to enhanced processing of the specific location (space-based effects) or specific object (object-based effects). Object-based effects are smaller and less robust than space-based effects and prone to large individual differences. Moreover, the temporal dynamics of object-based effects have been found to differ largely between individuals. Studies on space- and object-based effects are often based on a two-rectangle paradigm with target distribution biased to the cued location. To assess whether and how the target's spatial probability modulates the temporal dynamics of attentional effects, we manipulated cue validity from 80% over 50% to 33% in three experiments. We investigated the temporal dynamics of space- and object-based effects on group level and for individual participants. We observed that the magnitude and the prevalence of space-based effects heavily decrease with reduced cue validity. The low prevalence of object-based effects did not change across experiments, as independent of cue validity, only a few participants showed significant effects in each cue-to-target interval. Our results highlight that cue validity is a key factor for the strength and prevalence of space-based effects but does not account for the low prevalence of object-based effects.

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