Visual crowding, the difficulty of recognizing elements when surrounded by similar items, is a widely studied perceptual phenomenon and a trademark characteristic of peripheral vision. Perceptual Learning (PL) has been shown to reduce crowding, although a large number of sessions is required to observe significant improvements. Recently, transcranial random noise stimulation (tRNS) has been successfully used to boost PL in low-level foveal tasks (e.g., contrast detection, orientation) in both healthy and clinical populations. However, no studies so far combined tRNS with PL in peripheral vision during higher-level tasks. Thus, we investigated the effect of tRNS on PL and transfer in peripheral high-level visual tasks. We trained two groups (tRNS and sham) of normal-sighted participants in a peripheral (8° of eccentricity) crowding task over a short number of sessions (4). We tested both learning and transfer to untrained spatial locations, orientations, and tasks (visual acuity). After training, the tRNS group showed greater learning rate with respect to the sham group. For both groups, learning generalized to the same extent to the untrained retinal location and task. Overall, this paradigm has potential applications for patients suffering from central vision loss but further research is needed to elucidate its effect (i.e., increasing transfer and learning retention).

Background: Macular Degeneration (MD), a visual disease that produces central vision loss, is one of the main causes of visual disability in western countries. Patients with MD are forced to use a peripheral retinal locus (PRL) as a substitute of the

Background: Amblyopic observers present abnormal spatial interactions between a low-contrast sinusoidal target and high-contrast collinear flankers. It has been demonstrated that perceptual learning (PL) can modulate these low-level lateral interactions, resulting in improved visual acuity and contrast sensitivity. Objective: We measured the extent and duration of generalization effects to various spatial tasks (i.e., visual acuity, Vernier acuity, and foveal crowding) through PL on the target’s contrast detection. Methods: Amblyopic observers were trained on a contrast-detection task for a central target (i.e., a Gabor patch) flanked above and below by two high-contrast Gabor patches. The pre- and post-learning tasks included lateral interactions at different target-to-flankers separations (i.e., 2, 3, 4, 8 λ) and included a range of spatial frequencies and stimulus durations as well as visual acuity, Vernier acuity, contrast-sensitivity function, and foveal crowding. Results: The results showed that perceptual training reduced the target’s contrast-detection thresholds more for the longest target-to-flanker separation (i.e., 8 λ). We also found generalization of PL to different stimuli and tasks: contrast sensitivity for both trained and untrained spatial frequencies, visual acuity for Sloan letters, and foveal crowding, and partially for Vernier acuity. Follow-ups after 5–7 months showed not only complete maintenance of PL effects on visual acuity and contrast sensitivity function but also further improvement in these tasks. Conclusion: These results suggest that PL improves facilitatory lateral interactions in amblyopic observers, which usually extend over larger separations than in typical foveal vision. The improvement in these basic visual spatial operations leads to a more efficient capability of performing spatial tasks involving high levels of visual processing, possibly due to the refinement of bottom-up and top-down networks of visual areas.

Contrast sensitivity for a Gabor signal is affected by collinear high-contrast Gabor flankers. The flankers reduce (inhibitory effect) or increase (facilitatory effect) sensitivity, at short (2λ) and intermediate (6λ) target-to-flanker separation respectively. We investigated whether these inhibitory/facilitatory sensitivity effects are modulated by transcranial random noise stimulation (tRNS) applied to the occipital and frontal cortex of human observers during task performance. Signal detection theory was used to measure sensitivity (d’) and the Criterion (C) in a contrast detection task, performed with sham or tRNS applied over the occipital or the frontal cortex. After occipital stimulation results show a tRNS-dependent increased sensitivity for the single Gabor signal of low but not high contrast. Moreover, results suggest a dissociation of the tRNS effect when the Gabor signal is presented with the flankers, consisting in a general increased sensitivity at 2λ where the flankers had an inhibitory effect (reduction of inhibition) and a decreased sensitivity at 6λ where the flankers had a facilitatory effect on the Gabor signal (reduction of facilitation). After a frontal stimulation, no specific effect of the tRNS was found. We account for these complex interactions between tRNS and flankers by assuming that tRNS not only enhances feedforward input from the Gabor signal to the cortex, but also enhances the excitatory or inhibitory lateral intracortical input from the flankers. The boosted lateral input depends on the excitation-inhibition (E/I) ratio, namely when the lateral input is weak, it is boosted by tRNS with consequent modification of the contrast-dependent E/I ratio.

Background: In recent years, the introduction of visual rehabilitation for patients with homonymous visual field defects has been met with both enthusiasm and caution. Despite the evidence that restitutive training results in expansion of the visual field, several concerns have been raised.Objective: We tested the effectiveness of a new rehabilitative protocol called “Neuro Restoration Training” (NRT) in reducing visual field defects and in restituting visual functions in the restored hemianopic area.Methods: Ten patients with homonymous visual field defects (lesion age >6 months) where trained in detecting low contrast Gabor patches randomly presented in the blind field, which refers to regions of 0 dB sensitivity, and along the hemianopic boundary between absolute (0 dB) and partial blindness (>0 dB). Training included static, drifting, and flickering Gabors in different blocks. Positions along the hemianopic boundary were systematically shifted toward the blind field according to the threshold reduction during the training. Before and after the training, we assessed visual field expansion and improvement in different high-level transfer tasks (i.e., letter identification and shape recognition) performed in the hemianopic boundary and in the blind field.Results: NRT led to significant visual field enlargement (≈5 deg), as indicated by the conventional Humphrey perimetry, and two custom made evaluations of visual field expansion with eye movement control (one static and one dynamic). The restored area acquired new visual functions such as small letter recognition and perception of moving shapes. Finally, for some patients, NRT also improved detection, either aware or not, of high contrast flickering grating and recognition of geometrical shapes entirely presented within the blind field.Conclusion: These results suggest that NRT may lead to visual field enlargement and translate into untrained visual functions.