Visual field asymmetries vary between children and adults.

Visual perception in human adults varies throughout the visual field, both across eccentricity - decreasing with distance from the center of gaze - and around isoeccentric locations - that is, with polar angle at a constant distance from the center of gaze. At isoeccentric locations, the same visual information yields better performance along the horizontal than vertical meridian (horizontal-vertical anisotropy, HVA) and along the lower than upper vertical meridian (vertical-meridian asymmetry, VMA). These perceptual polar angle asymmetries in adults have been well characterized. Poor perception at upper visual field locations would be particularly detrimental to children: in their perceptual world, given their height, many important events occur above eye level. Developmental aspects of visual perception have been well characterized1, and some basic dimensions, such as contrast sensitivity, continue to develop through childhood2, but there is no research on polar angle asymmetries before adulthood. Here, we investigated whether these asymmetries are present in children, and if so, whether they differ from those of adults. We found clear differences between children and adults in performance around the visual field: the HVA is less pronounced and the VMA is not present for children.

Transcranial magnetic stimulation entrains alpha oscillatory activity in occipital cortex.

Parieto-occipital alpha rhythms (8-12 Hz) underlie cortical excitability and influence visual performance. Whether the synchrony of intrinsic alpha rhythms in the occipital cortex can be entrained by transcranial magnetic stimulation (TMS) is an open question. We applied 4-pulse, 10-Hz rhythmic TMS to entrain intrinsic alpha oscillators targeting right V1/V2, and tested four predictions with concurrent electroencephalogram (EEG): (1) progressive enhancement of entrainment across time windows, (2) output frequency specificity, (3) dependence on the intrinsic oscillation phase, and (4) input frequency specificity to individual alpha frequency (IAF) in the neural signatures. Two control conditions with an equal number of pulses and duration were arrhythmic-active and rhythmic-sham stimulation. The results confirmed the first three predictions. Rhythmic TMS bursts significantly entrained local neural activity. Near the stimulation site, evoked oscillation amplitude and inter-trial phase coherence (ITPC) were increased for 2 and 3 cycles, respectively, after the last TMS pulse. Critically, ITPC following entrainment positively correlated with IAF rather than with the degree of similarity between IAF and the input frequency (10 Hz). Thus, we entrained alpha-band activity in occipital cortex for ~ 3 cycles (~ 300 ms), and IAF predicts the strength of entrained occipital alpha phase synchrony indexed by ITPC.