Retro-cue alerting effects on conscious perception across different levels of target visibility

Can alerting retro-cues improve the conscious perception of stimuli that would otherwise remain unseen? While pre-stimulus alerting is known to facilitate conscious access, the effects of retro-cues remain ambiguous due to methodological confounds in existing literature. Specifically, most studies finding retro-cue benefits have relied on spatial features (such as lateralized targets or cues), which confound alerting with spatial selection. Our design addresses this gap by employing central visual targets and non-lateralized auditory cues, thereby isolating the temporal boost of phasic alerting from spatial orienting. Across four experiments, participants reported the presence and orientation of a central Gabor patch presented at near-threshold ([Formula: see text] detection) or higher visibility ([Formula: see text] detection) levels. An auditory alerting tone was presented prior to, simultaneously with, or after the Gabor, at various short and long stimulus onset asynchronies, with both short and long temporal ranges. Results consistently showed that pre-stimulus and simultaneous cues significantly enhanced conscious perception, increasing both seen rates and (in some experiments) perceptual sensitivity. Crucially, the presence of retro-cue benefits was observed at higher stimulus visibility, but not at near-threshold, suggesting a potential influence of target visibility on retro-cue efficacy. When targets were near-threshold, retro-cues did not reliably improve conscious perception, whereas tones presented 200 ms after target offset significantly increased the proportion of seen reports when target visibility was increased. These findings indicate that non-spatial auditory retro-cues can modulate conscious report when the underlying sensory trace is sufficiently robust. More broadly, they show that the timing of conscious access can be influenced by late alerting signals even in the absence of spatial information, providing a behavioural platform to refine models of how alerting and evidence strength interact in conscious perception.