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Theories of rhythmic perception propose that perceptual sampling operates in a periodic way, with alternating moments of high and low responsiveness to sensory inputs. This rhythmic sampling is linked to neural oscillations and thought to produce fluctuations in behavioural outcomes. Previous studies have revealed theta-and alpha-band behavioural oscillations in low-level visual tasks and object categorization. However, less is known about fluctuations in face perception, for which the human brain has developed a highly specialized network. To investigate this, we ran an online study (N = 179) incorporating the dense sampling technique with a dual-target rapid serial visual presentation (RSVP) paradigm. In each trial, a stream of object images was presented at 30 Hz and participants were tasked with detecting whether or not there was a face image in the sequence. On some trials, one or two (identical) face images (the target) were embedded in each stream. On dual-target trials, the targets were separated by an interstimulus interval (ISI) that varied between 0 to 633 ms. The task was to indicate the presence of the target and its gender if present. Performance varied as a function of ISI, with a significant behavioural oscillation in the face detection task at 7.5 Hz, driven mainly by the male target faces. This finding is consistent with a high theta-band-based fluctuation in visual processing. Such fluctuations might reflect rhythmic attentional sampling or, alternatively, feedback loops involved in updating top-down predictions.The brain is confronted with a constant influx of sensory input and yet is able to form a stable ongoing visual experience. Despite the seemingly continuous operation, evidence has shown that sensory sampling works in a periodic way, with moments of high and low responsiveness to external stimulations interleaving with each other. This temporal structure of visual processing is reflected in ongoing neural oscillations, where the phase and power of prestimulus theta-(3-7 Hz) and alpha-band (8-12 Hz) activity have been shown to predict perceptual

Studies on behavioral oscillations demonstrate that visual sensitivity fluctuates over time and visual processing varies periodically, mirroring neural oscillations at the same frequencies. Do these behavioral oscillations reflect fixed and relatively automatic sensory sampling, or top-down processes such as attention or predictive coding? To disentangle these theories, the current study used a dual-target rapid serial visual presentation paradigm, where participants indicated the gender of a face target embedded in streams of distractors presented at 30 Hz. On critical trials, two identical targets were presented with varied stimulus onset asynchrony from 200 to 833 ms. The target was either familiar or unfamiliar faces, divided into different blocks. We found a 4.6 Hz phase-coherent fluctuation in gender discrimination performance across both trial types, consistent with previous reports. In addition, however, we found an effect at the alpha frequency, with behavioral oscillations in the familiar blocks characterized by a faster high-alpha peak than for the unfamiliar face blocks. These results are consistent with the combination of both a relatively stable modulation in the theta band and faster modulation of the alpha oscillations. Therefore, the overall pattern of perceptual sampling in visual perception may depend, at least in part, on task demands. Protocol registration The stage 1 protocol for this Registered Report was accepted in principle on 16/08/2022. The protocol, as accepted by the journal, can be found at:https://doi.org/10.17605/OSF.IO/A98UF.

The pre-saccadic preview of a peripheral target enhances the speed and accuracy of its post-saccadic processing, termed the extrafoveal preview effect. Peripheral visual performance -and thus the quality of the preview- varies around the visual field, even at iso-eccentric locations. To investigate whether these polar angle asymmetries influence the preview effect, we asked human participants to preview four tilted Gabors at the cardinals, until a central cue indicated to which to saccade. During the saccade, the target orientation either remained or was flipped (valid/invalid preview). After saccade landing, participants discriminated the orientation of the (briefly presented) second Gabor. Gabor contrast was titrated with adaptive staircases. Valid previews increased participants' post-saccadic contrast sensitivity. This preview effect was inversely related to polar angle perceptual asymmetries; largest at the upper, and smallest at the horizontal meridian. Our finding reveals that the visual system actively compensates for peripheral asymmetries when integrating information across saccades.